Earlier this year, Michael C. Knorz, MD, professor of ophthalmology at the University of Heidelberg, Germany, presented data from a European multicenter study trial of the AcrySof? Cachet phakic intraocular lens (IOL), showing it had a minimal effect on corneal endothelial cell health in patients followed up to four years after implantation.

The AcrySof Cachet (Alcon Laboratories) is an angle-supported, anterior-chamber IOL made from the same hydrophobic acrylic as other AcrySof lenses. It received CE mark approval for phakic use in Europe in 2008, but is not yet available in the United States. A pooled analysis of 3-year data on 104 trial subjects in Europe, Canada and the U.S. is currently in press.

Benefit of Angle Fixation?
In his presentation at Hawaiian Eye 2010, Dr. Knorz said that there was an acute loss of corneal endothelial cells, averaging 3.3 percent in the first six months. But after this reaction to surgery, the IOL's impact on the endothelium appears to be minimal, Dr. Knorz said.

"The Cachet IOL fixates in the angle, about ? of the anterior chamber depth away from the endothelium," Dr. Knorz said. "It is also very thin because of the material's high index of refraction. These two facts most likely explain why there is very little endothelial cell loss."

Only 1% Loss per Year
After this acute loss in the first six months, Dr. Knorz determined the chronic loss rate was about 1 percent per year over the subsequent four years.

The mean annualized cell loss during the 4-year period was ?1.15 percent in the corneal periphery and ?0.99 percent in the center (range: ?0.27 to ?2.03 percent periphery; ?0.38 to ?1.6percent central), Dr. Knorz said. By comparison, the ISO 11979-10:2006 standard for phakic IOLs accepts an annual loss of up to 2 percent.

In the US FDA trial that led to approval of the Visian ICL (Staar Surgical), endothelial cell counts fell 10.6 percent (SD:9%) between the pre-op baseline and four years.¹ Long-term studies of the Artisan phakic IOL (Ophtec BV) showed an average loss of endothelial cell density of 8.3 V at five years (1.7V per year)² and 8.9V at 10 years (0.9percent per year).³

Lens Specifications
The Cachet is an angle-supported phakic IOL with a 6.0 mm optic, an overall length of 12.5 to 14.0 mm and a refractive range of -6.0 D to -16.5 D. It is injected through a 2.6 mm incision with the Monarch III injector and a special cartridge. Iridectomy or iridotomy is not required.

The four-year refractive results in the 48 AcrySof Cachet patients include:

• UCVA: 97.9% at ?20/40; 72.9% at ?20/25; 47.9% at ?20/20.
• BSCVA: 100% at ?20/32; 97.9% at ?20/25; 72.9% at ?20/20; 43.8% at ?20/16.
• Predictability: 68.1% within ±0.5D of target refraction; 89.4% within ±1.0 D.

Few Adverse Events
The European trial showsno instances of pupil ovalization, cystoid macular edema, corneal stromal edema, hyphema, hypopyon, IOL dislocation, pupillary block or lens repositioning.

The four-year cumulative incidence of cataract formation is 4.7 percent; synechiae 4.2 percent; and secondary surgical intervention 4.7 percent. There has been one case each of corneal haze, retinal detachment and a loss of BSCVA >0.2 logMAR (Snellen equivalent: >2 lines).

The IOL has four symmetrical haptic footplates, designed for even distribution of the fixation forces in the angle. The four haptics also prevent the lens from rotating, although an earlier version of the IOL with a 5.5 mm optic did have this problem, Dr. Knorz said.

No Pupil Ovalization
"The soft material results in very little pressure, and only on the angle, even if the IOL is accidentally oversized. I believe this is one of the reasons why we did not find any pupil ovalization in our study," Dr. Knorz said.

"Rotation was reported in a small number and is most likely due to too small an IOL diameter," he said. "In the study, we used manual measurement of the white-to-white distance to size the IOL. After the study, we now use the IOL Master or optical coherence tomography, which gives us better results without rotation."

Dr. Knorz has implanted about 250 of the lenses, six of which have been implanted for 10 years. He has never had to explant a lens. He predicts that cataract surgeons will find the Cachet an ideal phakic IOL to add to their practices.

Good News: Ease of Use
"The beauty of this IOL is that it is really easy to implant. The learning curve is very short," he said. "It is not necessary to use hundreds of them to stay current. A few per month should be OK."

The only challenging aspect of working with the Cachet occurs at the end of the surgery, he said. "The surgeon must practice the removal of the viscoelastic. It is safest to use bimanual irrigation/aspiration for this. If the surgeon is familiar with bimanual I/A from his cataract procedures, the transition is very simple. If not, we recommend that the surgeon practices bimanual I/A first in his cataract patients."

Financial Disclosure:
Dr. Knorz is a consultant to Alcon Laboratories, which sponsored the clinical studies of the AcrySof Cachet. Alcon provided assistance with the statistical analyses and Dr. Knorz's presentation.

References:
1. Staar Surgical. FDA-approved Visian ICL Product Information (2005).
2. Saxena R, Boekhoorn SS, Mulder PG, Noordzij BG, van Rij G, Luyten GP. Long-term follow up of endothelial cell change after Artisan phakic intraocular lens implantation. Ophthalmology 2008; 115:608-613.
3. Tahzib NG, Nuijts RM, Wu WY, Budo CJ. Long-term study of Artisan phakic intraocular lens implantation for the correction of moderate to high myopia: ten-year follow up results. Ophthalmology 2007; 114:1133-1142. 4. Benedetti S, Casamenti V, Benedetti M. Long-term endothelial changes in phakic eyes after Artisan intraocular lens implantation to correct myopia: five-year study. J Cataract Refract Surg. 2007;33:784-790.