Flashcards in CL 2-3: GP Fitting 1 Deck (25):

1

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Empirical Fitting: what 3 things are needed?

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

2

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1. What's the benefit of Empirical Fitting?

2. What's the Benefit of Diagnostic Fitting?

###
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

3

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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?

###
1. Optic Zone while providing good lag with the Blink

2. 65-80% of the OAD.

4

## What 3 Factors influence the Choice of OAD size?

###
1. Lid Position (Primary Factor)

2. Pupil Size

3. Corneal Curvature

5

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OAD Factors: Lid Position (PRIMARY FACTOR!)

1. Upper Lid relative to Superior Limbus:

a. Above

b. At

c. Below

###
1. Fit smaller lens (Goal: Interpalpebral Fit)

2. Fit smaller Lens (Goal: Interpalpebral Fit)

3. Fit Larger Lens (Goal: Lid Attached Fit)

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?

###
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

7

##
OAD Factors: Corneal Curvature

1. To maintain Optimum Centration/Stability:

a. Select LARGER OAD for what BCR?

b. Smaller OAD for what BCR?

###
1. a. for FLATTER BCR

b. for STEEPER BCR

8

##
OAD in GPs for Normal Corneas

1. Small

2. Average

3. Large

4. They're Available in increments of what?

###
1. About 8.8-9.0 mm

2. 9.2-9.4 mm

3. 9.6-9.8 mm

4. 0.1 mm increments

9

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BC (BCR)

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

### 1. FTK; On K; STK

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

###
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

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?

###
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

12

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

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

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?

### 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

14

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1. K Values are generally stated in what?

2. BCR is stated in what?

###
1. DIopters

2. mm or Diopters

15

##
Sagittal Depth

1. The Sag of a lens is Dependent on what 2 Factors?

2. how to explain Sagittal Depths?

###
1. BCR, and OAD

2. S1: Original Fit

S2: Effectively Steeper (Larger Sag)

S3: Effectively Flatter (smaller Sag)

S2 > S1 > S3

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?

###
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)

17

##
General Rule to KEEP SAME FITTING RELATIONSHIP:

1. FLATTEN BCR by what?

2. STEEPEN BCR by what?

###
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

18

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

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

19

##
Power Determination

1. Diagnostically?

2. Empirically?

###
1. Over-Refraction

2. Calculations

20

##
1. Prescription Delivered by SCL = ?

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

###
1. Power of SCL

2. Power of GP + Power of Tear Lens

21

##
GP Fit FLATTER than K

1. What does this induce (for the TEAR LENS)?

2. Tear Lens (D) = ?

###
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)

22

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GP fit ON K

1. What kind of Tear lens is Induced?

###
1. A ZERO TEAR LENS!

(Tear lens = Plano)

23

##
GP Fit STEEPER than K

1. What does it induce for the Tear Lens?

**Eqn: Rx Delivered by GP = ?

###
1. Induces a POSITIVE TEAR LENS!

** = Power of GP + Power of Tear Lens

24

##
Compensating for Tear LEns

1. SAM & FAP

2. What is CALCULATED RESIDUAL ASTIGMATISM?

###
1. Steeper add MINUS

and

Flatter ADD PLUS

2. Whatever is predicted to be left UNCORRECTED.

25