The great debate: Monofocal vs. multifocal
by Jena Passut EyeWorld Staff Writer
Ever since Nov. 29, 1949, when Sir Harold Ridley, M.D., F.R.S., first successfully implanted an IOL in a patient in a London hospital, surgeons have researched, debated, and sometimes obsessed over the best surgical lens to use.
Nearly 62 years later and after many advances in the surgical technique and the lenses themselves, the discussion continues—this time over multifocal versus monofocal IOL implants for presbyopia correction.
While monofocal IOLs are still considered the standard, especially in distance vision, advocates for the latest in multifocal implants say that patients’ push for spectacle independence make multifocals a more attractive choice.
An exciting study led by Fuxiang Zhang, M.D., in the March issue of the Journal of Cataract and Refractive Surgery did a head-to-head comparison of the technologies, with both continuing to show great promise.
In the study, researchers set out to compare how patients with bilateral diffractive multifocal IOLs stacked up against those who were implanted with monofocal IOL monovision.
Forty-three patients received either the AcrySof ReSTOR SN60D3 multifocal IOL (Alcon, Fort Worth, Texas) or the monofocal AcrySof SN60WF IOL (Alcon) as monovision. At the 3-month mark, investigators found that the multifocal IOL group did slightly better in terms of bilateral uncorrected distance and near vision, but the difference was not statistically significant. The monovision group experienced better intermediate vision, which allowed them to use computers with significantly less difficulty than their multifocal counterparts. Monovision scored higher in terms of satisfaction, fewer complaints, and less out-of-pocket costs. The pseudophakic monovision patients achieved comparable distance and near vision, but without the risk of disturbing visual symptoms sometimes associated with multifocal IOLs.
James A. Davison, M.D., Marshalltown, Iowa, said multifocal and monofocal lenses represent strategies to improve spectacle-free real world vision performance, but both come with their own set of optical compromises.
Dr. Davison said he prefers multifocal lenses because they are
“high-performance” devices, which provide simultaneous bilateral fine stereoscopic vision. He mostly uses ReSTOR lenses and said the latest lens would have fared better in Dr. Zhang’s JCRS article.
“The problem with the article is that it used the first generation ReSTOR lens,” Dr. Davison said. “The more modern generation lens would have an expectation to overcome some of the results that were mentioned in the [JCRS] article. It has an aspheric surface, which will help with contrast sensitivity.”
The newer lens is better for “quality of vision, fewer halos, less glare, and improved computer distance near performance,” he said.
“Achieving a plano result is our biggest challenge because of the cumulative effect of the contributions of all the various error sources,” Dr. Davison continued. “These include measurements of axial length, keratometry, anterior chamber depth, lens thickness, and formula application and computations for each individual patient, and then having to pick between IOLs that only come in 0.5 D increments.”
Dwayne K. Logan, M.D., Atlantis Eyecare, California, said he prefers the Tecnis multifocal IOL (Abbott Medical Optics, AMO, Santa Ana, Calif.) because, in his opinion, it offers excellent distance and near vision, as well as intermediate vision comparable to other multifocal lens options.
Because the diffractive rings on the Tecnis lens extend out to the periphery of the lens, patients are able to see better in dimmer light, Dr. Logan said.
“With a lot of my patients, when I am recommending these premium lenses for multifocality, I’m selling the fact that patients are going to be able to see at distance and near in all levels of light,” Dr. Logan said.
Although he will use other multifocal lenses when needed, Dr. Logan said it benefits his patients for him to stick with his favorite premium lens.
“I have a very high conversion rate because I’ve found what I’m selling and that’s what I sell. I’m not all over the place,” he said.
There are drawbacks, however, including some dysphotopsia.
“I tell patients that with this lens they’re going to lose some contrast sensitivity, but the nature of the lens is such that if we have all of our parameters corrected, the vision will be relatively comparable,” he said. “They may lose one line of vision, but the brain would not know the difference if we eliminate all of the other variables.”
The multifocal lens is better for patients who want to achieve total spectacle independence, Dr. Logan said. To that end, ophthalmologists should maintain a “brilliant” relationship with the patient’s primary care physician, as well as make sure that refractive errors are corrected “in order for patients to really enjoy these lenses.”
The face of an ideal multifocal patient is shifting from younger, active patients to anyone who might appreciate spectacle independence, Dr. Logan said.
“I used to say that they were for patients who are still working and are young, enthusiastic, and motivated, but I have patients who are 80-90 years old and they enjoy these lenses as well,” he said. “They enjoy not having to wear glasses, and it makes them more active. They’re out and about, and it’s almost like it turns back the clock a little.”
Multifocals are contraindicated in patients who have any type of maculopathy, corneal disease, or opacification of the cornea. They would not do well in patients who have conditions that might affect the transmission or processing of light back to the brain—for example, a stroke, some type of atrophy from glaucoma, or a type of genetic disorder that affected the retina, optic nerve, or the brain, Dr. Logan said. “That is why we have to have a brilliant relationship with the primary care doctor, so that we know what the patient’s medical condition is.”
Dr. Logan said the utilization of multifocal lenses is low because surgeons don’t believe that they can achieve as good vision as with the monofocal approach.
“The whole goal now is to have doctors educate their patients on the fact that lens technology has improved significantly, to the point where we’re getting results comparable to monofocal lenses. That wasn’t the case with the first generation of these lenses,” he said.
Focusing on monovision
For his part, Graham D. Barrett, F.R.A.N.Z.C.O., clinical professor, Lions Eye Institute, Perth, Australia, and Sir Charles Gairdner Hospital, Perth, said he has several reasons for preferring monovision.
First and foremost, it offers the option of reversal.
“At any time, patients can put on their spectacles and get full binocular vision with no compromise,” Prof. Barrett said. Vision can be adjusted with a refractive procedure such as LASIK, he added.
“If you have an unhappy multifocal patient, explantation is sometimes required because there’s no way you can correct multifocal vision,” Prof. Barrett said.
Vision with monofocal lenses is more robust, and the procedure is easier to explain to patients, he said.
“Monovision will tolerate astigmatic defocus much better than a multifocal lens,” he said. As for the patients, “Monovision is something patients can easily comprehend. You can demonstrate the type of vision they’re going to get. It makes the whole exchange easier and faster.”
Patient satisfaction after the procedure is a benefit.
“It is rare to experience an unhappy patient,” Prof. Barrett said.
He added that he was pleased to have this thought backed up in Dr. Zhang’s study, which showed the overall satisfaction score is higher in monofocal patients.
“I wasn’t surprised to see [the results], but it was nice to see a head-to-head comparison,” he said. “This is a good study because it’s a prospective group, and, overall, it’s a well-conducted study. There were a lot of parameters across a broad range of features.”
While traditional monovision aims for –2 D of myopic defocus, which offers excellent near vision, Prof. Barrett warned that amount of separation may not be tolerated by every patient.
He prefers, instead, to target about 1.25 D of myopia.
“At that level, you can be almost certain that a patient will not experience problems of disassociation between the two eyes,” Prof. Barrett said.
Lower levels of myopic defocus also will preserve contrast sensitivity and stereoacuity.
“However, at that lower level, you don’t get quite the same ability to read up close,” Prof. Barrett said. “That patient will require, in some cases, spectacle correction for reading a book for prolonged periods. It’s a small percentage of the time because intermediate vision is so good. The trade-off is that you can be much more certain of patient acceptance.”
With the smaller levels of myopic defocus being used, some could contest the use of the term monovision, Prof. Barrett said.
“It’s a poor description because patients have binocular vision and it doesn’t describe the situation very well,” he said. “The two eyes are used synergistically.”
J.E. “Jay” McDonald II, M.D., Fayetteville, Ark., said he prefers monovision because it preserves the complete visual pathway and signals.
“The issue is that when you use a multifocal lens you decrease the energy level of light by about 18%, and on each retina you have a superimposed, out-of-focus image that varies depending on the pupil size,” Dr. McDonald said. “That is true of all diffractive multifocal lenses.”
Giving up that much energy in the eye is problematic, especially if the eye later becomes symptomatic with macular degeneration, glaucoma, or vein occlusions.
“With monovision, if you lose the sight in one eye or partial sight in one eye, you haven’t given away any of the person’s visual potential because of loss of optics,” Dr. McDonald said.
The weaknesses of the monofocal approach are much the same as those of the multifocal approach, he said.
“You have to hit your targets,” Dr. McDonald said. “You have to clean up refractive errors that are off more than 0.5 D of either sphere or cylinder.”
Dr. McDonald, too, keeps the separation of the two eyes small.
“We are down to –1.25 D,” he said. “At that difference, the only true difference between what you see in the focused eye and the out-of-focus eye is some loss of higher spatial frequencies in the out-of-focus eye, but in the mid and low spatial frequencies, 90% of the same information is there. With monovision, you don’t see with one eye and suppress and then see with the other eye. You actually see with both eyes.”
Dr. McDonald said there are a small number of people who are strongly right- or left-eye dominant. Those people might have trouble
adjusting to monovision. Dr. McDonald and colleagues are in the process of developing a neurocognitive quantitative test to help look for that issue. E
J Cataract Refract Surg 2011;37:446–453 Q 2011 ASCRS and ESCRS.
Editors’ note: Dr. Barrett has no financial interests related to his comments. Dr. Davison has a financial interest with Alcon. Dr. Logan has financial interests with AMO and Alcon. Dr. McDonald has financial interests with Bausch & Lomb (Rochester, N.Y.), Hoya Surgical Optics (Chino Hills, Calif.), and STAAR Surgical (Monrovia, Calif.).