The relationship between soft contact lens adverse events and corneal sagittal depth

To determine if individuals who develop soft-contact-lens adverse events (corneal infiltrative events or microbial keratitis) have a shallower corneal sagittal depth than the population mean.

Participants (N = 25) with an adverse event within the last two years were recruited for a prospective, case-control study. Corneal sagittal depth was calculated from topography (central keratometry, eccentricity, 12 mm diameter) for comparison with an historical control (published, population mean ± SD = 2.74 ± 0.15 mm, N = 18,387 eyes) using one-sample t-tests. Bland-Altman analyses compared topography-calculated sagittal depth to measurements from anterior segment optical coherence tomography (AS-OCT) images (12 mm chord), for validation. Contact lens movement and fit were measured from images/videos.

Participants (mean ± SD age = 27.4 ± 10.4 years, range 18 to 65 years) were predominantly female (19 of 25). Topography-calculated sagittal depth was slightly larger than, but highly correlated with, AS-OCT measurements (mean of the differences ± SD = 0.14 ± 0.08 mm, t = 8.97, p < 0.0001; r = 0.82, p < 0.0001). The mean ± SD sagittal depth for participants (2.64 ± 0.14 mm) was significantly shallower than the population mean (t =  - 3.52, p = 0.002). Primary gaze contact lens movement (mean ± SD) was 0.24 ± 0.17 mm, range: 0.06 to 0.82 mm and up gaze was 0.45 ± 0.33 mm, range: 0.05 to 1.16 mm.

Contact lens wearers with adverse events had a corneal sagittal depth that was significantly shallower than the population mean. These data suggest that one-size-fits-most soft contact lenses may have a sagittal depth that is too deep for patients with a shallower-than-typical corneal sagittal depth, which presumably inhibits the eye's natural defenses. Future studies should compare the relative risk of corneal sagittal depth to other known risk factors and determine clinical guidelines for fitting soft contact lenses based on sagittal depth.