contact lens case reports

Viewing Corneal Thinning in Keratoconus

BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO

In 1931, Professor Alfred Vogt at the University of Zurich described in detail the classic biomicroscopic findings of keratoconus. Later, Von der Heydt and Appelbaum further classified the corneal changes into distinct types of tissue alterations that include apical thinning, Fleischer's ring, ruptures in Bowman's layer, vertical striae, increased visibility of the corneal nerve fibers and ruptures in Descemet's membrane. These changes may appear at varying periods throughout the course of the condition and may not occur in all cases of keratoconus.

Figure 1. Inferior, paracentral corneal thinning in keratoconus.

This month we'll highlight a unique perspective of the clinical finding of corneal thinning.

Corneal Thinning

When you view an eye that has advanced keratoconus in optic section, the central or paracentral corneal thickness can be onethird that of the peripheral cornea (Figure 1). Due to the excessive corneal curvature, it may be difficult to keep the entire section in exact focus at one time. In the later stages of the condition, the resulting ectasia can result in Munson's sign, the angular curve present at the lower lid margin when the patient looks down.

In the early stages of the condition, apical thinning is often difficult to detect with the slit lamp; therefore, other positive slit lamp findings such as vertical striae often precede apical thinning.

Case History

Our patient is a 38-year-old male who underwent penetrating keratoplasty to his right eye in September 1996. The post-surgical follow up was uneventful and the patient ultimately achieved 20/20 visual acuity with a GP lens. The only remarkable finding occurred when we performed anterior segment optical coherence tomography (OCT) on his right eye.

OCT is a new anterior segment viewing technique recently introduced in the Visante (Carl Zeiss Meditec, Inc.), which uses a time delay of back scattered light to view the anterior segment of the eye. Our patient's OCT showed the preoperative, inferior corneal thinning, but it also showed the thickness of the transplanted cornea, which jettisoned out into the anterior chamber (Figure 2).

This case illustrates yet another unique viewing perspective of the anterior segment afforded by OCT. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #145.

Figure 2. Anterior segment OCT post-penetrating keratoplasty.

Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Paragon Vision Sciences and SynergEyes, Inc. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision and SynergEyes, Inc.