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?