Optical coherence tomography analysis of axonal loss in band atrophy of the optic nerve

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Abstract
Aims: To measure axonal loss in patients with band atrophy of the optic nerve caused by optic chiasm compression using optical coherence tomography and to evaluate its ability in identifying this pattern of retinal nerve fibre layer (RNFL) loss. Methods: Twenty eyes from 16 consecutive patients with band atrophy of the optic nerve and permanent temporal hemianopia due to chiasmal compression, and 20 eyes from an age and sex matched control group of 16 healthy individuals, were studied prospectively. All patients were submitted to an ophthalmic examination including perimetry and evaluation of the RNFL using optical coherence tomography. Mean RNFL thickness around the optic disc was compared between the two groups. Results: The mean (SD) peripapillary RNFL thickness of eyes with band atrophy was 101.00 (9.89) μm, 62.21 (12.71) μm, 104.89 (12.60) μm, and 50.13 (16.88) μm in the superior, temporal, inferior, and nasal regions, respectively. The total RNFL mean was 79.94 (7.17) µm. In the control group, the corresponding values were 140.10 (16.06) μm, 86.50 (12.17) μm, 144.60 (15.70) μm, and 97.94 (16.02) μm. The total RNFL mean was 117.72 (9.53) µm. The measurements were significantly different between the two groups. Measurements in each of twelve 30° divisions provided by the equipment also showed significantly different values between eyes with band atrophy and normal controls. Conclusions: Optical coherence tomography was able to identify axonal loss in all four quadrants as well as in each of the twelve 30° segments of the disc. Thus, it seems to be a promising instrument in the diagnosis and follow up of neuro-ophthalmic conditions responsible for RNFL loss, even if predominantly in the nasal and temporal areas of the optic disc.

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