Toric IOL expands options for pre-existing astigmatism

May 15, 2013

Lens demonstrated excellent rotational stability, visual outcomes in clinical trials

Reviewed by Kerry Assil, MD, and Farrell C. “Toby” Tyson, II, MD

 

TAKE-HOME:

Abbott Medical Optics has received FDA approval to market its hydrophobic acrylic, monofocal aspheric 1-piece toric IOL (model ZCTXXX, Tecnis Toric IOL).

 

 

The FDA approval of the Tecnis Toric 1-Piece IOL (model ZCTXXX, Abbott Medical Optics) will allow cataract surgeons to deliver improved visual outcomes to their patients with pre-existing corneal astigmatism, according to surgeons having experience with the new lens.

 

 

The toric IOL is available in four cylinder powers (1.50, 2.25, 3 and 4 D at the IOL plane) that are recommended to correct between 1 and 3.62 D of corneal astigmatism. It is based on the time-tested platform of the hydrophobic acrylic, monofocal aspheric Tecnis 1-piece IOL (ZCB00) that offers material and design benefits that are especially well-suited for toric IOL technology. Clinical trial outcomes for the Tecnis Toric IOL show excellent clinical performance in terms of intraocular stability, refractive correction, and functional outcomes, and it is a surgeon-friendly lens that is easy to insert and align.

“I consider toric IOL implantation the best modality for providing excellent uncorrected distance vision in patients with more than 1 to 1.5 D of astigmatism,” said Farrell C. “Toby” Tyson, II, MD, private practice, Cape Coral Eye Center, Cape Coral, FL, and an investigator in the premarketing, North American Tecnis Toric IOL clinical trial. “With the Tecnis Toric IOL, surgeons now have a valuable new option to help them achieve this goal.”

 “The [IOL] offers a cluster of desirable features that together enable surgeons to provide superior vision for patients with pre-existing corneal astigmatism,” said Kerry Assil, MD, who is in private practice, Assil Eye Institute, Los Angeles. In a symposium held during the annual meeting of the American Society of Cataract and Refractive Surgery last month in San Francisco, he was the first U,S. surgeon to implant the lens following its FDA approval.

The North American clinical trial evaluating the safety and effectiveness of the IOL had two arms. In a randomized, double-masked arm, 197 eyes received the Tecnis Toric ZCT150 (1.5 D cylinder correction at the IOL plane) or the one-piece, aspheric monofocal Tecnis IOL (model ZB00). The second arm of the trial had an open-label design, included 72 eyes, and evaluated the other three cylinder powers (models ZCT225, ZCT300, and ZCT400).

Rotational stability

IOL rotational stability was assessed by software analysis of high-resolution digital slit lamp photographs taken at serial visits from 1 day to 6 months postoperatively. Of 174 eyes with the Tecnis Toric IOL implanted, 148 had photographic data at all follow-up visits. Between day 1 and 6 months, mean absolute axis change was <3º. The axis changed by ≤5º between 1 and 3 months in 93% of eyes and between 3 and 6 months in 94% of eyes.

“The new American National Standards Institute criterion for rotational stability of a toric IOL requires that at least 90% of eyes have no more than a 5º axis change between consecutive visits at least 3 months apart,” Dr. Tyson said. “These data show the Tecnis Toric IOL exceeds this tough standard.”

Dr. Tyson and Dr. Assil attribute the rotational stability of the Tecnis Toric IOL to its long overall diameter, 13 mm, and proprietary offset, forward-mounted, rigid haptics design (Tri-Fix).

“The optic sits posteriorly and with the haptics, creates three points of fixation with the capsular bag that makes undesired secondary rotation unlikely,” Dr. Assil said.

Other clinical trial results showed mean reduction in cylinder was significantly greater in eyes with the toric IOL implanted than in the controls receiving the ZB00; overall, residual refractive cylinder was <1 D in 94% of Tecnis Toric IOL eyes and <0.50 D in 72% of the eyes.

The refractive difference favoring the toric IOL group over controls translated into significantly better uncorrected distance visual acuity (UDVA) for the toric IOL eyes and a higher rate of spectacle independence for distance. In the randomized study arm at 6 months, mean monocular UDVA was logMAR 0.10 (Snellen 20/25) in the toric IOL eyes compared to logMAR 0.1 6 (Snellen 20/29) in the controls. The results with toric IOL implantation were similar in the open label arm in which mean logMAR UDVA at 6 months was logMAR 0.11 (Snellen 20/26). The proportion of eyes achieving 20/20 or better UDVA was 44% for the toric IOL group and 24% for the controls; rates for 20/40 or better UDVA were 97% and 87%, respectively.

Visual acuity outcomes

Both Dr. Tyson and Dr. Assil noted that even if eyes have some minor residual sphere and cylinder, the Tecnis Toric IOL still provides good acuity. They attribute that performance to several factors.

“Eyes achieve crisper vision with better correction of spherical aberration (SA) and particularly eyes that already have reduced contrast acuity secondary to some retinal pathology,” Dr. Tyson said. “Since the Tecnis aspheric technology fully compensates for population average SA of +0.27 μm, it is likely to come close to the ‘sweet spot’ of zero SA in more eyes than the AcrySof IQ Toric IOL that corrects only 0.1 μm of SA. With its greater SA compensation, the Tecnis Toric IOL is also preferred in eyes with a history of myopic LASIK that tend to have higher-than-average positive corneal SA.”

Visual quality in eyes with the Tecnis Toric IOL implanted is also enhanced by the lens material, Dr. Assil said.

“The Tecnis hydrophobic acrylic polymer has very low chromatic aberration, is clear without any tint, and starts out and remains glistening-free,” he said. “It is a superb optical material providing excellent contrast acuity and clarity that helps to forgive slight residual refractive errors.”

Considering the clinical trial outcomes, Dr. Assil said that the Tecnis Toric IOL calculator seems to be providing precise results. It is also intuitively simple to use and allows surgeons to aim for slight under- or overcorrection of cylinder if they desire, he said.

The implant also has very favorable handling characteristics. It delivers smoothly through a 2.2- to 2.4-mm incision. Once in the eye, it can be dialed into the desired position before the haptics engage the capsular equator.

“With this material, the haptics don’t stick to the optic, and the lens can be easily rotated clockwise or counterclockwise, thus allowing me to fine-tune the lens position by as little as 5º based on intraoperative aberrometry,” Dr. Tyson said.

 

 

Kerry Assil, MD

E: kerry2020@gmail.com

Farrell C. “Toby” Tyson, II, MD

E: tysonfc@hotmail.com

Dr. Assil and Dr. Tyson are consultants to Abbott Medical Optics.