**6.3 Refractive surgery**

*A Practical Guide to Clinical Application of OCT in Ophthalmology*

Bowman's layer significantly decreases in eyes after photorefractive keratectomy, and was on average 14.0 μm compared with normal eyes at 18.7 μm. There is significant variability after photorefractive keratectomy with some regions thicker than in normal eyes but most much thinner. The procedure also causes uneven epithelial

*A prototypical cross-sectional UHR-OCT image of a human cornea with Limbal stem cell deficiency; a hyperreflective material (yellow stars) which replaces anterior stroma and Bowman's layer with irregular overlying* 

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

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,

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

**5.4 Eyes after refractive surgery**

**6. Corneal pathology within stroma**

**6.1 Corneal inflammatory and infectious diseases**

which was not seen in Terrien marginal degeneration [73].

**6.2 Stromal corneal dystrophies**

thickness [24].

*epithelium (red stars).*

**Figure 3.**

zone [10].

**10**

membrane [60].

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