**6.5 Keratoconus**

Eyes with keratoconus had a thinner stromal thickness than normal eyes for the entire vertical meridian profile. In the keratoconus group, the thinnest central stromal thickness was 383.8 μm [51]. Sandali et al. used Fourier-domain OCT to create a reproducible classification scheme for patient with keratoconus [76]. Fuentes et al. used Fourier-domain OCT (5 mm of axial resolution) to look for risk factors for hydrops in advanced keratoconus. They revealed that features such as increased epithelial thickness, Bowman's layer hyper-reflection, and stromal thinning at the cone may be associated with increased risk [77]. UHR-OCT is also useful to identify depth of crosslinking (**Figure 4**). However, Rocha et al. demonstrated that there were no significant differences in regional stromal thickness profiles at any corneal location after corneal collagen crosslinking for eyes with either keratoconus or postoperative corneal ectasia [52].

#### **Figure 4.**

*Prototypical cross-sectional UHR-OCT images of keratoconus before (a) and 1 month after collagen cross-linking (B); cross-linking demarcation band thickness (red arrow), depth (yellow arrow), and base (blue arrow).*
