Flashcards in CL 2-3: GP Fitting 1 Deck (25):
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)
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
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.
What 3 Factors influence the Choice of OAD size?
1. Lid Position (Primary Factor)
2. Pupil Size
3. Corneal Curvature
OAD Factors: Lid Position (PRIMARY FACTOR!)
1. Upper Lid relative to Superior Limbus:
1. Fit smaller lens (Goal: Interpalpebral Fit)
2. Fit smaller Lens (Goal: Interpalpebral Fit)
3. Fit Larger Lens (Goal: Lid Attached Fit)
OAD Factors: Pupil Size
1. Measure when?
2. OZD needs to be bigger than what?
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
3. 65-80% of OAD
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
OAD in GPs for Normal Corneas
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
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
Choosing a BCR for a 9.2 mm OAD
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
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
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
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
1. K Values are generally stated in what?
2. BCR is stated in what?
2. mm or Diopters
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
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)
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
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)
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
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)
GP fit ON K
1. What kind of Tear lens is Induced?
1. A ZERO TEAR LENS!
(Tear lens = Plano)
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
Compensating for Tear LEns
1. SAM & FAP
2. What is CALCULATED RESIDUAL ASTIGMATISM?
1. Steeper add MINUS
Flatter ADD PLUS
2. Whatever is predicted to be left UNCORRECTED.