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Abstract
The sclera is often thought of as the unchanging white surface of the eye (used by humans to indicate gaze direction). The lacrimal fluid covering the sclera, however, is less homogeneous due to its association with circulating serum. This study used a novel method to assess whether light reflection from the sclera can act as a biomarker for variation in blood values (e.g., bilirubin). Young and older subjects were evaluated. Contrary to previous assumptions, this study found only small differences in color appearance (mostly non-significant) between older and younger sclera (with few differences between most biomarkers measured). One exception was increased specular reflections associated with high-density lipoproteins. Most aspects of the sclera, however, were relatively stable with age in this healthy sample (suggesting that significant changes may be due to disease, e.g., jaundice). Mechanisms aimed at keeping the sclera constant may have evolved due to its usefulness in social communication.