Prescribing for Astigmatism

Toric Intraocular Lenses and Keratoconus

By Pam Satjawatcharaphong, OD, & Timothy B. Edrington, OD, MS, FAAO

Several articles have been published in professional journals reporting on the prescribing of toric intraocular lenses (IOLs) for patients who have keratoconus. The reported outcomes have overall been encouraging. However, we have managed keratoconus patients post-toric IOL surgery who continued to need GP lenses to provide them with satisfactory vision. Unfortunately, the over-refractions resulted in large amounts of residual cylinder.

We feel that IOL surgeons and co-managing practitioners providing the contact lens postsurgical care should heed suggestions included in a Jaimes et al (2011) article in the Journal of Refractive Surgery. They recommend prescribing toric IOLs for patients who have mild forms of keratoconus whose manifest refraction provides acceptable and stable vision. Stable vision was primarily determined by repeatable refractions and corneal curvature measurements over a period of at least one year.

Toric IOLs will not correct or negate a patient's irregular astigmatism; it will only correct regular astigmatism. Jaimes and colleagues also suggest implantation for patients older than 40 years whose corneas are less apt to change curvature over time due to nature's effect of corneal “cross-linking.”

GP lenses provide a smooth anterior optical surface that neutralizes a significant portion of irregular astigmatism. Generally, keratoconus patients achieve acceptable vision without the need to prescribe a toric GP design or spectacles with cylinder to correct the resultant over-refraction astigmatism. However, there is a good possibility that after toric IOLs have been implanted, the GP over-refraction cylinder will be increased to the point that spectacles will be necessary to provide optimal vision.

Monocular IOL Procedures

Keratoconus tends to be significantly asymmetric in its clinical presentation. We have also provided care to keratoconus patients who had received a unilateral spherical IOL. Because the eye that receives the IOL is often “fully” corrected, patients may be unable to comfortably wear a spectacle correction due to the high amount of anisometropia and the resulting difference in image magnification between the eyes. If the patient has an IOL (non-accommodative) implantation in the second eye to resolve the anisometropia, inform him that he will lose accommodation and require a reading prescription to perform near tasks.

Educate

Patient education is the key. Discuss the pros and cons of all lens and surgical options given the patient's condition and vision needs. Also address the risks of the surgical procedure and possible post-surgical side effects such as glare. If GP lens wear discomfort is the primary reason for pursuing an IOL, then consider scleral GP lenses or silicone hydrogel keratoconus contact lenses. Before toric IOL surgery is performed, trial frame the manifest refraction to simulate the anticipated vision outcome.

Bottom Line

If a keratoconus patient cannot see satisfactorily and consistently through a pair of spectacles, then toric IOLs should not be pursued. Also, the patient's refraction and corneal topography should be followed over time to verify that the condition is not still progressing prior to toric IOL surgery. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #199.