Use of multifocal IOLs is complex in glaucoma patients

May 15, 2008

Many features that are specific to glaucoma patients raise concerns about whether they are appropriate candidates for multifocal IOLs. In the absence of extensive clinical data to guide decision-making, the benefits and compromises must be considered carefully in each patient.

Key Points

Chicago-In parallel with the trend in the general population, patients with glaucoma may have growing expectations for a full range of vision and decreased dependence on glasses after cataract surgery. Nevertheless, further study is needed to establish the role of multifocal IOLs in eyes with glaucomatous damage, said Ike Ahmed, MD during the glaucoma subspecialty day here at the annual meeting of the American Society of Cataract and Refractive Surgery.

Several unique issues exist relating to the safety and efficacy of those presbyopia-correcting IOLs are specific to glaucoma patients, he said. They include the potential for the implant to affect contrast sensitivity, scotopic/mesopic vision, visual field testing, and structural imaging, as well as for anatomic features relevant to glaucoma patients, such as small pupils and capsular and zonular issues, to affect vision outcomes.

"There is a paucity of data on many of these questions, and further study is required to define what issues have clinical versus theoretical relevance. For now, use of presbyopia-correcting IOLs in patients with glaucoma should be undertaken cautiously," said Dr. Ahmed, assistant professor of ophthalmology, University of Toronto.

"However, even when a patient seems to be a suitable candidate, the preoperative counseling on benefits and compromises must go above and beyond the usual presbyopic discussion," said Dr. Ahmed.

Safety considerations

Contrast sensitivity is an important issue to consider given that it is reduced in glaucoma and also by multifocal IOLs, and perhaps more with refractive versus diffractive designs. Although reduction of contrast sensitivity and the degree of visual field loss are correlated, contrast sensitivity can be reduced even in patients with mild disease who have minimal visual field changes and no visual acuity changes, said Dr. Ahmed.

He noted that with multifocal IOLs, near contrast sensitivity is worse than distance, mesopic contrast sensitivity is worse than photopic, and the loss is greater at higher versus lower spatial frequencies.

"While glaucoma is associated with a greater loss of contrast sensitivity at lower spatial frequencies, the loss is also higher under mesopic conditions, and so there is a double whammy with the effect of a multifocal IOL," Dr. Ahmed said.

"Remember, however, that cataract extraction alone with implantation of any IOL will significantly improve contrast sensitivity. So the question becomes how much improvement can be obtained, and at what cost?"

Effects of multifocal IOLs on vision in decreased illumination also is a concern considering that some evidence suggests greater impairment of mesopic visual quality and slower dark adaptation in the glaucoma patient.

Another important issue is the scarcity of data on the potential of multifocal IOLs to affect functional and structural assessments of glaucomatous damage severity and progression. For that reason, if a multifocal IOL is to be implanted, new baselines must be established.

Dr. Ahmed suggested that clinicians might expect a depression in the overall threshold values of between 2 and 4 dB, but he noted that his anecdotal experience derived from about 75 patients with mild-to-moderate visual field defects shows that multifocal IOL implantation has minimal to no effect on those values.

Although previous research indicates no effect of monofocal IOLs on high-pass resolution central perimetry, a loss of sensitivity occurs in the multifocal IOL group. Diffractive multifocal IOLs performed best, which might be expected considering the effect of different IOLs on the availability of light for specific tasks.

"Based on these principles, one recommendation for visual field testing in glaucoma patients with a multifocal IOL would be to use the optimal add for near. The possibility of a small depression in the gray scale, raw values, total deviation, and mean deviation should be considered, whereas pattern deviation plot, glaucoma hemifield test, pattern standard deviation, and the Glaucoma Probability Analysis are less likely to be affected by focus effects," Dr. Ahmed said.

He noted that frequency doubling technology (FDT) is less dependent on refraction than white-on-white perimetry. For that reason and because it is performed with a larger target, multifocal IOLs would be expected to have a minimal effect on patient performance with FDT. It appears that multifocal IOLs have minimal effect on optical coherence tomography, and no impact is expected on other structural imaging techniques, although data are lacking.