Corneal Microlayer Optical Tomography Review

*Vatookarn Roongpoovapatr, Jane C. Cook, Taher K. Eleiwa, Sonia H. Yoo and Mohamed Abou Shousha*

## **Abstract**

Anterior segment ultra-high resolution OCT (UHR-OCT) uses a resolution of 1–4 μm to provide non-invasive imaging of the tear film and cornea. This new high definition imaging technology increases our understanding of normal structure and pathological changes in the cornea, and resolution has continued to improve over time. UHR-OCT is useful in the treatment of disease such as dry eye, subclinical keratoconus, keratoconus, and ocular surface pathology. It also aids clinicians in fitting contact lenses and screening tissue for corneal transplantation. In this review, we summarize applications of imaging the normal and pathologic ocular surface and cornea. Novel developments, such as the new-generation micro-OCT, Anterior segment OCT angiography and artificial intelligence have the potential to continue to increase our knowledge.

**Keywords:** optical coherence tomography, optical biopsy, corneal microlayer, graft rejection, corneal imaging

## **1. Introduction**

Speed and image quality of Optical Coherence Tomography (OCT) technology have made great strides over the past few decades [1–3]. OCT has long been a critical part of imaging the posterior segment, but is now starting to become more helpful for the anterior segment as well [3].

As anterior segment OCT has evolved, the precision of axial resolution has increased, from 15 to 20 μm resolution of time domain (TD-OCT) to 4–7 μm of spectral domain (SD-OCT) and Fourier-domain OCT (FD-OCT) and 1–4 μm of Ultra- high resolution OCT (UHR-OCT) [4, 5]. Speed has improved and UHR-OCT allows for real-time imaging and minimizes motion artifacts compared with older models [6–8]. Scan width of UHR-OCT has also improved to the current 5–12 mm [2–9].

This high definition imaging shows the *in vivo* pathological changes in microlayers of the cornea. Many publications have described the utility of UHR-OCT in clinical diagnosis and management of corneal disease [2, 10–13]. In the following review, we summarize the clinical applications of imaging the ocular surface and cornea based on anatomical structure and will focus on UHR-OCT.
