Brightness Settings Affect Cup-to-Disc Ratio Estimates

Brighter intensity of non-stereoscopic disc images is associated with a larger cup-to-disc ratio, according to a study published in BMC Ophthalmology.

Researchers constructed an image library consisting of optic disc photographs obtained during routine examinations. The library consisted of 50 eyes analyzed under dark, medium, and bright lighting. The images were then assessed by 9 glaucoma specialists for cup-to-disc ratio grading.

Investigators found that cup-to-disc ratios were graded as significantly larger in bright photos compared with medium or dark settings (both P <.001). Researchers identified no associations between the glaucoma specialist’s years in practice and cup-to-disc ratio grading differences (P =.76).

Overall, 18% of participants would be considered glaucoma suspect by means of the dark-intensity setting compared with 26% using the bright-intensity setting.

This finding suggests that a patient’s glaucoma progression could be over or underestimated, which could affect their level of care in different settings. 

“Since [cup-to-disc ratio] remains a useful measure for glaucoma detection in community screening programs and retrospective studies, a standard protocol for light intensity setting may improve the accuracy of both,” according to the researchers.

Study limitations include a failure to assess interobserver reliability and the lack of a standard method of cup-to-disc ratio analysis.

Reference

McSoley MJ, Rosenfeld E, Grajewski A, Chang TC. The effect of photographic light brightness on cup to disc ratio grading. BMC Ophthalmol. Published online December 13, 2021. doi:10.1186/s12886-021-02209-6