Time Spent Outdoors Associated With Corneal Stiffness And Tomographic Changes In Healthy Children

To explore associations between sleeping habits, outdoor activities, corneal morphology, and corneal biomechanics in healthy children.

Department of Ophthalmology, Centro Hospitalar Universitário do Porto, Porto, Portugal.

Prospective study that included healthy subjects aged 8 to 18 years. Exclusion criteria were ocular or systemic disorders, use of contact lenses or any kind of eye drops. Subjects underwent a questionnaire about the time spent outdoors (hours per day), number of outdoor activities (per week), preferential sleeping position (ventral or dorsal), eye rubbing habits and on-screen time (hours per day). The subjects’ parent or guardian could intervein in the questionnaire to corroborate the answers. Subjects underwent a corneal examination with Oculus Pentacam and Oculus Corvis ST. Only the right eye of each subject was analyzed. Significance was set at p<0.05.

Seventy-one subjects were included. Mean age was 14.2 ± 2.6 [8.8-18.6] years. Time spend outdoors was 3.1 ± 2.2 [0.0-10.0] hours per day. Time spent outdoors correlated with posterior corneal astigmatism (r=-0.247, p=0.044) and corneal stress-strain index (SSI, r=0.360, p=0.002). There were no significant associations with age, with other tomographic measurements or with first generation biomechanical indexes. There were no significant differences regarding eye rubbing habits, sleeping position or on-screen time. Posterior corneal astigmatism did not correlate with SSI.

Children that report to spend more time outdoors seem to have stiffer corneal biomechanics and reduced posterior corneal astigmatism. Our findings may relate to collagen cross-linking that occurs naturally when the cornea is exposed to ultra-violet light originated from the sun. Increased posterior corneal curvature and decreased corneal stiffness are associated with corneal ectatic disorders, namely keratoconus. Outdoor activities and sun exposure should be considered protective factors for the development and progression of corneal ectatic disorders.