Physiological Optics I Flashcards

Question

Markings on lenses: U

Answer 1

Scale number for UV filters

Answer 2

IR filters

Answer 3

Visible filter

Answer 4

Variable tints

Answer 5

manufacture logos, impact mark, and standard mark

Answer 6

* high mass impact (drop ball test): pointed projectile, 500mg dropped from 50” * High velocity impact: steel ball, 0.25” in diameter, fired at 150ft/s

Answer 7

+/- 2% sphere power

Answer 8

4% of cyl power

Answer 9

one surface is flat and the other is curved

Answer 10

both surfaces convex or concave

Answer 11

half of the total power is due to the front surface and half is due to the back surface

Answer 12

convex front and concave back

Answer 13

one flat surface and one cylinder surface

Answer 14

one toric surface and one spherical surface

Answer 15

• specified in terms of power • Always on the front surface for single vision lenses • Spherical lens: front surface • Plus cylinder: BC is flatter on the front. The other curve is the cross curve, the back curve is the sphere curve • Minus cyl: back flatter curve is the toric BC. The other back curve is the cross curve • BC for CL ◦ On the BACK

Answer 16

* minus lens is thicker in the periphery than in the center, while a plus lens is thicker in the center than the periphery * Note that for a lens with one flat surface, s1 or s2 is zero * When calculating edge thickness, it is good to draw a picture of the lens. Then you do not have to worry about the sign convention for si, but can instead use geometry + lens: tc=te+S1+S2 - lens: tc=te-S1+S2

Answer 17

R1=h^2/2Sfi | F=(n2-n1)/r1

Answer 18

- r2=h^2/2Sfi | - F=(n3-n2)/r2

Answer 19

• curves drawn on paper cross to show the curves on which thickness is the same

Answer 20

point on the datum line halfway between the two vertical lines which ar tangent to the edges

Answer 21

horizontal length of box. Eye size refers to frame, lens size refers to lens itself

Answer 22

vertical length of the box

Answer 23

Bridge size | shortest horizontal distance between the lenses

Answer 24

the longest diameter of the lens | A+DBL

Answer 25

the longest diameter of the lens

Answer 26

-d=(frame PD-wearer’s PD)/2 Frame PD=A + DBL

Answer 27

distance between the center of one pupil to the center of the other pupil

Answer 28

the smallest size lens blank needed to make the lens. M=ED+2(d)+2mm ED=effective diamter D=decentration (mm)

Answer 29

• Major reference point (MRP): point on the lens through which the line of sight (visual axis) passes.

Answer 30

0mm. The OC is located at the seg line

Answer 31

-r, the radius of the sag

Answer 32

* Hard design: short corridor and/or high add power | * Soft design: long corridor and/or low add power

Answer 33

• 1/2 the add power in the intermediate zone

Answer 34

``` ◦ Increase panto tilt ◦ Decrease vertex distance ◦ Spread the pads ◦ Move pads up by adjusting pad arms ◦ Stretch the bridge ```

Answer 35

``` ◦ Narrow the pads ◦ Move pads down by adjusting the pad arms ◦ Increase vertex distance ◦ Reduce panto tilt ◦ Shrink the bridge ```

Answer 36

• turn glasses around backwards in the lensometer • Measure the distance power; only the sphere needed • Measure the near power • The difference in the near and distance powers gives the add power • Must flip the lenses in the lensometer if the power is higher ◦ In practice we can estimate without turning the lenses around in the lensometer.

Answer 37

longest horizontal dimension of the segment

Answer 38

longest vertical dimension of the segment

Answer 39

distance from the lowest point on the lens to the top of the seg

Answer 40

vertical distance between the MRP and the top of the seg

Answer 41

distance from the GC to the MRP. (Frame PD-dist PD)/2

Answer 42

accounting for near PD. Distance from the MRP to the center of the seg. (Dist PD-near PD)/2

Answer 43

inset of seg as measure from the OC of the lens. Distance from the GC to the center of the seg. (Frame PD-near PD)/2

Answer 44

pull in temples, bend down temple tips, and/or pull in nose pads to tighten the fit

Answer 45

straighten the temples

Answer 46

reduce panto, narrow the bridge or pads to raise frame, and/or narrow the bridge pads to increase the vertex distance

Answer 47

narrow the pads, shrink the bridge, or decrease face form to move the lenses further away

Answer 48

narrow the bridge, add pads, or lower the vertical position of the pads to move the frames up on the face

Answer 49

1.523/58.9

Answer 50

• distort image quality (spherical, coma, radial astigmatism) or deform the image plane (curvature of field and distortion)

Answer 51

◦ Based on paraxial approximation not always being accurate

Answer 52

◦ Rays in the periphery | ◦ Bent more than central rays and therefore focus closer to the lens compared to central rays

Answer 53

◦ Marginal rays focus to a different point compared to paraxial rays ◦ A point object is no longer forming a point image ◦ LSA occurs for both on and off axis points ◦ Contributes to nocturnal myopia

Answer 54

◦ Only for off axis point ◦ Asymmetric comet shaped blur ◦ Results from the fact that magnification is varies

Answer 55

◦ In very high powered lenses, spherical aberrations are a problem where they are not a problem in lower powered lenses. We have to compensate by Rxing aspheric lenses which modify the surface without changing the power ◦ -23.00 to +7.00D ◦ Flatten the lens reduces magnification ◦ Reduce the weight of the lens ◦ Progressive lenses

Answer 56

◦ Both coma and longitudinal SA increase with the square of the system aperture ◦ Lateral SA increases with the cube of the aperture ◦ Increase in pupil size typically leads to a decrease in image quality owing to increased aberrations

Answer 57

◦ Oblique or marginal astigmatism ◦ Rays hitting the lens or interface obliquely ◦ Tangential rays and saggital rays are altered asymmetrically ◦ A flat object plane yields an asymmetrically warped image plane ◦ Reduce by picking the correct base curve ‣ Picking correct BC can minimize • Curvature of field • Radial astigmatism

Answer 58

◦ Base curve vs Fv plot ◦ Best value for BC for eliminating oblique astigmatism ‣ Wollaston and Oswalt Curve • We use Oswalt curve to pick BC (Flatter of the two) ◦ Limits=upper limit is +7.50D. Use aspheric above this. Lower is 22D

Answer 59

◦ image points formed by all points on the paper do not lie in a plane ◦ Quality of an image on a flat screen decreases for larger distances ◦ Relation to RA: curvature of field is intertwined with radial astigmatism where there is a different warping along two principle axes

Answer 60

◦ Image surface created by a system with no radial astigmatism ◦ Still warped due to curvature of field ◦ Curvature of field will present in an ophthalmic lens system any time the petzval surface doe snot correspond to the far point sphere of the eye

Answer 61

◦ Lenses that have corrected for radial astigmatism, curvature of field, or both fall under the heading “corrected curve” lenses ◦ Point focal lens: a lens corrected completely for radial astigmatism; curvature of field is uncorrected ◦ Percival form lens: a lens corrected completely for curvature of field; radial astigmatism is uncorrected ◦ Lenses are typically designed as a compromise between point focal and percival form so that both radial astigmatism and curvature of field are partially corrected.

Answer 62

◦ Magnification of a point object depends on the objects distance from the optical axis. ◦ Barrel=minus lenses ◦ Puncushion=plus lenses ◦ Minimized by a combination of lenses known as an orthoscopic doublet

Answer 63

* Rectus from the fact that the RI n is slightly dependent on wavelength. * Shorter wavelengths (blue) bend more as they pass through an interface or optical system than do longer wavelengths * The image will vary in location (longitudinal chromatic aberrations) and size (lateral chromatic aberration * Patient’s wearing high powered lenses may see colored fringes around objects because of this. * Chromatic aberrations underlay the use of RG balance in refractions.

Answer 64

◦ Series of point images along the axis | ◦ Inversely related to v, the Abbe value

Answer 65

◦ Different size images depending on the wavelength ◦ Related to prismatic effect ◦ More harmful to vision ◦ Inversely related to v

Answer 66

◦ Quantifies chromatic aberrations ◦ Inversely related to the magnitude of chromatic aberration ◦ Math for LCA: CA=F/v ◦ Math for TCA (chromatic power): CA=dF/v

Answer 67

Combine a positive lens of one material with a negative lens of another material to elimate CA. The resulting lens is called an achromatic doublet. ◦ Lens with Abbe number combined with a lens of another Abbe number eliminates CA ◦ The ratio of the v values equals the ratio of the powers

Answer 68

Use shorter vertex distances ‣ Use monocular PD ‣ Include sufficient panto tilt

Answer 69

Oblique astigmatism Curvature of field Distortion

Answer 70

* light bends towards the base | * Image shifts towards the apex

Answer 71

◦ Prism diopter ◦ A prism with a power of xZ will shift a beam of incoming light x cm on a wall 1m away. Prism=y(cm)/x(m)

Answer 72

◦ We can find the deviating angle with: d=A(n-1) (DAN-1) ◦ A is the apex angle in degrees, and d is the deviation angle in degrees

Answer 73

◦ math: prism=100(g(n-1))/l ◦ g is the difference in thickness between the apex and the base, l is the apec to base length.

Answer 74

◦ Effective power of prism depends on the location of the prism in relation to the patient’s eye

Answer 75

BU BD BI BO

Answer 76

Vector addition Prism=square root of H^2+V^2 ``` • vertical prism combination ◦ If same direction in each eye, subtract ◦ If opposite directions, add • Horizontal prism combo ◦ Same direction=add ◦ Opposite direction-subtract ```

Answer 77

``` • associate a prism power to each point on a lens • Uses ◦ Decentration ◦ Vertical imbalance-2 eyes ◦ Image jump-add type+power ◦ Total prismatic effect-1 eye • Math: prism=dF ```

Answer 78

◦ Plus lenses: the decentering direction correspond to the base direction of induced prism ◦ Minus lenses: the decentering direction corresponds to the apex direction of the induced prism

Answer 79

◦ Can not use prentice’s rule with so called sin-squared formula, which estimates the power in the oblique meridian ◦ This combination can be used when the decentering (or looking) is only vertical or only horizontal ◦ Useful for vertical imbalance ◦ If given a lens that is both decentered horizontally and vertically, use prentice’s rule for each direction individually. Then the total prism is the vector of the two sums

Answer 80

• vertical prism induced in each eye • If these amounts differ, there is a vertical imbalance • Results from different vertical prismatic effects in each eye • To find vertical imbalance, we want the DIFFERENCE in the amount of vertical prism in each eye • Correcting vertical imbalance ◦ Slab off=more mins lens gets more BU (BUMM) ◦ Dissimilar Segs= optical centers of the R and L segs at diff places ◦ CL ◦ Fresnel Prism=attached to the lens

Answer 81

* sudden displacement of an image at the bifocal line * Due to added prismatic effect that comes from the distance portion of the lens * When the eyes cross the bifocal line, the prismatic effect is changed by an additional amount

Answer 82

• we must sum the prism induced from looking away from the seg OC and the prism induced from looking away from the distance OC.

Answer 83

Spectacle magnification Corrected image size/uncorrected image size

Answer 84

◦ Need shape and power for this equation ◦ SM= (shape Factor) x (power factor) ◦ Where shape factor = Ms=1/(1-(t/n)F1) ◦ Where t is the central thickness of the lens (in m), F1 is the front surface power of the spectacle lens, n is the index of refraction of the lens ◦ Where power factor= Mp=1/(1-hFv) [h=vertex+3mm] ◦ Where h is the distance between the back surface of the lens and the entrance pupil of the eye (mm), and Fv is the back vertex power of the lens

Answer 85

used to compare retinal image of a corrected eye with the retinal image of a standard eye. Standard eye defined to be +60D • Math: RSM=Ia/Is ◦ Where Ia is the retinal image size in a corrected ametropic eye and Is is the retinal image size in the standard eye

Answer 86

Rule for RSM. RSM=1 if a thin lens is placed at the primary focal point of the eye

Answer 87

Increased h (vertex) Increases thickness Increased BC Decreased n

Answer 88

Decreased h (vertex) Increased thickness Decreased n Increased BC

Answer 89

◦ Myope image size > emmetropia size> hyperope size

Answer 90

◦ CL yield the same results as above, spectacles make RSM 1

Answer 91

◦ All retinal image sizes are the same

Answer 92

◦ CL make RSM=1, spectacles result in larger image for hyperope, and smaller image for the myope.

Answer 93

• difference in the size or shape of the images seen by the left and right eye

Answer 94

discrepancy in density of PR

Answer 95

optics of the corrected eye, difference in spec magnification

Answer 96

difference in cyl power. Prominent in one meridian | ◦ A vertical object might appear to be tilted to a patient with meridonial aniseikonia

Answer 97

Rx equal BC and equal thickness

Answer 98

Rx thin, flat lenses for the eye with the highest RSM, Rx thickener, steeper Lenses for the eye with the lowest RSM

Answer 99

Axial | Specs

Answer 100

1% 3% is a problem (around 3D difference)

Answer 101

• refractive state of the left eye differs from the right eye, usually by more than 1D ◦ Pts with myopic anisometropia have poor uncorrected distance acuities in both eyes, with the most myopic eye having the worst acuity ◦ Pts with hyperopic anisometropia have relatively good uncorrected distance acuity in both eyes, but they may have eyestrain

Answer 102

• Accommodation occurs equally in both eyes. Therefore there is no distance at which a hyperopic anisometrope can see clearly with both eyes. In myopia aniso, a person will typically learn to use the more myopic eye for near vision and the less myopic eye for distance. Hyperopic aniso will likely use the same eye (the least hyperopic) for all distances, putting at risk for amblyopia in early childhood

Answer 103

◦ One eye is hyperopic and one eye is myopic

Answer 104

• loss of light when passing through the lens | ◦ When light passes through a lens, it is reflected at both surfaces and also absorbed by the lens material

Answer 105

measures the amount of light energy that gets through an optical system. Ranges from 0-

Answer 106

1. Reflected at the front and rear surface R=((n2-n1)/(N2+n1))^2 -this would occur at each surface, to convert to tranmisttance, use Ts=1-R 2. Absorbed by the medium: assume the amount transmitted (not absorbed) by the medium is Tm=1-(amount of light absorbed by the lens). For a lens, we combine those 2 factors: T=(Ts1)(Ts2)(Tm) There T is the total transmittance through the lens

Answer 107

Back vertex power (Fv) Fv=F2+(F1)/(1-(t/n)F1) • if a center thickness is provided in the problem, always treat a contact lens as a thick lens and calculate the back vertex power. Otherwise, you can approximate the CL as a thin lens

Answer 108

• effective power of a lens changes depending on where the lens is located in front of the eye • Plus lenses effectively become weaker as they move closer to the cornea, thus hyperopes will require more plus power • Minus lenses effectively become stronger as they move closer, myopes rewuire less minus power in CL • For both plus and minus lense, mor eplus power is necessary when the lens is moved from the spectacle plane to the cornea (CL have more plus power than specs) • Vertex equation: Fc=Fs/(1-dFs) • the effective vergence equation should be used to determine the power at the corneal plane for any spec Rx > +/-4.00D

Answer 109

◦ A layer of tears is formed between the GP CL and the cornea. It has a certain power that is dependent on the front surface of the cornea and the back surface of the CL. ◦ Exploded system: consider the CL in air, the lacrimal lens in air, and the cornea in air. ◦ Refraction and GP CL ‣ PLL+PGP+PC=corneal plane refraction ‣ This equation must hold for a CL to perfectly correct an ametropic eye. We must account for the lacrimal lens when Rxing GPCLs

Answer 110

‣ Determined by the surface of the cornea and the back surface of the GPCL ‣ Back surface of the lacrimal lens has a radius of curvature that is equal to the radius of curvature of the cornea ‣ Front surface of the lacrimal lens has a radius of curvature that is equal to the BC of the CL ‣ Tear lens power=337.5/r(mm)

Answer 111

‣ If the BC of the CL equals the curvature of the cornea, there will be a total lacrimal lens power of 0 ‣ If the BC of the CL is steeper than the curvature of the cornea, the lacrimal lens will be plus power ‣ If the BC of the CL is flatter than the cornea, the lacrimal lens will be minus power ‣ Whenever the BC of the GPCL is changed, the power of the lacrimal lens will change; the power of the GPCL must also be modified in order to compensate for the change in the lacrimal lens power • Steeper add minus, flatter add plus (SAMFAP) ‣ For every 0.1mm change in the BC of the GPCL, the power of the lacrimal lens and the total power of the GPCL will change by appx 0.50D.

Answer 112

‣ Convert to diopters (337.5/r) ‣ Tear lens: GPBC-corneaBC=tear lens ‣ Solve GPCL equation: P(LL)+P(GP)+P(C)

Answer 113

Usable area of optics in CL

Answer 114

Increased SAg=steeper

Answer 115

Decreased sag=flatter

Answer 116

The BC should be adjusted by 0.25D in order to maintain the same fitting relationship between the GPCL and the cornea

Answer 117

uncurved distance of the CL from edge to edge ◦ Average is 9.4-9.6mm ◦ Adjusted in 0.4mm steps

Answer 118

• lacrimal lens will completely correct the corneal astigmatism

Answer 119

◦ The total amount of astigmatism in the eye is equal to the amount of corneal astigmatism plus the amount of internal astigmatism (lenticular). Residual astigmatism is the amount of astigmatism not corrected by a GP ◦ For a GPCL, the amount of residual astigmatism is simply the amount of astigmatism not attributable to the cornea ◦ Patients can often tolerate <1.00D WTR astigmatism and < 0.75D ATR or oblique astigmatism. If more than this is present, fit with a toric GPCL

Answer 120

◦ Allows one to empirically predict the total astigmatism correction at the spectacle plane using the results from keratometry. ◦ A(RX)=1.25Ac+(-0.50D x 090) ◦ Ac is the corneal astigmatism, add 0.50D because the average amount of internal astigmatism is roughly -0.50Dx090

Answer 121

◦ Determine the BVA with CL fit, and to help empirically determine the total power of the CL and the amount of residual astigmatism ◦ If the over refraction for a spehiercal GPCL is not Plano, simply add the OR to the CL power in order to determin the new CL power. Note that the OR will already take into account the power of the lacrimal lens.

Answer 122

◦ Allow alignment between the CL edge and the peripheral cornea ◦ prevent the edge of the CL from bearing on the cornea during movement of the CL ◦ Promote tear exchange underneath the CL to maintain adequate metabolism ◦ Support tear meniscus at the edge of the CL to promote CL centration

Answer 123

ideal thickness to promote lid attachment is the edge thickness of a -3.00D GPCL ◦ More plus than -1.50D tend to drop inferiorly. A Plano/minus carrier lenticular may be added to thicken the edge ◦ More minus than -5.00D edges are too thick and ride high. A plus lenticular or CN beveling added to decrease edge thickness

Answer 124

distance between the peripheral edge of the GPCL and the cornea. Changed in 0.1mm steps ◦ Excessive edge lift: excessive peripheral pooling of NaFL. Results in decreased CL centration, increased awareness of CL on eye, and cornea desiccation (3 and 9 O’clock) ◦ Inadequate edge lift: minimal pooling of NaFL. Results in debris trapped underneath the CL, poor CL movement with a greater risk of CL adherence, inadequate tear exchange, and vascularized limbal keratitis

Answer 125

influences O2 transmissibility, flexure, and center of gravity. Changed in 0.03mm steps ◦ A thinner CT as greater oxygen tranmission, better centration, more flexure ◦ Thicker CT has less oxygen transmission and less flexure, drops inferiorly ◦ Higher DK lenses require thicker CT in order to mimize flexure

Answer 126

◦ The more posterior the center of gravity, the better the centration of the CL

Answer 127

can be fit on corneal astigmatism because of the lacrimal lens • Large amounts of corneal astigmatisms may lead to a poor fit with a spherical GP ◦ Tori GPCL may be better

Answer 128

◦ Corneal astigmatism >2.50D is necessary to have a toric back surface ◦ A toric front surface is also required in addition to the toric back surface (bitoric) in patients where the spectacle astigmatism is not equal to 1.5 x corneal astigmatism ◦ A back surface GPCL provides more astigmatism correction that what is expected based on the BC measurement. A toric front surface is necessary in order to compensate for the additional astigmatism correction provided by the toric back surface, resulting in a bitoric CL. ◦ Fitting bitoric on-K: usually too tight. Most recommend fitting 0.25D flatter than K

Answer 129

equal alignemtn in both principle meridians. Fit 0.25D flatter. Most appropriate in ATR/oblique

Answer 130

fitting on K to 0.25D flatter than K for the flat K, and 0,75-1.00D flatter than steep K. • This is the most popular fitting philosophy for bitoric GPCL

Answer 131

◦ Indicated in patients >2.5oD corneal astigmatism AND the magnitude of spectacle astigmatism is eucalyptus to 1.5x corneal astigmatism ◦ In pts with spec astigmatism=1.5x corneal astigmatism, the extra cyl correction provided by the toric back surface perfectly correct for the total amount of astigmatism in the eye ◦ The rule that spec astigmatism=1.5x corneal astigmatism is usually met in pts with ATR astigmatism

Answer 132

◦ Spherical back surface and a toric front surface ◦ Indicated for patients with corneal astigmatism < 2.50D and with an unacceptable magnitude of residual astigmatism ◦ The front toric surface will correct the residual astigmatism ◦ More susceptible to rotation on the eye, must use prism ballast

Answer 133

◦ Progressively flatten towards periphery ◦ Improved alignment, better centration and comfort, decreased SA and decreased tear exchange ◦ Back surface aspheric ‣ ATR astigmatism, irregualr corneal astigmatism, or bordering corneal astigmatism ◦ Front surface aspheric ‣ Excessive residual astigmatism or patients who have hypercritical VA demands ◦ Main disadvantage is decreased tear exchange

Answer 134

◦ Simultaneous design: both distance and near power are located within the pupil at the same time ‣ Centration is critical! • Dependent on the size of the pupil ◦ translating deisgn ‣ Lens is segmented ‣ Prism ballasted ‣ Crescent, executive bifocal, trifocal designs

Answer 135

• P=Dk • Oxygen permeability is essential to prevent excessive corneal edema • High Dk values (51-99) or hyper Dk values (>100) for extended wear • Low Dk (25-50) daily wear • Total amount of gas that actually passes through= transmissivity (T) T=(P/t)=Dk/t. T=thickness in cm • the amount of oxygen transmitted through the CL increases when the permeability of the CL material increases, and the thickness decreases

Answer 136

◦ GPCL contain little water, oxygen permeability is dependent on the concentration of silicone/fluorine within the CL material. ◦ PMMA ‣ DK=0, original material ‣ Corneal edema, complete lack of O2 ◦ Silicone acrylate (SA): ‣ DK=12-56 ‣ Flexure, deposits, and poor wetability ◦ Fluoroscilicone acrylate (FSA) ‣ Dk=18-163 ‣ Better wetability, less deposit, less flexure, less dryness

Answer 137

◦ Patients previously fit with PMMA should be refit into low DK materials ◦ Myopes: low Dk (25-50) for daily wear, high Dk (51-99) for extended wear ◦ Hyperopes: high Dk for daily wear, hyper-DK (>100) for extended wear

Answer 138

◦ Reduce CL wear time ◦ Fit pt with a looser CL ◦ Choose higher DK CL material

Answer 139

◦ Lid attached- interacts with superior eyelid | ◦ Interpalpebral—superior eyelid located above limbus

Answer 140

<2.50D corneal astigmatism)

Answer 141

(<2.50D corn astig, residual astigmatism)

Answer 142

corneal astig >2.50D and spec astigmatism=1.5x corneal astigmatism

Answer 143

>2.50D corneal astigmatism and spec astigmatism that does not equal 1.5x corneal

Answer 144

ATR or borderline astigmatism

Answer 145

Higher oxygen, more flexure, increased CT | -high DK extended wear, low DK daily wear

Answer 146

* ONLY WHEN ON THE EYE * Plus GPCL tend to maintain shape, as do minus GP corneal CL with a center thickness greater than 0.13mm * Flexure increases the amount of residual astigmatism * Can be seen with keratometry * Only occurs when ON THE EYE

Answer 147

``` Increased thickness > 1.50D cyl Increased OZD Increased DK Steeper BC ```

Answer 148

◦ K readings are spherical—CL is maintain shape | ◦ K readings are toric—CL is exhibiting flexure

Answer 149

• Warpage=ON and OFF the EYE ◦ Reduced VA ◦ Permanently-induced toricity of the GPCL ◦ Result of excessive digital cleaning. ◦ It occurs when the GPCL is on OR off the eye ◦ Differentiated from flexure using a radiuscope ‣ Warped GP will have toric BC ‣ GP that is flexing on the eye will have a spherical BC ◦ can alter the magnification properties and increase the effects of marginal astigmatism

Answer 150

• total flexure • Lacrimal lens power is always Plano • Do not correct corneal astigmatism • Making the BC flatter or steeper than K will not change the power of the soft CL • One exception to the rule of SCL conforming to the shape of the cornea: ◦ It is possible that a very thick SCL used to correct aphakia may form a minus power lacrimal lens • In general, pts can be fit with spherical SCL if they have <1.00D WTR astigmatism or <0.75D ATR or oblique astigmatism

Answer 151

indicated for >0.75D ATR/oblique pr 1.00D WTR residual astigmatism ◦ Front surface is most commonly the toric one ◦ Prism ballasting: BD prism in bottom to reduce rotation . Greater prism needed for smaller diameter ◦ Periballasting: BD prism out side of the OZ o

Answer 152

Both inferior and superior portions of the lens are thinned

Answer 153

inferior and superior removed, thinner edge

Answer 154

portion of the lower CL removed

Answer 155

◦ Doctors view ◦ Left ADD (clockwise) ◦ Right subtract (counterclockwise) ◦ Only works if the lens consistently rotates to the same postion on the eye SCL

Answer 156

◦ BC selection: SCL are typically fir with a BC that is 4D flatter than K ◦ Diameter: HVID + 3mm

Answer 157

good centration. Extend 1.5mm beyond limbus, will move 0.25-1mm with blink, and will habe 1mm of lag with superior, temporal, and nasal gaze

Answer 158

good centration, Good comfort, will not move with blink or digital rotation

Answer 159

poor centration, poor comfort, excessive movement. CL may be wrinkled, easily dislodged

Answer 160

well centered, extend 1.5mm beyond limbus, move no more than 5 degrees, quickly returns, stable OR

Answer 161

different orientation each time its on eye, minimal rotation

Answer 162

excessive rotation, slow movement of the CL to original position after blink, unstable OR

Answer 163

Lower water, nonionic

Answer 164

High water, nonionic

Answer 165

Low water, ionic

Answer 166

High water, ionic

Answer 167

With higher water content that are ionic Groups 3 and 4

Answer 168

◦ Stiffness ◦ Depends on thickness and the modulus of elasticity ◦ As water increases, modulus decreases ◦ Benefits of high modulus: better handling, easier removal, easier to tell where it is ◦ Drawbacks: GPC, SEALs, LEH, mucin balls, edge fluting

Answer 169

high permeability (high DK) for hydrogel low silicone content=low permeability (DK) for silicone

Answer 170

◦ Hyperopes accommodate less with CL ◦ Myopes accommodate more with CL ◦ Pt with presbyopia and myopia may need a reading add earlier when wearing CL

Answer 171

◦ Hyperopia=less mag in CL ◦ Myopes=increased mag in CL ◦ If the most amreopic eye has axial ametropia, spectacles will minimize the induced aniseikonia. If the most ametropic eye has refractive ametropia, CL will minimize the induced aniseikonia

Answer 172

◦ Less vergence in CL for hyperope; less induced BO | ◦ Nor evergence in CL for myope; less induced BI

Answer 173

Old distance/new distance

Answer 174

New size/old size

Answer 175

* result of an increase in the retinal image size of an object by introducing an optical system between the object and the eye * Unlike RDM and RSM, angular magnification is NOT a result of a change in the location or the size of an object * Hand held magnifiers, stand magnifiers, and/or telescopes

Answer 176

* ML compares the ratio of the object size to the image size formed by an optical system. Math: ML=L/L1 or Hi/Ho * MA compares the ratio of the original retinal image size to the retinal image size when the object is viewed through an optical system

Answer 177

◦ High plus lens ◦ Typically places in front of th eye so that the object of interest is located at the primary focal point of the magnifier ◦ Also known as a collimating magnifier (light leaves the system in form of plane waves ◦ Accommodation (and thus an ADD) are NOT required in order for the patient to view the object clearly though the HHM because the image is formed by plane waves (zero image vergence)

Answer 178

MT=|u|F | U=dist btwene object and eye

Answer 179

and MT will remain the same (moving the magnifier-same MAG and decreased FOV

Answer 180

standard working distance of 25cm, referred to as effective magnification ‣ Math: M=(0.25)(F)=F/4

Answer 181

◦ High plus powered lens ◦ Object to lens distance is fixed ◦ Object is located inside the primary focal point ◦ Creates an upright, magnified, and virtual image ‣ Math: MT=mM (lat magxRDM) ◦ Patient must wear an add ‣ Stand/Add combo math: M=Fe/4 ◦ Max magnification: Mmax=F/4 + 1 ◦ Require the patient to accommodate or wear an add in order to see the image clearly

Answer 182

* magnify distance objects * Objective and ocular lens set up so the secondary focal point of the objective lens coincides with the primary focal point of the ocular lens. * Plane light waves enter and plane light waves leave (parallel in, parallel out)

Answer 183

-Foc/Fobj Can also be detmeined using the entrance nad exit pupil diameters M=Dent/Dex

Answer 184

AXB, A is magnification and B is the objective lens diameter

Answer 185

dependent on the diameter of the exit pupil and the diameter of the entrance pupil of the patients eye ◦ Telescopes with a given magnification, increasing the entrance pupil diameter (size of the objective lens) will increase the exit pupil diameter, and therefore the FOV ◦ Will continue to increases as the exit pupil diameter of the telescope is increased up until the exit pupil becomes larger than the size of the patient’s pupil. The patients pupil diameter becomes the limiting factor. ◦ FOV can also be increased by aligning the exit pupil of the telescope as close as possible to the patients entrance pupil.

Answer 186

◦ Objective and ocular are plus lenses ◦ Objective lens forms a real, magnified, and inverted image ◦ Longer tube length and heavier ◦ Exit pupil: located outside the telescope larger FOV ◦ Be more easily aligned with the entrance pupil of the patient’s eye ◦ Exit pupil is small ◦ Images appear dim ◦ Have higher magnification

Answer 187

◦ Mag up to 4x ◦ Increasing the power increases the overall magnification, but also reduces the tube length. There is a limit to how much of the power of the ocular lens can be increased and the tube length decreased before the ocular lens physically touches the objective lens in the telescope

Answer 188

Inside telescope

Answer 189

Outside telescope

Answer 190

Upright Mag Vitreal

Answer 191

Mag Inverted Real

Answer 192

◦ Used to view near objects ◦ 2 solutions to eliminate the need for accommodation when viewing a near object with a telescope ‣ Adjust the tube length ‣ Add a reading cap to the objective side of the telescope ◦ A reading cap acts as a hand held magnifier. Object is located at the primary focal point of the reading cap. Neutralize the incoming divergent waves from the object, allowing plane waves to enter, so zero accommodation required. ◦ A combination of a telescope and a reading cap is known as a telemicroscope

Answer 193

M=M(reading cap)x M(telescopes_

Answer 194

continuous viewing, watching sports, concerts, movies, TV ‣ Minimal training ‣ For patients with dexterity or cognitive issues ‣ Should not walk around while wearing a center fit spec mounted scope

Answer 195

upper portion, good for spotting. Used for classroom work, driving, traveling in airports, at he grocery store ‣ Significant training required ‣ Poor dexterity or cognitive issues are generally not good candidates for this ◦ A reading cap can be added to a spectacle mounted telescope so the patient can view near objects

Answer 196

``` ◦ Expand VF, good for RP and glaucoma ◦ Accomplished by turning the scope around so that the patient looks through the objective lens rather than the ocular lens. ◦ Will minify objects ◦ Must have good central VA ◦ Often hand held ◦ Used for spotting objects ◦ 2.5X to 4x galilean most often used ◦ Beyond 4x, minification is too small ◦ Minus lenses can also be used to expand the FOV by minifying objects, similar to reverse telescopes ‣ Held at arms length ‣ For spotting ‣ -5 to -10D lenses used ```

Answer 197

◦ 1. Hemianopsia or visual neglect due to stroke | ◦ 2. VF constriction (glaucoma/RP)

Answer 198

for temporal visual field loss. Placed on the nasal side of the eye with the defect so that the temporal field is reflected into the mirror ◦ They often cause confusion ◦ Often induce scotomas ◦ Cause nausea and poor cosmesis

Answer 199

◦ Used to relocate the missing area of the VF into the patient’s line of sight. ◦ Binocular or monocular ◦ Base towards the side of the defect ◦ 1 degree=2PD

Answer 200

Scanning technique

Answer 201

◦ Generally due to macular disease ◦ Difficulty with near tasks, reading signs, and recognizing faces, they may also have poor contrast sensitivity ◦ Require magnification, glare control ◦ Do not have trouble with mobility

Answer 202

◦ RP, advanced glaucoma | ◦ Poor mobility, poor night vision, and glare

Answer 203

20/12 to 20/25

Answer 204

20/30 to 20/60 | ◦ A patient with 20/60 BCVA cannot resolve 1M at 1m, but can resolve it a 1/3m

Answer 205

20/70 to 20/160 ◦ Because the patient can read at a distance of 25cm or less, in order to see 1M print, it is often difficult for the patient to maintain binocular vision due to increased demand on convergence ◦ Require BI prism to reduce the demand on convergence ◦ In general, when patients rewuire reading glasses > +4.00D, prescribe BI prism to reduce the convergence demand. The amount of BI prism per eye is 2 + D (the sphere power of the eye). ‣ +8.00D readers = 10 PD BI

Answer 206

◦ Require BI prism to reduce the demand on convergence ◦ In general, when patients rewuire reading glasses > +4.00D, prescribe BI prism to reduce the convergence demand. The amount of BI prism per eye is 2 + D (the sphere power of the eye). ‣ +8.00D readers = 10 PD BI

Answer 207

20/200-20/400 ◦ Usually use monocular viewing ◦ Considered legally blind in the USA

Answer 208

◦ Patient cannot read any letters on the 20/100 line in the better seeing eye ◦ VF diameter is 20 degrees or less in the better seeing eye

Answer 209

20/500 to 20/1000 ◦ In order to read 1M print, the patient must hold the reading material VERY close to the eye (typically < 5cm), causing reading to be very difficult

Answer 210

Worse than 20/1000

Answer 211

acute, bilateral blindness due to damage to the visual cortex rather than the eyes themselves; common causes include stroke, trauma, surgery, lesions, and congential causes.

Answer 212

• Continuous text charts (Lighthouse) should be used to provide a functional assessment of patients reading abiltiy

Answer 213

◦ Lighthouse charts are used in low vision use the M unit ◦ 1M is defined as the size of a symbol that subetneds 5 arcminutes at 1m. Equivalent to snellen 20/20 ◦ Most newspaper size print at 40cm is 1M ◦ Finding snellen equivalent: (Test d)/(M dist)=20/x ◦ 1M newspaper print at 40cm is equivalent to 20/50 snellen acuity 0.40/1M=20/X X=50

Answer 214

◦ Visual goals ◦ Ocular history: what diseases is the patient suffering from, and what type of vision loss is it causing (central scotoma) ◦ Co-morbidities: dexterity issues ◦ Glare/lighting/contrast issues

Answer 215

the patients central and eccentric viewing BCVA should be assessed at distance and near; recall that central BCVA ◦ EDTRS (Lighthouse), Bailey-Lovie chart, Feinbloom chart

Answer 216

JND=snellen denominator/100 ◦ The JND is the smallest lens power change that the patient can detect. JND=the denominator of the 20 ft snellen acuity/100

Answer 217

◦ Watch for eccentric viewing ◦ Patient can easily turn their head and eyes in order to sue eccentric viewing if they have scotomas ◦ Eccentric viewing occurs when the patient uses a retinal point other than the fovea to view the object. The point is often located adjacent to the scotoma and is known as the preferred retinal locus (PRL) ◦ More accurate than the phoropter

Answer 218

Distance mag=what you got/what you need

Answer 219

Near mag=what you got/what you need

Answer 220

Inverse of the patients distance VA to determine the starting add power ‣ A patient presents with distance BCVA 20/200. The predicted add power is 200/20=+10.00D ‣ Not the most accurate to determine the near mag

Answer 221

the predicted add is equal to ((patients current near VA)/(patients Goan near VA)) x working distance (in diopters) ‣ May require more mag if they have reduced contrast sensitive

Answer 222

``` ‣ Stand magnifiers ‣ HHM ‣ High plus readers ‣ Head borne/spectacle mounted magnifiers • Good for longer working distances ‣ Electronic magnifiers ```

Answer 223

‣ Hand held telescopes ‣ Center fit spectacle mounted ‣ Bioptic telescope

Answer 224

◦ Large print or audio books, a scanner, talking watch, talking blood glucose meter, talking alarm clocks, bump dots, typoscope, high contrast dish ware

Answer 225

◦ Most patients with low vision also have reduced contrast sensitivity and increased glare. ◦ Pelli-Robson chart: letters of uniform size ◦ Vistech Contrast Test System: series of sine wave gratings of various contrasts and frequencies. ◦ Bailey-Lovie Chart ◦ Enhancing contrast and decreasing glare help to improve a patient’s mobility. Can use filters to help ‣ Neutral density filters: no effect on contrast, gets rid of glare ‣ Blue blockers (amber tints): reduction in glare AND enhanced contrast

Answer 226

Peripheral field loss and central field loss

Physiological Optics I Flashcards

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