**1.2 Optical coherence tomography angiography addresses current challenges in glaucoma diagnosis**

Glaucoma is diagnosed using three parameters: measurement of IOP, evaluation of the optic nerve anatomy, and VF testing. However, this approach is limited by its inherent subjectivity and measurement inconsistencies. One key challenge is that IOP measurement is not standardized and can be affected by the central corneal thickness (CCT), type of tonometer used, time of day, as well as the skill and training of the clinical staff obtaining the measurements. Similarly, visual assessment of the optic nerve and VF testing are subject to high degrees of inter- and intra-examiner variation, limiting their abilities to diagnose and follow patients with glaucoma accurately and objectively.

Due to these challenges, optical coherence tomography (OCT) technology has grown in popularity due to its ability to provide additional objective information about the structure and morphology of the optic nerve and retina. Specifically, peripapillary retinal nerve fiber layer (RNFL) analysis is widely used for glaucoma diagnosis, as RNFL thinning can indicate glaucomatous damage [5]. While OCT has greatly improved the accuracy and consistency of glaucoma diagnosis, it is still limited since it cannot probe the vascular degradation that occurs in glaucoma. Particularly, it is extremely challenging to distinguish between differing degrees of glaucoma severity, identify patients with optic cupping who have normal vascular perfusion, as well as monitor patient response to treatment over time.

*The Role of Optical Coherence Tomography Angiography in Glaucoma DOI: http://dx.doi.org/10.5772/intechopen.110272*

**Figure 2.**

*Aqueous humor dynamics in the healthy (top) and glaucomatous (bottom) eye as hypothesized by the mechanical theory (left) and vascular theory (right).*

#### **Figure 3.**

*Cross section of the optic nerve in the healthy (top) and the glaucomatous (bottom) eye as hypothesized by the mechanical theory (left) and vascular theory (right).*

Improvements in the OCT technology has led to the development of optical coherence tomography angiography (OCTA), a rapid, noninvasive imaging modality that can provide quantitative and volumetric assessment of both the structure and vascular aspects of the retinal and optic nerve. Thus, OCTA has addressed prior limitations of OCT and has revolutionized the evaluation of several ophthalmic diseases, including glaucoma by allowing clinicians to distinguish between glaucoma suspect, healthy, and glaucomatous eyes [6–9].
