Electromyographic Study for the Objective Evaluation of Glare-Induced Discomfort in Patients With Keratoconus

To use a portable electromyographic (EMG) system for the objective evaluation of glare-induced discomfort in patients with keratoconus.

Fifty-five eyes of 31 patients and 24 controls were enrolled in this retrospective case-control study. The electrical activity of the mimic muscles was recorded at three different luminances (500, 3000, and 6000 lux) using a portable EMG system. A discomfort glare value was obtained as the signal/noise ratio for each recording. All the patients were asked to grade their discomfort after exposure to each luminance using the subjective de Boer scale. Corneal topography-based wavefront analysis, pupil size, and angle kappa were calculated to identify possible significant correlations.

Mean values of discomfort glare index (signal/noise ratio) for the patients' group were 1.66 ± 1.5 at 500 lux, 2.71 ± 1.68 at 3000 lux, and 3.16 ± 1.92 at 6000 lux; for the control group, 1.4 ± 0.4 at 500 lux, 1.9 ± 0.86 at 3000 lux, and 2.13 ± 0.9 at 6000 lux. There was a statistically significant difference at the level of 0.05 between the two groups only at the 6000-lux illuminance level. There was a significant Spearman's correlation at all luminances between the objective electromyographic recording and the subjective grading of the discomfort feeling. There were no statistically significant correlations between electromyographic responses and keratometric values, pupil size, or angle kappa. Trefoil and coma were significantly correlated with discomfort glare-estimated electromyographic values.

Patients with keratoconus experience higher levels of discomfort when exposed to a glare source, as measured objectively with electromyographic recordings, which may affect their quality of vision.