Introducing the enVista IOL

The absence of glistenings in this new hydrophobic acrylic lens is a welcome additional advantage.

By Mark Packer, MD, FACS, CPI

When the enVista IOL was approved by the FDA in June, it became the first single-piece hydrophobic acrylic IOL with this statement on its label: “No glistenings of any grade were reported for any subject at any visit in the clinical study.”^1,2 The enVista IOL is made from a hydrophobic acrylic material, which is the most widely implanted IOL material class in the United States.³ However, it’s also the material class in which glistenings have been most frequently observed.⁴ Therefore, the availability of a single-piece hydrophobic acrylic lens option with a higher likelihood of remaining glistening-free is a welcome development.

Glistenings, fluid-filled microvacuoles that can form in an IOL, are believed to be influenced by a variety of factors, such as material composition, packaging, manufacturing process, changes in equilibrium water content caused by temperature fluctuations, use of ocular medications, glaucoma, and ocular conditions in which the blood-aqueous barrier breaks down.⁴ Method of sterilization, warming or handling lenses prior to implantation, and temperature changes in the anterior chamber after implantation have also been identified as contributing factors.⁵

Typically, glistenings are noticeable at the slit lamp. Studies have reported that glistenings occur in as many as 86% of hydrophobic acrylic IOLs and tend to increase over time.^6-8 Exactly how and to what extent they affect patients’ vision is less clear based on the available literature. Some studies have suggested glistenings reduce visual acuity and contrast sensitivity,^9,10 while others have not detected an impact.¹¹ From a clinical practice perspective, it’s hard to believe glistenings, especially when they are severe, would not be problematic. At the very least, we don’t want to see them in an IOL. We would not, for example, order a new car with an imperfect coat of paint. Even if the spots don’t affect the performance of the car, we still wouldn’t want them to be there. With multifocal presbyopia-correcting IOLs in particular, which are already prone to reducing contrast sensitivity and increasing glare, adding the potential for glistenings is certainly not desirable.

Combination of Features Make enVista an Attractive Option

The enVista IOL is a single-piece lens with an aspheric, aberration-free, 6-mm optic, a 360° square posterior edge and modified C haptics. It’s available in powers from 0D to +34.0D (0.0D to +10.0D in 1-D increments; +10.0D to +30.0D in 0.5-D increments; and +30.0D to +34.0D in 1-D increments). Surgeons who prefer a wound-assist technique, more popular outside the United States, can implant the enVista using a 2.2-mm incision. Its propensity to be glistening-free combined with its other features make it an attractive option for today’s cataract surgeons.

The enVista material was originally developed by Advanced Vision Science (a Santen subsidiary). It’s a durable material that’s resistant to abrasion and wear,¹² yet the optimized water content (4%) enhances flexibility and foldability. When inserted into the eye, it unfolds in a controlled manner, which facilitates positioning in the capsular bag and removal of viscoelastic. (See next article, “Surgeon Has Early Success with enVista.”) The material has been used in Japan as the Eternity IOL since 2008. In 2009, Bausch + Lomb obtained the right to develop, manufacture and market the material in other countries, including the United States.

To prevent glistenings, the enVista IOL is prehydrated to equilibrium water content so it will neither gain nor lose water. It’s then packaged in physiologic (0.9%) saline solution, the same salt concentration as the eye, to eliminate fluid exchange with the aqueous humor. In addition, because drastic changes in temperature have been linked to vacuole formation, the enVista is sterilized with gamma irradiation instead of heat. As a result, when the IOL is placed in the eye, nothing changes and water-filled vacuoles do not form.

In the six-site, 122-eye clinical trial that led to FDA approval of the enVista IOL, glistenings were evaluated via retroillumination slit lamp examination, and photographs of each lens were taken and sent to a reading center for analysis and grading. No glistenings were seen in any of the IOLs at any time point.

Also at the 6-month postoperative study visit, 100% of patients (n=118) had best-corrected visual acuity of 20/40 or better, which is superior to the FDA grid of historical controls (96.7%).

The trial also provided encouraging information about the enVista and posterior capsule opacification (PCO). Several enVista design elements are aimed at long-term PCO prevention. The lens has a square posterior edge, which is known to be associated with a low rate of PCO.¹³ The square edge covers 360°, which has been shown to inhibit lens epithelial cell migration more effectively than a square edge that is interrupted at the haptic-optic junction.¹⁴ The lens fenestrations promote even pressure on the square edge, and the haptics vault the optic posteriorly for direct contact with the capsular bag.

Rotational stability was another characteristic evaluated closely in the enVista trial, and the results were outstanding. 100% of patients had ≤ 5° of IOL rotation between days 30 and 180. This type of stability bodes well for future development of a toric version of the lens.

Aiming for Clear Vision: Short-term and Long-term

Based on the design of the enVista and its performance in the clinical trial, we can expect that it will not only stay free of glistenings, deter PCO, remain stable in the eye and provide good visual acuity, but may also give patients their best possible quality of vision. It utilizes Advanced Optics technology — two aspheric surfaces, zero aberration and uniform power from center to edge — to reduce spherical aberration and enhance contrast sensitivity.¹⁵ (See “Aberration-Free Optics Enhance Performance,” on page 6.)

References

1. enVista Directions for Use.

2. Tetz MR, Werner L, Schwahn-Bendig S, Batlle JF. A prospective clinical study to quantify glistenings in a new hydrophobic acrylic IOL. Paper presented at: American Society of Cataract and Refractive Surgery (ASCRS) Symposium & Congress; April 3-8, 2009; San Francisco, CA.

3. Market Scope 2012 Report on the Global IOL Market.

4. Werner L. Glistenings and surface light scattering in intraocular lenses. J Cataract Refract Surg. 2010;36(8):1398-1420.

5. Shiba T, Mitooka K, Tsuneoka H. In vitro analysis of AcrySof intraocular lens glistening. Eur J Ophthalmol. 2003;13(9-10):759-763.

6. Moreno-Montañés J, Alvarez A, Rodríguez-Conde R, Fernández-Hortelano A. Clinical factors related to the frequency and intensity of glistenings in AcrySof intraocular lenses. J Cataract Refract Surg. 2003;29(10):1980-1984.

7. Colin J, Praud D, Touboul D, Schweitzer C. Incidence of glistenings with the latest generation of yellow-tinted hydrophobic acrylic intraocular lenses. J Cataract Refract Surg. 2012;38(7):1140-1146.

8. Colin J, Orignac I, Touboul D. Glistenings in a large series of hydrophobic acrylic intraocular lenses. J Cataract Refract Surg. 2009;35(12):2121-2126.

9. Dhaliwal DK, Mamalis N, Olson RJ, et al. Visual significance of glistenings seen in the AcrySof intraocular lens. J Cataract Refract Surg. 1996;22(4):452-457.

10. Christiansen G, Durcan FJ, Olson RJ, Christiansen K. Glistenings in the AcrySof intraocular lens: pilot study. J Cataract Refract Surg. 2001;27(5):728-733.

11. Colin J, Orignac I. Glistenings on intraocular lenses in healthy eyes: effects and associations. J Refract Surg. 2011;27(12):869-875.

12. Mentak K, Martin P, Elachchabi A, Goldberg EP. Nanoindentation studies on hydrophobic acrylic IOLs to evaluate surface mechanical properties. Paper presented at: XXV Congress of the European Society of Cataract and Refractive Surgery; Sept. 8-12, 2007; Stockholm, Sweden.

13. Nishi O, Nishi K, Osakabe Y. Effect of intraocular lenses on preventing posterior capsule opacification: design versus material. J Cataract Refract Surg. 2004;30(10):2170-2176.

14. Nixon DR, Woodcock MG. Pattern of posterior capsule opacification models 2 years postoperatively with 2 single-piece acrylic intraocular lenses. J Cataract Refract Surg. 2010;36(6):929-934.

15. Pepose JS, Qazi MA, Edwards KH, Sanderson JP, Sarver EJ. Comparison of contrast sensitivity, depth of field and ocular wavefront aberrations in eyes with an IOL with zero versus positive spherical aberration. Graefes Arch Clin Exp Ophthalmol. 2009; 247(7):965-973.

Dr. Packer is managing partner with Drs. Fine, Hoffman & Packer in Eugene, Ore., and a clinical associate professor of Ophthalmology at Oregon Health & Science University. He served as the Medical Monitor for the clinical trial that led to FDA approval of the enVista IOL.