Bowman Layer Thickness: An Early Indicator In Suspect Vs Normal Cornea?

To study the use of Bowman layer thickness (BLT) in classifying a clinically suspect cornea using wide field ultrahigh resolution polarization sensitive optical coherence tomography (PS-OCT).

Narayana Nethralaya, Bangalore

In this study, a total of 60 eyes were imaged using our custom-built PS-OCT when presented with clinically healthy or suspicious anterior curvature obtained from MS-39 (CSO, Italy). Bowman’s curvature was also obtained from MS-39 using custom algorithm.  PS-OCT was used to measure PR enface maps (10×8 mm) (obtained from the posterior corneal surface) and BLT (8×8 mm). To determine BLT, Epithelium, Bowman's layer (BW), and stroma were segmented using the additional contrast provided by PS-OCT, thus providing “True” BLT. Further, all eyes were imaged at least 3 times to ensure reproducibility.

BLT in healthy eyes was observed to be 15 ± 2 µm with high reproducibility. Healthy eyes with thin corneal thickness (<500 µm) showed thin BW (11 – 13 µm). Eyes with healthy topography depicted uniform BLT with healthy PR distribution. Suspicious eyes showed profound changes in Bowman’s curvature which were not evident in anterior curvature. Interestingly such eyes showed irregular / non uniform BLT from ultrahigh resolution imaging. In few cases, BLT appeared to compensate for the regional thinning of epithelium thickness.

Non uniform BLT was observed in suspicious corneas. Wide field ultrahigh resolution PS-OCT can be used in routine clinical practice and longitudinal studies could help us better understand the role of BW in determining healthy or suspicious corneas.