Purpose: The purpose of this study was to evaluate corneal hypoxic edema after overnight (closed eye) wear of scleral lenses. Hypoxia of the cornea leads to accumulation of lactic acid in the corneal stroma, and subsequent corneal edema.
Methods: Eleven healthy subjects were selected and pre-screened for any ocular pathology or ocular surface/corneal abnormalities. The study was performed in two phases: on the first night subjects slept without contact lenses on. Corneal thickness was measured immediately before sleep, and then again immediately upon awakening to establish baseline nocturnal swelling. During the second night subjects wore had a scleral contact lens (Boson XO2 material with Dk 141) on the right eye. Both corneas were evaluated again immediately upon wakening. Corneal pachymetry was performed usingmeasured with the Zeiss Visante OCT and a sonographic pachymeter.
Results: The average amount of overnight corneal swelling in the right eyes following the overnight wear of a scleral lens was 8.54% when measurement variability was considered, and an average physiological swelling was 2.5% using anterior segment OCT measurement. All subjects reported some degree of visual haze in the scleral lens-wearing eye upon awakening and average visual acuity loss was 1 line of Snellen chart that lasted up to 2 hours.
Conclusion: The results of this study appear to indicate that therapeutic, overnight wear of scleral lenses needs to be approached with caution. This study highlights the need for higher Dk lens materials (for overnight lens wear) and/or lens solutions that contain oxygen soluble particles (i.e. fluorocarbons) that can provide additional oxygen to the ocular surface in the closed eye environment. In patients requiring the therapeutic, overnight use of scleral lenses a risk to benefit should always be considered.
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