Ability of Optical Coherence Tomography in Early Detection of Primary Open Angle Glaucoma

Abstract

Introduction: As glaucoma is one of the leading causes of blindness, its early diagnosis is crucial. Standard Visual Field (VF) examinations are used in the diagnosis and follow-up of glaucoma, but the major drawback is that the abnormalities do not appear until 20-40% of ganglion cells are lost. Defects in the Retinal Nerve Fiber Layer (RNFL), measured by Optical Coherence Tomography (OCT), is an excellent objective and quantitative method in the diagnosis and management of glaucoma at earlier stages. Aim: To assess the ability of OCT in diagnosing early glaucomatous changes using RNFL, Optic Nerve Head (ONH) and macular thickness parameters. Materials and Methods: A hospital-based case control study was done for 18 months at Department of Ophthalmology, Sawai Man Singh (SMS) Hospital and Medical College, Jaipur, Rajasthan, India. Fifty patients meeting the inclusion criteria were evaluated in the study as case group. To compare the results with those of a normal population 50 age and sex matched subjects were included. Each subject underwent detailed ocular examination and RNFL, ONH and macular thickness parameters were measured using Spectral Domain (SD) OCT. The unpaired t-test was used to compare continuous variables and Chi-square test was used to compare categorical variables. The Area Under the Curve (AUC) with its 95% Confidence Interval (CI) was calculated. The p-value <0.05 was considered significant. Results: A total of 50 glaucoma or glaucoma suspect cases and 50 controls partcipated in the present study, i.e., 100 eyes in each group were studied. Mean RNFL thickness, superior thickness, inferior thickness and temporal thickness were significantly (p<0.05) lower among cases than controls. Cup area, cup/disc (C/D) area ratio, horizontal and vertical cup to disc ratio (CDR) were significantly (p=0.0001) higher among cases than controls. Vertically Integrated Rim Area (VIRA) was significantly (p<0.05) lower among cases (0.19±0.13) than controls (0.28±0.05). There was no significant (p>0.05) difference in disc area between cases and controls. All the macular thickness parameters were significantly (p<0.05) lower among cases than controls except fovea. Overall, ONH and macular thickness parameters had high sensitivity and specificity than RNFL parameters in glaucoma patients. Conclusion: The present study found that a combination of RNFL, ONH and macular thickness parameters improved the diagnostic accuracy of OCT in early detection of Primary Open Angle Glaucoma (POAG).