Step It Up: The Quarter-Diopter Option

Can 0.25 D-step intraocular lenses help improve refractive outcomes?

By Robert J. Weinstock, MD, and Neel R. Desai, MD

Despite the revolution and continuing evolution within the world of refractive cataract surgery, what remains constant is our desire to improve the precision of refractive outcomes and reduce spectacle dependence for patients after cataract surgery. Many devices and technologies have helped refractive cataract surgeons deliver these outcomes, including advanced phacoemulsification software, femtosecond laser technology, intraoperative aberrometry, improved biometry devices and a host of implant technologies.

One evolution in technology over the past several years that appears to allow us to more precisely target specific refractive outcomes are implants available in 0.25 D steps. Traditionally, posterior chamber intraocular lenses have been manufactured in 0.50 steps in common powers and whole diopter steps in very low and high powers.

More recently, however, some companies have sought to improve manufacturing processes to allow the delivery of 0.25 D IOLs in an effort to match the increasing demands of refractive cataract surgeons. Only two lens implants are available in 0.25 D steps in the United States at present — the Crystalens AT50AO (Bausch + Lomb) and the Softec HD (Lenstec). Both of these lenses, hence, allow surgeons to choose a more customized lens power for the patient with the aim to more deliberately target the patient's postoperative vision. Here, we detail our experience using each lens to obtain the optimal vision demanded by refractive-cataract patients.

Your IOL Options for Achieving Precision

■ The Crystalens AT50 AO. Not only is this the sole FDA-approved accommodating implant, but the Crystalens is further distinguished as the only presbyopia-correcting implant available in 0.25 D steps — between the most commonly used range of 18 D to 22 D. Below and above that range, this IOL comes in standard 0.50 D steps. The A-constant for the Crystalens AO is 119.1; the optic diameter is 5 mm and the overall diameter is 11.5 mm. Also, the Crystalens model AT52 AO has an overall length of 12 mm. However, this lens is currently not available in 0.25 D steps.

Bausch + Lomb's Crystalens AT50A0

Surgeons experienced with Crystalens have come to realize that targeting the dominant eye close to plano and the non-dominant eye between -0.37 D and -0.50 D provides a nice range of binocular range of vision without glasses. However, important steps in achieving these specific targets are to perform accurate biometry and to choose a lens power that most closely matches the desired refractive outcome.

Having 0.25 D-step IOLs available allows the surgeon to be even more precise in achieving and predicting postoperative refractions. In addition, many surgeons like to refract the first eye postoperatively prior to proceeding with the second eye to further refine the IOL power selection and use this 0.25-step capability to achieve the desired postoperative result in the second eye.

■ The Softec HD. The other implant available in 0.25 D steps, the Softec HD, is the only such monofocal lens available in the United States. This lens is marketed as a high-definition microincisional monofocal implant with precision diopters in 0.25 D steps between the powers of +15 D to +25 D. The manufacturing process of this lens also boasts a greater precision in lens power as labeled, at levels that exceed the international standards for deviation between actual and labeled lens powers.

The Softec HD's optic size is 5 mm and it has an equal conic bi-aspheric optic design reported to provide greater depth of field and spontaneous reading vision in some patients. Overall length of the Softec HD is 12 mm and it has a modified haptic style, with 0-degree angulation, singlepiece construction. It is a hydrophilic acrylic material with a 26% water content and the A-constant is 118.

Lenstec's Softec HD

The lens is also available in 0.50 D steps between 10.5 D and 29.5 D, and full-diopter steps between 5 D and 36 D. It is a monofocal lens with an aspheric design that provides very high quality and high contrast vision. For patients undergoing refractive cataract surgery where the surgeon is targeting excellent distance vision, near vision, or monovision and wishes to use a monofocal lens, the Softec HD with the 0.25 D steps can be advantageous.

Hopefully, these manufacturers will increase the range of lens powers available in 0.25 D steps in the future, and perhaps include toric capabilities, while other companies follow suit in adapting to the increasing needs of refractive cataract surgeons and patients for precision.

0.25 D Caveats

Certainly, the availability of 0.25 D-step IOLs alone is not sufficient to deliver precision outcomes. Such customization of lens power selection will only contribute to overall refractive targeting, in so far as one can also consistently and accurately obtain precision biometric data and treat astigmatism. Surgeons must use more advanced biometry and intraoperative aberrometry, as well as laser or manual astigmatism correction, in harmony with the 0.25 D-step IOLs as a symphony of technologies all orchestrated toward more precise outcomes.

Some surgeons may feel that using 0.25 D-step IOLs in cataract surgery is overkill, and that because the biometry, surgery and healing process have limitations in terms of predicting the outcome, 0.25 D steps in IOLs won't change their results. To some degree, surgeons who feel this way are justified.

Simply choosing IOLs in 0.25 D steps is not going to miraculously make you a better surgeon or dramatically improve outcomes. Rather, once you have made a commitment to refractive cataract surgery, logic dictates you must also commit to adopting all means available to improve precision at every step of the preoperative, intraoperative and postoperative stages. Then, and only then, will the addition of 0.25 D steps allow you to really raise the bar.

While we know our patients have long been expecting it, perhaps unrealistically, many surgeons, including ourselves, feel that the goal of achieving LASIK-like precision in outcomes with cataract surgery is now reasonably within reach. Using these 0.25 D-step implants is yet one more essential tool in the refractive-cataract surgeon's armamentarium to help achieve excellent results for patients. OM

Robert Weinstock, MD, and Neel Desai, MD, are cataract and refractive surgeons at The Eye Institute of West Florida, Largo.