Fitting and Evaluation of RGP

Question 1

Empirical fit

Answer 1

• Quicker and more efficient
• Provides lab with measurements
• Considered more custom

Question 2

Diagnostic Fit

Answer 2

• Requires a fitting set
• More initial chair time
• Can observe the fluorescein pattern/fit of lens immediately
• Considered a trial lens
• Assess residual astig

Question 3

Selecting a diagnostic lens

Answer 3

• Minus cyl & vertex comp.
• Lens should be same material and similar thickness to the lens ordered
• A -3.00D fitting set works for low and moderate myopes
• Base curve should range 7-8.4mm

Question 4

Fit Process

Answer 4

• Allow 10-15 minutes for lens to settle
• Measure VA and perform OR
• Eval fluorescein pattern in central and then peripheral
  *Wratten 12 helps see better

Question 5

Alignment fitting

Answer 5

Lens normally fitted with lid attachment, a quarter to a third of lens should be tucked under lid and should move downward with each blink.
- Fit on K for higher astig
- Fit 0.50D flatter for low astig
- Best fit on WTR

Question 6

Fluorescein Pattern for Lid attachment

Answer 6

• Thin even limbal edge to edge layer of fluorescein
• Adequate peripheral clearance
• Apical alignment or slight apical/central pooling
• Midperipheral touch
• Fulcrum at 3-9 oclock

Question 7

Interpalberbral Fitting

Answer 7

• Thin lenses with tapered edges
• Steeper base curve, 0.50D steeper than K in low astig
• Smaller diameter
• Works well with ATR, pts who have problems with lens adherence with flat BC and large diameter, and pts who experience` corneal changes from lid attachments

Question 8

Fluorescein Interpalperbral

Answer 8

• Should have slight apical clearance
• Centers well, no air bubbles
• No impingement on limbus and no periph seal off
• Lack of lens movement
• Comfortable due to tighter fit

Question 9

Correcting a flat lens

Answer 9

1. Increase diameter by 0.4mm
2. Steepen base curve by 0.1mm
3. Remember to change power (FAP)
   *For every half step change in base curve the power changes by a quarter

Question 10

Correcting a steep lens

Answer 10

1. Decrease diameter by 0.4mm
2. Flatten base curve by 0.1mm
3. Change power (SAM)

Question 11

RGP lens designs

Answer 11

1. Spherical
2. Front surface toric
3. Back surface toric
4. Bi toric

Question 12

Spherical

Answer 12

Most common
Used when there is a small amount of cylinder
Corneal and Refractive are within 0.50D of each other

Question 13

Front surface toric

Answer 13

Spherical posterior, toric anterior curve
Corrects lenticular astigmatism
Used when Refractive cyl is greater than 0.75D than corneal

Question 14

Back surface toric

Answer 14

Toric posterior, spherical front surface
Used when refractive cyl is 40% greater than corneal cyl
Often used for ATR and oblique

Question 15

Bi toric

Answer 15

Toric curves on both front and back surface
Used when there is significant corneal astigmatism
Designed to improve CL positioning
Corrects any residual refractive astigmatism