**6. Corneal pathology within stroma**

#### **6.1 Corneal inflammatory and infectious diseases**

UHR-OCT can help with the diagnosis of Acanthamoeba and herpetic keratitis. Acanthamoeba cysts show up are seen as highly reflective dots in the stroma and radial keratoneuritis presents as thickening of the corneal nerves with ragged borders [10]. In post-herpetic keratitis corneas, UHR-OCT shows corneal thinning with areas of calcification and lipid deposition as single highly reflective scattering zones. Corneal neovascularization also appears as a hypo-reflective zone [10].

UHR-OCT is especially useful for assessment of corneal thinning in cases of impending perforation. Rodriguez et al. evaluated the use of UHR-OCT in the differentiation of inflammatory versus non-inflammatory, such as Terrien Marginal Degeneration, causes of peripheral corneal thinning. In the inflammatory group, UHR-OCT revealed a hyper-reflective subepithelial band in the area of thinning, which was not seen in Terrien marginal degeneration [73].

#### **6.2 Stromal corneal dystrophies**

UHR-OCT can evaluate the depth of deposits in stromal corneal dystrophies, which can be used to guide surgical therapy. Eyes with granular dystrophy show hyper-reflective material in the anterior stroma and clear intervening spaces. Macular dystrophy corneas show hyper-reflective stroma with areas of discrete, small hyper-reflective deposits in the subepithelial space, stroma, and Descemet's membrane [60].

**11**

**Figure 4.**

*Corneal Microlayer Optical Tomography Review DOI: http://dx.doi.org/10.5772/intechopen.84750*

UHR-OCT can be used to analyze the integrity of the corneal flap. High resolution structural characteristics of the opaque bubble layer can predict incomplete lamellar flap dissections. The opaque bubble layer can also be seen to extend

anterior to the flap dissection plane up to Bowman's membrane [74]. UHR-OCT can

Xu et al. reported that stromal vertical thickness profiles in eyes with subclinical keratoconus were thinner inferiorly compared with normal eyes [51]. Another group showed focal inferotemporal thinning, slightly more inferior than temporal. However, the degree of relative thinning was not as significant as on the epithelial

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].

*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).*

also image progression of flap melt and epithelial ingrowth [2].

**6.3 Refractive surgery**

**6.4 Subclinical keratoconus**

pattern deviation map [75].

**6.5 Keratoconus**
