Refractive surgeons are likely to enjoy success with monovision for presbyopia if they aim for a maximum of 1.50 D of residual myopia in the non-dominant eye, exclude patients with pre-existing strabismus, and monitor for signs of strabismus.
By Laird Harrison; Reviewed by Edward E. Manche, MD
Recent research has refined the art of monovision, providing insights into this widely used treatment for presbyopia, according to Edward E. Manche, MD.
Refractive surgeons are likely to enjoy good success if they aim for a maximum of 1.50 D of residual myopia in the non-dominant eye, exclude some patients with pre-existing strabismus, and monitor for signs that strabismus is emerging, Dr. Manche said.
“It’s still the most commonly employed option for presbyopia,” said Dr. Manche, professor of ophthalmology, Stanford University, Stanford, CA.
Monovision has been used for decades with contact lenses, with reported success rates ranging from 70% to 76%. In refractive surgery-including LASIK, PRK, conductive keratoplasty (CK) clear lens extraction, phakic IOLs, cataract surgery, and corneal inlays-the success rate ranges from 72% to 93%, he noted.
The exam should reveal any tropia or phoria. Dr. Manche recommends taking a detailed history to rule out previous strabismus or strabismus surgery because monovision may cause decompensated strabismus in some patients.
“If I see somebody has strabismus and they’re not wearing any prism in their glasses, I consult with a strabismus ophthalmologist,” he said. “In most cases, it’s okay.”
The next step is a trial with monovision contact lenses. The lenses correct at the corneal plane, so they are a good predictor of success with surgery, Dr. Manche said.
Compared with spectacles, they minimize aniseikonia and do not produce prismatic effects. The trial allows the patient and practitioner to experiment with refractive powers and see whether the treatment fits the patient’s lifestyle.
In Dr. Manche’s practice, about one-third of emmetropic presbyopic patients like monovision, with the proportion higher among older patients.
“It’s not for everyone,” Dr. Manche said.
For example, a highly competitive tennis player may notice decreased binocularity. A patient doing intensive close work may need a different correction from a patient doing more intermediate work.
Dr. Manche recommends patients wear the lenses for 2 to 3 days from morning to night, experimenting with their typical activities, such as watching movies, driving, working at a computer, and tweezing eyebrows in the mirror.
“If they’re uncertain, I ask them to go at least a week,” he said. “If they say it’s great, that’s usually adequate for me.”
The next step in patients who have elected monovision is to determine which eye is dominant, Dr. Manche said.
This can be done with a card that has a hole in it. The patient holds the card at arm’s length, sights a distant object (such as a letter on an eye chart) through the hole, and gradually brings the card closer. The patient will eventually align the hole with the dominant eye.
Most monovision patients benefit from setting the dominant eye for distance and nondominant eye for near vision. A small proportion prefers the opposite, but research suggests this is less successful.
“The only time I do that is if they have been wearing contact lenses that way for a number of years,” Dr. Manche said.
When patients have particularly strong ocular dominance, they may not be able to suppress blur as well and may have decreased binocular depth of focus.
“Most studies have shown that with monovision it’s very, very important to get the dominant distance eye absolutely spot on because distance visual acuity is determined solely by the dominant eye,” Dr. Manche said.
The choice of refractive powers depends on the results of the monovision contact lens trial. In a 2006 study (Trans Am Ophthalmol Soc. 2006;104:366-401), Daniel S. Durrie, MD, tested 50 patients aged 50 to 66 years with a contact lens at +0.75 D, +1.50 D, and +2.50 D.
Pre-treatment, mean distance stereopsis was 32 seconds of arc. This increased to 44 seconds at +0.75 D, 77 seconds at +1.50 D, and 182 seconds at +2.50 D.
Mean uncorrected distance visual acuity decreased with each increasing lens power, reaching 20/80 or worse with +2.50 D. Mean uncorrected near visual acuity improved with increasing power, reaching logMAR 0.11 at +2.50.
Pre-treatment, patients reported completing 46% of tasks without near vision spectacles. This rose to 55% at +0.75 D, 79% at +1.50 and 82% at +2.50.
On a scale where 0 is the best and 10 is the worst, patients rated their near vision 8.7 pretreatment, 6.1 at +0.75 D, and 4.5 at both +1.50 D and +2.50 D. Their ability to judge distance followed the opposite trajectory, with 1.7 pre-treatment, 3.1 at +0.75 D, 2.9 at +1.50 D and 5.1 at +2.50 D.
Halos and starbursts also increased slightly with increasing power, with a significant jump at +2.50 D.
From these results, Dr. Durrie concluded that +1.50 D is the monovision “sweet spot” for the near vision eye, and Dr. Manche recommends against targeting more than that correction of residual myopia to maintain fusion and stereopsis.
Edward E. Manche, MD
This article was adapted from Dr. Manche’s presentation at the 2017 meeting of the American Society of Cataract and Refractive Surgery. Dr. Manche is a consultant for Avellino Laboratories, Best Doctors Inc., Carl Zeiss Meditec, Gerson Lehrman, and Johnson & Johnson Vision. He owns equity in Calhoun Vision Inc., Seros Medical LLC, and Veralas Inc. He performs sponsored research for Avellino Laboratories, Allergan, Carl Zeiss Meditec, Johnson & Johnson Vision, Ocular Therapeutix, and Presbia.