Light-colored irises were associated with a 6.6% relative increase in corneal densitometry compared with dark-colored irises, according to a recent study.
In an observational study, investigators included 91 eyes from 47 healthy White participants aged 21 to 41 years. All of the participants had normal visual acuity and intraocular pressure and no history of ocular surgery or corneal pathology. Scheimpflug imaging was performed using the Pentacam HR under standardized dark-room conditions. For each eye, 25 meridional images were acquired, and corneal densitometry was calculated as the mean pixel intensity of the segmented cornea averaged across images.
Raw images without gamma correction were processed using automated segmentation with median filtering and Canny edge detection to delineate the cornea, iris, and lateral brightness regions. Brightness artifacts were quantified using an adaptive intensity threshold defined as corneal mean pixel intensity plus three times its standard deviation. The percentage of pixels exceeding this threshold within iris and lateral regions was calculated and averaged across images for each eye.
Corneal densitometry rose with iris-related brightness artifacts (r = 0.47), and eyes with lighter irises showed higher mean densitometry values compared with darker irises (50.3 vs 47.2 arbitrary units). Iris pigmentation, quantified using a continuous objective metric, correlated negatively with iris brightness (r = −0.83) and with corneal densitometry (r = −0.52), and lighter irises exhibited higher reflected brightness and higher corneal densitometry values.
Iris color was objectively characterized from slit-lamp photographs converted from RGB to CIELAB color space. After normalization of the L*, a*, and b* components using median and interquartile range values, the investigators derived a composite IrisColor metric (−Ln + an + bn), in which negative values represented lighter irises and positive values darker irises. Linear mixed-effects models with subject as a random effect were used to account for inter-eye correlation when evaluating associations.
Limitations included the narrow age range of healthy young adults involved in the study, which may have limited generalizability to older patients or those with corneal disease. Although mixed-effects models were used, not all of the participants contributed both eyes, and residual inter-eye variability may remain. In addition, imaging was performed using a single Scheimpflug device under standardized laboratory conditions, which may have limited applicability to other imaging systems or routine clinical settings.
The authors reported no conflicts of interest.
Source: Journal of Optometry
