**Abstract**

Glaucoma is the leading cause of irreversible, yet preventable, blindness throughout the world. Since it is a disease which can be treated but not cured, it is crucial for the treating ophthalmologist to catch the disease as early as possible. The diagnosis of glaucoma is currently based on the appearance of the optic disc and standard achromatic perimetry. However, to detect glaucoma in its early stages, there are various diagnostic modalities of which optical coherence tomography serves as a novel tool. Optical coherence tomography has emerged over the years with the ability to detect changes in the optic nerve head, retinal nerve fiber layer, and currently the ganglion cell layer much earlier than the defects manifest functionally. Thus, optical coherence tomography acts as an important diagnostic aid to diagnose and monitor the progression of this sight threatening disease called glaucoma.

**Keywords:** optical coherence tomography, pre perimetric glaucoma, ganglion cell complex, retinal nerve fiber layer, spectral domain optical coherence tomography, time domain optical coherence tomography
