Correlation of retinal nerve fiber layer thickness with perimetric staging in primary open-angle glaucoma – A cross-sectional study

BACKGROUND: Glaucoma is a progressive optic neuropathy, characterized by structural optic nerve damage with corresponding field defects. Primary open-angle glaucoma (POAG) is the most common. Although perimetry is the gold standard, retinal nerve fiber layer (RNFL) thickness by spectral-domain optical coherence tomography (SD-OCT) has proved reliable in the detection of pre-perimetric glaucoma. There is preferential involvement of various sectors of the peripapillary RNFL in the different stages of POAG. PURPOSE: The purpose of this study is to assess RNFL thickness and determine preferential involvement of different sectors of peripapillary RNFL in the various stages of POAG using SD-OCT. MATERIALS AND METHODS: Forty-nine patients with POAG underwent complete ophthalmic examination including visual field testing and RNFL thickness measurement. Perimetric findings were used to categorize them into mild, moderate, and severe stages of glaucoma. The RNFL thickness values were analyzed and compared with perimetric results. RESULTS: The average RNFL loss in mild, moderate, and severe POAG was 25.44%, 29.67%, and 44.15%, respectively. A statistically significant correlation (P < 0.05) between RNFL loss and severity of glaucoma was found in all except the superior and temporal sectors. A statistically significant (P < 0.05) negative correlation was noted between visual field index and RNFL loss in all sectors except the nasal-superior in moderate POAG and all sectors in severe POAG. Mean deviation and RNFL loss showed a significant positive correlation in temporal-inferior (TI) sector in mild POAG and all sectors in the severe group. CONCLUSION: RNFL thickness decreases with increase in glaucoma severity and is a reliable parameter to differentiate mild from severe POAG. The TI followed by nasal-inferior RNFL sector is the most sensitive to glaucomatous damage in all three stages.