Contrast sensitivity key consideration for IOL selection

May 15, 2008

IOL effects on contrast sensitivity are a major consideration for selecting implants in patients with glaucoma who are undergoing cataract surgery. On this basis, an aspheric IOL is preferred except in the rare patient with a history of hyperopic LASIK, whereas presbyopia-correcting IOLs are best avoided.

Key Points

Chicago-An aspheric IOL may be considered the implant design of choice for most patients with glaucoma who require cataract surgery, said Richard L. Lindstrom, MD, at the glaucoma subspecialty day of the annual meeting of the American Society for Cataract and Refractive Surgery.

"Much research is needed on the issue of IOL selection in patients with glaucoma. However, quality of best corrected vision is paramount in these visually compromised individuals. Patients with glaucoma are known to have reduced contrast sensitivity that is related to a reduction in retinal ganglion cells," said Dr. Lindstrom, founder and attending surgeon, Minnesota Eye Consultants, Minneapolis.

"Given this neuronal influence, I think it is rational to do whatever we can to maximize contrast sensitivity on the basis of optics, and that is accomplished best with the use of an aspheric IOL."

Contrast sensitivity concerns

Regarding optic sphericity and considering eyes without previous refractive surgery, Dr. Lindstrom said that good evidence exists from multiple studies that spherical aberration reduces mesopic contrast sensitivity and that it can be reduced with an aspheric IOL.

In the United States, several aspheric IOLs are now available (Tecnis, Advanced Medical Optics; AcrySof IQ, Alcon Laboratories; SofPort AO, Bausch & Lomb), he said, and all have new technology status.

"I would encourage use of an aspheric IOL in most patients with glaucoma to compensate for the positive spherical aberration of the cornea. The exception is the patient with negative corneal spherical aberration after previous hyperopic LASIK. In these rare, atypical patients, a standard, spherical IOL would be preferred," said Dr. Lindstrom.

Based on the issue of contrast sensitivity, Dr. Lindstrom said that he prefers to avoid multifocal IOLs in patients with glaucoma and significant visual field loss.

"If patients are highly motivated for achieving spectacle independence, a multifocal IOL might be considered in those with glaucoma and mild visual field loss, ocular hypertension, or who have suspected glaucoma and if they are expected to stay that way," he stated.

Looking to the future, Dr. Lindstrom said that a next-generation version of a proprietary accommodating IOL (crystalens HD-100, eyeonics) appears to offer better contrast sensitivity than earlier models. (Editor's Note: The next-generation version of the accommodating IOL is not FDA-approved.) When it becomes available, an accommodating IOL may be considered a reasonable compromise in select patients who want to reduce their dependency on glasses, he said.

This next-generation accommodating IOL has a modified optic design that enhances depth of field, improves near vision, and reduces spherical aberration when the pupil size is larger, Dr. Lindstrom said. In mesopic contrast sensitivity testing comparing an older version of the IOL (crystalens AT-45) and the investigational model, the results were slightly better with the investigational model, although the difference between implants was not statistically significant. In addition, laboratory measurements of modulation transfer function, which correlates with contrast sensitivity, show that the investigational IOL outperformed the older version as well as several multifocal presbyopia-correcting implants.

"Contrast sensitivity with the [next-generation accommodating IOL] is not as good as with an aspheric lens, but it is better than with a standard monofocal lens. Therefore, I might be comfortable using the [investigational lens] in an eye with compromised contrast sensitivity," Dr. Lindstrom said.

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