Cornea (Wills Eye Institute Atlas Series)

CHAPTER

Ectatic Conditions of the Cornea 4

KERATOCONUS K eratoconus is a fairly common condition characterized by corneal thinning, pro trusion, and irregularity. It is almost always bilateral, although the severity of involvement is often asymmetric. Etiology ● Sporadic or autosomal dominant with in complete penetrance ● Gradually decreasing vision, typically be ginning in adolescence and progressing into adult life ● Patients often relate a history of not being able to attain good vision despite multiple changes of glasses or soft contact lenses. ● May have a history of eye rubbing or fist pushing into eye while sleeping ● Can develop acutely decreased vision and pain due to hydrops with advanced disease ● Eye rubbing Symptoms

Signs ● Earlier ■ Progressive myopia and astigmatism

■ Scissors reflex on retinoscopy ■ Irregular mires on keratometry

■ Inferior steepening on computed corneal topography ( Fig. 4-1A ) and tomography ( Fig. 4-1B and C ). Eyes with “low-sagging cones” can demonstrate a mild crab-claw topographic pattern ( Fig. 4-1D ), which is similar to the pattern seen in pellucid marginal degeneration. ■ Central or paracentral stromal thinning of the cornea with the greatest protrusion at the apex of the thinning ( Fig. 4-1E , eFig. 4-1E) ■ Epithelial thinning at the apex of the cone often with surrounding epithelial thickening in a “doughnut” shape seen on imaging, such as anterior segment optical coherence tomography (Fig. 4-1F) ■ Fleischer ring: epithelial iron deposition at the base of the cone ( Fig. 4-1G ) ■ Prominent corneal nerves ( Fig. 4-1H )

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