Corneal dimensions in various types of corneal dystrophies and their effect on penetrating keratoplasty

Abstract

To achieve a high optical performance and a low rate of immunologic graft reactions after penetrating keratoplasty (PK) an optimal graft outline has to be chosen. The purpose of this study was to compare the corneal dimensions of patients with various types of corneal dystrophies to normal control eyes. In patients with keratoconus (n = 117), Fuchs' (n = 100), granular (n = 28), lattice (n = 26) and macular corneal dystrophy (n = 25) and normal controls subjects (n = 93) standardized slit lamp photographs of the cornea were taken. Using a computerized planimeter (SummaSketch III, Summagraphics Corp., Seymour, USA) 13 x 18-cm color prints (total magnification x12) were assessed morphometrically. On average, the maximal and the minimal diameter of corneas in patients with macular dystrophy (12.3 mm/10.6 mm) and normal controls (12.1 mm/10.5 mm) were significantly smaller (p < 0.02) than in patients with keratoconus (12.6 mm/10.9 mm), granular (12.7 mm/10.8 mm) and lattice dystrophy (12.8 mm/10.8 mm), but significantly larger (p < 0.02) than in patients with Fuchs' dystrophy (11.9 mm/10.4 mm). In Fuchs' dystrophy the corneas were significantly (p < 0.0001) more elliptical than in all other dystrophies and controls. The rotation of the maximal diameter from the horizontal ranged from 36 degrees nasal inferior to 44 degrees nasal superior and did not differ between dystrophies and controls. In patients with keratoconus, lattice and granular dystrophy larger grafts may be considered to improve the optical performance without promoting the risk of immunologic graft reactions after PK. As a rule, we use 8.0/8.1 mm (recipient/donor) for keratoconus and 7.5/7.6 mm for Fuchs' dystrophy. However, the graft diameter has to be determined individually in each single eye immediately before trephination.