Cataract
Spring 2024

by Liz Hillman
Editorial Co-Director

One might think that the topic of ocular dominance is simple, set, well understood. But in actuality, there are some recent findings that might have an impact on the concept and its relevance to lens selection and target setting for monovision and blended vision.

“There’s more to it than we think,” said Arthur Cummings, MD.

“The message is: We’re learning more about dominance, and there is some data now to prove there is more to learn,” said Daniel Durrie, MD. However, he added, further research is needed to understand the implications of this new data.

‘New breakthrough data’ 

There are two new facts when it comes to the topic of ocular dominance, which physicians like Dr. Durrie and Dr. Cummings are beginning to call sensory dominance.

1. There is variance in the level of dominance among patient populations.
2. An individual might have a different preference for dominance when you test them for distance vs. near. 

Dr. Durrie started studying ocular dominance with the SimVis Gekko (2EyesVision). Prior to using this device, which not only assigns an ocular dominance preference score but allows the wearer to experience different intraocular lenses and blended vision, Dr. Durrie said ocular dominance was often tested with a hole in a card or with a finger triangle test.

A group of ophthalmologists in the U.S. decided to use the SimVis Gekko to test for sensory dominance more definitively in their patient populations, assessing what the brain really prefers as far as dominance. This study included 269 patients enrolled at five centers.

“The way that it’s done is by putting a 1.5 lens in front of the eye electronically and asking the patient if they prefer one or two. [The SimVis Gekko] does it 10 times really quickly,” Dr. Durrie said.

The group found the majority of people (more than 50%) are strongly dominant (90–100% preference for one eye), about a quarter have weaker dominance (70–80% preference for one eye), and a quarter have equidominance (50–60% preference for one eye).

“This is new breakthrough data that we have no idea what to do with yet,” Dr. Durrie said, noting that the group that gathered the data would soon be discussing its possible implications, which could lead to future studies.

Dr. Durrie said that because the SimVis Gekko is easy to use and integrates well into clinic flow—and because of its usefulness to simulate different types of IOLs and vision options—a practice could start gathering real-world data on patients’ sensory dominance and their distance and near preferences. “Record the data on a group of patients, then keep doing what you’re doing with your IOL selection. Retrospectively come back and if you have patients who were having trouble adapting to their lenses, you can say, ‘Let’s look back and see what preference group they were in,’” he said.

IOL selection and target setting for mono/blended vision

Dr. Durrie said that while there is now an expanded understanding of ocular dominance/sensory preference, it’s too soon to make any practice changes. “Keep doing what you’re doing and let the research develop,” Dr. Durrie said. “This is new information, and I don’t want it to complicate IOL discussion with patients until more data is gathered.”

Dr. Cummings said eye dominance remains critically important for lens and target selection. He said it is “the difference between success and failure.” Like the findings Dr. Durrie spoke about, Dr. Cummings, and Andrew Kopstein, MD, both said they consider not motor dominance but sensory dominance when helping patients choose a lens and setting their target.

“Most think that this is motor dominance, where the finger point or thumb forefinger aperture is determinant. It is not. It relies on ‘sensory dominance,’ which is tested by showing one eye corrected to distance and the other to a myopic target, then compared to the reverse scenario where the fellow eye is corrected to distance and the other to the same myopic target. The combination that feels better is ‘sensory dominance.’ My experience is that motor and sensory dominance correspond 85% of the time,” Dr. Cummings said.

Dr. Cummings incorporates several tests to determine whether a patient will tolerate monovision, mini-monovision, or blended vision and to determine which eye tolerates which tasks. He shows the patient their eyes fully corrected, followed by 0/–1.50 (fully correcting the right eye and correcting the left eye to a myopic target). He asks the patient to rate this out of 100 compared to their prior fully corrected vision.

“If this is rated at 80% or higher, the odds of blended vision working are well above 95%,” he said.

Then he’ll move to –1.50 in the right eye and fully correct the left. “Score this against the 100% score. If this is scored at 85% or 90%, you have the answer. Correcting the left eye to emmetropia and the right eye for reading is destined to work.”

If the score is less than 80%, he puts the patient in a trial frame with the right eye targeted to –1.5 and left eye targeted for emmetropia, giving the patient up to 30 minutes to test this range of vision.

“Some will come back saying they love it. … Others will say they dislike it, and that rules out blended vision. Others will say that they need more time or that they want to test this in their own home and work environment, and they continue with [a contact lens trial],” Dr. Cummings said.

Dr. Cummings tests suppression with the Worth four dot test. Furthermore, he said once the decision is made on the dominant eye, a stereo target is put up on the chart and stereopsis is assessed. Correct both eyes to emmetropia and assess stereopsis. “In my experience, 95% of patients will have good distance stereopsis,” Dr. Cummings said. “Now start defocusing the eye assigned to reading. Ask the patient to continually assess the stereo target and to note when distance stereo is lost. Defocus to –0.25, –0.50, and –0.75. Almost everyone still enjoys stereopsis for distance vision at this level. Once the defocus is –1.00 in the reading eye, some will start losing their stereo vision. For these, their reading target should not exceed –0.75 D. Some can maintain stereo vision up to –1.50 and lose it at –1.75 D. Their reading eye target should not exceed –1.50. A small part of the population can maintain stereo vision at –1.75 and even –2.00 D and have the freedom to select their target.”

Dr. Cummings added that with mono/blended vision being set with laser vision correction or ICL surgery, there is likely still some residual accommodation, and these patients might receive a slightly less myopic reading target. With a monofocal IOL, he said some may target –1.0 but still require readers or target –2.0 and then need assistance at intermediate vision. With advanced technology IOLs like EDOF, target emmetropia in the distance eye and –0.75 to –1 in the reading eye for a complete to near complete range of vision, he said.

If a patient is seeking a full range of vision but needs to drive at night, Dr. Cummings said dominance again plays a key role in creating a “custom match.” This approach starts with a diffractive trifocal IOL in the non-dominant eye. Prior to the second eye surgery, glare and halo tolerance is assessed. If it’s not bothersome, the patient can choose a trifocal for their dominant eye as well; however, if the patient is bothered with the glare and halo in the non-dominant eye, they receive a non-diffractive EDOF IOL in the dominant eye..

“With this combination, they have an excellent range of vision and can still drive at night thanks to there being no glare and halos in the dominant eye [with a non-diffractive EDOF],” Dr. Cummings said.

Distance and near preferred vision and the LAL

Dr. Kopstein, whose sole private practice is performing refractive lens exchange (RLE), said assessing distance and near preferred eyes is important with the Light Adjustable Lens (LAL, RxSight).

“It’s an important technology. … It’s powerful because it can be adjusted, and it’s equally powerful because of the quality of the optics and the EDOF that you get from the LAL,” Dr. Kopstein said, noting that the original LAL has allowed his practice to get 92% of people completely out of glasses; he thinks this number will rise to 95% with the LAL+.

When it comes to distance and near preferred eyes, Dr. Kopstein said his practice has learned that in about 20% of patients, the dominant eye is not their distance preferred eye.

“I am one of those people. If you put me in contact lenses that fully correct me for distance and you hold a +1 lens over my right eye and a +1 lens over my left eye, I will tolerate the blurring on my right eye more than I will on my non-dominant left eye. About 20% of patients are like this, so it’s important to do dominance testing but also to verify that the dominant eye is indeed the distance preferred eye,” he said. “If you end up adjusting the LAL in the non-dominant eye for reading and that’s actually the eye the patient prefers for distance, you will likely have an unhappy patient.”

Dr. Kopstein said the conversation with LAL patients about its EDOF qualities after the light delivery device adjustment calls into question for some patients why you wouldn’t just use monofocal lenses to achieve monovision/blended vision effects.

“We have been gathering data to answer the question: What are the distance characteristics of the near-preferred eye after bilateral LAL lock-in?” he said. “The range of refraction for the near preferred eye with the LAL is plano to –1.75 in our first thousand bilateral ‘lock-ins’ (average –0.75). … For these near-preferred eyes, the distance vision range is 20/20 to 20/80 (median 20/30). This is very different from ‘standard IOL’ monovision, where the patient closing their distance eye rarely has useful distance vision in the near-preferred eye. This appears to be a unique feature of the LAL compared to the standard monofocal IOL.” 

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About the physicians

Arthur Cummings, MD
Medical Director
Wellington Eye Clinic
Dublin, Ireland

Daniel Durrie, MD
Chairman, iOR Partners
Overland Park, Kansas

Andrew Kopstein, MD
K2 Vision
Seattle, Washington
Scottsdale, Arizona

Relevant disclosures

Cummings: Alcon
Durrie: 2EyeVision
Kopstein: None

Contact 

Cummings: abc@wellingtoneyeclinic.com
Durrie: ddurrie@iorpartners.com
Kopstein: akopstein@myk2vision.com