Keratoconus: diagnosis and treatment

At a minimum, the refractive surgeon should use the patient's history, refraction, keratometry, and slit-lamp examination to determine the status of a patient's cornea. A diagnosis of keratoconus easily can explain a patient's symptoms or greatly alter a plan of action for refractive surgery. If the surgeon finds automated topography useful as a screening device for keratoconus, for patient education, and for the documentation of corneal status, it also should be included in the patient's examination. Indeed, most cases of keratoconus will be demonstrated by automated topography. However, the surgeon must resist the notion that automated topography replaces manual keratometry. The two modalities should be additive to provide increased information about the patient's cornea and should not be considered in competition with each other, as implied by some. The most important information obtained from automated topography is the determination of the optical quality of the cornea. This information greatly affects the choice of refractive surgery and explains postoperative problems. Far too much attention has been paid to the exact dioptric power at different corneal sites indicated by automated topography. Indeed, current automated topography techniques can only estimate the dioptric values of an aspherical cornea several millimeters from the center of the cornea. Refraction is the most accurate means for determining the refractive status of the eye. Refractive surgery is designed to correct a refractive error; it is not a topographical map. Those topography units that afford the observer the most accurate information about corneal irregular astigmatism will become very valuable. Because irregular astigmatism is linked directly to keratoconus, the more sensitive an automated topography system is in detecting irregular astigmatism, the better will it detect the subtle levels of keratoconus. Above all, the astute corneal diagnostician must learn to appreciate irregular astigmatism and should train extensively with a manual keratometer to detect subtle yet very meaningful levels of preoperative keratoconus and irregular astigmatism following refractive surgery.