Photo: Angela Chappell, Department of Ophthalmology, Flinders Medical Centre, Adelaide
The grafted cornea (above) was fitted with a mini-scleral lens by a local optometrist about a year ago. At that stage there were a few small blood vessels only to the graft margin, typical of those seen in a post-penetrating keratoplasty case.
Within one year, the graft has become significantly vascularised, effectively making future regrafting highly likely to be unsuccessful. This will have a profound effect on the patient’s future visual status.
Mini-scleral lenses have been an extremely useful adjunct to the contact lens practitioner’s armamentarium, particularly in formerly hard to fit cases such as decentred cones, pellucid marginal degeneration, Terrien’s marginal degeneration and so on.
The problem with the lens is its thickness (200-300 µm) and the thick and often stagnant retro-lens tear layer (also around 300 µm thick). The total thickness (500-600 µm) represents a possible major barrier to oxygen flux, perhaps reminiscent of the original thick polyHEMA lenses.
Sometimes the corneal irregularity allows a small retro-lens tear flow. In other cases, the tear layer can be almost stagnant with an obvious long-term risk to the eye.
Problems may occur many years after fitting and could represent a potential time bomb if patients are not carefully monitored. Regular after-care in such cases is absolutely essential.