Melanocytoma of the Optic Disk Associated With Visual Field Defect: Clinical Features and Imaging Using Spectral Domain Optical Coherence Tomography

Abstract

Purpose: : To study the clinical features and high definition optical coherence tomography (OCT) characteristics of melanocytoma of the optic disk with consistent visual field defects.

Methods: : Spectral Domain Optical Coherence Tomography (SDOCT) allows the acquisition of raster scans covering large regions of the retina at a very high speed (approximately 26000 A-scans/second). An observational study was performed in two patients diagnosed clinically with melanocytoma of the optic disk with consistent visual field defects using a commercially available (5 µm axial resolution) SDOCT system (Cirrus^TM, Carl Zeiss Meditec, Inc). SDOCT scans were obtained using two protocols- First, 5 high density B-scans (each having 4096 A-scans) were obtained in 0.5 seconds; and second, 128 B-scans (each having 512 A-scans) were obtained in 2.6 seconds, covering a 6x6mm area of the retina.

Results: : The fundoscopic appearance of melanocytoma is characterised by a deeply pigmented lesion with feathery edges, involving the optic disk and peripapillary choroid. Complications may include progressive slow growth, retinal vascular occlusions, choroidal neovascularization and rarely malignant transformation. OCT revealed an elevated lesion in the region of the optic disk having a highly reflective inner layer with posterior shadowing. SDOCT reconstructed fundus images obtained from these B-scans allowed accurate image registration. Regions of the melanocytoma that had deeper pigmentation had a thinner band of inner retinal reflectance and more posterior shadowing. In some regions, the highly reflective pigment band appeared to extend beyond the lamina cribrosa. Three-dimensional visualization of these lesions was possible following segmentation of the internal limiting membrane (ILM) and retinal pigment epithelium (RPE). These lesions appeared elevated in the peripapillary region and the retinal nerve-fiber layer was considerably thinner in the retina surrounding the tumor that corresponded to the altitudinal visual field defects in the hemisphere opposite to the tumor.

Conclusions: : SDOCT provided useful information about the morphology and extent of melanocytoma. Clinical exam, visual field and OCT may be useful in conjunction when monitoring patients with melanocytoma and consistent visual field defects.

Keywords: melanocytes • optic nerve • imaging/image analysis: clinical