Morphometric Analysis of Deposits in Granular and Lattice Corneal Dystrophy: Histopathologic Implications for Phototherapeutic Keratectomy

Objective: To quantify the distribution and size of deposits in granular and lattice corneal dystrophies and to estimate the impact of these findings on the potential benefit of phototherapeutic keratectomy (PTK) as primary treatment in these corneal disorders. Methods: Central histologic sections of consecutive corneal buttons (34 granular dystrophy specimens of 27 patients (mean age 53 ± 12 years) and 20 lattice dystrophy specimens of 20 patients (mean age 50 ± 17 years) obtained from central penetrating keratoplasty were examined by light microscopy using Masson trichrome and Congo Red stains. Localization and anterioposterior diameter of the most superficial, the deepest, and the largest deposits were quantified in the central and the two peripheral thirds of the specimens. Bowman layer status and thickness of the epithelium were recorded. The clear central corneal zone size before and after a hypothetical superficial PTK (100-μm ablation) was calculated. Results: Central deposits in granular dystrophy were mostly superficial (mean distance from the epithelium 28 ± 19 μm) and associated with Bowman layer and epithelial changes. In lattice dystrophy, deposits were mostly midstromal (mean distance from the epithelium 79 ± 54 μm, P < 0.001) with a larger scatter, showing minor superficial involvement. After a fictitious PTK, a significant increase in mean clear central zone was achieved (P = 0.004). This increase in mean clear central zone was more pronounced in granular (from 484 ± 389 μm to 1451 ± 1954 μm) than in lattice (from 258 ± 183 μm to 846 ± 784 μm) dystrophy (P = 0.004). Deposits were completely removed in 22% of the granular dystrophy samples. In both dystrophies, a clear central "pinhole" greater than 1 mm in diameter was achieved in around one third of corneas. Conclusion: According to the histopathologic corneal deposit size and distribution, PTK may be an effective treatment to increase visual acuity in patients with granular dystrophy more than in those with lattice dystrophy, to delay or even avoid penetrating keratoplasty.