Ultrastructural study of peripheral and central stroma of keratoconus cornea.

Purpose: Assess the lamellar organisation of the peripheral and central stroma of the keratoconus (KC) and normal cornea.

Methods: Five normal and three KC corneas were fixed in 2.5% glutaraldehyde and processed for electron microscopy. The ultrathin sections were observed under JEOL 1400 TEM, and digital images were taken with a bottom-mounted 11-megapixel Quamisa camera, using the iTEM software. Measurements of the lamellae were carried out using the iTEM software. Statistical analysis was performed using the SPSS software.

Results: The lamellar organisation at the centre and periphery of the KC cornea was disrupted by the presence of multiple undulations, which were more aggressive at the posterior stroma. Among the KC cornea, the mean lamellar thickness of the peripheral middle (1030.32±86.25 nm) and posterior (615.68±30.94 nm) stroma was also significantly (p<0.05) thinner than their corresponding areas of the central KC cornea (1151.1±48 nm; 783.57±31.10 nm). At the periphery of KC cornea, just above the Descemet's membrane (DM), small undulations appeared to emerge out from the DM. Furthermore, the anterior stroma of the peripheral cornea contained several lamellar sutures. The mean lamellar thickness of the peripheral and central KC cornea was significantly (p<0.0001) thinner than the corresponding areas of the normal cornea.

Conclusion: The present study reveals the involvement of lamellae in the peripheral stroma in the pathogenicity of the KC cornea. The emergence of small undulations in the DM suggests that the formation of undulation might be starting from the DM.