Surgeons take different approaches to handling monovision in their practices, but all of them become more confident if a patient has already worn it in their contact lenses.
“First of all, I won’t do monovision in anyone under 45,” says Mobile, Ala., surgeon Richard Duffey. “In other words, you can’t anticipate presbyopia, even though you know a patient is going to be presbyopic. The patient won’t appreciate that you left one eye nearsighted, he only will know that he can’t see well in the nearsighted eye. Having said that, if someone comes in already doing monovision in his contact lenses, and likes it, I’ll do the same with LASIK. However, if a patient has never tried monovision, we seldom bring it up. If, however, someone comes in and neither eye is perfect for up close but he brings up monovision, I’ll suggest that we do a contact lens trial first, with the non-dominant eye refracted for about -2.25 to see how he likes it. If he likes it, even if the trial is for a day, I’m willing to do monovision with the laser.”
Asim Piracha, MD, associate professor at the University of Louisville’s Department of Ophthalmology and Visual Sciences, will talk about it with patients over 40. “For plano presbyopes, I don’t recommend much treatment,” he says. “I tell them to stick with their readers. But if they hate their readers, I’ll have them do a contact lens trial with monovision, wearing the lenses all day during all activities. I want to make sure they’re comfortable with it.
“If the patient is a hyperopic presbyope who’s a successful monovision contact lens wearer, I’ll do monovision LASIK on him,” Dr. Piracha continues. “However, if the hyperopic presbyope is over 45 and has never tried monovision, I lean toward refractive lens exchange with a multifocal intraocular lens over laser vision correction. This is because hyperopic patients are a little trickier with LASIK and, in general, their LASIK results aren’t as good: I get 5 to 7 percent fewer 20/20 outcomes and a little bit higher enhancement rate. You also have the issue of the initial overcorrection from the hyperopic treatment that then regresses. I tell the patients it takes about two weeks for the distance vision to come around and about two months before it’s stable. And if you do monovision in a hyperopic presbyope, they’ll have good near vision day one but no distance vision, and will be at 20/50 or 20/60 in the distance eye. A lot will call back and say they can’t see, but it’s because they’re still myopic from the hyperopic treatment, even though you discussed it with them.”
Dr. Duffey is wary of doing high corrections with monovision. “I won’t take someone who is -7 D in both eyes and purposely shoot for plano in one and -2.25 D monovision in the other unless he’s done monovision previously with contact lenses and liked it,” he says. “Because if he doesn’t like the monovision surgery, then I’ve got to go back and operate a second time on that first eye. Also, for the hyperopic presbyope, there’s a limit to how much hyperopia you can treat. If someone is +3.5 D in both eyes, that’s the limit of what I’ll fix with hyperopic LASIK and therefore I don’t have any room to make an eye -2 D because I’d have to correct +5.5 D in total.”
Majid Moshirfar, MD, director of refractive surgery for the Moran Eye Center at the University of Utah, reminds patients—and surgeons—that monovision has its limitations. “It’s not a panacea,” he says. “Eventually, the patient’s accommodation will reduce and, when it does, the monovision won’t work the way it used to. The other thing is, if you do monovision on the non-dominant eye and correct the dominant eye for distance, you have to pray that the distance vision ends up 20/20 and great. If the distance eye ends up 20/25 or 20/30 the individual won’t be happy because neither eye is good for distance. As a result, the patient will come to you for an enhancement. In my practice, most of the patients who come and ask for an enhancement are monovision patients in whom the dominant eye went down to 20/25 or 20/30 over three or four years. And the non-dominant eye is not helping the dominant eye.”
Setting the Targets
Surgeons will take many factors into account when deciding on the amount of anisometropia to create.
Though Dr. Moshirfar finds himself relying on monovision less in his practice than he did 15 years ago, he does have certain correction ranges for patients who are candidates. “For the 46 to 52 age range, I aim for -0.71 to -1 D,” he explains. “For patients over age 52 I aim for -1.25 to -1.75. For people who need more, I won’t go above -2 D because of the anisometropia that is created, and because patients with a high amount of monovision are more sensitive to any loss of distance clarity in the dominant eye.” Dr. Piracha also does a conservative level of monovision. “I am aiming to give patients distance and intermediate vision, with the need for glasses for near work or small print. For patients in their 40s, I’ll go for -1 D,” he says. “If they’re 50 or older, I’ll do -1.25 D. Almost everyone will tolerate that amount.”
“I tell patients that they may be able to get by with daily functions such as using the iPad, reading a restaurant menu or writing a check,” Dr. Piracha continues. “But if they want to read small print such as stock quotes, they’ll need readers. I’ll also counsel them that, though not everyone needs glasses for driving at night, it might help to have a pair of glove box glasses if it’s raining at night or they’re in an unfamiliar environment, because you need good depth perception in those situations.”
Dr. Duffey goes more for what would be considered the traditional level of monovision. “I like to set -2.25 D for most, unless they’re already over the age of 60 and they know they’d like -2.5 D, in which case I’ll set them closer to 2.5 D,” Dr. Duffey says. “That way, whether they’re 45 or 60 they’ll have a decent level of monovision so they have really good near vision and there’s not so much anisometropia that they have a hard time tolerating it. I have tried mini-monovision, but for the most part I’m not trying to do that. I want to get these patients closer to plano for distance and truly set them for monovision.” REVIEW