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Sofia C. Peixoto-de-Matos, Vicente Compañ, Sergio Moya, Jorge Jorge, Jose M. Gonzalez-Meijome; Oxygen Diffusion Behind Modern Scleral Rigid Gas Permeable Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6105.
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Scleral lenses are used to compensate corneal irregularities creating a vaulting effect over the cornea. The goal of this study is to develop a model to define the theoretical oxygen tension behind modern scleral contact lenses made of different rigid gas permeable (RGP) materials and thickness and assuming different thickness of the tear layer behind the lens.
Simulations of the partial pressure of oxygen across the cornea behind scleral contact lenses made of different materials (Dk=75 to 200 barrers) and different thickness (Tav=100 to 300 microns) were performed. A post-lens tear film thickness (Tpost-tear=100 to 350 microns) in the range of 150 to 350 microns was considered.
Combinations of thicker lenses with lower permeability fitted to create a pos-lens tear film thicker than 150 microns reduce the partial pressure of oxygen at the corneal front surface below 50 mmHg, similar to closed eye conditions without lenses. The lower the oxygen permeability of the lens material, the more significant the contribution of post-lens tear film layer to the depletion in oxygen availability to the cornea. A 100 microns increase in lens thickness will reduce between 17 and 21% the partial pressure of oxygen at the corneal surface for a 75 barrers material and about 6% for a 200 barrers material. The same increase in tear film thickness will have an impact of 14 to 16% in the partial pressure of oxygen at the corneal surface for a 75 barrers material and about 12 to 14% for a 200 barrers material.
Tear film layer behind scleral RGP CL can significantly limit the diffusion of oxygen to the cornea. This effect is more significant for lower Dk values considered even when they fall in the range of 75 to 125 barrers. Scleral RGP CL must be manufactured with materials of at least 150 barrers of oxygen permeability in order to avoid a significant hypoxic effect under open eye conditions.
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