Contact Lens Fitting: Sometimes 2+2=5

People kind of think that contact lenses are "1 size fits all" or standard for everyone. I could go into all the reasons why that's not true, but trust me: its not. Gas perms are custom-fit. I always joke that fitting soft contacts is usually like fitting tee-shirts: small, medium, large, X-large, XX large, etc. That's really not true, either, because of base curvature & material, but its a decent analogy that's understood by most of the population. Most adults can't wear small tee-shirts...but SOME can. Most children do not need XX large, but SOME do, etc.

Usually we take auto keratometry readings of a patient's corneal curvature, measure the Rx with refraction, look at the overall diameter of the cornea with a biomicroscope, and pick a contact lens that has an appropriate size & shape, accounting for the patient's preferred modality (if they want to sleep in them or if they've had GPC, etc). This method works well over 95% of the time. Probably more like 99%.

Well I just had a statistical outlier. He was a young patient with a normal-sized cornea, average keratometry readings and a low spherical Rx (no astigmatism). Usually these are slam-dunk cases: put on almost any "median" base curve, average diameter soft lens & he's good to go. Not with this kid, tho. The 1st 4 pairs of lenses we tried on him fit horribly. Excessive movement, displacement, great discomfort, etc. All of those "should" have fit based on his normal corneal measurements, but they very much did not fit. In the end we ended up going with a lens that in theory should have been way too steep for his cornea, but it fit well & was comfortable. Sometimes you can't "play by the rules".