Posterior chamber phakic IOLs can correct refractive errors associated with keratoconus and can also be combined with other surgical techniques when necessary, according to researchers.
The lenses offer an alternative to corneal transplantation in patients who are intolerant to contact lenses, according to Dr José Juan Esteve-Taboada of the University of Valencia, Spain, and colleagues.
They published their review of the literature in the Journal of Cataract and Refractive Surgery.
In keratoconus, the cornea thins progressively, causing myopia and irregular astigmatism, and higher-order aberrations reduce image quality. Corneal collagen crosslinking (CXL) can halt this process.
However, spectacles can improve the refractive error in only middle cases, and most patients instead rely on rigid contact lenses. In the past, when they lost their tolerance for these lenses, they would need corneal transplants.
More recent alternatives include excimer laser surgery, intrastromal corneal ring segments (ICRS) and phakic IOLs (pIOLs). ICRS and pIOL procedures do not remove corneal tissue, so they are less likely to weaken the cornea and trigger progression of the disease.
ICRS implantation reshapes the cornea to improve the topographical irregularities, but most patients still require additional optical solutions to correct residual myopia or astigmatism. Implantation of pIOLs may help these patients.
Anterior chamber pIOLs, fixed to the iris by enclavation, can significantly improve visual acuity. But they cannot completely correct astigmatism.
Posterior chamber pIOLs include the Visian Implantable Collamer Lens and the Visian Toric Implantable Collamer Lens (Staar Surgical).
Composed of hydrophilic porcine sclera tissue, their plate-haptic form allows posterior chamber pIOLs to be inserted through a clear corneal incision. They are permeable to gas and metabolites, enabling maintenance of normal crystalline lens metabolism and preventing cataracts.
They lie between the iris and crystalline lens. Although they significantly improve visual acuity, they can correct only spherical and cylindrical errors. They cannot address the vertical coma, primary coma and coma-like aberrations that frequently mar the vision of patients with keratoconus.