Variability of Scheimpflug Densitometry Measurements in Clear and Opaque Corneas Under Different Lighting Settings

To evaluate whether variability in ambient light levels affects Scheimpflug corneal optical densitometry measurements in clear and opaque corneas.

Eyes with clear corneas (N = 60) or infectious corneal opacity (N = 49) underwent Scheimpflug densitometry (Pentacam, Oculus) under 3 ambient lighting conditions: dark room (1.8 ± 0.9 lux), mild ambient light (7.9 ± 0.9 lux), and bright light (>1000 lux). Densitometry measurements in grayscale units (GSUs) were obtained for the anterior, middle, posterior, and entire cornea and concentric corneal zones. The Wilcoxon signed-rank test and generalized estimating equation models were used to compare measurements across lighting settings.

Under bright light, densitometry measurements could not be obtained in 90% of clear corneas and 92% of opaque corneas because of machine error, while measurements that were obtained were significantly elevated (P < 0.001). Comparing dark room versus mild ambient light settings, clear corneas showed significantly higher readings under mild ambient light for anterior (1.0 GSUs, P = 0.004), middle (1.5 GSUs, P < 0.001), and posterior (1.5 GSUs, P < 0.001) layers, all concentric corneal zones, and the entire cornea (all P < 0.05). Among opaque corneas, all regions except the anterior and far peripheral cornea (P > 0.05) showed significant differences (1.3-2.4 GSUs, all P < 0.05). Overall, 88.3% of clear corneas and 73.5% of opaque corneas demonstrated higher readings under mild ambient light compared with dark room conditions.

Scheimpflug densitometry should not be performed under regular room lighting because of frequent errors and measurement overestimation. Dark room conditions are recommended for optimal measurement, particularly when quantifying subtle changes in opacity.