RGP Keratoconus Fitting KL 2013
description
Transcript of RGP Keratoconus Fitting KL 2013
-
26/4/2013
(c) Simon Lam 1
Specialty RGP Fitting Igel E-conus Lens
By Simon Lam
BSc in Opt, PD in Opt, MBAAssociate Lecturer, Republic Polytechnic
Clinical Consultant, Optic Point Eyecare Centre, Singapore
Evaluation of RGP Fitting
Position (static centration)
Movement (displacement and speed)
Fluorescein Pattern
-
26/4/2013
(c) Simon Lam 2
Summary of Keratoconus Shapes
Corneal Shape affect RGP fitting
-
26/4/2013
(c) Simon Lam 3
Rules of Thumb for K-conus Lens Fitting
Igel E-conusNormal Fitting Criteria:Average K - 0.2mm
Igel E-conusFlat Peripheral Fitting Criteria:BC + 0.2mm
Igel E-conusLarge Diameter Fitting Criteria:OAD + 0.4mm
Tailor-madeScleral lens
Two Point Touch Large Diameter Fitting Criteria
Tailor-made Scleral lens
Two Point Touch Large Diameter Fitting Criteria
Topo map Shape Lens Use Remarks
Mild to Moderate Keratoconus with relatively normal corneal shape
These corneas have normal characteristics in the mid periphery
Fit with lenses of base curves in the range 7.10 8.00 in the same way as normal corneas.
If the peripheral cornea was relatively steep and may need to be fitted as steep periphery type.
-
26/4/2013
(c) Simon Lam 4
Cornea with steep central/inferior area and steep mid-periphery/periphery
Cornea demonstrates steep central K readings and a relatively steep mid peripheral and peripheral curvature, even compared to a normal cornea.
The corneal profile appears to have steep sides and this corneal shape is best fitted with base curves between 5.50 to 6.50 from the Fitting Set.
Cornea with steep central/inferior area and relatively flat mid-periphery
The mid periphery tends to be even flatter than normal corneas and it is advised to start with Fitting Lenses in the range 6.10 7.30.
For nipple cones, the difference between central and mid peripheral areas is even more extreme and suggested first choice Fitting Lens is FK +0.7xCorneal Cyl and a periphery equivalent to (BC -0.2mm).
-
26/4/2013
(c) Simon Lam 5
Static Centration
Horizontal: nasal/temporal (0 mm) Vertical: superior/inferior (0 mm) Movement: 1 mm, smooth, vertical Speed of movement: fast
Static Decentration
Horizontal: temporal (1 mm) Vertical: Superior (1mm) Movement:
-
26/4/2013
(c) Simon Lam 6
Static Decentration
Horizontal: temporal (1 mm) Vertical: Superior (2 mm) Movement: > 2mm, apical rotation Speed of movement: Average
Centration Assessment Not Enough
Static and dynamic centration assessment need to accomplish with NaFL assessment
-
26/4/2013
(c) Simon Lam 7
Fluorescein Pattern
Fluorescein Dye
Cobalt Blue Filter
Yellow Wratten Filter
WrattenWrattenCobaltCobalt
Fluorescein Patterns Interpretation
Central
Mid-peripheral
Edge lift
-
26/4/2013
(c) Simon Lam 8
Central Steep Fit
BC = 7.65mm Central pooling, mid-peripheral touch Edge-lift tight
Central Slightly Steep Fit
BC = 7.85mm Slight central pooling, mid-peripheral clearance Edge-lift tight
-
26/4/2013
(c) Simon Lam 9
Central Alignment Fit
BC = 7.95mm Central clearance, mid-peripheral clearance Edge-lift sufficient
Central Slightly Flat Fit
BC = 8.05mm Central touch, mid-peripheral pooling Edge-lift sufficient
-
26/4/2013
(c) Simon Lam 10
Central Flat Fit
BC = 8.15mm Central touch, mid-peripheral pooling Edge-lift excessive
Peripheral Assessment
Edge-lift width
-
26/4/2013
(c) Simon Lam 11
Tight Edge-lift
Thin NaFL, dull reflection Width < 0.2mm No tear exchange
Loose Edge-lift
Thick NaFL, bright reflection Width > 0.4mm Excessive tear exchange
-
26/4/2013
(c) Simon Lam 12
Adequate Edge-lift
Moderate NaFL, medium bright reflection Width > 0.2mm and < 0.4mm Adequate tear exchange
Comparison of Edge-lift
Acceptable range: 0.2mm < x < 0.6mm Adequate tear exchange
-
26/4/2013
(c) Simon Lam 13
Working Through The Pictures
Over-Refraction For most of the Over-Rx on RGP, we will
use spherical power only. If corneal cylinder is higher than 2.50DC, we
should use toric form of RGP. Over-Rx can help to determine the fitting of
the lens while over or under power may indicate less than optimum fit.
Over-Rx with more than +/- 4.00D needs to be vertex.
Visual Acuity (VA) < 6/9 may indicate lenticular
astigmatism present.
-
26/4/2013
(c) Simon Lam 14
Patient Comfort Rating
Patient may not feel comfortable if he/she is the first time RGP wearer. So, the rating should be done only after half an hour or one hour of wearing.
The most discomfortable is 0 mark and the most comfortable is 5. If the RGP can score 3 to 4 mark is considered acceptable.
Final Prescription and Communication with the Lab
Make sure you follow the Labs requirement and language that they are using.
Eg, Given to lab: K-reading: 44.00/42.00 Lab will make lens with FK = 44.00 not 42.00 as
the labs habit is that the first number is always the FK.
Remember: Lab people are not Optometrists! Dont take for granted they will fix the problem
for you.
-
26/4/2013
(c) Simon Lam 15
RGP Modification
For todays RGP lenses, most of them are manufactured by computerized CNC lathe-out machine with high precision and accuracy. They are difficult in modifying or changing their parameters. BC is definitely cannot be changed with existing lens.
OAD can reduce size but not enlarge.
Power (Rx) can increase maximum +/-0.50D.
Edge-lift can make flatter but not steeper.
Problem Solving For RGP Fitting
-
26/4/2013
(c) Simon Lam 16
Progress Evaluation Procedures
A. Lenses On 1. Visual Acuity 2. Retinoscopy (Over-Refraction) 3. Sphere-Cylinder 4. Biomicroscopy
a. Lag b. Surface Quality c. Edema
Progress Evaluation Procedures
B. Lenses Off 1. Biomicroscopy
a. Staining b. Limbal Vasculature c. Lids
2. Keratometry 3. Subjective 4. Verification
-
26/4/2013
(c) Simon Lam 17
Common RGP ProblemObjective Findings Probable Cause Solution
Excessive Movement Lens too flat Lens too steep excessive tearing
Change fit according to fluorescein pattern
No movement Lens too large/too steep inadequate edge lift
Flatten BC Decrease OAD Flatten PC
Displacement by upper lid
Thick edge Lens too large Flat fit
Reduce edge thickness ( + lenticular/ CN bevel) Reduce OAD Steepen BC
Excessive Edge Lift PC too wide or flat Narrow/steepen PC
3-9 Staining Periphery too flat Improper OAD
Steepen secondary curve Flatten BC Change OAD
Thank You
Questions?