Influence of Room Illumination on Corneal Densitometry

To evaluate the effect of room illumination on corneal densitometry measurements obtained with Scheimpflug imaging and optical coherence tomography (OCT) and on corneal geometric parameters.

Twenty-five healthy participants (50 eyes) were imaged under four controlled illumination conditions: extreme scotopic (0.003 lx), dim-light/mesopic (30 lx), low photopic (130 lx), and moderate photopic (220 lx) conditions. Corneal densitometry was quantified as the mean pixel intensity for both the Scheimpflug and the OCT images, with speckle contrast additionally computed for the OCT images. Corneal geometry (central corneal thickness and keratometry readings defined as corneal power in the flattest [K1] and steepest [K2] meridians) was extracted from Scheimpflug tomography. Linear mixed-effects models were used to assess the effect of illumination on corneal parameters.

Scheimpflug-derived corneal densitometry increased significantly with illumination (P < 0.001), rising from 45.8 ± 4.3 arbitrary units under extreme scotopic conditions to 69.5 ± 11.5 arbitrary units under moderate photopic illumination. Significant differences were observed between all illumination levels (all P < 0.01). In contrast, the OCT-derived mean pixel intensity and speckle contrast remained stable across conditions (P > 0.05). The corneal geometric parameters showed no significant changes with room illumination (all P > 0.05).

Scheimpflug-based corneal densitometry is highly sensitive to room illumination, even within clinically plausible lighting conditions, whereas the OCT-derived metrics are robust to such variations.

Room illumination-induced changes may bias corneal densitometry readings and should be carefully controlled and reported in densitometry studies.