Topographic Thickness of Bowman's Layer Determined by Ultra-High Resolution Spectral Domain–Optical Coherence Tomography

Bowman's layer and the basal lamina are important in the maintenance and support of the ocular surface.1 For instance, the integrity of Bowman's layer and the basal lamina prevent the eyes from developing persistent epithelial defects after transplantation.2 Additionally, a cellular proliferative response initiated by disruption of the Bowman's layer and the basal lamina occurs in advanced bullous keratopathy.1 Recently, characteristics of the central and peripheral Bowman's layer, close to the limbus, have drawn increased clinical attention, especially for designing refractive surgery and detecting corneal disease. A variety of techniques have been used to assess Bowman's layer in both healthy and diseased human corneas.3–5 However, each of these methods has some limitations. Confocal microscopy is an invasive technique with the potential of causing corneal lesions or transmitting infections, and it is impossible to measure exactly the same locations within the cornea in serial examinations. Electron microscopy allows only histopathologic findings. Thus, there are only a few published characterizations of Bowman's layer at the periphery, close to the limbus. Recent advances in optical coherence tomography (OCT) have enabled exact and rapid cross-sectional imaging of the cornea without direct contact between the eye and the instrument. OCT has excellent repeatability and accuracy.6–8 Spectral domain OCT (SD-OCT) is an advanced technique that has enhanced resolution compared with conventional time domain OCT. The high-speed imaging modality enables analysis of the topographic thickness of the epithelium, Bowman's layer, stroma, and the total cornea. The purpose of this study was to evaluate by ultra-high resolution SD-OCT the epithelial and Bowman's layer profile along the horizontal meridian in healthy human eyes.