Abstract

Aim: To assess the effects of acute orbital volume changes after retrobulbar injection on optic nerve head topography.

Methods: The study population consisted of 95 patients with type 2 diabetes mellitus with clinically significant macular oedema who required focal pattern laser photocoagulation therapy in one eye. Before each laser treatment, 49 patients required a retrobulbar injection (approximately 7 ml of a mix of lidocaine 2% with epinephrine and bupivacaine 0.75% in equal volumes) to provide ocular akinesia. Both eyes of all patients underwent optic nerve head topographic analysis once before laser treatment (within 30 minutes), and repeated within 1 hour, 1 day, 1 week, 2 weeks, and 4 weeks after treatment, respectively. Topographic analyses were performed using a confocal scanning laser ophthalmoscope, HRT-II. The disc area, topography standard deviation, and a total of 12 topographic parameters were calculated by HRT-II.

Results: The mean age of the patients was 37.9 (SD 3.2) years. The mean disc area of the subjects was 2.12 (0.44) mm². Fellow eyes which were not treated with laser, and those treated eyes which did not receive retrobulbar injection before therapy were found not to reveal significant changes in disc topography in any of the examinations (all p values >0.05). In the topographic examinations in the first hour, first day, and first week, laser treated eyes which underwent retrobulbar injection demonstrated significant increase in the disc area, rim area, rim volume, rim area/disc area, and cup shape measure parameters while optic cup parameters significantly decreased (all p values <0.05). In the second week examinations, they did not show significant difference in disc area measurements (p>0.05). By the fourth week, all of the optic nerve head topographic variables were not significantly different from the pre-injection values (all p values >0.05). Colour stereoscopic photographs did not reveal any differences in optic disc appearance.

Conclusion: Acute orbital volume change following retrobulbar injection may cause significant topographic evidence of optic disc oedema lasting approximately 1 week. Significant changes in optic rim and cup area may last for 2 weeks after injection, with all topographic changes returning to baseline by 1 month after injection. The present findings could be a model to reflect the pathological processes that occur in cases of acute orbital volume changes such as retrobulbar haemorrhage.