There are a number of clinical studies demonstrating ocular surface damage from natural UV exposure, but there’s limited evidence of the experience of indoor sun tanning sessions. In a new study, researchers evaluated the ocular surface clinically and at a microstructural level using in vivo confocal microscopy.

Female participants between ages 20 and 29 were enrolled into a study group with a history of UV indoor tanning, and a control group with no prior history. The study subjects participated in voluntary tanning sessions performed with standard equipment and maintained their usual routine for eye protection. Slit lamp biomicroscopy and in vivo confocal microscopy were performed at baseline before undertaking a series of sun tanning sessions (10 sessions of 10-minute durations over a 15-day period), within three days after the last session and four weeks after the last session. Control group participants were examined at baseline and eight weeks later and did not participate in tanning sessions.

No clinically significant changes were observed in either group over time using slit lamp biomicroscopy; however, statistically significant differences were observed between the study and the control group for all corneal layers imaged using confocal microscopy. Characteristic cystic conjunctival lesions with dark centers and bright borders were observed in 95% of the study group before and in 100% after the sun tanning sessions.

This study found that the corneas of sunbed users had lower keratocyte and endothelial cell counts when compared with age-matched populations, but exposure to UV light also damages notably the epithelium of the cornea immediately after several tanning sessions.

“Although the overall corneal damage cannot be directly correlated to the UV damage, the short-term, reversible epithelial damage has no other common causative agent in our study group,” the authors explained in their paper. “The number of conjunctival cystic lesions was greatest in the superior and inferior conjunctiva. While peripheral light focusing has the greatest impact on the nasal conjunctiva—when in the supine position—the most unprotected part of the limbus might be the lower limbus due to Bell’s phenomenon in which the eye rotates up, and the ‘slit’ effects of the palpebral fissure, which directs parallel rays of light towards the lower cornea.”

The study concludes that sun tanning leads to clinically undetectable, microstructural changes affecting the cornea and the bulbar conjunctiva. The long-term effect of those changes would lead to “UV aging of the anterior ocular surface,” which appears to be similar to microstructural skin damage from UV exposure.