Diagnosing Keratoconus ... Are We Sounding the Alarm Too Soon?

By Karla Zadnik, O.D., Ph.D.
SEPT. 1997

The diagnosis of keratoconus might appear straightforward. The clinician skilled in using a slit lamp biomicroscope looks for signs of corneal thinning, Vogt's striae and a Fleischer's ring. He or she assesses corneal irregularity with sophisticated instruments like a videokeratographer or with cruder, but arguably equally effective, instruments like a direct ophthalmoscope, a retinoscope, a keratometer or a handheld Placido's disk. Applying a rigid contact lens parallel to the flat keratometric reading that shows apical touch is a particularly compelling diagnostic test.

Today, however, there is enormous interest in the scientific community in the so-called early detection of keratoconus. Researchers work hard to develop indices to describe early keratoconus, early keratoconus, and nothing but early keratoconus from a processed videokeratographic image. And many tout the value of diagnosing early, preclinical, subclinical or form fruste keratoconus in eliminating candidates for refractive surgery.

WHO NEEDS TO KNOW WHAT WHEN?

However, the clinical importance of such early diagnosis is debatable. What should we tell the patient about his or her diagnosis when the the long-term outcome for that patient is unknown? Should we screen for every disease we know how to screen for? Should we alert patients to the mere possibility of a disease we know how to manage but not how to cure?

We can certainly diagnose subtle corneal abnormalities in the form of inferior corneal steepening with videokeratography, but to the best of my knowledge, there is only one carefully documented case of early inferior corneal steepening progressing to what any of us would label clinical keratoconus.

LIMITING CAREER CHOICES

The value of early diagnosis may be debatable in light of its ability to hinder people in their career choices. Should inferior corneal steepening in the absence of any other signs of keratoconus limit a military trainee from entering flight training? What about limits that might be placed on other professions with uncorrected visual acuity requirements, like firefighters, corrections officers and police officers? Should the mere possibility of future keratoconus, however remote, limit a person's current career options?

Should patients be alarmed about a condition that they may be at risk for but might never develop? To date, keratoconus has been relatively obscure, known primarily to those who have it. But it was the subject of an article in a recent issue of People magazine, with a description of the vision associated with keratoconus as looking through a dirty windshield on a rainy night without windshield wipers. Should we frighten people with inferior corneal steepening into thinking they will soon (and inevitably) be windshield wiperless?

KERATOCONUS: 1 OR 2?

We don't even know for certain the meaning of inferior corneal steepening in the fellow eye of a patient with what appears to be unilateral keratoconus. Will the fellow eye necessarily progress rapidly to clinical keratoconus? If so, how soon? Is there truly unilateral keratoconus?

One study has shown that few keratoconus patients who appear to have unilateral disease have completely normal corneal curvature in the fellow eye. Do we really need to tell these patients that their fellow eye is progressing right behind the affected one? Or can we wait until we detect more positive clinical signs, leaving the patient to rely on the more normal eye's vision for as long as he is able?

These issues may not seem to be the weighty ones confronting the medical and scientific genetics communities as they wrestle with informing patients they carry a gene for breast cancer or Huntington's disease. But we do have a tool that gives us information about keratoconus that patients may or may not want to know. And we are, as a community, still unsure exactly what the information about early keratoconus means to patients.

We must exercise the utmost professionalism and caution as we move toward screening for a disease for which we have no early treatment, no cure, and for which the ultimate, individual prognosis is highly variable. CLS

Dr. Zadnik chairs the Collaborative Longitudinal Evaluation of Keratoconus Study. She is an assistant professor at The Ohio State University College of Optometry in Columbus.