Impairment of visual acuity (VA) due to postoperative astigmatism—and particularly distance VA—may be more prominent in eyes implanted with a trifocal IOL than in bifocal IOL eyes, a new study published online in the American Journal of Ophthalmology reports.

The team of researchers from Japan also found trifocal IOLs allowed for good VA at all distances when the refractive astigmatism was 0.75D or less. On the other hand, bifocal IOLs might be a better choice for eyes with postoperative astigmatism within 0.75D and 1.00D, the investigators noted.

The study enrolled 50 eyes with trifocal IOLs and 50 eyes with bifocal IOLs. The researchers measured corrected logMAR VA after simulating astigmatism by adding cylindrical lenses of zero, 0.50D, 0.75D, 1.00D and 1.50D.

The researchers reported VA at most distances significantly worsened in proportion to the added astigmatism with no significant difference in near VA at 0.3m in the trifocal group or in intermediate VA at 0.7m in the bifocal group. The investigators noted the intermediate VA at 0.5m was significantly better in the trifocal group than in the bifocal group when the astigmatism was 0.75D or less, but distance VA and at 5m was significantly worse in the trifocal group when the astigmatism was 0.50D or more. Useful mean logMAR VA of 0.20 at all distances was achieved when the astigmatism was 0.75D or less in the trifocal group and 1.00D or less in the bifocal group.

Clinically, when the residual astigmatism is assumed to be greater than 0.75D, surgeons should perform astigmatism correction procedures, including the use of an IOL with a toric component and a corneal relaxing incision, the investigators suggested. Otherwise, bifocal IOLs might be a better selection for eyes that are assumed to have a postoperative astigmatism within 0.75 and 1.00D, they added.

Because the present study was a simulation, the effect of residual refractive astigmatism should be confirmed in actual postoperative eyes implanted with the trifocal IOL, the researchers said. As such, further studies are necessary to examine the effect of residual astigmatism on the performance of trifocal IOLs, they added.