Posterior Pole Retinal Thickness for Detection of Structural Damage in Anterior Ischaemic Optic Neuropathy

Abstract

This objectives of this study were to compare posterior pole retinal thickness (PPRT) and peripapillary retinal nerve fibre layer thickness (RNFLT) between the affected eyes of patients with previous nonarteritic anterior ischaemic optic neuropathy (NAION) and their unaffected eyes and to assess the structure-function relationship. Eighteen eyes with NAION and 14 contralateral unaffected eyes were included in this cross-sectional study. Humphrey visual field (VF) sensitivities were obtained. RNFLT (six sectors) and PPRT (four quadrants) were measured with spectral-domain optical coherence tomography (Spectralis; Heidelberg Engineering, Heidelberg, Germany). These parameters were compared between both eyes of patients with unilateral NAION. The correlation of RNFLT and PPRT with VF mean sensitivity (MS) values (linear units) was also analysed. The main outcome measure was the correlation of MS values with PPRT and RNFLT. A significant difference existed between the affected eyes and the unaffected fellow eyes in the MS values, all sectors of RNFLT, and all quadrants of PPRT. A significant linear correlation was observed between RNFLT and PPRT and corresponding MS values in global and regional measures. The strongest correlation was between inferior temporal VF and its corresponding superior nasal retinal quadrant thickness. The area under the receiver operator characteristic curves comparing superior nasal PPRT and RNFLT between the normal and affected eyes was 0.97 and 0.96, respectively. The results show that PPRT and RNFLT provide equivalent performance to detect structural damage in ischaemic optic neuropathy.

Keywords: ischaemic optic neuropathy; nerve fibre layer thickness; retinal thickness; spectral-domain optical coherence tomography.

FIGURE 1

Visual field (24-2) (A) sensitivity and (B) grey scale plots from a patient with anterior ischaemic optic neuropathy of left eye with inferior nasal field loss. Division of the visual field test points and corresponding retinal nerve fibre optic nerve (RNFL) profile (C) into sectors. For example, sector 3 field region maps to the superior temporal RNFL sector from 41° to 80°. The 34 points (central 15°) contained in the central blue square (A, D) correspond to an area covered by posterior pole retinal thickness scan (E). Division of these points into four quadrants and mirror image of VF test points superimposed to the corresponding area of posterior pole (D). In this patient, inferior nasal VF quadrant maps to superior temporal posterior pole retinal thickness that shows marked retinal thinning. IT = inferior temporal; IN = inferior nasal; ST = superior temporal; SN = superior nasal; N = nasal; T = temporal; RNFL = retinal nerve fibre layer.

FIGURE 2

(A) The linear model shows change in retinal nerve fibre layer (RNFL) thickness of the inferior temporal disc with changes in mean sensitivity (MS) sector 2 region for 32 eyes of patients with anterior ischaemic optic neuropathy. (B) Scatterplot shows the correlation between inferior temporal quadrant mean sensitivity (MS) value and superior nasal posterior pole retinal thickness. (C) The correlation of superior temporal quadrant MS value with inferior nasal posterior pole retinal thickness. (D) The linear model shows change in retinal nerve fibre layer (RNFL) thickness of the superior temporal disc with changes in mean sensitivity (MS) of inferior temporal visual field region (sector 3) for calculating residual nerve fibre layer thickness.