Physiological Correlates and Predictors of Functional Recovery After Chiasmal Decompression

The goal of our study was to look for the presence of homonymous ganglion cell layer-inner plexiform layer complex (GCL-IPL) thinning using spectral-domain optical coherence tomography (SD-OCT) in patients with a history of adult-onset injury to the postgeniculate pathways with rigorous radiological exclusion of geniculate and pregeniculate pathology. We performed a retrospective review of twenty-two patients (ages 24-75 y, 6 men, 16 women) with homonymous visual field (VF) defects secondary to postgeniculate injury examining the GCL-IPL with SD-OCT. An additional fifteen patients (ages 28-85 y, 5 men, 10 women) with no visual pathway pathology served as controls. Using segmentation analysis software applied to the macular scan, a normalized asymmetry score was calculated for each eye comparing GCL-IPL thickness ipsilateral vs contralateral to the patient's brain lesions. We found that 15 of the twenty-two subjects had a relative thinning of the GCL-IPL ipsilateral to the postgeniculate lesion in both eyes (represented by a positive normalized asymmetry score in both eyes), whereas a similar pattern of right/left asymmetry was found in 4 controls (P = 0.0498). The magnitude of asymmetry was much greater in subjects compared with controls (P = 0.0004). There was no association between the degree of GCL-IPL thinning and the mean deviation on automated VF testing. A moderate correlation (R = 0.782, P = 0.004) between the magnitude of thinning and latency from onset of retrogeniculate injury was observed only after excluding patients beyond a cutoff point of 150 months. This data provides compelling new evidence of retrograde transsynaptic degeneration causing retinal ganglion cell loss after postgeniculate visual pathway injury.