Modified prolate IOL good choice for piggybacking

"Results from bench studies confirm that the benefits of the aspheric surface can still be maintained when the Tecnis IOL is piggybacked with a spherical implant, and clinical experience has been favorable as well," said Dr. Chu, medical director, Chu Vision Institute, Edina, MN. "So far, we have used the Tecnis IOL in a piggyback situation in about 10 eyes, and with follow-up extending up to about 12 months, all have maintained excellent vision without any complications."

The bench studies he referred to were performed by Patricia Piers, MSc, an optical research scientist with AMO, and their results showed that the negative asphericity of the Tecnis outweighs the small amount of positive asphericity of the spherical IOL. For example, in the situation where a +30- D IOL is needed, use of the 913 implant (CeeOn, AMO) would result in +0.197 µm of spherical aberration. However, the total spherical aberration resulting from combining a +20-D Tecnis IOL with a +10-D 913 lens would be only 0.019 µm.

"When piggybacking these IOLs, the negative spherical aberration of the Tecnis IOL outweighs the small amount of positive spherical aberration induced by a normal spherical IOL, resulting in a net spherical aberration in the eye of essentially zero. Therefore, the negative spherical aberration of the Tecnis corrects for the cornea and the positive lens with a low amount of residual spherical aberration," Dr. Chu explained.

When using the Tecnis IOL in a piggyback situation, Dr. Chu suggested using the Tecnis IOL as the higher-power lens and placing it in the bag while implanting the lower-power, spherical IOL in the sulcus to minimize the development of interlenticular opacification. With the risk of that complication in mind, he also chooses a silicone spherical IOL because that material seems to be associated with less chance for interlenticular opacification compared with acrylic. The silicone Clariflex IOL (AMO) is one good choice, he said.

Reverse optic capture, as described by Howard V. Gimbel, MD, MPH, is another potential technique for piggybacking the two IOLs. In that approach the Tecnis IOL is placed in the bag along with the haptics of the spherical IOL, and then the spherical IOL optic is brought anteriorly and captured in the capsulorhexis.

Dr. Chu noted there are some high plus IOLs available that might be used in lieu of piggybacking when a patient with high hyperopia undergoes cataract surgery. However, he believes piggybacking with the Tecnis IOL provides better-quality vision.

"There is an increased amount of spherical aberration present in very high plus lenses, and studies show that when IOL power exceeds about +33 or +34 D, the quality of vision is better if the power is divided into two lenses. Using the Tecnis IOL as one of the lenses in the pair further enhances the advantage derived from splitting the lenses in a piggyback technique," Dr. Chu said.