# Normative optical coherence tomography-based measurements and classification of optic nerve head parameters in adult Congolese subjects

## TL;DR

This study establishes normal optic nerve head measurements for Congolese adults using OCT, providing critical data for diagnosing eye diseases in this underrepresented population.

## Contribution

The study provides the first population-specific normative OCT data for optic nerve head parameters in Congolese adults.

## Key findings

- Optic disc area and other parameters in Congolese adults were significantly larger than in other populations.
- ODRA was significantly larger in women compared to men.
- None of the optic disc parameters showed correlation with age in the studied population.

## Abstract

Normative data on optic nerve head (ONH) topographic measurements are scarce among black people residing in Africa. Such measurements obtained with imaging modalities such as optical coherence tomography (OCT) are crucial for the diagnosis and management of optic nerve diseases, particularly glaucoma. They assist clinicians in identifying deviations that may indicate disease or abnormalities. The aim of this study was to determine normal reference values of ONH topographic measurements in a Congolese adult population using OCT.

Hospital-based cross-sectional observational study of 263 healthy adult subjects (18–76 years) who were scanned with a Topcon 3D OCT-2000 device using the optic disc scan pattern. The 2.5th, 5th, median, 95th, and 97.5th percentiles, and the mean of the optic disc area (ODA), optic disc vertical diameter (ODVD), optic disc horizontal diameter (ODHD), vertical cup-to-disc ratio (VCDR), area cup-to-disc ratio (ACDR), optic disc cup area (ODCA), and optic disc rim area (ODRA) were determined.

The median (IQR) was 2.70 (0.92) mm2 for ODA, 2.03 (0.32) mm for ODVD, 1.70 (0.5) mm for ODHD, 0.57 (0.20) for VCDR, 0.89 (0.81) mm2 for ODCA, 1.74 (0.75) mm2 for ODRA. The lower and upper limits of normality were 1.88 and 4.67 mm2 (ODA), 1.64 and 2.64 mm (ODVD), 0.00 and 0.81 (VCDR), 0.00 and 2.60 mm2 (ODCA), and 1.63 and 3.22 mm2 (ODRA). For OCT classification, the range of 2.02-4.19 mm2 was considered normal for ODA, 1.73-2.51 mm for ODVD, 0.23-0.76 for VCDR, 0.04-0.63 for ACDR, 0.11-2.33 mm2 for ODCA, and 1.69-3.01 mm2 for ODRA. ODRA was significantly larger in women than men. None of the optic disc parameters correlated with age.

This study provides population-specific normative data describing ONH morphology in healthy Congolese adults, addressing a critical gap for African populations that remain underrepresented in ocular imaging research. These ONH measurements were significantly greater than found in other populations. They may be used for diagnostic reliability and classification of Congolese subjects.