A New-Generation Hydrophilic Acrylic IOL

The continued development of new IOL technologies has provided cataract surgeons more lens-based options than ever before. Surgeons must carefully evaluate which IOLs may be best for their patients and their practices. In April 2010, the Softec HD IOL (Lenstec Inc., St. Petersburg, Florida) was granted approval by the US Food and Drug Administration (FDA) for use in the United States. The Softec HD, a posterior chamber IOL, has been available for approximately 10 years outside of the United States. This article briefly compares and contrasts the Softec HD with other available IOL options.

SOFTEC HD SPECIFICATIONS

The Softec HD is an ultraviolet (UV)–light-absorbing, onepiece, modified C-loop IOL with a symmetrical anterior and posterior surface aspheric design. Its uniplanar design and equal-biconvex optic configuration allows surgeons to implant the lens without regard to whether it is placed rightside up. This IOL is manufactured from a medical-grade copolymer of hydrophilic acrylic hydroxyethylmethacrylate (HEMA; 26% water content) and a polymerizable UV blocker. The overall length of the lens is 12.0 mm (Table 1). The lens optic, which is 5.75 mm long, has a 360° square-edge design for IOL placement within the capsular bag. The lens is offered in 0.25 D steps across an 18.00 to 25.00 D range, allowing precise power correction. It is also available in 0.50 D increments from 10.50 to 29.50 D and 1.00 D increments from 5.00 to 36.00 D. A preloaded injector system allows the IOL to pass easily through a 2.5-mm corneal incision.¹

ADVANTAGES OF HYDROPHILIC ACRYLIC MATERIAL

In the United States, hydrophilic acrylic IOLs have not gained the same broad use as hydrophobic acrylic IOLs due to early reports of calcification and opacification.² However, the latest generation of hydrophilic acrylic IOLs appears to avoid these problems, with several proposed advantages, including less dysphotopsia, excellent biocompatibility, good optical clarity, resistance to damage, and protection from biocontamination.

Less dysphotopsia. Hydrophilic acrylic IOLs have higher water content and a lower refractive index relative to hydrophobic acrylic IOLs, minimizing glare, external and internal reflections, and other unwanted visual phenomena.

Excellent biocompatibility. These IOLs appear to have a minimal effect on the blood-aqueous barrier and may be excellent options for patients with uveitis and diabetes.

Good optical clarity. New-generation hydrophilic IOL materials have shown no evidence of calcification over the past 5 years and appear not to be associated with the glistenings and inclusions seen in earlier hydrophobic acrylic IOLs.

Resistance to damage during insertion. Hydrophilic acrylic IOLs are resistant to fold marks and forceps damage.

Protected from biocontamination. Bacteria may be less adhesive to this lens material than to polymethyl methacrylate (PMMA) or hydrophobic acrylic IOLs.

ZERO-ABERRATION ASPHERIC IOLS

Aspheric IOLs reduce optical aberrations, especially spherical aberrations, at the level of the retina. A biconvex IOL with spherical surfaces exhibits positive spherical aberration. Consequently, spherical IOLs add positive spherical aberration to patients’ already positive corneal spherical aberration. Aspheric IOLs attempt to improve pseudophakic vision by controlling spherical aberrations. One strategy is to design a lens with negative spherical aberration to balance the normal positive corneal spherical aberration in the cornea. Another strategy is to design a lens with minimal spherical aberration so that no spherical aberration is added to the corneal spherical aberration.

Using the Kooijman eye model to compare the performance of IOLs in different settings, Holladay et al³ showed that spherical IOLs performed poorly, and IOLs with negative spherical aberration performed best when the lenses were centered. With 1.0 mm of IOL decentration, zero-aberration IOL designs performed best, even when the trend for decentration did not depend on pupil size or corneal eccentricity. When Holladay and colleagues tilted the IOLs, they found that the performance of all designs was comparable in most cases. In cases of 0.50 D of defocus in 3.0- and 5.0-mm pupils, the performance of all IOLs was also about equal. These findings suggest that specific conditions affect IOL performance. As a general rule, aspheric IOLs performed better than IOLs with a spherical surface.

INCREASED IOL POWER PRECISION

The International Organization for Standardization has set standards for IOL manufacturing tolerances. Although all manufacturers claim to exceed these tolerances, Lenstec claims that its degree of IOL accuracy, ±0.11 D in the 18.00 to 25.00 D power range and ±0.125 D at all remaining IOL powers, is the best in the industry. Aiming to create the most accurate aspheric IOL available, Lenstec supplies its product in 0.25 D increments from 18.00 to 25.00 D. In its pivotal FDA clinical trial, the Softec HD IOL achieved BCVA and overall visual acuities of 20/40 or better in 97.1% and 96.4% of patients.

CONCLUSION

The roles of refractive index, water content, optic coloration (blue- or violet-light–blocking), and design of acrylic IOLs are widely debated among surgeons. Ease of use, availability, cost, and surgeon preference are also important factors that influence surgeons’ IOL selection.

The Lenstec Softec HD provides cataract surgeons with a high-quality acrylic IOL option for their patients. Its hydrophilic material helps minimize dysphotopsia and maintain biocompatibility, optical clarity, and resistance to damage and biocontamination. The IOL’s zero-aberration aspheric design optimizes visual outcomes. Further study of the Softec HD IOL is required to assess the effect of its aspheric surface on spherical aberration, contrast sensitivity, and visual acuity at different distances. A controlled, randomized clinical trial comparing aspheric with spherical IOLs would further assist surgeons in IOL selection

Steven D. Vold, MD, is President and Chief Executive Officer and Glaucoma and Cataract Surgery Consultant at BoozmanHof Eye Clinic, P.A., in Rogers, Arkansas. Dr. Vold states that he has no financial interest in the companies or products mentioned. He may be reached at e-mail: svold@cox.net.

1. Espandar L,Sikder S,Moshirfar M.Softec HD hydrophilic acrylic intraocular lens:biocompatibility and precision.Clin Ophthalmol. 2011:10;5:65-70.
2. Werner L.Calcification of hydrophilic acrylic intraocular lenses.Am J Ophthalmol.2008;146(3):341-343.
3. Holladay JT,Piers PA,Koranyi G,van der Mooren M,Norrby NE.A new intraocular lens design to reduce spherical aberration of pseudophakic eyes.J Refract Surg.2002;18(6):683-691.

TAKE-HOME MESSAGE
• New-generation hydrophilic acrylic IOLs have not been associated with calcification and opacification as earlier models were.
• Proposed advantages of hydrophilic acrylic material include less dysphotopsia, excellent biocompatibility, good optical clarity, resistance to damage during insertion, and less susceptibility to biocontamination than PMMA or hydrophobic IOLs.
• The Softec HD is a hydrophilic acrylic posterior chamber IOL with a symmetrical anterior and posterior surface aspheric design.