The phenomenon is called “midday fogging” and it is estimated that up to 30% of scleral lens wearers complain of hazy or cloudy vision after a few hours of wear. Eye doctors believe that there are a number of factors that might be to blame. Most likely, microscopic debris is accumulating between your scleral lens and your cornea. Normal pressure caused by blinking usually causes the particulate matter to move around the chamber fluid and dissipate. In some cases blinking doesn’t accomplish this; the deposits may settle and this may affect vision as the day progresses. Low viscosity of your own tears may also contribute to fogging. And another likely factor that may impact whether or not you will suffer from foggy vision is the fit of your scleral lenses. If, because of your keratoconus, you have a greater than average lens vault, the cup size is larger and there is more room for particulate to build up.
Researchers have found that the reaction to fogging is highly individualized. Lab tests performed on the fluid found beneath scleral lenses after several hours of wear have shown no specific agent to be ubiquitously responsible for creating the fog.
Experts recommend that if you find you experience midday fog, you should try using high viscosity, preservative free artificial tears to fill the scleral lenses rather than plain saline solution. Dr. Maria Walker, OD, Visiting Assistant Professor at the University of Houston-College of Optometry recommends either Allergan’s Refresh Optive or Alcon’s Systane Ultra artificial tears when a patient complains of midday fogging. When a patient needs even higher viscosity, she recommends Allergan’s Celluvisc single-use vials. Walker noted, “Some patients will figure out a ‘cocktail’ of preservative free tears and sterile saline to put in the back of the lens so that they do not run through the artificial tears too quickly.” She finds that one vial usually fills either a full lens or about ¾ of it, depending on the size of the lens. She finds that patients will ‘top off’ the lens with saline after using one vial.