CUSTOM CONTACT LENSES
Fitting Guide
Semi - Scleral
Indications
This 13.50 – 14.00 diameter RGP lens is designed as a problem solving lens. It is fitted as a sealed or ventilated semi scleral lens, utilizing the most modern materials and a design worked out over the last 20 years.
The Stoker Semi Scleral design is suitable for fitting the following categories of patients:- dry eyes either cosmetic or pathology - Keratoconus, especially those that defy conventional RGP fitting or which are associated with a dry eye. - Irregular corneas due to traumatic injury, Radial Keratotomy, surgery etc.
The results depend heavily on the ability of the fitter, please do not hesitate to call Custom if you are having a problem with the fitting .
I have extensive experience with Semi-scleral fitting (25+ years)
Material
Design
Trial Fitting
Wearing Schedual
What to Look for on Return Visits
Care and Maintenance
Due to the nature of the fitting technique it is essential to fit these lenses with as high a Dk factor as possible. We are currently utilizing a 100 DK material (Silperm 100) specially developed for the large diameter RGP lenses
The lens is designed to fit as a semi-scleral lens, overlapping the limbus by about 1- 1.5 mm. The central optical radius (Base Curve) should be selected utilizing the fitting set, such that it is preferable to have a minimum central touch. In the case of Keratoconus patients it is essential to minimize, but not eliminate any central touch.
This set is based on Saggital depth, so star midway and initially fit the lens for minimum central clearance, going to a higher sag # if the lens has too much central touch and a lower # if no touch.
Scleral fit
In all fittings it is essential to have at least 1/3 of the edge showing some clearance, otherwise the tear layer becomes static and may cause problems.
In order to control the edge lift off we have included in the fitting set an edge lift number, this number controls the peripheral curves being put on the lenses. If the trial lens shows a good central fluorescein pattern and a tight edge, then order the actual lens with an increase in the edge lift number (i.e. from .25 EL to say .35 EL) and visa versa if the edge lift is excessive.
Larger diameter lenses can be made if the limbal overlap is too small and smaller lenses if the overlap is too big, however we find that the 14.50 diameter works well for most patients.
Thickness will of course vary to some extent with the power, but it should be noted that excessive thickness will cause some increase in edema. I suggest that in high powers you specify small anterior optic zones.
Do all your normal pre-examination for contact lens fitting, including Corneal measurements and if possible spectacle RX. Where there is a difficulty obtaining a true refractive end point, I suggest that you put a known Hard Gas Permeable lens on the eye close to the expected RX and over refract. From this information we can work out the optimum power. If the fitting set power is close then utilize the fitting set.
Utilizing fluoresceine on the upper sclera.
Fit for 1/ Minimal central touch
2/ A minimum of 1/3 of the periphery should show some edge lift.
Note if the fluoresceine does not go under the lens easily, then remove the lens and drop some fluoresceine into it, together with non preserved saline.
Lens movement with a blink is not essential, however check to make sure there is no binding or sucking on. This can be done by gently pushing on the lower edge of the lens to see if there is some movement with a push.
3/ the lens should show a touch pattern about 1 mm in from the limbus.
When inserting the lens ask the patient to sit forward so that their eye is almost parallel to the ground. Clean the lens and wet with a GP wetting solution , rinse lightly with the saline ( Purilens) and fill the lens with the saline, being careful not to spill the saline. This is often easier for the patient to do. Check with the slit lamp, if there is a large bubble trapped under the lens, remove the lens and re-insert with fresh saline.
3/ Allow the patient to sit in your waiting room for 30 minutes and then check the fit and if good over refract the trial lens.
4/ Order the final lens quoting the Base curve , diameter, power , edge lift and anterior and posterior optic zones if different to the trial lens.
A well fitting lens should show some central touch, at least 30% of the periphery should show some edge lift off and the edge of the lens should be 1mm or more outside the limbus.
For corneas up to 11.50 diam use 13.50 mm lenses for larger use 14.50 mm lenses
you can vary the diameter for better comfort or stability.
For better fluoresceine pictures add a drop of fluorescein to the saline prior to insertion.
This depends on the practitioner, however for most patients I would suggest 4 hours for the 1st day and increase this by 2 hours per day until all day wear is achieved. Do not allow your patients to sleep in the lens.
The eye should be clear, no redness and no corneal edema after all day wear.
After a few weeks of wear the edge may tighten down as the central touch
compresses the cornea, at this stage the tear exchange may be reduced, the peripheral curves should be flattened by adjustment or a remake.(increase the edge lift)
1/ Check the edge lift, by placing a drop of fluoresceine on the upper limbus and waiting a minute and then checking if the fluoresceine is permeating under the lens. Check how much of the edge is lifting off and if the lens is binding to the sclera. (Deep indentation all the way round and sealing of peripheral blood vessels)
2/ Check for edema and the usual visual checks. If there is a residual cylinder take a K reading over the lens.
3/ Remove lens and check for corneal staining.
4/ Check the condition of the lens, if there is an excessive build up of protein on the surface then re-polishing or the use of a protein removing tablet (Overnight) may be indicated.
On removal the lens should be cleaned with an RGP cleaner, I suggest Miraflow or equivalent, rinsed with Purilens saline and stored in an RGP suitable solution.(Solo Care works well)
On insertion, rinse lens with saline, rub both surfaces with an RGP wetting agent rinse lightly with the saline , fill the lens with saline and insert.
Note : As the solution will be held in the pre corneal fluid, any disposition to an allergic or sensitive reaction to the preservatives will show as a corneal response, which should be corrected by changing to another solution or increasing the rinsing with the non preserved saline.
Lens removal:
With the patient looking slightly down, lift the top lid and gently push the lid margin under the lens whilst holding the lower lid tight on the lower edge of the lens.
If this is not easy, as happens with patients with loose lids, use a suction cup.
Hold the top lid up and place the suction cup on the temporal edge of the lens, then gently releasing the pressure lift the lens from the cornea.
Contra Indications and precautions.
The usual contact lens contra indications apply, however as this lens is designed for overcoming problems normally associated with pathological conditions, care must be taken to fully understand the implications of this design before proceeding to fit this lens.
Fitting requires skill and patience, in that the lens must fit well to work , but the rewards come in getting the patient to all day wear with a reasonable visual acuity and the minimum of edema.
Custom Contact Lenses
STOKER SEMI SCLERAL DIAGNOSTIC SET
Chordal
Base Curve Diameter Power Edge lift
7.10 13.50 -6.00 .50
7.20 13.50 -5.00 .45
7.30 13.50 -4.00 .40
7.40
13.50 -3.00 .35
7.50
13.50 -3.00 .30
7.60
13.50 -3.00 .30
7.70 13.50 -3.00 .30
7.80
13.50 -3.00 .30
7.90 13.50 -3.00 .30
8.00
13.50 -3.00 .30
8.10 13.50 -3.00 .28
8.20
13.50 -3.00 .27
8.30 13.50 -3.00 .26
8.40
13.50 -3.00 .25
Posterior OZ 10.5 mm