Oculoplastics
Monofocal lenses under the microscope

Monofocal IOLs chart

Cataract surgery continues to make refractive advances, notably with premium presbyopia-correcting IOLs, yet for fiscal reasons, ophthalmologists continue to implant a multitude of monofocal IOLs each year.
The financial expense of multifocal and pseudoaccommodative IOLs is considerable, but even so, some ophthalmologists say that regardless of cost, monofocal IOLs continue to have their own technological advantages.
Image quality is superb with monofocal IOLs, for example. Higher-order aberrations rarely affect patients with these lens implants. Some monofocal lenses also have unique advantages in terms of current technology. Toric IOLs, for example, currently have no Food and Drug Administration (FDA)-approved multifocal counterpart, although that may change.
In addition, patients accustomed to monovision in contact lenses often do extremely well with monovision after cataract surgery. In the current financial climate, monofocal lenses are here to stay, and even if the medical economy vastly improved, patients still would desire this proven conventional technology.

The best of spherical aberration correction

“The quality of vision we can achieve with any of the technologies is today highest with an aspheric monofocal lens that is custom-matched to the patient’s cornea to get as close as possible to zero spherical aberration,” said Mark Packer, M.D., clinical associate professor of ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Ore. “I have been a proponent of that idea for a while.”
In fact, when Dr. Packer is choosing among a variety of multifocal lenses, all things being equal, he opts for the one that most closely matches the patient’s spherical aberration. That means he’s oftentimes reaching for a Tecnis aspheric IOL (Abbott Medical Optics, AMO, Santa Ana, Calif.). “Two-thirds of the population fit into this Tecnis category” for spherical aberration correction, Dr. Packer said.
According to AMO, “the Tecnis IOL corrects for –0.27 microns of spherical aberration, just like the average crystalline lens did between the ages of 19 and 25.”
There is a larger range of spherical aberration correction in lenses outside of the United States, but domestically, this is the most suitable monofocal lens for the majority of patients, Dr. Packer said.
Other spherical-aberration correcting lenses are available in the United States, including the AcrySof IQ (Alcon, Fort Worth, Texas) (which corrects –0.20 microns) and the Hoya iSymm IOL (Hoya Surgical Optics, Chino Hills, Calif.) (which corrects -0.18 microns).
Meanwhile, these companies have their own reasoning to correct varying amounts of spherical aberration. “The overall effective SA [spherical aberration] of the iSymm IOL is –0.18 μm, for a residual SA of approximately +0.1 μm, which approximates the total ocular SA in a young phakic (age 25) eye,” according to a Hoya white paper.
Hoya adds that “Unlike other 1stgeneration negative SA aspheric IOLs, the iSymm IOL has unique aspheric zones designed to decrease the impact of misalignment between the lens and the visual axis (decentration) on quality of vision, providing good refractive predictability and quality of vision for a wide range of pseudophakic patients.”
“Of all of those, people that are basically about –0.235 microns or greater are best suited for the Tecnis IOL,” Dr. Packer said. “Below–0.235 microns down to 0.2 microns, the AcrySof IQ is a better choice.”
Dr. Packer said he has developed a protocol for his technicians to use, whereby after performing topography on cataract surgery candidates, a lens is selected based on the protocol involving spherical aberration correction. Further, although there is less controversy mixing and matching monofocal IOLs than doing so with multifocal IOLs, Dr. Packer said he likes to put the same lens in both eyes. “There is an integration that occurs when you have the same imaging system duplicated in both eyes,” Dr. Packer said.

Image quality at its best

Monofocal IOLs also carry many fewer higher-order aberration symptoms. “You don’t get the optical side effects of a multifocal lens,” Dr. Packer said. That means that essentially, 1/4–1/3 of patients getting a multifocal implant are going to have at least some degree of moderate halos, Dr. Packer said. “Monofocals don’t create halos to that extent,” Dr. Packer said. “Two to three percent will say they experience halos.”
Multifocals are vastly improved, but “glare and halos still rear their heads,” said Steven D. Vold, M.D., BoozmanHof, Rogers, Ark. On the other hand, he said, “A lot of new lenses with aspheric optics provide highest quality of vision and UV protection,” Dr. Vold said.
Dr. Vold likes the Softec PS mono-focal lens (Lenstec, St. Petersburg, Fla.), which comes in quarter diopter increments, although he noted that the Crystalens (Bausch & Lomb, Rochester, N.Y.) also has received quarter-diopter approval from the FDA.
Monofocal lenses also are advantageous in patients with advanced glaucoma, diabetic retinopathy, macular degeneration and epiretinal membranes, Dr. Vold said. “My guess is that there always will be a place for monofocals,” he added. “Some people really like monovision.”
Toric monofocal lenses especially have an important place in ophthalmology today, Dr. Vold said. “When a patient has more than a diopter-and-a-half of astigmatism, most will be getting a toric lens or astigmatism procedure,” Dr. Vold said. “I still implant a ReStor with an LRI [limbal relaxing incision] and I do the same thing with Crystalens, but with higher amounts of astigmatism, the LRI is less predictable. That’s where the toric lens stands out.”
Significant astigmatism after a premium IOL implantation likely won’t make patients happy.
“It’s a lot easier to tolerate a diopter of astigmatism if you didn’t spend $2,500 dollars for it,” Dr. Vold said. Apart from the Softec lens, Dr. Vold likes the Tecnis IOLs and AcrySof series.

When monovision works

“In order to be a successful monovision candidate, one has to suppress an unwanted image,” Dr. Packer said. “The brain has to ignore the blurred image in the nearsighted eye, for example, if you’re reading in the distance. Not everybody can do that.” But those who can do that often do so fabulously. “For people who can do it in contact lenses, I think monovision is a great solution,” Dr. Packer said.
An office trial may not be sufficient to determine monovision success or failure. “Some surgeons are comfortable doing an office trial,” Dr. Packer said. “I am not quite satisfied.” Instead, he believes cataract surgery candidates need a real contact lens trial. Even then, some people can’t wear contacts, and some people have cataracts so bad that “there’s not much appreciation for what their vision is going to be like postoperatively,” Dr. Packer said.
Monovision has its hurdles, but for many patients, those challenges may be worth the reward of better vision—perhaps even better than if they had opted for a multifocal lens.

Editors’ note: Dr. Packer has financial interests with Abbott Medical Optics (Santa Ana, Calif.) and Bausch & Lomb (Rochester, N.Y.). Dr. Vold has financial interests with Alcon (Fort Worth, Texas).

Contact information

Packer: 541-687-2110, mpacker@finemd.com
Vold: 479-246-1751, svold@cox.net