CL 2-3: GP Fitting 1

Question 1

Empirical Fitting: what 3 things are needed?

Answer 1

1. Call in order for starting lens based on the following 3 parameters (Ks, Rx, and Lid Position)

Question 2

1. What’s the benefit of Empirical Fitting?

2. What’s the Benefit of Diagnostic Fitting?

Answer 2

1. Usually has a Benefit of Having the FIRST Experience with GP lenses being a visually POSITIVE ONE
2. of obtaining Optimum fit thru the application of lenses

Question 3

Choosing a Diameter

1. OAD of a GP needs to be LARGE ENOUGH to allow for a sufficient what?
2. OZD typically Encompasses what % of OAD?

Answer 3

1. Optic Zone while providing good lag with the Blink

2. 65-80% of the OAD.

Question 4

What 3 Factors influence the Choice of OAD size?

Answer 4

1. Lid Position (Primary Factor)
2. Pupil Size
3. Corneal Curvature

Question 5

OAD Factors: Lid Position (PRIMARY FACTOR!)

1. Upper Lid relative to Superior Limbus:
   a. Above

b. At
c. Below

Answer 5

1. Fit smaller lens (Goal: Interpalpebral Fit)
2. Fit smaller Lens (Goal: Interpalpebral Fit)
3. Fit Larger Lens (Goal: Lid Attached Fit)

Question 6

OAD Factors: Pupil Size

1. Measure when?
2. OZD needs to be bigger than what?
   a. Why?
3. OZD makes up what % of OAD?
4. A Lens w/a LARGER OAD usually has a LARGER WHAT?

Answer 6

1. light and dark
2. than pupil size in Dim illumination in order to MINIMIZE FLARE at NIGHT
   (that’s why)
3. 65-80% of OAD
4. OZD

Question 7

OAD Factors: Corneal Curvature

1. To maintain Optimum Centration/Stability:
   a. Select LARGER OAD for what BCR?
   b. Smaller OAD for what BCR?

Answer 7

1. a. for FLATTER BCR

b. for STEEPER BCR

Question 8

OAD in GPs for Normal Corneas

1. Small
2. Average
3. Large
4. They’re Available in increments of what?

Answer 8

1. About 8.8-9.0 mm
2. 9.2-9.4 mm
3. 9.6-9.8 mm
4. 0.1 mm increments

Question 9

BC (BCR)

1. 3 terms are used to describe how BC of a GP CL compares to Corneal Curvature: What are they?

Answer 9

1. FTK; On K; STK

Question 10

Choosing a BCR for a 9.2 mm OAD

Corneal Cyl

1. 0-0.50 D
2. 0.75 - 1.25 D
3. 1.50 D
4. 1.75-2.00 D
5. 2.25-2.75 D
6. greater than or equal to 3.00 D

Answer 10

1. 0.50-0.75 D FTK
2. 0.25-0.50 D FTK
3. On K
4. 0.25 D STK
5. 0.50 D STK
6. Bitoric design recommended

Question 11

Corneal Vs. Spectacle Cyl

1. Spectacle (Manifest) Cylinder: What is it?
   a. What components could it have?
2. Corneal Cyl: What is it?
   a. It may be different than what?

Answer 11

1. it’s the Actual Cyl in a Pt’s Refraction
   a. can have a Corneal Component, an Internal (Lenticular) Component, or Both
2. Difference in Curvature b/w the 2 Major Corneal Meridians
   a. May be different than the Spectacle Cyl

Question 12

Javal’s Rule (you know the eqn): What does it Provide?

Answer 12

1. Provides an ESTIMATED PREDICTION of the Manifest Cylinder Based on the Corneal Toricity

Question 13

1. The chart says to fit 0.50-0.75 FTK

and your Cyl difference is at the higher end (0.50 K cyl): What do you fit?

Answer 13

1. the higher the K Cyl, the steeper the BC chosen; So, Fit 0.50 D FTK since K Cyl is on the high end of the range listed

Question 14

1. K Values are generally stated in what?

2. BCR is stated in what?

Answer 14

1. DIopters

2. mm or Diopters

Question 15

Sagittal Depth

1. The Sag of a lens is Dependent on what 2 Factors?
2. how to explain Sagittal Depths?

Answer 15

1. BCR, and OAD
2. S1: Original Fit

S2: Effectively Steeper (Larger Sag)

S3: Effectively Flatter (smaller Sag)

S2 > S1 > S3

Question 16

Sagittal Depth

1. In order to keep the same fitting relationship, you can compensate for a change in diameter by adjusting what as Necessary?

Answer 16

1. the BCR

so if you’re using a fitting set that has 8.6 mm lenses, you may use a steeper base curve than the chart says

Question 17

General Rule to KEEP SAME FITTING RELATIONSHIP:

1. FLATTEN BCR by what?
2. STEEPEN BCR by what?

Answer 17

1. by 0.25 D for every 0.5 mm INCREASE in OAD

2. 0.25 D for every 0.5 mm DECREASE in OAD

Question 18

1. If you INCREASE the OAD by 0.5 mm, what are you doing?

Answer 18

1. you’re effectively STEEPENING the Fit by 0.25 D w/o having to change the BASE CURVE! (and vice versa)

Question 19

Power Determination

1. Diagnostically?
2. Empirically?

Answer 19

1. Over-Refraction

2. Calculations

Question 20

1. Prescription Delivered by SCL = ?

2. Prescription delivered by GP (Rx at the Corneal Plane) =

Answer 20

1. Power of SCL

2. Power of GP + Power of Tear Lens

Question 21

GP Fit FLATTER than K

1. What does this induce (for the TEAR LENS)?
2. Tear Lens (D) = ?

Answer 21

1. Induces a NEGATIVE Tear Lens

2. GP BCR (D) - K Value (D) (difference b/w Curvature of the Lens and the Curvature of the Cornea)

Question 22

GP fit ON K

1. What kind of Tear lens is Induced?

Answer 22

1. A ZERO TEAR LENS!

Tear lens = Plano

Question 23

GP Fit STEEPER than K

1. What does it induce for the Tear Lens?

**Eqn: Rx Delivered by GP = ?

Answer 23

1. Induces a POSITIVE TEAR LENS!

** = Power of GP + Power of Tear Lens

Question 24

Compensating for Tear LEns

1. SAM & FAP
2. What is CALCULATED RESIDUAL ASTIGMATISM?

Answer 24

1. Steeper add MINUS

and

Flatter ADD PLUS

2. Whatever is predicted to be left UNCORRECTED.

Question 25

1. What is Residual Astigmatism?
   a. So if a Spherical GP is put on the eye, the RA is what?
   b. How do you Calculate it? (CRA) = ?
2. What can Calculated Residual Astigmatism (CRA) be used to help us determine?
   a. When would we use a Spherical GP?

Answer 25

1. Refractive Astigmatism that is still Uncorrected when a CL is placed on an eye.
   a. It’s about equal to the Difference b/w the K Cyl and the Manifest Cyl
   b. Rx Cyl - K Cyl
2. if we can use a spherical GP or not. Too much cyl left uncorrected by a spherical GP, then we need to use a Toric GP of some kind.
   a. when CRA is LESS THAN or EQUAL TO 0.75 D
   b. Toric GP when CRA is > 0.75 D