Clinical, ultrasonographic and optical coherence tomography correlation of optic nerve head cupping in glaucoma patients

Abstract

Purpose: To ascertain if ultrasound (USG) B-scan examination of the optic nerve head (ONH) can be a useful tool to diagnose and quantify glaucomatous cupping.

Methods: A cross-sectional observational study of 48 eyes of 48 patients with clear ocular media and cup-disc ratio of (CDR) ≥0.6 were included. The disc was studied by + 90D examination, USG B-scan and ONH Optical coherence tomography (OCT) by three masked observers. Observer-1 assessed the clinical CDR, observer-2recordedopticcup diameter on USG B-scan and observer-3performed ONH OCT to note the software computed average CDR. Measurements of cupping obtained by these 3 methods were compared and their relative strengths determined. The interdependency between variables was further studied using regression analysis.

Results: Clinically assessed disc ratios of 0.6, 0.7, 0.8, 0.9, and total corresponded to USG cup measures of 1.02 ± 0.11 mm, 1.23 ± 0.14 mm, 1.35 ± 0.072 mm, 1.45 ± 0.084 mm, 1.75 ± 0.15 mm and OCT average CDR of 0.62 ± 0.087, 0.68 ± 0.060, 0.75 ± 0.078, 0.81 ± 0.036, 0.89 ± 0.038, respectively. There was an excellent correlation between the three arms, with Pearson's co-efficient (r) of 0.87, P < 0.001 between clinical and USG cupping; r = 0.89, P < 0.001 between clinical and OCT cupping; and r = 0.88, P < 0.001 between USG and OCT cupping. A relation of y = 1.64x + 0.03 was obtained between them, where y stands for USG cup diameter and x stands for the observed clinical CDR.

Conclusion: Ultrasonographic measurement of optic cup diameter corresponds well to clinical ONH cupping. Therefore, it can reliably be used in quantifying ONH cupping in cases of media opacities which preclude optic disc visualization.

Keywords: B scan ultrasound; optic nerve head cupping; optical coherence tomography.

Figure 1

(a-e) Clinically documented optic disc cupping from 0.6 to total cupping A (0.6), B (0.7), C (0.8), D (0.9), E (total). (f-j) Respective OCT documented cupping from 0.6 to total. (k-o) Ultrasonographically quantified cupping from 0.6 to total. The amount of excavation along the optic nerve head is quantified in millimetres and the same has been depicted in the right upper corner of each ultrasound picture

Graph 1

Graph showing correlation between Clinical cup-disc ratio (CDR) and ultrasound (USG) Cup diameter. Cup-disc ratio (CDR), Ultrasonography (USG). y: Predicted USG cup diameter, x: Clinical CDR