Macular Thickness- An Early Predictor of Diabetic Macular Oedema

Introduction: Diabetic Macular Oedema (DME) accounts for visual morbidity in about three fourth of Diabetic Retinopathy (DR) patients. Traditional examination on 90D slit lamp or stereoscopic fundus photograph may not be able to identify early maculopathy. Optical Coherence Tomography (OCT) is a sensitive, non invasive modality which may detect early retinal thickness changes in DME. Aim: To identify any increase in macular thickness in diabetic patients with early DR without any clinically detectable macular oedema. Materials and Methods: This cross-sectional analytical study was conducted from September 2018 to July 2020 in the Ophthalmology Department at Bharati Vidyapeeth Medical College and Hospital, Pune, Maharashtra, India. A total of 277 eyes of 184 subjects were evaluated. Of these 182 eyes were of diabetic patients (124 patients) and 95 eyes belonged to controls (60 subjects). Amongst the diabetic eyes evaluated, group I consisted of 100 eyes with no evidence of DR and group II consisted of 82 eyes with mild Non Proliferative Diabetic Retinopathy (NPDR). Group III included 95 eyes of non diabetic age matched controls. Macular thickness was measured using the Topcon 3D OCT-1 Maestro System. The central 1mm macular thickness of the three groups was analysed and compared using student's t-test. Results: The mean Central Macular Thickness (CMT) showed no statistically significant difference (p-value<0.7) between group III (222.4 +/- 10.8) and group I (223.0 +/- 13.7 pm). However, a significant increase in CMT (p-value<0.0001 and, p-value<0.0006) was noted in group II (230.7 +/- 15.6 pm) when compared with group III (222.4 +/- 10.8 pm) and group I (223.0 +/- 13.7 pm). Macular thickness amounting to Subclinical Macular Oedema (SCME) was seen in only in 6.09% of eyes in group II, five eyes of the total number of 82 eyes with mild NPDR. Conclusion: Increased CMT was detected in mild NPDR patients on Optical Coherence Topography (OCT) even without any clinical evidence of macular oedema. Since eyes with SCME, diagnosed at base line assessment, are at a higher risk of developing clinical macular oedema subsequently, it is recommend that a base line OCT be performed in all patients detected to have mild NPDR irrespective of the absence of clinical findings suggestive of DME.