Variable structure and function relationship of compressive optic neuropathy at the time of diagnosis

Purpose: To illustrate the structure-function relationship of compressive optic neuropathy (CON) at the time of diagnosis. Patients and methods: Thirty-two eyes of newly diagnosed suprasellar CON and 60 healthy eyes were included in the study. The peripapillary retinal nerve fiber layer (RNFL) thickness and macular ganglion cell-inner plexiform layer (GCIPL) thickness were obtained using Cirrus spectral domain optical coherence tomography (SD-OCT). CON eyes were stratified based on the similar degree and pattern of both RNFL and GCIPL. Results: From 32 eyes of newly diagnosed suprasellar CON eyes, 27 eyes had a predominantly nasal hemiretina thinning of macular GCIPL, 4 eyes showed a generalized macular thinning, and 1 eye showed a predominantly superior macular thinning. The corresponding temporal peripapillary RNFL thinning with nasal hemiretina GCIPL thinning were inconsistently manifested. Structure-function analysis of stratified CON eyes with similar thinning profiles showed that a range rather than a fixed value of visual field loss based on mean deviation (MD) index was associated to each thinning profile. The maximal limit of visual field loss range was ubiquitously nonrestricted to any structural thinning profile. While the minimal limit of the associated MD range was gradually reduced from 0 to about -16.0 dB, the nasal hemiretina macular GCIPL thinning was the only manifestation and decreased from 75 to 45 mu m. However, the different degrees of temporal hemiretina macular GCIPL and superior-inferior peripapillary RNFL thinning were only seen in 10 of 32 eyes of which their nasal hemiretina GCIPL and temporal RNFL thinning had reached significant thinning. Interestingly when present, the minimal limit of associated MD range continued to decrease from -16.0 to -32.0 dB. Conclusion: CON eyes can present with variable structure and function relationship at the time of diagnosis. Using structural parameters at the time of diagnosis to predict the prognosis should be used with caution.