Aspheric, aberration-free IOL leverages technology for performance

Special to Ophthalmology Times®

No truly perfect approach to completely restoring the eye’s accommodative ability currently exists.

A variety of today’s presbyopia-correcting IOLs can, however, correct patients’ distance refractive error while at the same time improve both intermediate and near vision.

Surgeons increasingly can provide more spectacle independence for patients; however, not all patients are candidates for such premium technologies.

Related: Presbyopia: Rethinking approach to better meet patients’ needs

Surgeons have come to understand that specific amounts of higher-order aberrations (HOA), particularly spherical aberration, can increase a patient’s overall depth of focus.

With the finding that IOLs specially designed to neutralize spherical aberration could improve quality of vision, IOL manufacturers began to develop aspheric implants.

Today, many surgeons implant aspheric IOLs—with negative spherical aberration—to neutralize the inherent spherical aberration of the cornea.

The industry has also introduced aspheric aberration-free implants that are made to preserve the cornea’s preexisting corneal aberration.

Related: Study focuses on HOA measurements in normal keratoconic eyes

Background
The enVista (Bausch + Lomb) family of IOLs are aspheric and aberration-free. Because no aberrations are induced with the enVista platform, surgeons are able to preserve the cornea’s natural positive aspherical aberration of, on average, + 0.24 um to + 0.27 um for a 6-mm pupil size.¹

These factors are important for patients’ visual function because there is a strong correlation between spherical aberration and depth of focus.² There are benefits to the eye’s having a specific amount of spherical aberration to enhance the depth of focus.

There is a “sweet spot” of about 0.30 to 0.4 um of aberration.

Too much aberration, and quality of vision will suffer; patients with significant aberration may see halos or glare around lights, as well as decreased contrast sensitivity.¹

But with the enVista MX60E monofocal implant, for example, patients targeted for plano can experience good distance vision and depth of focus.³

Related: Presbyopia-correcting IOLs: Expanding, improving last frontier


Due to the defocus tolerance with this platform’s monofocal implant, excellent image quality is provided.⁴

A variety of factors such as pupil size, total corneal HOA, and corneal asphericity (Q value) affect individual patients’ range of vision with monofocal IOLs, so it is important to note no single lens provides a one-size-fits-all solution.

Ultimately, pseudo-accommodation is relative to the unique features of the patient’s optical system, not just the implant chosen or postsurgical changes.

After an IOL is placed in the capsular bag during cataract surgery, a natural decentration of about 0.3 mm to 0.4 mm occurs. Moreover, the aberration-free attributes make the lens more tolerant to this natural decentration.⁵

An aberration-free implant platform is especially important for eyes that are not perfect.³

To be most successful at achieving the target refraction, I always perform optical biometry with IOLMaster (Zeiss), corneal topography, and tomography.

Related: Striving for perfection: Creating the perfect IOL

Because ocular surface disease can masquerade a patient’s astigmatism, corneal imaging is also crucial. In addition, I perform an examination of the macula with optical coherence tomography to rule out any retinal pathology.

Toric model
To allow patients to achieve the best visual outcomes possible, it is incumbent on refractive cataract surgeons to also correct astigmatism at the time of the procedure.

Almost three-quarters of cataract patients have more than 0.50 D of astigmatism,⁶ yet toric implants account for less than 10% of procedures.

Even just 0.50 D of residual astigmatism may have an impact on both patients’ functional and low-contrast acuity.⁷

The enVista toric platform provides 110° of capsular bag contact. The toric implant also features a greater than 300% radial compression force compared with traditional hydrophobic acrylic implants.⁸

In the FDA approval study for the MX60T (n = 108), 94.4% of eyes implanted with the technology had 5° or less rotation from the close of case through 180 days, and no patients required a secondary surgical intervention.

Related: Accurate data key for planning toric IOL surgery

In a prospective, single surgeon study of the enVista toric (n = 53), 92% of patients had less than 0.50 D of residual astigmatism, and 94% of patients could see well enough to pass a driver’s license vision test without glasses.⁴

Additionally, 83% of patients had uncorrected distance visual acuity of 20/25 or better.⁴ These results are similar to what I have experienced in my practice.

Another added benefit to the enVista toric technology is its improved material properties that help enhance and speed up its optic recovery.*

Toric implants have a higher chance of rotation if not fully opened during the case; efficiency in terms of case time is also an important factor coupled with placement precision.

All implants on the enVista platform provide glistening-free optics^,11 and the technology is available in a range of cylinder powers as low as 1.25 D11 or about 0.77 D at the corneal plane.

Related: PODCAST: ASCRS 2020: Assessing aberration of monofocal toric IOL with enhanced optic recovery, alignment

This allows for a greater range of patients to have astigmatic correction^.6 The enVista toric lenses are currently the only IOLs in the United States that can correct less than 1.00 D of corneal astigmatism.

Conclusion
Surgeons must seek to understand each patient’s personality and discover which individual goals are key.

No matter the technology used, it is necessary to customize the implant choice based on the patient’s needs to achieve optimal refractive outcomes.

*Compared to the previous generation of enVista IOLs

Read more content on IOLs

About the author
Karolinne Maia Rocha, MD, PhD
e:KarolinneMaia@gmail.com
Karolinne Maia Rocha, MD, PhD, is associate professor of ophthalmology and director of the Cornea and Refractive Surgery Division at Medical University of South Carolina, Storm Eye Institute in Charleston. She is a consultant to Bausch + Lomb.

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References

1. Holladay JT, Piers PA, Koranyi G, van der Mooren M, Sverker Norrby NE. A new intraocular lens design to reduce spherical aberration of pseudophakic eyes. J Refract Surg 2002;18(6):683-691.

2. Rocha KM, Vabre L, Chateau N, Krueger RR. Expanding depth of focus by modifying higher-order aberrations induced by an adaptive optics visual simulator. J Cataract Refract Surg 2009;35(11):1885-1892. doi:10.1016/j.jcrs.2009.05.059

3. Rocha KM, Gouvea L, Waring IV GO, Haddad J. Static and dynamic factors associated with extended depth of focus in monofocal intraocular lenses. Am J Ophthalmol. Published online April 23, 2020. doi:10.1016/j.ajo.2020.04.014

4. Stephenson, PDG. Achieving astigmatism correction with new spherical aberration neutral monofocal toric IOL with intraoperative wavefront-aberrometry. Paper presented at: 2019 American Society of Cataract and Refractive Surgery Annual Meeting; May 3-7, 2019; San Diego, CA. Accessed June 19, 2020. https://ascrs.confex.com/ascrs/19am/meetingapp.cgi/Paper/57144

5. enVista. Package insert. Bausch + Lomb; 2018. Accessed June 19, 2020.https://www.bausch.com/Portals/77/-/m/BL/Global/dfu/4130300.pdf?ver=2019-04-01-093512-787

6. Hill WE. Prevalence of corneal astigmatism prior to cataract surgery. East Valley Ophthalmology. Accessed June 19, 2020. http://www.doctor-hill.com/physicians/docs/Astigmatism.pdf

7. Villegas EA, Alcón E, Artal P. Minimum amount of astigmatism that should be corrected. J Cataract Refract Surg. 2014;40(1):13-19. doi:10.1016/j.jcrs.2013.09.010

8. Bozukova D, Pagnoulle C, Jérôme C. Biomechanical and optical properties of 2 new hydrophobic platforms for intraocular lenses. J Cataract Refract Surg. 2013;39(9):1404-1414. doi:10.1016/j.jcrs.2013.01.050