Topographical Correlation Between Retinal Nerve Fiber Layer Thickness and Visual Field Sensitivity in Compressive Optic Neuropathy

Abstract

Purpose: : To investigate the topographical correlation between retinal nerve fiber layer (RNFL) thickness, measured with optical coherence tomography (OCT), and visual field (VF) sensitivity, measured with standard automated perimetry (SAP), in eyes with compressive optic neuropathy.

Methods: : Thirty eyes of 30 patients with compressive optic neuropathy confirmed by neuroimaging, were recruited from 3 tertiary neuro–ophthalmic clinics. All subjects had had surgical decompression 43.2 +/– 48 (range 3–180) months previously. Subjects underwent OCT imaging of the RNFL and SAP within 1 week of each other. OCT–RNFL measurements were compared to age–matched controls. The relationship between deviation from normal OCT– RNFL thickness at each clock hour, and the average pattern deviation(PD) in each VF zone was examined using linear regression(R2). Linear and logarithmic relationships were sought using VF sensitivities in the dB and the 1/L scales, both globally and in all sectors.

Results: : RNFL thickness was reduced by 17–54% for individual clock hours of the ONH. The temporal sector representing the papillomacular bundle demonstrated the most significant (54% thickness lost) and most frequent (73% <mean–2 SD) RNFL thinning. Widespread significant correlations were found between sectoral OCT–RNFL measures and SAP–PD with the strongest correlation being temporal RNFL thickness and its corresponding VF zone (R= –0.59, P=0.002). Mean RNFL thickness correlated with mean VF sensitivity (R²=0.47). When ‘time since surgery’ was incorporated into the multivariate linear regression model, the structure–function relationship became more predictable(R²=0.67). The relationship between RNFL thickness and VF sensitivity showed a trend towards being curvilinear in the dB scale, and significantly linear in the 1/L scale(P=0.004).

Conclusions: : RNFL thinning is topographically related to decreased VF sensitivity in compressive optic neuropathy, with the temporal RNFL representing the most stable predictor of visual field sensitivity. The structure–function relationship improves with increasing time from surgery, suggesting that OCT–RNFL thickness predominantly measures irreversible axonal loss in compressive optic neuropathy. Linear regression for 1/L VF sensitivity supports a continuous linear structure–function relationship in compressive optic neuropathy.

Keywords: neuro-ophthalmology: optic nerve • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • visual fields