Tips and Tricks for Fitting Scleral Contact Lenses3:39 PM
I probably don't need to wax poetic anymore about my love affair with scleral lenses, but click the link if you are interested in why I think they are such a great alternative for irregular cornea patients. Since I first started fitting sclerals, there has been a major learning curve and the excellent reps at Essilor have really helped me triage difficulties. My first few fits were a bit like walking in the dark -- no one seemed to be publishing information about sclerals! Now you have Contact Lens Spectrum devoting almost entire issues to sclerals, and excellent resources at the Scleral Lens Education Society page. But if anyone wants a cliff notes version of how I fit scleral lenses, here it is:
1) Flatter is Better
The concept of sclerals is that they don't interact at all with the cornea, so there should never be touch. But a lens that is too steep causes a lot of vision, comfort, and fit problems. There is some debate about just how much vault you want centrally in your lens, but I have been ascribing to the around 250 micron rule with excellent results. Apparently there may be some settling to the lens after a few hours or days of wear, so it is not a bad idea to check a patient back after dispensing lenses in a few days to see how they are doing (have them wear the contact lens in, and tell them to have had the lens on for at least 3-4 hours before coming). Not sure what 250 microns looks like? Don't worry, I don't have microscopic eyes either (or an anterior segment OCT). The average cornea is around 540 microns, so just aim for a vault that is about half the thickness of the cornea in an optic section beam on your slit lamp. Works like a charm!
2) Size Matters
When I first started reading about fitting sclerals the theory was that a larger lens is easier to fit. Well that is true if you have a large cornea, but so many people out there have small/tight eyelids. A large lens is going to be really difficult to fit in this case! I like to measure corneal diameter (I never did this at first and it caused me a lot of headaches) with my slit lamp --just turn the beam horizontally and measure width. If you have a small diameter cornea (anything around 10 mm) then a smaller diameter scleral is a better bet. Maybe start between 14 to 16 mm in diameter on your lens. In some cases, the cornea is too small and the lids are too tight to ever make a scleral fit appropriately, so if you are having no luck getting rid of bubbles in this type of fit, I have been advised to abort. The new toric peripheral curve lenses may help in future.
3) You Do Need a Perfect Fit (or at least really close to perfect if you want optimal lens performance; this means no bubbles, no conjunctival entrapment, and no scleral blanching)
|Blanching is Bad via|
To me a perfect fit means a nice even tear film under the lens. Scleral blanching is a huge no-no; check for this by letting the lens sit for 20 minutes in office. If the lens is too tight, the sclera will be blanched white underneath and result is a ton of discomfort and suction when the person tries to remove their lens. Small bubbles tend to not worry people much; they may be insertion related. But I have found bubbles do matter - - even small ones cause poor comfort after a few hours of wear, and can really wreck havoc on vision, even if you think that it is just a little peripheral bubble. Believe me, you want it gone. A central bubble means the lens is too steep of course. A reverse geometry design is sometimes necessary to get rid of those pesky mid-peripheral bubbles. Conjunctival entrapment, where the conjunctiva folds over the limbal cornea under the lens, used to be no big deal in the literature. Now there is evidence that this can cause neovascularization to form in the limbal tissue underneath, where the corneal tissue is being deprived of oxygen under the conj. Flattening the lens tends to help solve this issue (read here for more details).
4) Poor Comfort? Check the Edge
The peripheral edge is a major source of lens awareness in this lens. We spend a lot of time with sclerals looking at the central and mid-peripheral fit, but you need the edge of the lens as flush as possible against the conjunctiva. If the patient can feel the edge with blink, it is going to be exceedingly uncomfortable. A great tool in knowing if you have achieved a good fit is by checking the suction when the patient removes their lens with a plunger. Too steep centrally = a lot of suction. Too much peripheral edge lift = a lot of suction. Believe it or not, a properly fit lens will actually have very little suction when the patient removes it properly. It is a really nice feed back tool for your fit if you don't have the luxury of having an anterior segment OCT.
|Oh No!! Another non-wetting lens! There goes another 2|
weeks to order a new lens to check if vision is acceptable
or we need another over refraction! Via
5) Choose the Right Material
Nothing is more annoying than having that perfect fit lens, but the patient can't see out of it because the surface is non-wetting. In my experience, Tyro 97 is your best material to prevent that non-wetting surface issue. With that being said, Optimum Comfort is the material my Essilor rep tends to recommend for better comfort, but I have had too many wetting issues with Optimum Comfort to go that route anymore. Especially if the patient has MGD issues. Tyro 97 every time for me now.