Topographic differences between large and normal optic discs: a confocal scanning laser ophthalmoscopy study

The aim of the study was to investigate the optic nerve head parameters of healthy macrodiscs to provide standard measurements for them to be the basis for future quantitative comparisons.

Sixty-nine subjects with macrodisc (disc area larger than 2.82 mm(2)) and 91 healthy controls (disc area between 1.16 and 2.82 mm(2)) were recruited. After a complete ophthalmic examination, confocal scanning laser ophthalmoscopy was performed in all participants. The stereometric parameters of confocal scanning laser ophthalmoscopy examination and the proportion of subjects classified as normal, borderline, and glaucomatous by the Moorfield Regression Analysis were compared between groups.

A total of 160 subjects were included in the study. The average disc sizes in the control and macrodisc groups were 2.14 ± 0.33 mm(2) and 3.36 ± 0.36 mm(2), respectively. Cup area (p<0.001), rim area (p=0.01), cup volume (p<0.001), cup/disc area ratio (p<0.001), linear cup/disc ratio (p<0.001), mean cup depth (p<0.001), maximum cup depth (p<0.001), and cup shape measure (p<0.001) differed significantly between the 2 groups. The parameters of the optic nerve head which did not differ significantly between groups were rim volume (p=0.17) and height variation contour (p=0.88). A significantly higher number of eyes were erroneously identified as abnormal (15.1% vs 79.4%) by Moorfield Regression Analysis in the macrodisc group (p<0.001).

Rim volume and height variation contour were the only optic nerve head topographic parameters that were similar in eyes with large and normal disc sizes. They seem to be promising parameters in the evaluation and comparison of the optic nerve head of subjects with macrodisc.