Sem 1 Flashcards

Question

How do keratoplana, keratoconus, and post-LASIK corneas appear on topography?

Answer 1

Keratoplana (flat cornea): Dark blue. Keratoconus (steep cone): Red hotspot. Post-LASIK: Central blue zone (flattening).

Answer 2

Radius of curvature: 7.75 mm (43.50D). E value (asphericity): 0.47 (ellipse). P value: 0.80 (P = 1 – e²).

Answer 3

Determines potential optical aberrations. Guides optic zone diameter selection. Important for coloured & multifocal CL placement.

Answer 4

Distance between upper & lower eyelid in primary gaze.

Answer 5

Normal: 10–13 mm. Helps choose CL overall diameter. Size categories: Small: 10–10.8 mm, Medium: 11–11.8 mm, Large: >12 mm.

Answer 6

Advantages: - Great optical quality - Neutralizes irregular/regular astigmatism - Allows tear exchange - Long-lasting (1–2 years) - Cost-effective long-term Disadvantages: - Longer adaptation period - Requires diligent cleaning - Usually only one pair owned

Answer 7

Keratoconus patients Astigmats High refractive errors Presbyopic (multifocal) needs Best for patients who want full-time CL wear Ideal for corneal toricity & refractive cylinder cases

Answer 8

Lens parameters: - Diameter - Optic Zone Diameter - Base Curve - Back Vertex Power (BVP) Design & Material Centre & edge thickness are manufacturer-determined

Answer 9

Lid characteristics (tonus, position, aperture) Palpebral aperture size Corneal diameter & curvature Corneal cylinder (toricity) Spectacle refraction

Answer 10

Select Lens Diameter Select Starting Base Curve

Answer 11

Based on lid type, aperture, pupil & corneal size RGPs stay within the cornea, 2 mm smaller than corneal diameter Typical medium cornea (11.8mm) → lens diameter 9.0–9.5mm

Answer 12

Interpalpebral fit: Lens stays central within cornea Lid-attachment fit: Lens tucks under upper lid, moves with blinking

Answer 13

Tight lids (common in Asians): Larger diameters for lid attachment Loose lids: Smaller diameters suitable for interpalpebral fit Lid tonus & position dictate final lens position

Answer 14

Optic zone must fully cover pupil Larger pupils → require larger optic zones & lens diameters Prevents glare & halos if lens decenters

Answer 15

Larger corneas → typically flatter → larger lens Smaller corneas → typically steeper → smaller lens Average cornea is 11.8mm diameter → 9.0–9.5mm RGP typical

Answer 16

Pupil size (larger pupil → larger OZD needed) Lid characteristics (e.g., tight Asian lids need larger lenses for lid attachment) Corneal diameter: Large corneas (>12mm) → larger lenses Small corneas (<10mm) → smaller lenses Corneal curvature (K values): Steep corneas (>47D) → smaller lenses Flat corneas (<39D) → larger lenses

Answer 17

Small lens: <9.0 mm (OZD 7.0 mm) Small-Medium (S-M): 9.0–9.3 mm (OZD 7.5 mm) Medium-Large (M-L): 9.5–9.8 mm (OZD 8.0 mm) Large lens: >9.8 mm (OZD 8.5 mm)

Answer 18

Start near flat K If astigmatism is present, choose a BC steeper than flat K but not steeper than steep K For larger diameter lenses, select a flatter BC to match increased sagittal depth (lens fit compensation)

Answer 19

Larger lenses increase sagittal height To maintain proper fit, flatten the BC to compensate (avoid excessive vaulting or tight fit)

Answer 20

Assess pupil size, corneal diameter, lid type, corneal Ks Choose lens diameter based on anatomy Determine optic zone diameter (OZD) Select base curve near flat K, adjusted for astigmatism Flatter BC if larger diameter lens is chosen

Answer 21

If ΔK (K2 - K1) = 0.75D, fit lens on (or equal to) flat K. ## Footnote Example: +43.00D → BC = 7.85 mm (Use radius conversion: 337.5 / K)

Answer 22

Steepen by 1/3 of ΔK. Fit lens 0.25D steeper than flat K. ## Footnote ΔK = 43.75 – 43.00 = 0.75D; Adjusted K: 43.00D + 0.25D = 43.25D; BC = 7.80 mm

Answer 23

Calculate mid-K: (43.37 – 0.50D) = 42.87D; BC = 7.87 mm (from 337.5 / 42.87). ## Footnote Rounding to 42.75 (7.90 mm) or 43.00 (7.85 mm) is acceptable.

Answer 24

Method 1: Fit on flat K if ΔK ≤ 0.75D; Method 2: Steepen BC by 1/3 of ΔK; Method 3: Use mid-K for alignment fitting.

Answer 25

Choose method based on corneal toricity, patient needs, and clinical judgment.

Answer 26

CRA = Refractive Cylinder (Spectacle Rx) – Corneal Cylinder (ΔK) ## Footnote If corneal cylinder > refractive cylinder → overcorrection (plus tear lens forms opposite meridian) If corneal cylinder < refractive cylinder → residual minus cylinder remains uncorrected

Answer 27

TLP = Difference between corneal curvature (K) and CL base curve ## Footnote Steeper lens (smaller BC radius) → + TLP (adds plus power) Flatter lens (larger BC radius) → – TLP (adds minus power) Example: Cornea 43.00D, CL BC 43.25D → TLP = +0.25D Cornea 43.00D, CL BC 42.75D → TLP = –0.25D

Answer 28

Final RGP BVP = Ocular Refraction – TLP ## Footnote If TLP is +0.25D → Subtract 0.25D more from Rx Rx -7.00D → Final lens -7.25D If TLP is –0.25D → Subtract 0.25D less from Rx Rx -7.00D → Final lens -6.75D

Answer 29

RGP neutralises corneal astigmatism via tear lens optics. Residual astigmatism remains if lenticular/internal sources exist. Tear lens power must be considered to avoid over/under-correction. ## Footnote Clinical equivalents: Every 0.05mm change in BC ≈ 0.25D change in power (steeper add minus, flatter add plus)

Answer 30

Because the cornea is aspheric (steepest centrally, flattens peripherally), lenses need peripheral flattening to maintain proper fit and allow edge lift for tear exchange.

Answer 31

Multicurve, Aspheric, Tangent Cone

Answer 32

Adds sequential flatter curves beyond the central optic zone. Number of curves depends on lens size, central curvature steepness, and needed transition steps. ## Footnote Example notation: Base Curve/OZD form (e.g., 7.85mm/8.00mm) or 8.50/0.3 wide.

Answer 33

Bennett’s design: Quadcurve, fit 0.5D flatter than flat K, common size 8.8mm DIA, 7.4mm OZD. Mandell’s design: Diameter/OZD options like 9.6(8.0), 9.2(7.8), 8.8(7.5).

Answer 34

Eccentrically designed with smooth, continuous flattening. Creates an even, thin tear layer. Better for moderate astigmatic corneas. ## Footnote Example: “Centra” by Corneal Lens Corp.

Answer 35

Focuses on proper mid-peripheral landing zone. Aims to distribute pressure evenly and maintain tear exchange. Helps reduce lens lateral drift.

Answer 36

Different designs match different corneal shapes, improving fit, comfort, tear exchange, and stability.

Answer 37

To assess if the patient can see clearly through the lens, if the base curve and diameter are appropriate, and if the BVP provides the correct correction.

Answer 38

Lenses of the same base curve design (e.g., Centra), all with the same BVP (e.g., –3.00D or +2.00D). Larger clinics may have multiple sets for better accuracy in fitting.

Answer 39

It's the process of refining lens power while the patient wears the CL, done at the spectacle plane to estimate the required final BVP at the corneal (ocular) plane.

Answer 40

For spectacle plane over-refractions greater than ±4.00D — vertex to corneal plane to determine final BVP needed in the contact lens.

Answer 41

Vertex –4.75D → –4.50D (ocular plane) –3.00D (trial lens) + (–4.50D over-refraction) = –7.50D final BVP

Answer 42

Ensure the lens is not over-minused, and verify if the base curve is too flat (causing excess minus via tear lens effect).

Answer 43

Dynamic Fitting: Observes natural lens movement, blinking effects, tear exchange, lens recovery. Static Fitting: Evaluates lens-cornea relationship while lens is centred, without blinking influence.

Answer 44

Wait 20 minutes for adaptation Use topical anaesthetic Down-gaze for 5–10 mins Encourage gentle blinking Allow reflex tearing to equilibrate lens position

Answer 45

Lens movement during blinking (upward motion, returning down), centration or decentration (high, low, nasal, temporal, variable), stability (consistent centration or frequent shifting), whether lens stays within cornea or crosses limbus during gaze movements.

Answer 46

Observe lens edge movement in primary gaze during blink, measure in mm (ideal 1–2 mm), describe movement: smooth, rocky, drifting, vertical, lateral, oblique, lid-adhering.

Answer 47

Lens in primary gaze, no lid influence, assess tear layer thickness (central, mid-peripheral, edge zones), use cobalt blue light with Wratten filter, need ≥20μm tear layer to see NaFl.

Answer 48

Central: NaFl pooling (clearance), alignment, central touch; Mid-Peripheral (MP): MP touch (light/medium/heavy), alignment, fluorescein clearance; Peripheral: Edge pooling, tear reservoir width & depth.

Answer 49

Static: Light central clearance, light mid-peripheral touch (prevents lateral drift), edge clearance ~0.5mm width; Dynamic: Centre within 0.5mm, smooth vertical movement (1–2 mm), stable on-eye behaviour.

Answer 50

Static Issues: Excessive central touch, loss of mid-peripheral touch, excessive edge width or clearance; Dynamic Issues: Decentration >0.5mm, lateral/superior displacement, lens drifts inferiorly (unstable), excessive movement (>2mm), swiveling or rotational instability.

Answer 51

Lids press on the lens, preventing clear observation of the fitting relationship. ## Footnote Important to statically assess lens fit without lid influence.

Answer 52

Lens decentration, excessive movement, vision fluctuations, lens dislodges with eye movements, edge width >2mm (instead of ideal 0.5mm), base curve flatter than corneal curvature, more corneal surround visible (especially in small lenses).

Answer 53

Static Issues: Excessive central pooling, bubbles, heavy mid-peripheral touch, narrow edge width. Dynamic Fit: Appears acceptable. Indicates poor static fit despite dynamic fit being fine.

Answer 54

Loose Fit: Demonstrates poor dynamic fitting. Tight Fit: Demonstrates poor static fitting. Grading Severity: Off by 0.5D = Slightly loose/tight; Off by >2.5D = Excessively loose/tight.

Answer 55

Lens too large in diameter, lens curvature too steep (too round), lens hugs too much of the ocular surface.

Answer 56

Compromised fit in one or both meridians, risk of corneal warpage, spectacle blur due to tear layer inconsistencies, tight areas cause staining and dynamic fitting issues. ## Footnote Solution: Switch to non-spherical RGP design (e.g., toric).

Answer 57

RGPs: Lathe-cut from plastic, then polished. Soft Lenses (SCLs): Lathe-cut, then hydrated to soften. Mass Production: Spin casting & cast-moulding (liquid polymer injected into mould, then hydrated).

Answer 58

Increase surface hydrophilicity. Maintain hydration. Prepare lens for wear. Extend usability. Mechanical rubbing removes debris/microbes (3–4 log reduction). Chemical soaking disinfects & kills germs.

Answer 59

Biguanides: Cationic, bind to bacterial membranes (Gram+/Gram–). Polyquaterniums (Polyquads): Cationic, disrupt phospholipid membranes, large molecules = low toxicity. Hydrogen Peroxide: Produces hydroxyl radicals, destroys lipid membranes, must be neutralised before wear.

Answer 60

Time of exposure. Temperature. pH. Rubbing the lens. Proper hand hygiene.

Answer 61

Disinfection: Reduces microbial load but doesn’t eliminate all life forms. Sterilisation: Kills all microbes (bacteria, viruses, fungi, spores) using heat, chemicals, or pressure.

Answer 62

Uses wet heat (steam) at 121°C & 100 kPa for 20 minutes. Destroys all microbes. Suitable for RGP trial lenses. Not used at home (damages SCLs, denatures proteins).

Answer 63

Chlorine-based, red bottle, not safe for eye contact. Used for in-office RGP disinfection (5 min soak, rinse with saline). Not provided to patients. SCLs are never reused after office trial.

Answer 64

PHMB & DYMED: Biguanides with broad-spectrum antimicrobial action. Often combined for enhanced disinfection. High molecular weight → less absorption into lenses → reduced toxicity. Chlorhexidine used for RGPs only. Benzalkonium chloride: potent but binds soft lenses, less compatible. Thimerosal discontinued due to epithelial toxicity.

Answer 65

Wetting agents: PVP, PVA, PEG (improve wettability, comfort). Viscosity agents: Stabilise, emulsify, improve handling. Chelating agents: Maintain tear-like salt balance. Buffers: Control pH (failure → acidity → stinging, redness). Surfactants: E.g., Poloxamine (removes debris, enhances cleaning).

Answer 66

RGPs: Conditioning solution disinfects, wets, stores, prepares lens. Soft Lenses: Remain hydrated → less need for 'conditioning' term. Soft lens solutions focus on multipurpose cleaning/disinfecting.

Answer 67

Multipurpose: Combines cleaning, disinfecting, wetting, storing. Two-step systems: Separate surfactant cleaning (removes debris) & disinfection/conditioning. Two-step generally more effective for thorough cleaning.

Answer 68

PHMB, DYMED: Antimicrobials & hydranate (protein removal). Polyquad: Large cationic molecule (low toxicity, antifungal when combined with Aldox). Hydraglyde, Tetronic: Wetting agents. Hyaluronate: Added moisture, comfort. Peroxide systems: High-level disinfection, requires neutralisation.

Answer 69

Hydrogen peroxide (3%) is non-preserved & requires neutralisation before ocular use. Types include: - AOSept: Platinum disc neutraliser, criticised for short exposure to full-strength peroxide. - Oxysept: Neutralising tablet (catalase + Vitamin B12) → turns pink when safe. - Everclean Plus: Uses neutralising tablets. Used for troubleshooting & conventional lens disinfection, but more expensive than MPS.

Answer 70

Cleadew system: Uses sodium sulphite + proteolytic enzyme neutralising tablet. Solution turns clear when safe for CL wear. Effective alternative disinfectant for both SCLs & RGPs.

Answer 71

Bacteriostatic (not bactericidal): Rinse only. Leaving cap off increases contamination risk. Often confused with MPS but lacks disinfection. Used with two-step systems to rinse lenses & minimise Acanthamoeba risk.

Answer 72

Tear proteins denature & form white, milky deposits on CLs. More common in SCL & RGPs, less in disposables. Proteolytic enzymes: Subtilisin A, Papain, Pancreatin break down protein deposits. Protein cleaning is recommended every 2–4 weeks.

Answer 73

Hypochlorite Acid (Progent): Mixes Part A + B, soak 30 mins, rinse off. Monthly use. Boston One-Step Liquid Enzymatic Cleaner: Uses Subtilisin A, separate from Progent process. Both effectively remove tightly bound protein deposits.

Answer 74

Avizor Enzyme Cleaners Ultrazyme Universal Protein Cleaners Used every 2–4 weeks to maintain lens clarity & comfort.

Answer 75

Blink-N-Clean Drops (Tyloxapol): Cleans, moisturises, removes proteins & lipoproteins (surfactant action). Lacrifresh Cleaning (Avizor): Uses Poloxamer for cleaning & comfort.

Answer 76

Every 3 months to prevent biofilm build-up (bacteria, fungi, Acanthamoeba). Use antibacterial silver-treated cases & wash with soapy water. Avoid topping off old solution & never use tap water due to contamination risk.

Answer 77

Incorrect use (too much/little solution). Ingredient incompatibility (disinfectants, preservatives, buffers). Poor hygiene/compliance → contamination & biofilm. Hypersensitivity/Toxicity: Symptoms: Stinging, itching, redness, discomfort. Signs: Diffuse staining, SPK, microcysts, follicles, papillae, epiphora. Triggered by: Thimerosal, chlorhexidine, benzalkonium chloride, or solution changes. Management: Remove CL, irrigate eye, switch to gentler solution.

Answer 78

Papillae (0.3–0.9 mm): On superior palpebral conjunctiva (central/lateral). Often linked to lens deposits from poor cleaning. Inferior tarsal redness common. Corneal infiltrates: Caused by bacterial contamination, deposits, hypersensitivity, or hypoxia.

Answer 79

Always try changing the contact lens solution first before switching lenses. Particularly important in SCLs (which absorb preservatives).

Answer 80

Red/maroon caps: Surfactant cleaners – not for direct eye contact. Red bottles: Deep disinfectants (RGPs, 5-minute soak) – not for eye use. White caps: Safe for direct ocular use. Always rinse & dry trial lenses before storing.

Answer 81

A too steep base curve or too tight periphery restricts tear exchange, leading to a tight fit.

Answer 82

Fluorescein (NaFl) ring outlining the lens, lens sticking/binding, central bubbles, discomfort, redness, reduced vision, difficulty removing the lens.

Answer 83

Corneal indentations that appear as stained dots after lens removal.

Answer 84

Ring-shaped NaFl staining where the tight lens edges press into the cornea.

Answer 85

Flatten base curve, increase edge lift, widen peripheral curve, reduce lens size, or decrease optic zone size.

Answer 86

Good prognosis; symptoms typically resolve after proper adjustment.

Answer 87

Central NaFl staining (scuffing), conjunctival indentation staining (jarring), lens discomfort, lens dislodgement, and visual fluctuations.

Answer 88

Steepen base curve, narrow peripheral curve radius/width to reduce edge lift.

Answer 89

Good prognosis after proper lens fit adjustment.

Answer 90

Peripheral NaFl staining, foreign bodies, bubbles under lens, lens dislodgement, discomfort, excessive lens movement.

Answer 91

Reduce peripheral curve radius and width. For excess lift in one meridian, use a toric periphery.

Answer 92

Bubbles trapped in post-lens tear film create hemispherical epithelial pits, pooling with NaFl, affecting vision if central.

Answer 93

Reduce post-lens tear film clearance by lowering sagittal height and/or reducing edge lift.

Answer 94

Direct corneal damage, often from foreign bodies (FB) or abrasions, seen as localized fluorescein (NaFl) staining matching the injury site.

Answer 95

Grit, pollution, eyelashes, lid secretions, trauma from fingers, airborne particles.

Answer 96

Discomfort, tearing, irritation until FB removal or epithelial healing.

Answer 97

Greater edge lift increases the risk of foreign bodies entering and scraping the cornea.

Answer 98

Stop lens wear, irrigate with saline/artificial tears, check under eyelids, consider broad-spectrum antibiotics for deeper defects.

Answer 99

Corneal shape distortion from long-term high- or low-riding RGP lens wear.

Answer 100

Topography irregularities, irregular retinoscopy, indecisive refraction, spectacle blur, oedema, indentation patterns.

Answer 101

Cease lens wear, reassess topography/refraction every 1–2 weeks, refit lenses for better centration and oxygen transmission.

Answer 102

Avoid old lenses, expect some discomfort with new fit, use updated spectacles to reduce lens dependence.

Answer 103

Superficial punctate keratitis (SPKs) at 3 & 9 o'clock, sometimes 2 & 10 or 4 & 8 positions, often with limbal/conjunctival redness.

Answer 104

Discomfort, lens awareness, dryness, gritty or burning sensations; may be asymptomatic if mild.

Answer 105

Patient education, tear supplements, blink training, improve lens wettability, lens design adjustments; prognosis poor if severe.

Answer 106

RGP lenses split the tear film into front and back layers, needing good wettability for smooth gliding and ocular surface health.

Answer 107

Neophyte wearers may blink less, blink too forcefully, not close eyelids fully, or have widened palpebral aperture.

Answer 108

Dryness, burning, foreign body sensation, redness, and abnormal head positioning due to lens edge awareness.

Answer 109

Delayed blinking, incomplete lid closure, eye widening, conjunctival and corneal staining.

Answer 110

Optimise lens edge profile and edge lift, educate patient, and implement blink training for optimal lens movement.

Answer 111

Localised corneal thinning near the limbus, appearing as a shallow depression pooling with NaFl if epithelium is damaged.

Answer 112

Paralimbal elevation disrupting tear film oily layer, leading to localized dehydration.

Answer 113

Symptoms: vague irritation, photophobia. Management: stop lens wear, lubricate, address underlying cause.

Answer 114

Corneal vascularization, stromal degeneration, and inflammation.

Answer 115

An opaque, elevated lesion near nasal or temporal limbus causing discomfort, lens awareness, tearing, photophobia.

Answer 116

Mechanical irritation from large lenses with low edge lift, or overnight lens wear.

Answer 117

Stop lens wear temporarily, reduce wear time when resuming, redesign lens with smaller diameter and moderate edge lift.

Answer 118

Corneal vascularization, pseudopterygium, infiltrative keratitis.

Answer 119

Observation, sharp lens sensation, conjunctival jarring staining, lens awareness during blinking, foreign body sensation.

Answer 120

Significant defects: order new lens. Minor defects: polish or roll lens edge

Answer 121

Poor surface wetting, visible scratches, crackling sound, blurred vision, FB sensation, discomfort on blinking.

Answer 122

Yes, but they may also experience blurred vision, FB sensation, and discomfort, especially when blinking.

Answer 123

Irregular surfaces attract bacteria, increase conjunctival irritation, leading to papillary conjunctivitis, allergy, discomfort, and lens discontinuation.

Answer 124

Corneal staining, ocular redness, discomfort, papillary conjunctivitis.

Answer 125

Poor handling: pressing between fingers, against case, drying with residue, thin lenses, excessive pressure.

Answer 126

Atypical NaFl pattern, reduced vision, abnormal BC readings, thin centre thickness; px usually asymptomatic.

Answer 127

Verify parameters, replace lens, re-educate px on handling.

Answer 128

Lid oedema from mechanical irritation, lid traction, inflammation, nerve dysfunction, levator aponeurosis weakening.

Answer 129

Stop lens wear 1-3 months, review edge profile, refit with SCLs, refer for lid surgery if severe.

Answer 130

Hyperaemic, roughened palpebral conjunctiva with enlarged papillae due to mechanical irritation and immune response.

Answer 131

Lens awareness, increased lens movement, itching, reduced wear time, decreased vision.

Answer 132

Near RGP edge, central tarsal plate, lid fold.

Answer 133

Replace/polish lens, reduce wear time, prescribe antihistamines, mast cell stabilisers, olopatadine/ketotifen, fluorometholone.

Answer 134

CL-related, allergic, with mucous strands, cobblestone appearance, white points, 0.3–0.9mm, chronic inflammation.

Answer 135

Viral origin, no mucous strands, lymphocyte aggregates, pale, translucent, 0.2–2mm, not CL-related, less chronic.

Answer 136

Fitting issues, lens surface damage, incidental ocular insults.

Answer 137

Surface incompatibility, allergies, toxicity, hypoxia, inflammation, infection.

Answer 138

Lens sits too high, low, off-centre, moves too much or too little, mismatched diameter, poor edge lift, poor vision.

Answer 139

Refit with a different lens for reassessment or order a new lens with adjusted parameters.

Answer 140

Central bubbles, peripheral corneal impingement, rapid movement on blink.

Answer 141

Lens rides high, slips sideways or down, excessive edge lift.

Answer 142

Irregular pressure causes lens to rock up/down or left/right.

Answer 143

Adjust base curve first, recalculate final BVP to maintain clinical equivalence (0.1mm = ~0.50D).

Answer 144

Light diffraction at edge causes flaring or diplopia (double vision).

Answer 145

Increase optic zone size, possibly increase overall lens diameter to improve centration.

Answer 146

Smaller lenses have lower sagittal height (SAG), making them sit flatter on the eye.

Answer 147

Steepen base curve to compensate for lower sagittal height and maintain centration.

Answer 148

Larger optic zones increase SAG, making lenses tighter and reducing tear exchange.

Answer 149

Flatten the base curve (about 0.05mm flatter = 0.25D change).

Answer 150

Irritation near or over the limbus, increasing lens awareness.

Answer 151

Lens becomes steeper due to increased SAG, requiring base curve flattening.

Answer 152

Lens becomes flatter/looser, requiring a steeper base curve to maintain fit.

Answer 153

Steeper Add Minus, Flatter Add Plus.

Answer 154

Increases edge lift, causing lens to ride higher. Decreasing diameter reduces edge lift, making lens ride lower.

Answer 155

Fit tighter, move less, more edge lift, better lid attachment, but reduce tear exchange and oxygen flow.

Answer 156

Move more, allow better tear circulation and oxygenation, but less stable and prone to decentration.

Answer 157

Too low clearance limits tear flow, causing indentation, discomfort, removal issues; too high clearance causes excessive tear exchange, discomfort, epithelial damage.

Answer 158

Increase secondary curve radius (SCR), secondary curve width (SCW), total diameter, and optic zone diameter.

Answer 159

Clearance of 0.3–0.7 mm, width of 40–60 µm with gentle mid-periphery landing.

Answer 160

Increases mislocation forces from gravity and lid interaction, common with small lenses, flatter base curves, plus powers, thicker lenses.

Answer 161

Slides along the steep meridian, shifting off-centre, causing unstable vision and discomfort.

Answer 162

Flat base curve, excessive edge lift, small lens size, thick lens edge, surface deposits.

Answer 163

Heavy lens, steep base curve, patient's astigmatism, lid forces pushing lens downward.

Answer 164

Address base astigmatism, request minimum centre thickness, modify edge design, use lighter materials, increase edge lift or diameter.

Answer 165

Increases weight, anterior centre of gravity, reduces corneal oxygen supply.

Answer 166

Lens can flex, break, and be less comfortable.

Answer 167

Positive lenses have thinner edges than negative lenses.

Answer 168

A -3.00D lens edge thickness of 0.09–0.12mm.

Answer 169

Add a minus carrier to the lens edge.

Answer 170

Add a plus lenticular wedge to the lens edge.

Answer 171

Provides mechanical and optical stability.

Answer 172

Optical stability and wetting agent properties.

Answer 173

Silicone: oxygen transmission Fluorine: oxygen transmission and surface quality improvement.

Answer 174

HEMA: wetting agent Cross-linking agents: increase rigidity.

Answer 175

Polymer composition, O2/CO2 permeability, refractive index, specific gravity, hardness, modulus, UV blocking, tinting.

Answer 176

D (diffusion): gas passage ability K (solubility): oxygen absorption ability.

Answer 177

x10^-11 cm²/s.

Answer 178

Oxygen transmissibility through a lens of given thickness, units in Barrer/cm.

Answer 179

Dk = 0, no oxygen permeability; used for trial lenses only.

Answer 180

Dk = 150; excellent oxygen permeability but problematic for wettability.

Answer 181

Dk = 30–70, wettable, deposit resistant, masks negative charge, minimal protein binding, flexible, wettability decreases with higher Dk.

Answer 182

Refined polymers offering higher oxygen permeability with improved stability and wettability.

Answer 183

Dk increases, wetting angle decreases, specific gravity decreases.

Answer 184

Boston (ES, EO, XO, XO2), Paragon (Thin, HDS, HDS100), Optimum (Classic, Comfort, Extra, Extreme), Menicon Z, Acuity (100, 200).

Answer 185

Optimum series (Classic, Comfort, Extra, Extreme).

Answer 186

Improves wettability and ensures a smooth, stable tear film.

Answer 187

Denser materials (higher specific gravity) cause downward displacement; lighter materials fit better.

Answer 188

Low: 1.1, High: 1.27.

Answer 189

Higher RI allows same BVP with thinner centre thickness.

Answer 190

1.424 to 1.570 (average ~1.44).

Answer 191

Helps patients differentiate between left and right lenses.

Answer 192

To ensure sufficient oxygen supply for all-day wear.

Answer 193

High or hyper Dk/t lenses.

Answer 194

More robust, less surface deposits, less flexing, fewer surface scratches.

Answer 195

Lower oxygen permeability.

Answer 196

Affects lens position; denser lenses may displace downwards.

Answer 197

Reduces centre thickness while maintaining BVP.

Answer 198

More careful handling due to surface fragility.

Answer 199

For corneal astigmatism >2.50D (K-readings) or significant residual astigmatism uncorrected by spherical RGP fitting.

Answer 200

Uncorrected astigmatism found by over-refraction with a spherical RGP lens on the eye.

Answer 201

CRA = Spectacle cylinder - Corneal cylinder.

Answer 202

Internal astigmatism from crystalline lens or retina, usually ATR (against-the-rule).

Answer 203

Greater than 0.75D.

Answer 204

Oblique astigmatism > ATR > WTR.

Answer 205

If uncorrected RA does not significantly affect vision.

Answer 206

SE = Sphere + ½ Cylinder (using residual astigmatism values).

Answer 207

To correct significant residual astigmatism affecting vision.

Answer 208

Spherical back surface, toric front surface, medium-large diameter, often fitted slightly flatter for stability.

Answer 209

1–3 prism dioptres (pd), truncation (squared-off bottom), bottom prism bevel, rotation markers.

Answer 210

To stabilize the lens and prevent rotation.

Answer 211

Increases centre thickness, which may cause greater lens awareness or discomfort.

Answer 212

Flattening or squaring off the bottom of the lens to improve lid interaction and reduce rotation.

Answer 213

To allow practitioners to check lens rotation and alignment on the eye.

Answer 214

For former successful spherical RGP wearers who develop lenticular astigmatism, or hyperopic astigmats needing high oxygen permeability.

Answer 215

Due to the success and availability of soft toric lenses.

Answer 216

For patients with moderate corneal astigmatism who get good vision from spherical RGPs but experience uneven edge lift.

Answer 217

Spherical back optic zone with toric curves in the periphery.

Answer 218

TSP lenses have peripheral curves that differ at 90°, creating an oval optic zone; spherical lenses have uniform peripheral curves.

Answer 219

* TSP 0.6mm ≈ 1.50D * TSP 0.8mm ≈ 2.00D * TSP 1.0mm ≈ 2.50D * TSP 1.2mm ≈ 3.00D

Answer 220

No, they help edge lift but may still move, especially with flatter meridians.

Answer 221

Uneven edge lift, especially tight horizontal fit with inferior lift-off.

Answer 222

Managing upper-lower corneal curve mismatch and reducing inferior lens lift-off.

Answer 223

Up to 1.5 mm difference between upper and lower peripheral curves.

Answer 224

Keratoconus patients needing spherical optics with better peripheral fit.

Answer 225

The lower mid-periphery is steepened separately from the upper part, with a smooth blend to fit asymmetrical corneas.

Answer 226

Lens with four independently adjustable quadrants (A–D) for highly precise fitting.

Answer 227

Keratoconus and other cases of complex corneal asymmetry.

Answer 228

For regular but significantly toric corneas (>2.00D) to provide optimal alignment and stability. ## Footnote Bitoric lenses are specifically designed to accommodate the unique curvature of toric corneas.

Answer 229

Separate base curves are chosen for each meridian using K-readings and optical cross principles. ## Footnote K-readings refer to the curvature measurements of the cornea.

Answer 230

Making the vertical meridian slightly steeper than K. ## Footnote This adjustment helps in maintaining lens stability and comfort.

Answer 231

Steeper base curves add minus power, flatter base curves add plus power to adjust BVP. ## Footnote SAM-FAP stands for Steep Add Minus, Flat Add Plus.

Answer 232

Flat meridian base curve = flat K (plano tear layer); Steep meridian base curve = 0.1mm flatter than steep K (–0.50D tear layer). ## Footnote This strategy ensures optimal tear exchange and lens positioning.

Answer 233

1) Fit flat meridian close to K, steep meridian 0.1–0.2mm flatter (WTR). 2) Use Mandell-Moore chart based on corneal cylinder. ## Footnote WTR stands for with-the-rule astigmatism, where the steepest meridian is vertical.

Answer 234

0.4 mm (≈2.0D difference). ## Footnote This difference is important for achieving proper lens alignment on the cornea.

Answer 235

Due to differences in refractive indices of the lens, cornea, and tear film altering light refraction. ## Footnote This phenomenon can lead to unexpected visual outcomes.

Answer 236

A minus cylinder is induced at the flatter meridian axis, adding plus power in the steep meridian. ## Footnote Understanding this mechanism is crucial for effective lens design.

Answer 237

Lens base curve toricity and lens material refractive index. ## Footnote Both factors play a significant role in the overall optical performance of the lens.

Answer 238

About 25–45% of the lens’s base curve toricity. ## Footnote This percentage can vary based on individual patient characteristics.

Answer 239

Between 1.41 and 1.54. ## Footnote The refractive index influences the lens's optical properties and comfort.

Answer 240

When lens base curve toricity plus induced cylinder matches the patient’s refractive astigmatism, allowing a spherical front surface.

Answer 241

Easier manufacturing, better quality, simpler front surface modifications, and lower costs.

Answer 242

When refractive cylinder is 30–50% greater than corneal cylinder (ΔK), due to induced astigmatism.

Answer 243

Higher refractive index materials induce more astigmatism (25–45% of lens base curve toricity).

Answer 244

MF = (n of lens – 1) / (1.3375 – 1).

Answer 245

Boston EO (n=1.429): MF = 1.271 Boston ES (n=1.443): MF = 1.312 Paragon HDS (n=1.449): MF = 1.330 Fluoroperm 60 (n=1.473): MF = 1.401

Answer 246

Induced BVP cylinder = ΔBC (D) × MF.

Answer 247

Uses induced astigmatism from back surface toricity to reduce or eliminate need for front surface toricity.

Answer 248

Two base curves on back surface (90° apart) and two front surface curves, giving separate BVP for each meridian.

Answer 249

Powers in both meridians are equal (A = B).

Answer 250

Powers in each meridian are different (A ≠ B).

Answer 251

To align principal meridians and stabilize lens fit on toric corneas.

Answer 252

Rotation causes induced astigmatism from misalignment of tear layer optics and lens BVPs.

Answer 253

Toric front and back curves where ΔBVP matches ΔBC (A = B), resulting in no net cylinder on-eye.

Answer 254

Base curves 39.00D & 41.00D (2.00D difference), BVPs -3.00 & -5.00 (2.00D difference), cancelling out cylinder effect.

Answer 255

Parallel or compensated bitorics.

Answer 256

1. Assess need for back toric design. 2. Compare corneal vs spectacle cylinder. 3. Draw optical cross and plan parameters. 4. Calculate ΔBC. 5. Calculate ΔBVP. 6. Adjust for SPE (ΔBC = ΔBVP) or BST design.

Answer 257

They fill in tear layer gaps and neutralize corneal irregularities, improving visual quality.

Answer 258

Scissoring reflex on retinoscopy, atypical reflexes, Charleux oil droplet sign in red reflex (direct ophthalmoscopy).

Answer 259

Use the brightest reflex, adjust in large steps (±1.00D), avoid over-minusing, cycle sphere and cylinder adjustments, use fogging to balance endpoint.

Answer 260

Insert 1D/2D cylinder, let patient rotate axis for clarity, then refine power and axis using blur method.

Answer 261

Yes, if tolerated. Reduce only if needed for comfort or adaptation.

Answer 262

Yes, even if BCVA is only 6/15, glasses can be a useful backup to contact lenses.

Answer 263

Diameter, lens design, and central back optic zone radius (BCOR).

Answer 264

Peripheral curves, peripheral design or optic zone (OZ), and final back vertex power (BVP).

Answer 265

Start with BCOR halfway between steepest and flattest K readings; in advanced cases, steeper than 6.80 mm.

Answer 266

Follow manufacturer’s fitting guide (e.g., Rose K2), apply fitting factor based on cone severity.

Answer 267

Select BC in orange-green zone of normalised topography, adjust based on cone severity (yellow-orange for advanced).

Answer 268

Start with steep K lens, gradually flatten until light central touch is seen, aiming for pooling or feather-touch.

Answer 269

To avoid compressing the cone apex and reduce risk of corneal damage.

Answer 270

Poorer visual acuity, residual astigmatism, central bubbles, tight periphery.

Answer 271

Corneal staining, scarring, scuffing, hydrops.

Answer 272

Minimal clearance to protect the apex while achieving best safe visual acuity.

Answer 273

They have more peripheral flattening to match high corneal eccentricity.

Answer 274

Excessive edge lift and lens looseness.

Answer 275

Help predict lens settling areas and identify regions of excessive edge lift or tear pooling.

Answer 276

Diagnostically, through over-refraction with a known trial lens on-eye.

Answer 277

Steeper Add Minus, Flatter Add Plus to maintain optical consistency.

Answer 278

At 6.0 mm: 0.1 mm ≈ 0.75D At 5.0 mm: 0.1 mm ≈ 1.00D

Answer 279

D = 337.5 / mm mm = 337.5 / D

Answer 280

Small curvature changes cause larger optical effects, needing precise adjustments.

Answer 281

Wearing a soft contact lens under an RGP to improve comfort and center a low-riding RGP on irregular corneas.

Answer 282

Acts as a cushion, reduces mechanical irritation, and improves RGP centration.

Answer 283

Reduced to about 0.5–1.0 mm (normally 1–2 mm).

Answer 284

Use low plus powers (+1.50 to +3.00) to dome the cornea and help RGP fit better.

Answer 285

No, it’s mainly for fit and centration.

Answer 286

Use high molecular weight NaFl to avoid soft lens absorption, discard soft lens after testing.

Answer 287

Large-diameter rigid lenses for advanced keratoconus and post-surgical eyes, providing stability and comfort.

Answer 288

Stable fit, minimal lid interaction, reduced FB risk, supports post-surgical eyes, helps ptosis.

Answer 289

Complex manufacturing, large appearance, potential tightening on eye, require fluid-filled insertion.

Answer 290

Corneo-scleral: 12.9–13.5 mm Semi-scleral: 13.6–14.9 mm Mini-scleral: 15.0–18.0 mm Scleral: 18.1–24+ mm

Answer 291

They vault the cornea completely and rest on the sclera, avoiding corneal contact.

Answer 292

Light central clearance or alignment with minimal pressure, limited movement (~0.75 mm).

Answer 293

Use topography map, choose a base curve ~30% flatter than steepest area (yellow zone), apply flatter fit factor (1.0–1.2 mm).

Answer 294

To avoid limbal stem cell pressure, lens seal-off, and excessive edge lift.

Answer 295

BC 5.3–8.8 mm, DIA 12.0–15.0 mm, ±25.00D power, multicurve C6 design, asymmetric periphery options.

Answer 296

BC 6.4–8.0 mm, DIA 14.6 mm, customizable edge lift from +3 to -3.

Answer 297

Fit is based on sagittal depth (sag) rather than base curve; aims for 100–300 μm central clearance and good conjunctival alignment.

Answer 298

To maintain ocular health in the closed system with minimal tear exchange.

Answer 299

Post-graft eyes, advanced keratoconus, pellucid marginal degeneration, lens intolerance, unstable smaller lenses.

Answer 300

Slit-lamp and anterior segment OCT to evaluate central clearance and scleral landing.

Answer 301

Combines RGP center with SiHy skirt, offering RGP vision with soft lens comfort.

Answer 302

For normal corneas, BC 7.10–8.50 mm, DIA 14.5 mm, ±20.00D, 130 Dk RGP center, 84 Dk SiHy skirt.

Answer 303

For irregular corneas, vault 50–550 μm, skirt options (Flat, Medium, Steep), DIA 14.5 mm, same materials as Duette HD.

Answer 304

Provide RGP-level vision with improved comfort from the soft skirt.

Answer 305

A progressive ectatic disorder with corneal thinning and protrusion, causing a conical shape and irregular astigmatism.

Answer 306

Reduced protective enzymes, oxidative stress susceptibility, thinner epithelium, weakened stroma, reduced corneal thickness (<480 µm).

Answer 307

Create a smooth tear lens to neutralize corneal irregularities and improve vision (but do not halt progression).

Answer 308

Sodium fluorescein apex staining, central scarring, and vortex staining.

Answer 309

Atopy, eye rubbing, floppy eyelid syndrome, sleep apnea, mitral valve prolapse, Marfan's, Down’s, hypermobility, Ehlers-Danlos.

Answer 310

Approximately 1 in 2000 people, with higher rates in Māori and Pasifika populations.

Answer 311

Around 20%, with graft success rates near 90%.

Answer 312

Stabilizes the cornea and reduces progression of the disease.

Answer 313

May improve tolerance despite risks, due to scarring and nerve fibre changes.

Answer 314

Fogging (26.8%), limbal hyperaemia (23.7%), corneal staining (13.3%), conjunctival prolapse (25%), graft rejection (21%).

Answer 315

Placido disc-based, 32 rings, 15,120 points, default RGP fitting program, ±0.10mm accuracy.

Answer 316

Scheimpflug imaging, 25 scans, ±0.05mm accuracy, more sensitive than Placido, avoids 'ring jam' artefacts.

Answer 317

Pachymetry <480 µm, high I-S value, scissoring/swirl retinoscopy reflex, irregular astigmatism, monocular diplopia.

Answer 318

About 15–30% of cases have a genetic component.

Answer 319

A mild, non-progressive form of keratoconus, often only detectable with sensitive topography.

Answer 320

Buckling of the posterior cornea seen as vertical lines.

Answer 321

Iron deposits (ferritin) at cone base in basal epithelium, a key sign of keratoconus.

Answer 322

Sudden Descemet’s membrane split causing stromal fluid influx, painful swelling, potential scarring.

Answer 323

Resulting scar may flatten the cornea, sometimes aiding lens fitting.

Answer 324

Elevated corneal lump causing discomfort; managed with piggyback lenses or surgical removal.

Answer 325

Better localizes cone position and shape using normalised colour scales.

Answer 326

Nipple (<3mm, 29%), Oval (3–5.5mm, 44%), Global (>5.5mm, 6.7%), Marginal (irregular, 5.6%).

Answer 327

Both eyes are typically affected, though asymmetrically; true monocular KC is rare.

Answer 328

Confirm diagnosis, locate apex, monitor progression, differentiate from other ectasias.

Answer 329

Stage 1 (<48D): Glasses, soft torics Stage 2 (<53D): Custom soft, RGP, hybrids Stage 3 (>53D): RGP, hybrids, semi-scleral, piggyback Stage 4 (>55D): Same lenses, possible corneal graft.

Answer 330

Increased edge lift, smaller optic zone to vault cone, higher minus powers, varied fit (lid attachment vs interpalpebral).

Answer 331

Smaller than standard; e.g., 6.5mm optic zone for 7.0mm base curve lenses.

Answer 332

An alignment fit where the peripheral curves align properly, and the central back optic zone gently touches the cone apex.

Answer 333

Ensures definite clearance over the cone apex to avoid scarring, balancing vision and safety.

Answer 334

Tear film thinner than 20 µm may not show fluorescein staining, complicating fit evaluation.

Answer 335

To avoid tightness at 3 and 9 o'clock, prevent inferior lift-off, and match peripheral corneal toricity (up to ~1.4D).

Answer 336

For significant corneal toricity that standard spherical designs can't fit.

Answer 337

Bubbles under lens (dimple veil), epithelial wrinkling, apical scarring, and discomfort with extended wear.

Answer 338

A popular keratoconus RGP lens system with multiple designs and edge lift options to fit various cone types and post-surgical eyes.

Answer 339

Rose K2: Standard keratoconus Rose K2PG: Post-graft Rose K2IC: Irregular corneas Rose K2NC: Nipple cones Rose K2XL: Semi-scleral, oblate design Rose K2IQ: Thicker soft lens for irregularities

Answer 340

Menicon Z material with plasma coating, toric peripheries, back surface toric, bisymmetric (TSP, ACT).

Answer 341

Wearing a soft lens under an RGP to improve comfort and lens centration.

Answer 342

High Dk soft lenses like Acuvue Oasys (+0.50D, BC 8.4) for cushioning the RGP.

Answer 343

Often minimal adjustment needed as ~70% of soft lens power gets neutralised by the tear lens.

Answer 344

Rose K2 XN (nipple cones, interpalpebral fit), new oblate semi-scleral designs, and hybrid designs for enhanced comfort.

Answer 345

Larger RGP lenses, 13–18 mm diameter, used for managing keratoconus.

Answer 346

Larger size reduces lens movement on the eye, improving comfort.

Answer 347

Potential for reduced oxygen flow to the cornea due to lens thickness and tear layer.

Answer 348

Corneal swelling after 8 hours was only ~1.7%, lower than predicted, suggesting minimal hypoxia issues with modern materials.

Answer 349

Tear exchange, oxygen storage in post-lens tear film, and slow diffusion across lens surface.

Answer 350

RGP centre with a soft skirt, combining RGP vision clarity with soft lens comfort.

Answer 351

Higher Dk materials (RGP centre Dk 130, SiHy skirt Dk 84), better comfort and stability.

Answer 352

Protein build-up, allergic reactions, corneal staining, limbal neovascularisation.

Answer 353

Thicker soft lenses (e.g., Kerasoft IC, Rose K2 Soft) partially neutralise corneal irregularity, fitted steeper than standard lenses.

Answer 354

Their increased thickness (~0.25–0.50 mm) limits oxygen flow, so lens movement is crucial for corneal health.

Answer 355

Fit steep base curve first, then refine sphere and cylinder over-refraction, usually ending with toric correction.

Answer 356

Riboflavin + UVA light strengthens corneal collagen, halting progression and improving biomechanical stability.

Answer 357

Epi-off (epithelium removed) and epi-on (epithelium intact).

Answer 358

Helps stabilize progressive disease and reduce the need for corneal grafts.

Answer 359

Combines gentle excimer laser ablation to regularise corneal shape with immediate CXL to stabilise the cornea.

Answer 360

Small plastic rings inserted into corneal stroma to flatten the cornea, improving vision with glasses or contacts in mild cases.

Answer 361

20% failure rate, not suitable for thin or scarred corneas, outcomes vary widely.

Answer 362

They are reversible if needed.

Answer 363

CDVA of 6/18 or better before treatment. Evidence of progression (e.g., ↑K by 1D in 2 years, Rx change by 1D/year, 5% corneal thinning in 1 year).

Answer 364

Cornea <400 µm K >58D Age >35 years Stable keratoconus Corneal opacity History of uveitis, HSV keratitis Poor wound healing, post-LASIK ectasia.

Answer 365

Recommend referral for CXL immediately upon diagnosis of keratoconus.

Answer 366

↑0.75D max K ↑0.75D refractive cylinder ↓>10 µm corneal thickness 0.2mm change in CL base curve ≥1 line loss in BCVA.

Answer 367

Corneal thickness <380 µm (epi-off) or <350 µm (epi-on), and significant corneal scarring.

Answer 368

To prevent hydrops in the other eye, as minor scarring risk is acceptable compared to progression risk.

Answer 369

Risk of worsening scarring and reduced vision, even with correction.

Answer 370

Progression slows but doesn’t stop; 43.7% of >5-year follow-up eyes progressed vs. 11.1% in <5-year group.

Answer 371

A 61-year-old had a 3.4D corneal steepening, with I-S index increasing from 0.19D (2002) to 1.64D (2015).

Answer 372

Progression varies; some stabilize, others continue to worsen even in later life.

Answer 373

A corneal ectasia similar to keratoconus but with inferior peripheral steepening, creating a “crab claw” pattern on topography.

Answer 374

Their astigmatism often remains regular despite the corneal thinning pattern.

Answer 375

The steepening pattern makes it feel like fitting two different corneas.

Answer 376

Typically when contact lens intolerance occurs or when vision cannot be corrected adequately.

Answer 377

Regularises corneal shape, improving glasses and contact lens fitting.

Answer 378

When corneal elevation difference exceeds 350 microns.

Answer 379

Low ECD increases graft rejection risk, worsened by hypoxia from poorly fitted lenses.

Answer 380

DALK: ~1800 cells/mm²; PK: ~900 cells/mm².

Answer 381

To prevent neovascularisation and protect graft health.

Answer 382

High corneal astigmatism (12D cylinder) but manageable elevation difference (252 microns) allowed RGP fitting.

Answer 383

-122 microns (blue) to +130 microns (red), total 252 microns.

Answer 384

RO had a 14D cylinder and a large elevation difference of 410 microns, making RGPs unsuitable.

Answer 385

A hybrid lens, due to excessive elevation irregularity for RGP fitting.

Answer 386

Mid-periphery is steeper than the centre; requires an oblate contact lens design with steeper peripheral curves than the base curve.

Answer 387

Rose K XL semi-scleral oblate design: BC 7.2mm, DIA 15.0mm, +0.50 lift, -17.50D power, achieving 6/12 vision.

Answer 388

Contact Lens-Induced Ptosis; managed with blepharoplasty surgery, which destabilised lens fit post-op.

Answer 389

Right eye grafted in 1982 (steep), left eye with moderate oval keratoconus using Rose K since 2006.

Answer 390

Rose K1, BC 6.9mm, DIA 8.7mm, -9.50D power, standard lift, BCVA 6/12.

Answer 391

Flat, mobile, low position, wide edge lift, mild apical staining, variable vision.

Answer 392

Steepened to BC 6.7mm (2 steps steeper), DIA 8.7mm, -7.00D power, standard lift.

Answer 393

-6.00D addition, resulting in a final lens power of -12.50D, improving BCVA to 6/10.

Answer 394

Tried same BC 6.7mm but with decreased lift (-0.50) using Rose K2 design for better centration and edge control.

Answer 395

To ensure predictable results and maintain the successful DIA of 8.7mm while fine-tuning edge lift and centration.

Answer 396

Adjust lift in small increments (e.g., change from -0.50 to -0.30) using the lens exchange warranty if needed.

Answer 397

BC: 7.0mm (1982) → 6.9mm (2006) → 6.7mm (2022), indicating gradual steepening.

Answer 398

I’ve fitted a slightly steeper base curve adjustment to your lens, to stabilise the fit and your vision.

Answer 399

They drape over the cornea and sclera, are larger than the cornea, and have a base curve flatter than the cornea.

Answer 400

The lens edge should not cross over the limbus during movement.

Answer 401

Provide comfort, good vision, and avoid causing stress or damage to the eye.

Answer 402

They move less on the eye, reducing lens awareness and easing adaptation.

Answer 403

Can be worn part-time (e.g., sports, social events), not necessarily every day.

Answer 404

RGP ptosis, Dellen, 3 & 9 o’clock staining, corneal distortion affecting glasses, 3 & 9 o’clock redness, dust/grit trapping under the lens.

Answer 405

Larger optical zones reduce light scatter and halo effects.

Answer 406

Trial sets allow for quick fitting and patient satisfaction ('try before you buy').

Answer 407

Can change eye colour through coloured designs.

Answer 408

Soft lenses generally have lower up-front costs.

Answer 409

More delicate (prone to tearing) Require strict cleaning (porous material) Higher risk of infections/inflammation Oxygen permeability concerns High rates of non-compliance (overwear, poor hygiene).

Answer 410

Proteins, lipids, and mucus.

Answer 411

360° coverage with 1–1.5 mm overlap beyond the corneal edge.

Answer 412

0.4 to 0.7 mm vertical movement.

Answer 413

A loose lens fit.

Answer 414

A tight or steep lens fit.

Answer 415

Minimal lag = ideal Excessive lag = loose lens No lag = tight lens.

Answer 416

Small lag with prompt recentration = ideal No recovery = tight fit Large lag with no recentration = loose fit.

Answer 417

Lens stability under manual eyelid retraction.

Answer 418

Tight lens resists movement, recentres slowly Loose lens shifts easily, poor recovery.

Answer 419

Limbal redness Conjunctival compression Limbal indentation Dehydration-induced worsening tightness.

Answer 420

Discomfort Fluctuating vision Edge lift (fluting) Wrinkling Excessive displacement Limbus overhang.

Answer 421

Mimics looseness by flattening the fit, altering centration and movement.

Answer 422

Supports oxygen diffusion, CO₂ removal, tear exchange, and debris clearance.

Answer 423

Soft lenses come in limited curvatures Fit impacts comfort, movement, and ocular health.

Answer 424

SiHy (stiffer) lenses need more precise BC fitting High-water content lenses drape easier, less sensitive to BC variations.

Answer 425

8.3 to 9.0 mm.

Answer 426

Mid-K + 0.6 to 1.2 mm; often ~0.7 mm flattening from flat K.

Answer 427

Use a smaller flattening factor due to stiffer material properties.

Answer 428

Larger-diameter lenses may require a larger flattening factor for optimal fit.

Answer 429

Find mid-K, add flattening factor (e.g., 0.8 mm), and round to nearest base curve option.

Answer 430

Mid-K = 7.76mm + 0.8mm = 8.56mm → round to 8.60mm base curve.

Answer 431

13.8–14.5 mm (standard), 12.0–23.0 mm (custom).

Answer 432

1.0–1.5 mm beyond the limbus in all directions.

Answer 433

Mechanical irritation at the limbus, discomfort, ocular complications.

Answer 434

Steepen base curve (same/different brand), switch to a more supportive design, use a larger diameter, check for inside-out insertion.

Answer 435

Flatten base curve (same/different brand), use flatter shape design, reduce diameter (if still covering cornea).

Answer 436

Full corneal coverage, balance between tightness and looseness, correct BVP availability, suitable replacement schedule and material compatibility.

Answer 437

Soft lenses drape over cornea with no tear lens, so BVP matches spectacle Rx (adjusted for vertex if needed).

Answer 438

Sphere + ½ cylinder. Example: –4.50/–0.50 × 180 → SE = –4.75D (rounded to –4.50D if needed).

Answer 439

Apply vertex distance correction (e.g., –6.75 sph at 12mm vertex), choose closest available power.

Answer 440

±0.25D steps from +6.00D to –6.00D; ±0.50D steps beyond that range.

Answer 441

No, they are often not manufactured; must adjust selections accordingly.

Answer 442

Soft lenses drape over the cornea with no significant tear lens, unlike RGPs.

Answer 443

Calculate the spherical equivalent. ## Footnote E.g., –4.50/–0.50 × 180 → SE = –4.75, may round to –4.50.

Answer 444

Adjust –6.75 sph to –6.25 (12 mm vertex), then select closest available power. ## Footnote E.g., –6.00 if –6.25 not made.

Answer 445

±0.25D between +6.00 and –6.00, ±0.50D beyond that range.

Answer 446

Often not manufactured; adjustments are needed.

Answer 447

Daily disposable, fortnightly, monthly, frequent replacement (3–4 months), and annual conventional lenses.

Answer 448

Best hygiene, no cleaning needed, convenient for part-time wearers, travellers, and eye health-conscious users.

Answer 449

More economical for full-time wear but require more care routines.

Answer 450

For special prescriptions, unusual base curves/diameters, or when mass-produced lenses aren't suitable.

Answer 451

Require protein removers, complex care, limited solution availability in some countries. ## Footnote E.g., NZ.

Answer 452

Base Curve, Diameter, BVP (Back Vertex Power), Design/Lens Name, Manufacturer, Material, Water Content.

Answer 453

Oxygen permeability of the lens material.

Answer 454

Oxygen transmissibility through the lens (Dk value divided by lens thickness); critical for corneal health.

Answer 455

Measured for a –3.00 D lens as reference.

Answer 456

Influences oxygen transmission and wearing comfort.

Answer 457

Water content and ionic properties, affecting interactions with tears and proteins.

Answer 458

Spherical bicurve design with an 8.0 mm optical zone and ~14 mm total diameter for limbal coverage.

Answer 459

Back surface aspheric: Single, continuously flattening curve. Front surface aspheric: Reduce optical aberrations, but benefit varies.

Answer 460

HEMA (hydroxyethyl methacrylate) with ~38% water content, low oxygen transmission.

Answer 461

Methacrylic acid (MA), polyvinyl alcohol (PVA), N-vinyl-pyrrolidone (NVP).

Answer 462

Denotes hydrogel or silicone hydrogel composition.

Answer 463

In Barrer units (10⁻¹¹ cm²/s·mL O₂ / mL·mmHg) at 35°C, following ISO or ANSI/Fatt standards.

Answer 464

Oxygen transmissibility (Dk divided by thickness), measured in Barrer/cm, determines actual oxygen reaching the cornea.

Answer 465

Comfortable, moist, smooth texture, and help transport oxygen to the cornea.

Answer 466

Prone to evaporation and shrinkage. Fragile, clingy, harder to handle. May require increased thickness, reducing oxygen transmission.

Answer 467

Between 0.04 to 0.08 mm.

Answer 468

Thinner lenses improve oxygen transmission but can be flimsy, harder to handle, and prone to tearing.

Answer 469

Inferior corneal staining due to lens water evaporation pulling fluid from ocular surface.

Answer 470

Their low structural rigidity reduces movement, which may affect tear exchange and cause surface dryness.

Answer 471

Boosts Dk but increases fragility, evaporation, and protein/lipid deposits.

Answer 472

Use silicone (siloxane) for high Dk with lower water content.

Answer 473

Surface dryness, deposit formation due to hydrophobic nature, initial stiffness, and lower comfort.

Answer 474

By blending silicone with hydrophilic polymers or applying surface treatments.

Answer 475

Makes the lens ionic (negatively charged), improving wettability but increasing protein (e.g., lysozyme) deposits.

Answer 476

Acuvue 2 (etafilcon) — designed for 2-week wear because of protein buildup.

Answer 477

Group I: Low water, non-ionic Group II: High water, non-ionic Group III: Low water, ionic Group IV: High water, ionic.

Answer 478

Group I or III, though their behaviour differs from traditional hydrogels.

Answer 479

Thicker/stiffer lenses (e.g., high minus, torics) interact more with lids, increasing movement.

Answer 480

Drape closely with minimal movement; risk of tight fit and dehydration-related discomfort.

Answer 481

To assess tightness, as these lenses may appear immobile despite being too tight.

Answer 482

Tensile modulus (stiffness), surface treatment, fit, and water content.

Answer 483

EW lenses pose a higher risk and severity of hypoxic complications due to prolonged wear time.

Answer 484

Small vesicles of dead cell material above Bowman’s membrane due to hypoxia-induced slowed epithelial mitosis; more frequent in EW lenses (~10% in DW).

Answer 485

Visible with reverse illumination due to higher refractive index than cornea.

Answer 486

Increase oxygen supply (higher Dk/t lenses, reduce EW schedule). Recovery may show temporary increase before resolving over months.

Answer 487

Vertical lines in posterior cornea caused by stromal oedema from hypoxia, more common in EW lenses.

Answer 488

24×10⁻⁹ for DW lenses, 87×10⁻⁹ for EW lenses (to maintain corneal swelling <5%).

Answer 489

Vogt’s striae are associated with keratoconus and are not caused by lens wear.

Answer 490

Growth of blood vessels >0.75 mm into avascular cornea due to hypoxia, epithelial damage, or tight lens fit.

Answer 491

Increase oxygen transmission, improve lens fit, limit wear time, and use anti-inflammatory drops if severe.

Answer 492

Empty blood vessels that remain after active neovascularization has regressed.

Answer 493

Transient endothelial cell swelling due to acute hypoxia from anaerobic metabolism, leading to lactic acid and CO₂ buildup.

Answer 494

Appear as dark spots under specular microscopy, resolve after lens removal or adaptation; prevention focuses on ensuring adequate oxygen supply.

Answer 495

DW: Blebs appear within 10 mins, peak at 20–30 mins, resolve in 2–3 hours. EW: Resolution may take up to 8 days, indicating greater corneal stress.

Answer 496

Hydrogel (closed-eye): 7.4 blebs SiHy (closed-eye): 1.9 blebs SiHy (open-eye): 1.0 blebs.

Answer 497

Longer wear time reduces oxygen supply, causing metabolic issues like epithelial microcysts, striae, folds, and endothelial changes.

Answer 498

DW lenses: ≥24×10⁻⁹ EW lenses: ≥87×10⁻⁹.

Answer 499

Polymegathism: Endothelial cell enlargement (up to 20x). Pleomorphism: Loss of hexagonal shape, irregular forms.

Answer 500

A state where chronic hypoxia leads to reduced lens tolerance, requiring cessation of lens wear.

Answer 501

Increases bacterial enzyme activity, destabilising tear film, leading to dryness and epithelial staining.

Answer 502

Inflammatory stromal white spots, not infectious. Triggered by hypoxia, tight/dirty lenses, poor hygiene, or irritants in closed-lid EW environment.

Answer 503

Often asymptomatic but can cause mild discomfort, grittiness, or redness.

Answer 504

Use high Dk/t lenses Ensure proper fit Limit wear time Maintain strict hygiene.

Answer 505

Prolonged overnight wear reduces oxygen supply and allows irritants and microbes more time to act.

Answer 506

Improve hygiene Refit tight lenses Stop overnight wear Address lens deposits.

Answer 507

Focal corneal infiltrates near lid margin (4 or 8 o’clock) Linked to staph exotoxins and more common in EW users due to prolonged wear and closed-eye environment.

Answer 508

Infiltrates without fluorescein staining Limbal redness Symptoms: mild to moderate discomfort, FB sensation, tearing.

Answer 509

Discontinue lens wear Frequent lubrication Improve lid hygiene Address fit and hygiene habits for long-term prevention.

Answer 510

Immune memory from prior corneal inflammatory events.

Answer 511

To avoid hypoxia-induced swelling: DW: ≥24×10⁻⁹ EW: ≥87×10⁻⁹.

Answer 512

Epithelial microcysts Corneal striae Descemet’s folds.

Answer 513

Endothelial blebs Polymegathism (cell enlargement) Pleomorphism (cell shape irregularity).

Answer 514

Chronic hypoxia leads to reduced lens tolerance, potentially requiring permanent cessation of lens wear.

Answer 515

Growth of blood vessels into the avascular cornea due to chronic hypoxia and poor lens fit; indicates long-standing stress.

Answer 516

Longer wear time, reduced oxygen, increased exposure to deposits, poor hygiene, and tight fits.

Answer 517

Hypersensitive inflammatory reaction to gram-negative bacterial toxins trapped under lenses during sleep, causing intense redness, discomfort, and infiltrates.

Answer 518

Prolonged lens wear reduces tear exchange, traps bacteria/toxins, especially with poor hygiene.

Answer 519

CLPU: Sterile inflammatory infiltrate (<2 mm), mild staining, non-infectious, resolves with lens cessation & lubrication. MK: Infectious, large infiltrate (>1 mm), heavy staining, stromal excavation, severe inflammation.

Answer 520

Large, central infiltrate with heavy staining, stromal excavation, AC reaction, pain, photophobia, tearing, discharge.

Answer 521

Lenses are removed daily, restoring oxygenation and reducing bacterial load.

Answer 522

Stop lens wear immediately. Start intensive topical antibiotics (e.g., fortified cefuroxime + gentamicin, or fluoroquinolones). Culture scrape if lesion is large.

Answer 523

Intensive dosing every 5–15 mins initially, tapering based on clinical response.

Answer 524

Identifies causative organism to guide targeted therapy.

Answer 525

Less hypoxia, better tear exchange, lower microbial/inflammatory risks, safer for long-term ocular health.

Answer 526

Artificial tears for comfort and epithelial healing; cautious use of anti-inflammatory agents if inflammation persists.

Answer 527

EW soft lenses: ~20 cases per 10,000 wearers/year (4 with ≥2 line vision loss) DW soft lenses: ~2 cases per 10,000, minimal vision loss.

Answer 528

Daily disposable lenses and rigid gas permeable (RGP) lenses.

Answer 529

Sleeping in lenses Poor hand hygiene Overextending replacement schedule Poor case hygiene Weak disinfectant solutions Smoking, cosmetic lenses.

Answer 530

Reduces MK risk by ~43%.

Answer 531

Poor hygiene and corneal trauma (e.g., scratches) override oxygen benefits, enabling bacterial invasion.

Answer 532

Increase gram-positive bacterial load Impair healing Reduce corneal sensitivity.

Answer 533

Up to 10x increased risk of infection; ~70% of lens users don’t fully comply.

Answer 534

Swimming with lenses Poor hygiene during holidays Occasional lapses in cleaning routines.

Answer 535

Lower hypoxia, better hygiene opportunities, reduced microbial exposure, and significantly lower risk of MK and vision loss.

Answer 536

Acanthamoeba keratitis and viral keratitis, more common with EW and poor lens hygiene.

Answer 537

Severe, painful corneal infection linked to water exposure (e.g., swimming, tap water lens rinsing). Contact lens wear significantly increases risk, especially EW users.

Answer 538

Early: corneal haze, microcystic edema, patchy infiltrates. Hallmark: ring-shaped infiltrate + disproportionate pain.

Answer 539

Intensive, hospital-based care. Round-the-clock chlorhexidine or brolene (PHMB).

Answer 540

Fluffy, nummular infiltrates resemble bacterial or sterile infiltrates. Non-response to antivirals in contact lens users suggests reconsidering diagnosis.

Answer 541

Misdiagnosis delays appropriate treatment. Consider alternative diagnoses if antivirals fail.

Answer 542

DW lenses allow daily eye recovery, reduce hypoxia, lower microbial exposure, and dramatically cut infection risk. EW lenses exponentially increase complications, especially with poor hygiene.

Answer 543

Prioritise daily disposables, strict hygiene, avoiding water exposure, and adhering to proper wear schedules.

Answer 544

Patient prefers a soft lens. Refractive astigmatism ≥ -0.75D at corneal plane. Required back vertex power (BVP) is available.

Answer 545

-1.00 / -1.25 x 180 → toric needed. -1.00 / -0.25 x 180 → toric not needed.

Answer 546

Vertexing can reduce cylinder below -0.75D, eliminating the need for torics. ## Footnote Example: -7.50 / -0.75 x 20 → vertexed to -7.00 / -0.50 → toric not needed.

Answer 547

When lenticular astigmatism is the main contributor. RGPs do not correct lenticular cylinder effectively.

Answer 548

Corneal cylinder = 0, lenticular cylinder = -1.50 x 90 → refractive cylinder = -1.50 x 90 → soft toric preferred.

Answer 549

When lenticular astigmatism is the main contributor (CRA significant, ΔK << refractive cylinder).

Answer 550

Ocular cylinder > -1.00D Oblique cylinders need more correction than ATR or WTR Sphere:cylinder ratio < 4:1 or 3:1 (e.g., -2.00 / -1.00 = toric; -8.00 / -1.00 = sphere likely okay).

Answer 551

Sphere: -9.00D to +6.00D (some up to -10D, +8D) Cylinder: -0.75, -1.25, -1.75, -2.25 (sometimes higher) Axes: 10°–180° in 10° steps (daily disposables may limit oblique/high cyl options).

Answer 552

Hydrogel and silicone hydrogel, with custom materials (e.g., Polymacon, Definitive) for special cases.

Answer 553

Etafilcon A: supports -2.25D cyl, sphere -9 to +4D Nelfilcon A: supports up to -1.75D cyl.

Answer 554

Axes 10°–180° in 10° steps Spheres: +6.00D to -10.00D Cylinders up to -2.25D Added oblique axes like 70°, 80°, 100°, 110°.

Answer 555

Determine ocular refraction Calculate base curve (mid-K + 1.0mm) Consider HVID for diameter Choose lens design based on needs Select closest available BVP for diagnostic fitting.

Answer 556

Wear frequency Activities & environment BVP availability Material properties Cost Unusual K readings Corneal size anomalies.

Answer 557

Vertex each meridian if >4D Avoid over-minusing cyl (e.g., -1.00 / -1.50 x 20 → start with -1.00 / -1.25 x 20) Round axis towards less oblique (e.g., 162° → 160°).

Answer 558

Vision & over-refraction BVP component stability (sphere, cyl, axis) Lens indicator mark stability Coverage, centration, movement, lag Effect of stabilisation design on lens behaviour.

Answer 559

Markings indicate orientation, not the lens power axis. ## Footnote Exception: Biotrue & Ultra for Astigmatism have one mark at the axis and one for orientation.

Answer 560

Lens rotation causes axis misalignment, affecting vision clarity.

Answer 561

Effective axis becomes 170° (20° - 30° rotation = 170°).

Answer 562

Left rotation (clockwise) → Add degrees to spectacle axis. Right rotation (anti-clockwise) → Subtract degrees from spectacle axis. Always apply LARS based on the spectacle axis.

Answer 563

Order: -1.00 / -1.25 x 50. ## Footnote Adds 30° to spectacle axis to compensate rotation.

Answer 564

Subtract 10° from spectacle axis. Order: -1.00 / -1.25 x 10.

Answer 565

Incorrectly applying LARS to the trial lens axis instead of the spectacle Rx axis.

Answer 566

Even slight axis misalignments reduce vision quality. Proper LARS compensation ensures clear, stable vision.

Answer 567

False: Corrections are always made from the spectacle axis.

Answer 568

Correct spectacle Rx. Trial lens BVP matches spec Rx. No axis misalignment.

Answer 569

Visual acuity should be good. Over-refraction should be plano.

Answer 570

Manually rotate lens back to intended position and recheck VA. Perform Sphero-Cylinder Over-Refraction (SCOR) adding axis misalignment to trial Rx.

Answer 571

Helps confirm if rotation causes vision issues. Crucial for high-cylinder patients where small axis errors impact vision. Avoids delays with custom toric orders.

Answer 572

Resist twisting from lid forces. Minimise rotation during blinking and eye movements. Ensure quick realignment after displacement for stable vision.

Answer 573

Adds 1–1.5Δ base down prism to create inferior thickness. Stabilises well but can reduce oxygen transmission and increase lid awareness. Soft torics don't use truncation like RGPs.

Answer 574

Thins superior and inferior edges. Uses lid forces for orientation. Symmetrical, providing better comfort.

Answer 575

Features 4 nodules near the lid margin. Interacts with lid forces for rapid lens orientation.

Answer 576

Uses minus carrier design for inferior thickness. Thinner centrally compared to prism ballast. Partially relies on gravity for stability.

Answer 577

Acceptable if stable after settling. Problematic if rotation is inconsistent, especially with high cylinder lenses.

Answer 578

Rotate slit lamp beam parallel to lens marking through the pupil. Measure degree of rotation. Use LARS to adjust the axis accordingly.

Answer 579

Check lens marking rotation & stability. Assess corneal coverage. Evaluate centration. Observe lens movement (primary & upgaze). Check lag during eye movements. Inspect surface quality & wettability. Perform push-up test.

Answer 580

Let lens settle for ≥15 mins. Do a quick slit lamp check, over-refraction, then recheck rotation. Observe behaviour over multiple visits. Test lens stability with full range of eye movements.

Sem 1 Flashcards

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