Establishing Optic Nerve Diameter Threshold Sensitive and Specific for Optic Atrophy Diagnosis.

Abstract

To determine apotential threshold optic nerve diameter (OND) that could reliably differentiate healthy nerves from those affected by optic atrophy (OA) and to determine correlations of OND in OA with retinal nerve fiber layer (RNFL) thickness, visual acuity (VA), and visual field mean deviation (VFMD). This was aretrospective case control study. Magnetic resonance (MR) images were reviewed from individuals with OA aged 18years or older with vision loss for more than 6months and an OA diagnosis established by aneuro-ophthalmologist. Individuals without OA who underwent MR imaging of the orbit for other purposes were also collected. OND was measured on coronal T2-weighted images in the midorbital section, 1cm posterior to the optic disc. Measurements of mean RNFL thickness, VA and VFMD were also collected. In this study 47 OA subjects (63% women, 78eyes) and 75 normal subjects (42.7% women, 127 eyes) were assessed. Healthy ONDs (mean 2.73 ± 0.24 mm) were significantly greater than OA nerve diameters (mean 1.94 ± 0.32 mm; P < 0.001). Athreshold OND of ≤2.3 mmhadasensitivity of 0.92 and aspecificity of 0.93 in predicting OA. Mean RNFL (r = 0.05, p = 0.68), VA (r = 0.17, p = 0.14), and VFMD (r = 0.18, p = 0.16) were not significantly associated with OND. ONDs are significantly reduced in patients with OA compared with healthy nerves. Athreshold OND of ≤2.3 mm is highly sensitive and specific for adiagnosis of OA. OND was not significantly correlated with RNFL thickness, VA, or VFMD.