Retinal nerve fibre layer thickness measured by spectral domain optical coherence tomography amongst early primary open-angle glaucoma patients at Hospital Melaka

Abstract

Introduction: Glaucoma is second only to cataract as a cause of blindness worldwide and Asians account for almost half the cases. Retinal nerve fibre layer (RNFL) assessment is an important objective method for diagnosis and monitoring of glaucoma as it develops earlier than the development of visual field defects.
 Purpose: To estimate the proportion of primary open-angle glaucoma (POAG) patients with normal RNFL thickness (RNFLT) amongst early POAG patients who were under follow-up at the Ophthalmology Department, Hospital Melaka (Melaka, Malaysia).
 Study design: Observational cross-sectional study.
 Materials and methods: Consecutive sampling of 64 POAG patients who were diagnosed as early POAG as defined by the Glaucoma Staging System 2 (GSS 2) into stage 1 and 2 on Octopus visual field test were recruited in this study. Data collected included demographic data, refraction, slit-lamp examination, intraocular pressure (IOP), gonioscopy, peripapillary retinal nerve fibre layer thickness (RNFLT) measured by spectral-domain optical coherence tomography (SD-OCT), and fundus photography.
 Results: Among 64 eyes, 57.8% were found to have normal and 42.2% to have abnormal RNFLT classification. There was no difference in terms of age, gender or ethnicity between those with normal and abnormal RNFLT. Mean IOP at presentation, mean duration of POAG, and mean spherical dioptres were compared between the two groups. Only mean spherical dioptres showed a significant difference between the two groups, p < 0.001. An increase of spherical dioptres also had a moderate positive correlation with RNFLT in most optic disc quadrants except the nasal, temporal, superonasal, and inferonasal quadrants.
 Conclusion: OCT cannot be used as a diagnostic tool alone, especially in early glaucoma, as it showed a normal RNFLT in almost half the patients. RNFLT in early POAG had significant correlation with spherical dioptres in most quadrants.