Introduction

Contact lens fittings for irregular corneas represent one of the greatest challenges that practitioners have to face. It is widely known that fitting irregular corneas is relatively time consuming and costly, as it generally requires an increased number of patient visits and ordered lenses. Primary corneal ectasia such as keratoconus, or pellucid marginal degeneration, and irregular corneas resulting from corneal surgery such as keratoplasty, post-LASIK ectasia or corneal ring segment implantation, can cause high amounts of irregular astigmatism, which leads to poor visual acuity with glasses or conventional soft contact lenses. Rigid gas-permeable (RGP) contact lenses are considered the best solution for patients with irregular corneas, because they create  a tear layer between the lens and the cornea, which masks the corneal irregularity and reduces the impact that higher order optical aberrations of the anterior corneal surface have in the visual function. However, corneal RGP lenses may not be appropriate when corneal irregularity is excessive and the differences in height elevations among corneal sectors are great. Severe corneal distortions fitted with corneal RGP lenses result in lens decentration and/or excessive lens movement and results in poor comfort and unstable visual acuity. Furthermore, corneal RGP  lenses could be associated with the onset of corneal scarring. Hybrid lenses and piggyback lens systems might enhance lens stability and wearing comfort, but these techniques increase the cost and complicate lens storage and maintenance. Custom soft lenses with aberration control have been proposed as a potential solution in cases of irregular corneas, but they are not easily available. The relatively new special soft lenses for irregular corneas, with high central thickness (0.35 mm or more) also play a role in irregular cornea management, but they are only useful in mild or moderate amounts of irregularity.

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