01/06/2021
A short essay suggested by a patient comment this week...
Contact Lenses and Keratoconus
Bezalel Schendowich, O.D.
June, ‘21
One of the long-standing fallacies connecting contact lenses with keratoconus is that corneal (and perhaps other) contact lenses are physiologically good for the cornea upon which they rest. I consider this statement fallacious after a career of tending to many hundreds of keratoconus patients in many stages of the disease. I have witnessed progressive corneal scarring and other pathologies related directly to contact lens use and abuse.
What is the purpose of the contact lens in Keratoconus?
First and foremost, the contact lens in keratoconus and other cornea distorting conditions, both primary and secondary, is to improve vision and binocularity. More than this I would never promise a patient. With the anterior corneal surface delivering some eighty percent of the refraction of the eye, even small distortions will be deleterious to the optical images then transferred to the brain. Since keratoconus is known to progress asymmetrically, the firm contact lens, while providing a far more uniform refractive surface, will also help to reduce anisometropia induced by differing refractions between the two eyes.
What can contact lenses not do for an irregular cornea – either from disease or trauma?
A contact lens cannot mend or repair the corneal changes affecting and deteriorating vision. Increasing corneal irregularity will progressively deteriorate both acuity and the quality of the acuity. Compensation for irregularity is not the same as reorganizing corneal shape or rebuilding structure. Until this day patients, some new and some veteran, present explaining that they have been told that the contact lens will help the condition of their eyes. I hope that they believe me when I make my case for the truth.
What damage can a contact lens – even a well-fit lens – produce in a cornea?
One of the great conundra in contact lens care is that of best vision vs best fit. Most contact lens professionals will agree that a lens that is aligned to and even bearing upon the cornea will yield sharper acuity than one with even minimal apical clearance.
A lens that molds the shape of the cornea is too tight; is likely to scratch or erode; can produce corneal edema – each of these conditions can contribute to a worsening of an already weakened corneal structure.
Over my years in practice, I have made it a point to fit without bearing upon the apex of the conical cornea. For some eyes, I have been more successful than for others. In many cases patients complain, often vociferously, that the sharpness of their vision is far less distinct with the new lenses than that which they enjoyed with their old lenses – you remember, those that were very annoying and even painful to wear. They do not remember. The problem comes later on.
**Spoiler: this story may well be an artifact of history. With corneal cross-linking and an artificially stable cornea, the following may not occur again…we hope!**
Having satisfied myself with vision and fit, I send the patient home with instructions for the use of his new lenses. I require that he return in two weeks for a check-up and re-evaluation of fit and visual acuity after several hours of wearing time. To this visit many will come, it is the further follow-up visits that these patients begin to skip until…generally around a year, sometimes two, down the road they will call requesting an appointment. When these patients arrive, they complain of pain and severe sensitivity to light – they may even be wearing sunglasses inside the building. When they do remove the shades and allow me a gentle peek at the problem, at least one eye is red and teary and difficult to keep open. They will want me to believe that the contact lens is ruined and causing all of this agony. I have learned that this is generally not the case.
On careful examination, I have found erosions, often open sores of some dimension; a plus lens over-refraction; contact lenses that bear or rub and erode the apex of the cone. Proof that firm contact lenses do not in any way restrain keratoconus from continuing to progress.
Scleral lenses are also not fault-proof. If a lens is fitted with a vault that is too low, this lens can also rub and abrade. If the lens has too great a vault then potentially corneal edema will form causing a gradual reduction in acuity after many hours of lens usage. A high limbal zone can cause conjunctival chalasis – the membrane will move into the limbal area from under the edge of the lens as a result of negative pressure under the lens. These are only the most common possibilities, books have been written about the subject.
The bottom line
Contact lenses are rightfully described as medical devices. In this case, they are not designed to treat disease but rather to compensate for visual disabilities engendered by ocular disease – primarily of the cornea. The lens must be designed for the cornea to contribute to well-being without abusing the corneal and conjunctival tissues. Follow-up evaluations and required alterations in dimensions or material should be standard to achieve and maintain a lens-eye equilibrium.
