L&T: Lens Choices

Aug
2006

Depth of a Salesman

In September, the Advanced Medical Optics/Ophtec phakic intraocular lens, the Verisyse, became the first such lens to receive Food and Drug Administration approval for myopia. The lens was approved for the treatment of myopia from -5 D to -20 D, in eyes with 2.5 D of cylinder or less and anterior chamber depths of at least 3.2 mm. Ophtec is the maker, and AMO the distributor, of the lens.

“This gives us an opportunity to offer refractive surgery to people who were not candidates for LASIK or PRK,” says Emory University’s R. Doyle Stulting, MD, PhD, medical monitor for the Verisyse clinical trial. “These people tend to be those with high refractive errors and thin corneas, or a combination of the two.”

The Verisyse is a single-piece, PMMA lens designed to treat refractive errors through placement in the anterior chamber of the phakic eye. The diameter of the lens optic can be 5 mm or 6 mm, and the overall lens length is 8.5 mm, with a slight anterior vault.

The Verisyse clinical study consisted of 662 patients total. In 204 patients available for follow-up at one year, 93.6 percent see 20/40 or better, and 47 percent see 20/20 or better uncorrected. All patients see 20/40 or better with correction. As for predictability, 94.5 percent were within ± 1 D of the target refraction at one year.

The Verisyse lens may be available in October.

“I think we’re going to find that the quality of vision with phakic intraocular lens implants is probably superior to that of LASIK, though the clinical studies weren’t performed with that comparison in mind,” says Dr. Stulting. “When we perform LASIK, especially on high myopes, we induce some spherical aberrations that are not induced with phakic IOLs. So, we have an opportunity to preserve relatively normal corneal contours with the implant, where we wouldn’t have the ability to do that with LASIK.”

The most common adverse event in the study was surgical reintervention, necessary in 4.2 percent of cases. Explantation for reasons such as trauma, inflammatory response and patient anxiety represented 1.5 percent of these reinterventions, lens exchange accounted for 1.4 percent, lens reattachment for 0.7 percent and repair of retinal detachment in 0.6 percent. The lens labeling notes that none of these had an impact on safety or efficacy.

The labeling reports that eyes with brown irides and pigment dispersion had a statistically significantly higher rate of IOP spikes (11.7 percent) than non-brown eyes with pigment dispersion (3.1 percent).

Glaucoma from pigment dispersion wasn’t a long-term problem, says Dr. Stulting. “There were some incidences of elevated IOP early in the postoperative period, presumably due to retained viscoelastic, which is about what we’d expect,” he says.

Some surgeons have wondered about what effect an anterior-chamber lens would have on the corneal endothelium. In the FDA statement announcing the approval of the lens, the agency notes that, “The three-year data showed a continual steady loss of endothelial cells of 1.8 percent a year. At this point, it is not known whether this loss will continue at the same rate, or what the long-term effect of this device on the cornea’s health might be. To minimize any potential long-term effects of the device on the corneal endothelium, FDA is requiring the labeling for the new lens to specify that it should be used only on patients whose corneal endothelial cells are dense enough to withstand some loss over time.”

“Pretty much everything that’s on the labeling is what was anticipated,” says Dr. Stulting. “During the study, the cell loss was within the range that would be typical for intraocular surgery. There was nothing unanticipated. It was exactly as you’d expect if you put a lens in someone’s eye and took reasonable care in doing it.”

Though many steps of Verisyse implantation are similar to implanting an IOL during a cataract operation, there are a few stages that may test a surgeon’s skill.

“We learned from the study that surgeons need to be well-educated in how to properly attach the lens to the iris,” says Dr. Stulting. “Enclavation requires bimanual dexterity and a little bit of training so that the lens is properly positioned reliably. It also takes a little bit of experience to know where to attach it to the iris. But all of those things can be learned pretty easily.”

Any surgeon interested in implanting the Verisyse will need to be trained in its use. According to Ron Bache, AMO’s director of worldwide marketing for its refractive products, the company is currently offering one-day surgeon training and certification courses for $2,995, which includes the instruments required to implant the lens. The lenses cost $695 each or $13,375 for a complete set of 32.

USAF Studies Offer Insights on Contrast Sensitivity After PRK
The United States Air Force recently completed a longitudinal clinical study designed to evaluate PRK’s long-term effect on aircrew visual performance, an issue that can be of critical importance during combat. (PRK was the subject of the study because LASIK still isn’t considered as universal a corrective option for aircrew members; the flap can be displaced by blunt trauma and windblast, such as might be encountered when ejecting from an aircraft.)

Col. Douglas J. Ivan‚ MD‚ chief of the ophthalmology branch at the U.S. Air Force School of Aerospace Medicine and program manager for the USAF PRK research study project, explains that one purpose of the study was to evaluate the sensitivity of different contrast sensitivity testing methods. “We built a variety of quality-of-vision tests into our study, including charts and electronic contrast sensitivity testing, which is kind of a gold standard,” he says.
“Some contrast sensitivity tests aren’t sensitive enough to pick up subtle change. Yet that change may be operationally significant in the military.”
One section of the overall study, used the Freiburg Acuity and Contrast Test (FRACT) to monitor the effects of PRK on visual acuity (VA) and CS under different conditions over a two-year follow-up period. “We found that the Freiburg test was sensitive enough to show that there was a contrast sensitivity drop-off that was not picked up by traditional high contrast visual acuity testing,” Dr. Ivan explains.

As expected, the presence of glare degraded both VA and CS, and the presence of the windscreen (with its minute optical flaws from wear) made the impact of glare worse. However, two results were noteworthy. First, although the tests generally failed to detect significant changes in VA following PRK, the data showed long-term worsening of CS in many subjects that did not improve with healing.

Second, despite the equal luminance of the two glare sources, the laser glare interfered far more with both VA and CS than the broadband glare source. “We weren’t expecting that to be the case,” notes Richard J. Dennis, OD, MS, FAAO, a senior vision scientist at the AF Laser Research Laboratory.

“Because the military uses lasers for many purposes, this could be a significant concern.” Researchers observed that the laser glare produced coherent spatial noise—i.e., “laser speckle”—that may account for the increased visual interference.

In terms of contrast sensitivity, Dr. Ivan notes that not all PRK patients end up with “permanent” CS loss. “Those who still have a deficit two years out are a subset of this population. We’re trying to find the right tests to determine who those individuals are, and ultimately create a set of standards for this that we can get policy makers to buy into.

“We can’t afford to put pilots in the cockpit who may have subtle but significant loss of contrast sensitivity,” he adds. “After refractive surgery, older, traditional vision standards simply don’t tell us all that we need to know.”
Opt & Vis Sci 81;7:516-524

Statins May Protect Against Vitreous Hemorrhage
A retrospective analysis of 54 diabetic patients—20 with type I diabetes and 34 with type II diabetes—indicates that statin therapy may cause a delay in the appearance of vitreous hemorrhage, as well as a reduction in its recurrence. In contrast, regular use of aspirin or ACE-inhibitors doesn’t appear to have any effect on vitreous hemorrhage.

Researchers at Birmingham and Midland Eye Centre in England, noted that hemorrhage was detected in patients on statin therapy an average (mean) of 21.4 years after diagnosis; patients not taking HMGCoA reductase inhibitors were found to have vitreous hemorrhage an average of 16.2 years after initial diagnosis. This trend was not statistically significant.

The reduction in recurrence associated with statin use did reach statistical significance. The investigators reviewed 110 episodes of recurrent vitreous hemorrhage that occurred in 79 eyes of the 54 patients during follow-up. Use of aspirin, antiplatelet or anticoagulant agents or ACE-inhibitors was not associated with any significant effect on the one-year recurrence rate; nor was a patient’s age or gender, the type of diabetes, the presence of hypertension or hypercholesterolemia, or macrovascular complications. Statin use, however, did produce a statistically significant reduction in vitreous hemorrhage recurrence.

The authors also noted that the first occurrence of vitreous hemorrhage occurred significantly later in type I diabetics (21.9 years) than in type II diabetics (14.8 years).
Eye 18;August 2004:821-825

Bacteria-Fighter Helps Maintain Normal Eyesight
A family of genes long known to be integral to the immune system also plays a role in vision, perhaps preventing certain blinding diseases. The gene, TLR4, enables the eye to clear old outer segments, a function that is essential for maintaining normal vision, say researchers at the University of Michigan Kellogg Eye Center.

The gene belongs to a group of toll-like receptors (TLRs), which dispose of bacteria and other foreign matter in cells throughout the body. Howard R. Petty, PhD, a biophysicist at Kellogg, says the discovery will give scientists new ways of thinking about the chain of molecular events that lead to eye disease. Dr. Petty and his colleagues are the first to link TLR4 to the eye; his findings are reported in August’s Journal of General Physiology.

To maintain vision, the eye must continuously dispose of the aging or damaged outer segments of photoreceptor cells. “The process is a little like recycling,” Dr. Petty says. “As outer segments of photoreceptor cells become worn out, new outer segments are generated to replace them. If the eye cannot efficiently dispose of its worn out segments, a person will go blind.”

Knowledge about the gene may provide new avenues for studying such diseases as retinitis pigmentosa and age-related macular degeneration, says Dr. Petty. Dr. Petty is already conducting research to learn more about TLR4 and how its proteins interact with other elements involved in clearing outer segments.

Other studies have shown that TLRs play a role in stimulating oxidants. When oxidants accumulate in eye tissue, they cause retina cells to die. The build-up most likely occurs in small incremental steps, and may be a factor in AMD.
Scientists have known for years that TLRs participate in the immune system of Drosophila, or fruit fly. “We are looking at one of the oldest genes to participate in immune defense,” says Dr. Petty. “Fruit flies do not have antibodies; these evolved much later. So with TLR we are talking about innate immunity.”

“Nature likes to economize,” says Dr. Petty. “Maybe it’s not all that surprising that we have found a set of genes that are central to corresponding processes involving two different systems. The bottom line is that the TLR genes are there to get rid of things that don’t belong.”
The paper is available on line at jgp.org.

FDA Approval for Epi-Lift
VisiJet Inc. (Irvine, Calif.) received FDA approval for its EpiLift System, the ophthalmic surgical device designed for separating corneal tissue during Epi-LASIK.

During Epi-LASIK, the top layer of the epithelium is separated into an intact sheet of viable tissue. After laser ablation of the corneal bed, the epithelial sheet is returned to its natural position on the eye. VisiJet says a key attribute the EpiLift System provides is precision. It cleanly and safely separates the epithelium from the next layer of corneal tissue, Bowman’s membrane. By eliminating the cutting of stromal flaps, the company says, the EpiLift System eliminates the primary cause of LASIK complications.

VisiJet, Inc. received the European CE Mark approval for the EpiLift System earlier this year. The EpiLift technology joins the company’s proprietary water jet technologies, which are in final development stages.

 

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