Role of OCT in Diagnosis and Progression of Glaucoma
Optical Coherence Tomography (OCT) has become a common tool in ophthalmic community for imaging of optic nerve head and macula. In glaucoma, it is of utmost importance in early diagnosis and monitoring the progression of the disease. Measurement of peri-papillary RNFL thickness is a common method of diagnosing and monitoring glaucoma. Recently Ganglion Cell Complex (GCC) analysis of macula has also shown to be helpful in identification of early glaucoma and coincides with RNFL damage. OCT can identify the structural damage in eyes before visual field defects occurs. High myopia with large discs, tilting and peri-papillary crescents and occasional hypoplasia of optic disc makes diagnosis of glaucoma difficult. It may be helpful in these patients to map ganglion cell complex (GCC) rather than relying on RNFL thickness. In advanced glaucoma when RNFL thickness level decreases to below 40 – 50 µm, the OCT will be of not much value to record any progression. This is termed as floor effect. OCT has now become commonly available in all parts of the country and is frequently used to determine RNFL and macular thickness in suspected or established cases of glaucoma. It not only helps in diagnosis and progression of the disease but helps us to make the patient being aware of the disease. However, we clinicians should also be aware of various artifacts related to acquisition of scans by our technicians, disease itself and related to the scanner. We must realize the limitation of comparative normative database incorporated in various scanners and that not every RNFL thinning is due to glaucoma.
Key Words: Optical coherence tomography, optic nerve head, macula.