Optic nerve compression predicts acuity loss while orbital crowding predicts field defects in patients with...

Intraorbital space-occupying lesions impair visual function, yet whether this stems primarily from optic nerve compression, elongation or orbital apex crowding remains unclear. This study investigated the differential impact of these mechanical factors on visual acuity (VA) and visual field (VF) in patients with intraorbital cavernous haemangiomas.

This retrospective cohort study analysed 130 patients with unilateral intraorbital cavernous haemangiomas. Key imaging parameters were measured from CT/MRI and categorised into optic nerve elongation, compression (eg, optic-nerve aspect ratio (ONAR)) and orbital crowding (eg, tumour-to-orbit (TO) ratio, tumour mid-position (TMP)). Univariate and multivariate linear regression models were used to correlate these metrics with visual outcomes.

Regression analysis revealed two distinct injury mechanisms. Direct compression, best quantified by ONAR, was the strongest predictor for VA decline (R²=0.15, p<0.0001) but correlated weakly with VF loss (R²=0.09, p=0.0015). Conversely, orbital apex crowding (TO-ratio and TMP) correlated more strongly with VF defects (R²=0.19 and R²=0.20, p<0.0001) than with VA. Optic nerve elongation showed no significant correlation with visual dysfunction. The final multivariate model explained 17.68% of the variance in VA and 36.48% in VF.

Visual loss from orbital tumours involves two mechanical pathways: direct compression preferentially impairs central vision (VA), while orbital apex crowding predominantly affects peripheral vision (VF). Imaging metrics like ONAR and TO-ratio can effectively quantify these mechanisms. They may serve as supplementary reference indicators for evaluating visual risk and informing clinical follow-up and surgical consultation, with ONAR indicating risk to central vision and TO-ratio signalling impending field loss.