Histologic and Ultrastructural Changes in Corneas With Granular and Macular Dystrophy After Excimer Laser Phototherapeutic Keratectomy

Abstract

The histologic changes after phototherapeutic keratectomy (PTK) in corneas with granular and macular dystrophy were studied. We studied 3 corneas of 2 patients (1 granular, 2 macular dystrophy), who underwent penetrating keratoplasty (PK) at 0.8, 2.16, and 3.25 years after PTK; and 11 corneas (controls) from 10 PK patients (5 granular, 6 macular dystrophy) by light microscopy and by transmission electron microscopy. PTK was performed by using the Asclepion-Meditec MEL 60 excimer laser. After PTK the epithelium (15-40 versus 5-100 microm), and the upper stromal collagen lamella thickness (50-75 versus 50-100 microm) were less irregular than for the controls. In 1 eye (macular dystrophy) 10 months after PTK an acid mucopolysaccharide-positive band was detected in the subepithelial stroma, which could be removed by hyaluronic acid digestion. This fact suggests that it was "haze" formed after PTK, rather than a subepithelial recurrence of the dystrophy. All PTK corneas had deposits in the mid- and posterior stroma. Concerning controls, deposits were detected under the epithelium in all corneas. Electron microscopy of the study corneas revealed a mostly continuous basal lamina, occasionally forming projections into the subepithelial stroma, and large numbers of well-developed hemidesmosomes (5.2 +/- 0.8 per microm membrane length) present at greater density than in the controls (3.5 +/- 0.8). In stromal dystrophies, PTK was effective in removing large subepithelial stromal plaques. There were no subepithelial recurrences, and hemidesmosome density was increased.