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Editors Selection IGR 16-4
Examination methods: Laser scanning: Relation pupillary response, RNFL using OCT
Comment by David Greenfield on:
18069 Quantification of retinal nerve fiber layer thickness reduction associated with a relative afferent pupillary defect in asymmetric glaucoma, Tatsumi Y; Nakamura M; Fujioka M et al., British Journal of Ophthalmology, 2007; 91: 633-637
Assessment of pupillary responses provides useful information in eyes with glaucomatous and non-glaucomatous optic neuropathy. Although poorly embraced in clinical practice, a relative afferent pupillary defect (RAPD) may be quantified with neutral density filters and correlates well with the severity of optic nerve dysfunction. Tatsumiet al. (441) evaluated the pupillary responses of 29 subjects with glaucomatous optic neuropathy (9 unilateral, 20 bilateral) and studied the relationship with asymmetric visual function and retinal nerve fiber layer thickness using optic coherence tomography (OCT). A 0.6 log unit defect was defined as the minimal depth of a clinically detectable RAPD. The authors found a significant correlation between the RAPD magnitude and inter-eye difference in visual field mean deviation, and ratio of the average RNFL thickness in the more damaged eye compared to the less damaged eye. When an RAPD was clinically detected, the RNFL thickness in the more damaged eye was reduced to approximately 70% of that in the less damaged eye.
It is of interest to note that in eyes with a minimally detectable RAPD (0.6 log unit), considerable optic nerve damage existed as judged by visual field MD (mean inter-eye difference > 10 db) emphasizing the poor sensitivity of RAPD assessment for uncovering moderately severe asymmetric glaucomatous optic neuropathy. Furthermore, for any given RAPD value there was significant variability in the RNFL thickness asymmetry ratio and inter-eye MD difference in MD. For example, in the subgroup of eyes with a minimally detectable RAPD the RNFL thickness asymmetry ratio range was 0.55 to > 0.9, and the inter-eye MD values ranged from 7.5 to 20 dB. The broad range in values of structure and function are not limited to RAPD quantification. Similar findings would be expected if one measured RNFL thickness values among a population of glaucomatous eyes stratified by mean deviation values.
Tatsumi and colleagues have nicely illustrated a methodology by which neuroophthalmologists may gain further insight into the mechanism of dysfunctional pupillary reflexes. It will be of interest to see if high-speed fourier domain OCT may provide more useful information regarding the relationship between axonal loss and the development of an RAPD in glaucomatous and non-glaucomatous optic neuropathy.
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