Learn the Ins and Outs of The Latest Monofocal IOLs

The new generation of monofocal lenses will optimize vision quality for your cataract patients. Here’s how to choose the best lens for the individual patient.

Not long ago, the most challenging aspects of cataract surgery involved performing phacoemulsification and the perfect capsulorhexis, and creating an incision that would prevent wound leaks. However, exciting new developments in IOL technology have added another level of complexity to the art of cataract surgery. As a new ophthalmologist, you’ll need to understand the intricacies of the latest IOL choices — spheric and aspheric monofocal, multifocal and pseudo-accommodating — to provide the best visual outcomes for patients. You’ve probably read many reports about the benefits of multifocal and pseudo-accommodating IOLs.
In this article, I’ll focus on monofocal IOLs and compare the differences between the spheric and aspheric lenses so you can make the best recommendations to patients who demand higher-quality vision.

Balancing Aberrations
Surgeons have been implanting spheric monofocal lenses for a quarter of a century. When you replace a cataractous natural lens with a spheric IOL, which has some inherent positive spherical aberration, it increases positive spherical aberrations of the entire eye. Higher-powered, spheric IOLs can cause even more of these aberrations and reduce modulation transfer function (MTF), which affects contrast ac-
uity and contrast sensitivity — the two keys to high-quality vision. Pa-
tients implanted with these spheric IOLs need to wear spectacles to achieve best-corrected visual acuity. However, in addition to introducing spherical aberrations, spheric IOLs also reduce contrast sensitivity, and this tends to degrade vision. What’s more, the IOLs can compromise vision quality further because of the additional, positive spherical aberrations that result as the cornea ages.
These factors have led to the clinical rationale for and development of aspheric monofocal IOLs. As you know, the eye is an optical system in which the lens plays an important role. The cornea and the lens bend light as it enters the eye. Then, the light comes into focus on the retina if all is well with the eye. However, if your patients are age 50 or over, their corneas will develop some positive spherical aberrations that will reduce visual acuity and contrast sensitivity. To compensate for this in patients who require cataract surgery, several manufacturers have developed aspheric monofocal IOLs.

The Tecnis ZA9003 and Z9002 (AMO) and the AcrySof IQ SN60WF (Alcon) aspheric monofocal IOLs have built-in negative spherical aberration to compensate for the cornea’s natural positive spherical aberration.
The SofPort Advanced Optics IOL (Bausch & Lomb [B&L]) is an aspheric monofocal IOL without additional built-in negative spherical aberration, otherwise known as aberration-neutral.
According to B&L, if the lens becomes decentered, the visual outcome still will be better than what’s provided by a conventional spheric monofocal IOL. The disadvantage to the SofPort Advanced Optics lens is that you can only offer it to cataract pa-
tients who have no spherical aberrations of the cornea, which accounts for less than 7% of the entire cataract surgery patient population.

Staying Centered
Keep in mind that aspheric monofocal IOLs must be centered properly during implantation. A decentered lens — whether it occurs during surgery or postoperatively — will produce less-than-optimal vision. Some clinicians suggest that aspheric IOLs with built-in negative spherical aberration should be perfectly centered on the visual axis to avoid the risk of severe visual disturbances. However, it’s been my experience, and has been reported, that 2 mm to 3 mm of decentration has no adverse effect on outcomes.
When you analyze this issue from a practical perspective, you realize that if decentration oc-
curred often enough and to such a degree that it affected visual outcomes, there would be no anecdotal or published evidence showing that aspheric IOLs improve visual function.
Nevertheless, no matter what IOL you choose, you need to perform a capsulorhexis, ideally between 5 mm and 7 mm to center the lens well in the capsular bag. A capsulorhexis that’s too small (under 4 mm) may induce capsular contraction and cause capsular phimosis, which could lead to decentration. If the capsulorhexis is too large (greater than 8 mm), the lens could dislocate from the bag, causing a shift in refraction. So it’s imperative, as a new cataract surgeon, to become confident and proficient at performing a capsulorhexis.

Concerns and Contraindications
Let’s suppose, however, that you don’t perform the ideal capsulorhexis, or you believe your patient is at risk for additional decentration due to pseudoexfoliation or weak zonules. In these instances, you could choose an aspheric aberration-neutral IOL instead of an aspheric lens with negative spherical aberration.
A patient who’s had previous hyperopic LASIK or hyperopic PRK already has some negative spherical aberration as a result of the remolded cornea. If you implant an aspheric IOL with negative spherical aberration in these patients, you’ll likely induce additional negative spherical aberration, reduce contrast sensitivity and compromise vision quality. So, in my experience, it’s best to use an aberration-neutral IOL in patients who’ve had prior hyperopic refractive surgery.
There are rare cases in which patients can develop intraoperative complications, such as a ruptured posterior capsule, significant zonular dialysis or dehiscience, or an extension of the anterior capsulorhexis, that will prevent you from implanting an aspheric IOL into the capsular bag. In these instances, you could use a monofocal spherical lens that can be placed in the sulcus, such as the ClariFlex silicone IOL or the AR40e from AMO or the STAAR AQ2010.

Mesopic Conditions
To improve vision in various light conditions with an aspheric lens, I rely on the Tecnis aspheric monofocal IOL for my cataract patients who don’t want presbyopia-correcting lenses. The Tecnis IOL received special labeling from the FDA, stating that it can improve nighttime and daytime vision in rainy, snowy or foggy conditions. The approval was based on a clinical study that measured simulated nighttime-driving performance in cataract surgery patients. In a more recent study, Alcon’s aspheric IOL dem-
onstrated that it can improve nighttime driving performance better than a conventional spheric IOL.

IOL Evolution
As you can see, there’s no shortage of IOLs to meet the various needs of patients. And the evolution of these implantable lenses shows no sign of abating. The moment you think you have a clear understanding of the capabilities of each lens, a host of new and exciting IOLs come on the scene promising to improve vision for another segment of cataract patients. In the meantime, recognize that you have great options from which to choose, and it’s your job to make the right recommendations to patients to fit their versatile lifestyles. qnMD