Detection of preperimetric glaucoma using Bruch membrane opening, neural canal and posterior pole asymmetry analysis of optical coherence tomography

Abstract

We analysed retinal nerve fibre layer (RNFL) defects in eyes with normal circumpapillary RNFL (cpRNFL) thickness using posterior pole asymmetry analysis (PPAA) and investigated the parameters of Bruch membrane opening (BMO) and neural canals using enhanced depth imaging spectral domain optical coherence tomography (EDI-SDOCT). A total of 112 preperimetric glaucomatous eyes of 92 patients were examined to obtain cpRNFL thickness using SD-OCT. Posterior pole asymmetry analysis (PPAA) and central cross-sectional images of the optic nerve head (ONH) were obtained using EDI-SDOCT. Minimal and horizontal distances between the BMO and ONH surfaces (BMOM, BMOH) and the terminal of retinal pigment epithelium (RPE) and ONH surfaces (RPEM, RPEH) were measured. The distribution of the absolute black cells in PPAA was more concentrated in eyes with "U"-shaped neural canals (p < 0.0001). The area under the receiver operating characteristic curve of the ratio of RPEM to RPEH (RPE-R, 0.771 ± 0.08) was significantly larger than the ratio of BMOM to BMOH (BMO-R, 0.719 ± 0.009) for PPAA results. A U-shaped neural canal, lower ratio of RPEM to RPEH, and lower ratio of BMOM to BMOH were considered early indicators of RNFL defects in preperimetric glaucomatous eyes with normal cpRNFL.

Figure 1

The distribution of ovality index (A) and the angle between the fovea and ONH centre relative to the horizontal axis (B).

Figure 2. PPAA macular maps.

(A) The posterior pole map provides a retinal thickness value of 64 (8 × 8) cells within each cell; (B) Eight zones in the macular thickness map, labelled with different colours, together with the fovea-disc axis (white arrow) and optic disc (white triangle).

Figure 3. Consecutive absolute black cells in eyes in PPAA.

(A) Single absolute black cells (red arrow); (B) Two consecutive absolute black cells (red arrow); (C) Three consecutive absolute black cells (red arrow); (D) Four consecutive absolute black cells (red arrow).

Figure 4. Comparison between “W”- and “U”-shaped neural canal eyes with normal cpRNFL (green colour).

Absolute black cells in PPAA were obviously more concentrated in eyes with “U”-shaped neural canals than “W”-shaped neural canals. cpRNFL: circumpapillary retinal nerve fibre layer. The number in cpRNFL images revealed an average RNFL thickness in six directions (N: nasal, NS: nasal and superior, TS: temporal and superior, T: temporal, TI: temporal and inferior, NI: nasal and inferior) and the total average cpRNFL thickness (G). PPAA: posterior pole asymmetry analysis.

Figure 5. The morphology of ONH.

(A) “W”-shaped neural canal (green triangle and yellow line); (B)“U”-shaped neural canal (green triangle and yellow line); (C) Measurement of NCO included RPEM (a1), RPEH (a2), BMOM (b1) and BMOH (b2); BMO (red triangle); terminal of RPE (yellow triangle).

Figure 6. ROC curves of RPE-R and BMO-R.

The AUROC of RPE-R was 0.771 ± 0.08, and the AUROC of BMO-R was 0.719 ± 0.009.