Myopic shift during hyperbaric oxygenation attributed to lens index changes.

PURPOSE: To examine ocular lens parameters and structural changes to elucidate mechanisms underlying the myopic shift and cataract-related changes that occur in some patients during hyperbaric oxygen (HBO) therapy. METHODS: Scheimpflug images (Nidek EAS-1000) of the crystalline lens, measurements of scattered light, objective refraction, keratometry, tonometry, and axial length of the eye were obtained after the first day of HBO therapy and repeated when patients had completed 19 days of the treatment. RESULTS: Significant reduction in mean (±SD) optical density was found in the lens nucleus, -2.8 (±4.3) units (p = 0.009) and -2.2 (±4.1) units (p = 0.027) within circular and oval areas, respectively. Significant decrease in mean (±SD) backward scattered light was measured, -0.4 (±0.8) units (p = 0.022). Mean (±SD) myopic shift was -0.58 (±0.39) diopters (p < 0.001), whereas cortical optical density, forward scattered light, lenticular parameters, keratometry, tonometry, anterior chamber depth, and axial length of the eye appeared unchanged. CONCLUSIONS: Transient myopic shift reported in patients during HBO therapy is attributed to changes in the refractive index of the lens. No changes in lens curvatures or thickness were found after treatment.