[Optic disc features on OCT in glaucomatous and normal black Africans]

To determine the correlations between the size of the optic disc and glaucomatous defects in black Africans.

Retrospective observational study.

The study was conducted over a two-year period from November 2014 to October 2016, based on records of black Togolese patients who had undergone optic nerve head (ONH) OCT or ganglion cell complex OCT for assessment of glaucoma. The population was divided into 3 groups (I, II and III) depending on the size of the ONH. The ONH was considered small (Group I) if its size was less than the mean -1 SD, medium (Group II) if its size was within 1 SD of the mean, and large (Group III) if its size was greater than the mean+1 SD. Glaucomatous lesions were qualitatively identified on RNFL and or GCC. The ONH parameters were compared in the 3 groups. The Chi-square test was used to compare the percentages, and the t test to compare the means with statistical significance of 5%. The Pearson correlation coefficient (r²) was used to measure correlations.

A total of 586 eyes of 298 patients were examined, 314 glaucomatous eyes and 272 healthy eyes. The mean age was 41.0±15.7 [6; 86] years. There were 159 men vs. 137 women, with a sex ratio of 1.2. The mean surface area of the ONH was 2.80±0.55mm². Small ONH's (Group I) were defined as a surface area of less than 2.25mm², medium-sized ONH's (Group II) as an area between 2.25 and 3.35mm² and large ONH's (Group III) as an area greater than 3.35mm². Small ONH's represented 14.7%, (86 eyes), medium-sized 68.6% (408 eyes) and large ONH's 16.8% (98 eyes). The mean surface area of the neuroretinal rim, cup, the cup-disc ratio and the RNFL thickness were statistically significant in the 3 groups. Similarly, all these parameters were significant in groups of glaucomatous or non-glaucomatous eyes, except for the surface area of the cup. The RNFL thickness was weakly correlated with the surface area of the ONH (r²=0.39), moderately correlated with the surface area of the neuroretinal rim (r²=0.57). The surface area of the ONH was strongly correlated with the surface area of the cup (r²=0.7). The neuroretinal rim surface area was strongly correlated with the cup-disc ratio (r²=0.66).

The size of the ONH was correlated with the size of the cup, but it was not correlated to the surface area of the neuroretinal rim or the thickness of the nerve fibers. Analysis of the RNFL and GCC is essential for the diagnosis, especially in the case of large ONH's.