5.2.2. Manages the aftercare of patients wearing rigid gas permeable contact lenses.

Question 1

3 and 9 o’clock staining

Answer 1

• Drying @ nasal and temporal areas of the cornea
• Triangle shaped pattern in the periphery; base of triangle corresponds to lens edge
• Caused by thick lens edge design, TD minimal or excessive, insufficient edge clearance, incomplete blinking
• Nasal & temporal bulbar redness
• Can lead to progressive scarring & corneal vascularisation
• Often asymptomatic, possibly decreased WT / red or itchy eyes

**Management **
Cease wear 24-48 hours
Refit with increased TD
Reduce edge clearance
Refit with SCL
Blinking exercises
Modify WT

Question 2

Dimple veil staining

Answer 2

• Indentations of epithelium caused by pressure of gas/air bubbles trapped under rigid lens
• Small hemispherical pits in epithelium
• More prevalent in poor fitting hard lenses
• Poor lens cornea relationship
• Excessive corneal clearance
• Too flat (more common) or too steep
• Patient generally asymptomatic, may experience mild irritation

**Management **
Modify lens fit as required

Question 3

Other signs associated with RGP wear

Answer 3

• Bitot spots; build-up of keratin debris on the conjunctiva associated with long term conjunctival drying; consider thinner lens design
• Dellen; thinning of the cornea causing saucer like depression; long term consequence of desiccation
• FB track
• Lens warpage; replace lens
  *

Question 4

Deposits examples

Answer 4

• Protein
• Uneven haze on lens surface
• Very common with high water, ionic lenses (softs)
• Protein remover tablets
• Lipid
• High water, non-ionic lenses (softs)
• New lens, change material, increase surfactant cleaning
• Fungal growth
• Poor hygiene

Question 5

Rules of thumb:

Answer 5

• Every +0.50mm increase in TD, increased BOZR by 0.05mm
• Every 0.05mm lens is flatter than corneal radius = -0.25D tear lens
• Every 0.05mm lens is steeper than corneal radius = +0.25D tear lens
• If you increase TD, you centre the lens better & better lid hitch
• If you decrease TD, you centre the lens less but reduce rocking along the steeper meridian in a more astigmatic fit

Question 6

Assessor may ask you describe the design of the lenses:

Answer 6

• BOZR - Radius of curvature of the central, optic zone
• BOZD - Diameter of the central, optic zone of a contact lens
• HVID - horizontal visible iris diameter
• VPA - vertical palpebral aperture
• TD - total diameter of the lens
• Edge lift - Gap between cornea & back surface of peripheral curve (seen in NaFl fit)
• Curves:
  
  • Single curve - useless
  • Bicurve - rare/useless - central radius + one flatter peripheral curve (transition too sharp). Better for small diameter lens
  • Tricurve - most modern lenses - central radius + more flatter peripheral curves
  • Tetracurve - 3+ peripheral curves! Follows flattening of cornea very well. Best for larger diameter lens
  • Aspheric lenses - not spherical but follows rate of flattening of cornea very well again

Question 7

a. Front surface

Answer 7

i. Spherical back surface (for fit) with front surface cyl to correct residual astigmatism.
ii. Typically 1.5Δ BD prism ballast is used. Differential weight causes orientation with prism base downwards.
used when there is lenticular astigmatism for the most part & hardly any corneal. Front surface cyl corrects it whilst the spherical back surface is for the power of the rest of the lens. If a back surface was used, it would not align with the shape of the cornea (as the cornea would be more spherical) and would probably end up inducing more residual astigmatism

Question 8

b. Back surface

Answer 8

i. Back surface toric (for fit) with spherical front surface
ii. Stabilisation is normally unnecessary since lens radii align with principle corneal meridians
iii. Spherical tear lens - fluorescein appearance should be identical to that of spherical lens on spherical cornea
iv. In reality, rarely fitted (a bitoric is more common)
has closely aligned fit to steepest and flattest meridians, so much less toric rotation so no prism stabilisation. Back surface induces some residual astigmatism due to difference between tears and lens material refractive index hence why bitoric is better so its front surface can correct that

Question 9

c. Bitoric

Answer 9

i. BS toric (for fit) with FS toric power (for induced astigmatism)
ii. Shouldn’t need toric stabilisation, due to BS
iii. Used when back surface toric results in unacceptable amount of induced/residual astigmatism
iv. Spherical tear lens - fluorescein appearance should be identical to that of spherical lens on spherical cornea.
v. Power calculations – can always ask lab!
vi. Need to specify in each meridian…
used mostly instead of back surface as mentioned above & if front or back surface toric just don’t work well enough i.e. induce too much residual astigmatism

Question 10

d. Toric Periphery

Answer 10

i. Use tabulated data or go by fitting pattern
ii. Best results when difference between meridians is 0.6mm or greater
iii. Spherical centre with toric periphery
iv. Used to improve fit where corneal astigmatism is corrected by spherical BOZR
v. Allows even bearing and/or clearance at periphery resulting in improved centration and comfort
vi. Fluorescein pattern of a spherical RGP on a cornea with a spherical centre but toric periphery (edge clearance is too little in horizontal meridian but too much in vertical

Question 11

Reasons for using toric:

Answer 11

• >2.50D corneal astig (difference in K’s of 0.5mm)
• >0.75D residual astig (ocular minus corneal)
• Irregular astigmatism
• Poor fit with spherical RGP
• Excessive 3 and 9 o’clock staining
• Increase in toricity towards cornea periphery
• Large amount of lens flexure + corneal warpage
• Corneal ectasias e.g. keratoconus, PMD

Question 12

During the fluroscein assessment what must you look at:

Answer 12

 1. Central pooling:
* Look at the pooling (tear film) that is in centre of the cornea.
* Note the pooling in mm.
* Steep fit = Lots of central pooling (bright green area)
* Alignment fit = Apical clearance (dim green area)
* Flat fit = Central touch (dark area, no pooling)
 2. Mid-Peripheral touch:
* Look at the pooling (tear film) or touch at the mid-periphery when lens is at the centre of cornea.
* Estimate it in mm.
* Steep fit = Mid-peripheral touch is wide (dark area)
* Alignment fit = Slight touch/ even mid peripheral touch
* Flat fit = Pooling/ Mid-peripheral pooling is wide (green area)
 3. Edge Clearance:
* Look at the pooling (tear film) behind the edge of the lens.
* Steep= Edge clearance, narrow <0.2mm (dark area)
* Alignment= Edge clearance, even 0.2-0.3mm
* Flat= Edge clearance, wide >0.3mm (green area)

Question 13

What fits can you find and what may they look like:

Answer 13

AMENDING FIT
* Steep = Increase BOZR/ Decrease TD
* Flat = Decrease BOZR/ Increase TD
STEEP FIT
* Central pooling = lots (bright green)
* Mid peripheral touch = wide (dark area)
* Edge clearance, narrow <0.4mm
SLIGHTLY STEEP FIT
* Central pooling (green area)
* Mid peripheral touch = wide (dark area)
* Edge clearance = narrow
ALIGNMENT FIT
* Apical clearance
* Alignment
* Edge clearance = even, 0.4-0.5mm
SLIGHTLY FLAT
* Central touch (dark area)
* Mid-periphery pooling (green area)
* Edge clearance = wide, >0.5mm FLAT
* Little central touch (dark area)
* Mid-periphery pooling (green area)
* Edge clearance, wide >0.5mm
* The lens doesn’t stay central.