White-to-White Corneal Diameter: normal values in the adult black South African population obtained with the Nidek AL-Scan

Sun, Melody Wen-Lin
Journal Title
Journal ISSN
Volume Title
Background: White-to-white (WTW) is the horizontal corneal diameter that is clinically used to diagnose and monitor congenital glaucoma, microcornea and megalocornea. It is also used for the selection of various ophthalmic devices. Studies have investigated the normal WTW values in China, Middle East and the West; however, there is no research on the normal WTW distribution of adult black South Africans. Purpose: To describe the normal WTW values of adult black South Africans aged 40 to 90 years. The secondary objective is to stratify normal WTW values by race, age and gender. Methods: This is a retrospective comparative record review of WTW corneal diameter measured by the Nidek AL-Scan in adult black and white South African patients between 40 and 90 years. Results: A total of 1039 eyes from 1039 patients were included in the study; 680 were black patients (65.4%), and 359 were white patients (34.6%). The normal WTW range for black patients is 10.46mm to 12.7mm. Black patients had significantly smaller mean WTW distance than white patients; 11.58 mm (95% CI 11.55 – 11.64mm) vs 11.88 mm (95% CI 11.81 – 11.84 mm) (p < 0.001). Males overall had significantly larger mean WTW diameter (11.80 mm; 95% CI 11.75-11.86 mm) compared to females (11.67 mm; 95% CI 11.62-11.72 mm) (p=0.0001). Conclusions: This is the first study looking at normal WTW distance in the black South African population, showing a smaller WTW than white South Africans
A research report submitted in fulfilment of the requirements for the degree of Master of Medicine in Ophthalmology to the Faculty of Health Sciences, School of Clinical Medicine, University of the Witwatersrand, Johannesburg, 2021