Visual loss and recovery in chiasmal compression

Compression of the optic chiasm causes an optic neuropathy that may be associated with reversible visual loss often immediately following surgical decompression. While the precise pathogenesis of retinal ganglion cell impairment and eventual death remains poorly understood, a number of putative mechanisms may play a role. In this article we review the evidence supporting various stages of visual loss and recovery in chiasmal compression. These include conduction block, demyelination, ischemic insult, and retrograde and anterograde degeneration. We also describe novel advances in magnetic resonance imaging with specialized modalities such as diffusion tensor imaging have provided further information to explain the underlying mechanism of visual loss. Functional measures including electrophysiology are time-consuming but have shown moderate prognostic ability. Optical coherence tomography has provided novel new biomarkers for predicting outcome following surgical decompression. Both retinal nerve fiber layer thickness and ganglion cell complex thicknesses have shown to have excellent predictive power. Such advances serve to inform patients and clinicians of pre-operative factors that predict the extent of visual recovery following medical or surgical treatment of para-chiasmal lesions.