Predicting estimates of oxygen transmissibility for scleral lenses

Scleral lens influence on corneal curvature and pachymetry in keratoconus patients

“…The limited temporary increase in pachymetry in our study group was not expected to cause adverse physiological corneal responses; however, individual hypoxia responses may differ. In general, it is recommended to restrict hypoxia-induced swelling by application of highest Dk available materials and minimizing both lens thickness and the fluid layer between lens and cornea [31,32]. The thickness of the fluid layer between lens and cornea was not investigated in this study.…”

Corneal changes following short-term miniscleral contact lens wear

“…Michaud et al [8] recently modelled the oxygen transmissibility of scleral contact lenses taking into consideration lens thickness, oxygen permeability of the lens material and the postlens tear layer thickness. The authors calculated that a scleral contact lens with a Dk of 100, lens thickness of 300 m and central corneal vault of 400 m (similar to the lens and mean fitting characteristics in our study) would yield a predicted oxygen transmissibility of 12.5 Fatt Dk/t units which would not satisfy the Holden-Mertz criterion for successful daily lens wear (i.e.…”

“…This is particularly important since scleral lenses do not move upon blinking to allow freshly oxygenated tears to replenish the post-lens tear layer. The post-lens tear layer varies in depth with lens design, corneal shape and practitioner fitting philosophy and may act as a further barrier to atmospheric oxygen reaching the cornea [8]. Despite these potential hypoxic factors of increased lens thickness, minimal tear exchange and the presence of a thick post-lens tear layer, there are few clinical reports of significant corneal oedema associated with modern scleral lens wear.…”

Oxygen Diffusion and Edema With Modern Scleral Rigid Gas Permeable Contact Lenses

“…14 Further, the fitting characteristics of these devices also may have an important role. Despite recent publications that have suggested the importance of the postlens tear film thickness and its limited oxygen permeability as one cause, 15 to our knowledge no previous study has presented theoretical simulations with clinical evidence of such potential effect. Thick tear layers are necessary to support larger lenses (<18 mm), while smaller lenses (15-18 mm) are associated with a thinner tear thickness.…”