“The FDA approved the enVista IOL as glistening-free following a 122-eye clinical trial involving six sites,” says Peter Heiner, MD, from the Vision Eye Institute, Gold Coast, Australia. “All implanted lenses were evaluated by slit-lamp investigations and photography, and no glistenings were detected at any examination.”
Glistenings are fluid-filled microvacuoles that form in the optic of the IOL in an aqueous environment. They have been found in many lens types, but have been found most frequently in hydrophobic acrylic IOLs, which are the most commonly implanted lens type in the United States and Australia.1
These glistenings form within the superficial layer of an IOL, potentially causing some of the light coming into the eye to be scattered. Glistenings not only present an aesthetic issue post-surgery for surgeons, but they can impact visual function. “We know that, if you grade glistenings on a scale of 1 to 4, anything over 2 causes a decrease in visual acuity of one line,” says P. Dee Stephenson, MD, from Stephenson Eye Associates, Venice, Fla. “We know that glistenings affect vision, so why would you put a lens that has the potential for glistenings in a patient if you don’t have to?” Dr. Stephenson was one of the first ophthalmologists to implant the enVista lens in the United States outside of the pilot study.
“Two of the functions of the natural lens of the eye are to provide refractive power and to remain clear,” Dr. Heiner says. If the lens loses clarity, a cataract forms, and vision deteriorates. With the introduction of the enVista intraocular lens, we have a hydrophobic IOL that can provide refractive power and remain glistening-free.”
He notes that many surgeons are concerned about the presence of glistenings and the possible deleterious effects on quality of vision. A study conducted at the John Moran Eye Center found that glistenings occur frequently in AcrySof IOLs, another hydrophobic acrylic IOL.2 This study included 42 eyes that underwent phacoemulsification and implantation of an AcrySof IOL. Glistenings were graded at the slit-lamp from trace to 4+. The researchers found that all 42 of the IOLs had some degree of lenticular glistenings. They were graded as trace in 27 IOLs (64 percent), 1+ in five (12 percent), 2+ in five (12 percent), 3+ in three (7 percent), and 4+ in two (5 percent). In eyes with severe glistenings (2+ or higher), Snellen acuity was one-half line lower than in eyes with mild glistenings. The Brightness Acuity Tester score was just more than one-half line lower than the Snellen acuity. In eyes with glistenings graded above 2+, the difference was one full line. Of the 15 IOLs with glistenings graded higher than trace, 14 (93 percent) had been in the eye for more than one year. Researchers found no evidence that contrast sensitivity was affected by the glistenings.
Although it is uncommon, in some instances intraocular lenses have been explanted due to reduced quality of vision in the presence of dense glistenings. “With a tendency to operate on patients at an earlier age and for patients to live longer, it is comforting to implant a lens that will remain clear,” Dr. Heiner says.
enVista avoids glistenings through pre-hydration and packing in 0.9% saline. The lens is 4 percent water, so it is in equilibrium with the environment in saline, which means that there is no water movement in and out of the IOL.
This lens is made of a proprietary highly cross-linked acrylic co-polymer. The enVista IOL is a single-piece lens with a modified-C haptic design. It has a 360° posterior square edge, 6-mm aspheric optic, and it is 12.5 mm long. The refractive index is 1.54. It is available in diopter ranges of 0 D to 9 D and 31 D to 34 D in 1-D increments and in diopter ranges of 10 D to 30 D in 0.5-D increments.
Additionally, the lens is very durable. According to Dr. Stephenson, some lenses can be damaged by the inserter or forceps, but the enVista IOL resists abrasions. “Therefore, the clarity of this lens is incredible, and it looks beautiful in the eye,” she says. “The lens has a square edge and is aspheric. Aspheric lenses are aberration-free. They have uniform power from the center to the edge, so if they lens gets decentered or tilted, it will not induce any aberrations.”
Dr. Stephenson has implanted 50 lenses to date. Of these patients, 25 are six weeks or more postop. She uses the WaveTec Vision Ora system in the operating room to help improve her outcomes. All 25 patients’ uncorrected visual acuity is 20/40 or better. All of those 25 patients are within 0.50 D of absolute predicted error, with the mean being 0.17 ±0.11. Seventy percent of those patients are within 0.25 D of absolute predicted error, with the mean being 0.17 ±0.11 as well. “These are better results than historical LASIK outcomes,” she says.
She also notes that the lens does not move once it is in the eye. “In fact, 91 percent move less than 5°, which is nothing,” she says. “The lens unfolds slow and controlled. It is easy to rotate into the bag and remove the viscoelastic from behind the lens. She cites the features of the lens including a unique single-piece modified-C haptic design to provide rotational stability; fenestrated vaulted haptics with a 56° contact angle provide added stability; and it is vaulted, so the optic actually touches the posterior capsule.
Dr. Heiner recently presented a poster at the AAO meeting detailing a study he conducted using the enVista lens (Heiner P, Northcott M. Early clinical experience of a new hydrophobic intraocular lens. Presented at the 2012 annual meeting of the American Academy of Ophthalmology). The study included 46 consecutive eyes of 36 patients scheduled for cataract surgery with planned implantation of the enVista IOL. Patients’ mean age was 74 years, with a range of 56 to 87 years. Cataract surgery was performed using the Stellaris phaco machine. Dr. Heiner used peribulbar anesthesia with intracameral supplementation. He used 2.2-mm temporal, clear cornea, three-stepped, self-sealing, square incisions and the microburst ultrasound setting. The 2.2-mm incision was not enlarged. The lens was placed using a Medicel Accuject injector system. Patients were given 1 mg intracameral cephazolin.
Preoperatively, 30 percent of eyes had uncorrected visual acuity of 20/40 or better, and 5 percent had visual acuity of 20/30 or better. At two weeks after surgery, 98 percent had uncorrected visual acuity of 20/40 or better, 80 percent had uncorrected visual acuity of 20/30 or better, and 23 percent had visual acuity of 20/20 or better.
Three months postoperatively, 98 percent had uncorrected visual acuity of 20/40 or better; 82 percent had uncorrected visual acuity of 20/30 or better; and 45 percent had uncorrected visual acuity of 20/20 or better. Preoperatively, patients’ mean uncorrected visual acuity logMAR was 0.606 ±0.368 (or 20/80). At two weeks postop, patients’ mean uncorrected visual acuity logMAR was 0.115 ±0.129 (or 20/25-), and at three months postoperatively, patients’ mean uncorrected visual acuity logMAR was 0.075 ±0.130 (or 20/25+).
Dr. Heiner also tested best-corrected visual acuity. Preoperatively, 87 percent of eyes had BCVA of 20/40 or better; 63 percent had BCVA of 20/30 or better; and 9 percent had BCVA of 20/20 or better. At two weeks after surgery, 100 percent had BCVA of 20/30 or better, and 80 percent were 20/20 or better. Three months postoperatively, 100 percent had BCVA of 20/30 or better, and 89 percent were 20/20 or better. Preoperatively, patients’ mean BCVA logMAR was 0.179 ±0.135 (or 20/30). At two weeks postop, patients’ mean BCVA logMAR was -0.023 ±0.05 (or 20/20+-); and at three months postoperatively, patients’ mean BCVA logMAR was -0.037 ±0.054 (or 20/20+2).
To date, Dr. Heiner has implanted 221 enVista IOLs. “I have found that this lens gives good results in terms of unaided and corrected vision,” he says. “I routinely implant this lens through an unenlarged 2.2-mm temporal wound. This results in low surgically induced astigmatism of 0.4 D. To date, I have only needed to YAG eight eyes, which corresponds to a 3.6 percent rate.”
Interestingly, the enVista material has a relatively high glass transition temperature (Tg) of 28°C, which is responsible for the slow, controlled unfolding of the lens on implantation. According to Dr. Heiner, the lens centers well once it is inserted into the capsular bag.
“I have found the pace of the unfolding to be an advantage because it allows ample time for removing viscoelastic from behind the optic. I am able to insert the I/A tip between the optic and the posterior capsule and get all of the viscoelastic out before unfolding is complete,” he says.
Also setting enVista apart from currently available IOLs is its combination of aspheric and aberration-free Advanced Optics (AO) technology. Additionally, the enVista lens is designed to minimize posterior capsular opacification, which is a common post-surgical complication with IOLs.
“I feel like this is a significant addition to my IOL armamentarium,” Dr. Stephenson adds.
Full release of the enVista IOL is under way now that the coated insertion system has been approved. Additionally, the enVista toric lens has been approved in Europe and is in the pipeline in this country. REVIEW
Dr. Stephenson and Dr. Heiner are members of Bausch + Lomb’s speakers bureau.
1. Werner L. Glistenings and surface light scattering in intraocular lenses. J Cataract Refract Surg. 2010;36(8):1398-1420.
2. Christiansen G, Durcan FJ, Olson RJ, Christiansen K. Glistenings in the AcrySof intraocular lens: a pilot study. J Cataract Refract Surg. 2001;27(5):728-733.