IOLs 101

Understanding monofocal, toric, multifocal, accommodating, and extended depth of focus IOLs, and how to differentiate them to patients.

By Vin T. Dang, OD

Cataract surgery is the most common surgery performed in the United States today, with an estimated 3 to 4 million cataract surgeries performed annually.1,2 Due to the aging of the baby boomer generation, the US National Eye Institute has predicted an increase in the prevalence of patients with cataracts from the current level of nearly 25 million to almost 40 million by 2030.3

TO THE POINT

Knowing the benefits and risks of the IOLs available to your cataract patients will help you guide them toward an informed decision—and make you an expert in their eyes.

Cataract surgery, like all surgeries, carries inherent risks. However, with a good follow-up schedule and an experienced surgeon, it is fast, carries a low risk, and has a tremendous upside. Cataracts take decades to form, but surgical correction restores good vision overnight.

When patients are approaching cataract age or showing signs of developing cataract, it is important to initiate a conversation to prepare them for what is to come, as we do with presbyopia. When this conversation takes place, we can begin to introduce the different IOL options and explain how they might suit the patient’s lifestyle.

IOL technology has improved dramatically in the past few years, allowing clinicians to offer their patients multiple options to correct their vision. It is important to understand the key differences between monofocal, toric, multifocal, accommodating, and now extended depth of focus IOLs. Knowledge of the pluses and minuses of each type of IOL makes you the expert in the eyes of your patient.

MONOFOCAL

The basic IOL is the spherical monofocal implant. As the name suggests, these IOLs allow light to focus at one point, giving the patient the best visual acuity when correcting spherical refractive error. Surgeons can now use advanced biometry to measure keratometry, axial length, and other factors to determine the power of the IOL and minimize the refractive error at a desired distance—usually distance, or infinity.

Most modern monofocal IOLs now include asphericity to address the eye’s innate spherical aberration. The eye has positive spherical aberration in the cornea that is balanced by negative spherical aberration in the crystalline lens. When the crystalline lens is removed, the cornea’s positive aberration is no longer negated, and spherical aberration adversely affects contrast sensitivity and image quality. With aspheric IOLs, we can correct and minimize net spherical aberration, thereby enhancing visual outcomes.

TORIC

A fundamental shortcoming of spherical monofocal IOLs is their lack of astigmatic correction. Fortunately, we can now correct expected residual toricity with a toric IOL. Toric IOLs have come a long way in the past decade. There are now toric IOLs that correct toricity in a range from less than 1.00 D to approximately 5.00 D. Limbal relaxing incisions (LRIs), made manually or with the femtosecond laser during laser assisted cataract surgery can also correct low amounts of corneal astigmatism (<1.00 D). Arcuate corneal incisions can provide correction for minimal astigmatism.

PRESBYOPIA CORRECTION

Most monofocal and toric IOL surgeries typically target distance vision correction, leaving patients with the need for glasses for near-vision tasks. Before the advent of reliable presbyopia-correcting IOLs, the principal strategy used to decrease dependence on glasses was monovision, correcting the patient’s dominant eye for distance and nondominant eye for reading or intermediate vision, similar to what is done with contact lenses.

Monovision was the go-to choice for more than 2 decades, but in the modern world this choice is frequently inadequate. With the increased use of computers and other devices, many patients have multiple visual demands at distance, intermediate, and near points. If patients wish to decrease their dependence on glasses after cataract surgery, presbyopia-correcting IOLs provide alternatives.

A first generation of multifocal IOLs began in the late 1980s and early 1990s with the introduction of a diffractive optic design from 3M and a bulls-eye design from IOLab. Neither of these was successful, possibly due to the rigid PMMA material used, which required wide incisions for implantation with resulting residual astigmatism.

A more successful second generation of presbyopia-correcting IOLs started with the Array refractive multifocal IOL (Advanced Medical Optics, now Johnson & Johnson Vision). Similar to the refractive optics in some multifocal contact lenses, this IOL created simultaneous images from concentric optical zones. The Array was superseded by the Rezoom refractive multifocal IOL from the same manufacturer, in which the sizes of the concentric zones were changed to help decrease symptoms of glare and halos at night.

Other multifocal IOLs used the principle of diffractive optics. The first diffractive IOL approved by the US Food and Drug Administration (FDA) was the Restor (now the AcrySof IQ Restor Multifocal IOLs, Alcon). The Restor also employs the principle of apodization, in which steps of different heights are used to diffract the light to both distant and near foci. This minimizes haloes, but near visual acuity becomes dependent on pupil size. Therefore, vision at near is limited in a dim environment.

Another diffractive IOL that uses a pupil-independent approach is the Tecnis Multifocal IOL (Johnson & Johnson Vision). The Tecnis is made of acrylic material that minimizes chromatic aberration to enhance postoperative visual quality.

Both the Restor and the Tecnis Multifocal are now available in multiple add powers to allow physicians and patients to choose whether to accentuate near or intermediate distance in their postoperative vision.

One notable side effect of multifocal IOLs is the occurrence of nighttime glare and halos. It is important to set proper patient expectations when discussing multifocal implants. Most patients experience these symptoms at least transiently. It is also important to note that other contributing factors can cause the symptoms to appear worse. These include residual refractive error, large pupil size, and dry eye disease.

Another category of presbyopia-correcting IOL is the so-called accommodating IOL, exemplified by the Crystalens AO (Bausch + Lomb). Unlike multifocal IOLs, the Crystalens was created to mimic the natural behavior of the crystalline lens. The goal was to use the eye’s muscles to flex and accommodate in order to focus on objects in the environment at all distances. One advantage of the Crystalens is its mild symptoms of glare, halo, and starburst complaints at night due to its single-focus optic. However, patients may still require glasses to sharpen their near vision.

The newest category of presbyopia-correcting IOL is the extended range of vision or extended depth of focus (EDOF) IOL, the principal example of which is the Tecnis Symfony (Johnson & Johnson Vision). The Symfony delivers a continuous range of high-quality vision while reducing symptoms of nighttime halo and glare compared with multifocal IOLs. A proprietary achromatic diffractive technology corrects chromatic aberration to provide enhanced contrast sensitivity, and the lens’s increased range of vision improves its usability.

Our practice participated in the phase 3 FDA clinical trial for the Tecnis Multifocal IOL, the Tecnis low-add IOL, and the Tecnis Symfony IOL. Daniel H. Chang, MD, and I have seen truly remarkable results with the Tecnis family of IOLs in patients who are properly selected and counseled.

CONCLUSION

When we discuss cataract surgery and vision-correcting IOLs with patients, it is important to address the patients’ potential financial responsibility. Most medical insurance carriers will pay a portion of the cataract surgery fee with an aspheric monofocal IOL, but they typically will not cover the extra charges associated with the astigmatism- and presbyopia-correcting technologies discussed in this article.

With all the types of IOLs now on the market and available to patients, it is important for us to begin the IOL discussion with all patients over age 50. Optometrists should learn enough about these options to feel confident in their recommendations, as we are now comanaging these cases with more ophthalmologists. Optometrists should work with their local surgeons to provide patients with the most up-to-date information on surgery and IOL choices so that their patients can make informed decisions regarding which technologies best suit their needs.

1. Organisation for Economic Cooperation and Development. Cataract surgeries. In: Health at a Glance 2015: OECD Indicators. 8th ed. Paris, France: OECD Publishing.

2. Dang S. Cataract surgery infographic. American Academy of Ophthalmology. https://www.aao.org/eye-health/news/cataract-surgery-infographic June 10, 2014. Accessed September 20, 2017.

3. Cataracts. National Eye Institute. https://www.nei.nih.gov/eyedata/cataract. Accessed September 1, 2017.

Vin T. Dang, OD, FAAO
• Primary care optometrist, Empire Eye & Laser Center, Bakersfield, Calif.
• financial disclosure: consultant, Johnson & Johnson Vision
vdang@empireeyeandlaser.com