Contact lens fenestrations and channels in relation to tear exchange and corneal oedema.

Oxygen delivery and tear exchange are considered essential to maintain corneal homoeostasis during contact lens wear. Since the 1940s, fenestrations and back surface channels have been utilised in scleral, corneal rigid, and soft contact lenses in an attempt to enhance corneal oxygen transmission, facilitate the removal of carbon dioxide from the post-lens tear layer, minimise corneal oedema and prevent post-lens tear stagnation. This review examines the use of contact lens fenestrations and channels in both clinical and laboratory settings, and the effect of these modifications upon tear exchange and corneal oedema. Despite almost a century of modifying contact lenses to alter tear dynamics and promote corneal health, the evidence regarding the efficacy of fenestrations and channels is mixed.