Binocular vision disorders may affect outcomes after ophthalmic surgery
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For decades, eye care providers dedicated the majority of our attention to vision clarity.
With spectacles, contact lenses and refractive surgery, we aimed to bring our patients as close to 20/20 — or better — as possible, and we used best corrected visual acuity as the barometer of success. Vision comfort took a back seat to clarity and was almost an afterthought.
This paradigm has changed considerably with the expansion of digital device dependence and the emergence of digital vision syndrome. Pervasive reliance on smartphones and computers for work and school entails hours of up-close work, and this can lead to ocular discomfort, dry eye sensation and even headaches. These symptoms, along with others, including neck and shoulder pain, can be associated with binocular vision issues. Research suggests that binocular vision disorders lead to increased effort by the visual system to realign and that repeated effort to realign causes an overstimulation of the trigeminal nerve. This sensory irritation results in painful stimulation of several parts of the eye, head and neck, leading to trigeminal dysphoria, with symptoms such as headache, neck pain and eye strain.
One example of a vison discomfort issue that has been overlooked and underdiagnosed is dry eye sensation in patients who either do not exhibit signs of dry eye or have symptoms that are disproportionate to their signs. This is sometimes referred to as “pain with no stain.” In many cases, these patients do not respond to dry eye therapy, and this can become frustrating for both the patient and their eye care provider.
A red flag here is that these patients are comfortable in glasses but uncomfortable in contact lenses. And many eye care providers do not realize that this scenario suggests a possible binocular vision problem. The glasses prescribed for myopia are thick on the edge and thin in the center, and with up-close work, the pupils get smaller, and the eyes turn inward. There is some base-in prism effect — and as a result comfort — as the eyes turn in with myopic glasses. That effect is absent with contact lenses and can contribute to their intolerance.
Ophthalmic surgery connection
Binocular vision disorders, trigeminal dysphoria and digital eye strain are often thought of as issues that fall primarily within the purview of our optometry colleagues. However, these conditions are equally relevant to ophthalmic surgery. If someone is contact lens-intolerant but comfortable in glasses because of a binocular vision disorder, it is important to know this before performing LASIK or cataract surgery. If this binocular vision problem goes undiagnosed and the patient experiences feelings of dry eye, eye strain or headache postoperatively, they can suffer tremendously. They may even be considered a casualty of neuropathic pain from a severed nerve during LASIK.
The evolution of refractive surgery has taught us that information we gather preoperatively, about a prospective patient’s ocular pathophysiology, can help us plan the procedure and manage expectations. For instance, it is unthinkable to do LASIK without first performing corneal topography because of the wealth of information that these maps provide.
Another way to gather valuable supplementary information is with the Neurolens Measurement Device, Gen 2 (NMD2, Neurolens). The NMD2 is an eye tracking device that measures the degree of eye misalignment at distance and near. It takes into account heterophoria, fixation disparity and accommodative vergence response. The device was developed to acquire the measurements necessary to prescribe customized contour prism spectacle lenses for patients whose binocular vision cannot be sufficiently corrected by a traditional prism. Most patients with symptoms of digital vision syndrome exhibit different magnitudes of eye misalignment at different viewing distances. Standard prisms are limited to providing correction at only one distance.
Postoperative considerations
If a person with myopia presents for a LASIK consultation and their history shows that they failed contact lenses and were much more comfortable in glasses — but a thorough exam shows that they do not have dry eyes (or dryness out of proportion to their symptoms) — you should suspect the possibility of a binocular vision problem. If you have the NMD2, you can diagnose the presence and extent of a binocular vision disparity and let the patient know that after LASIK they may still need contoured prism spectacles, especially when they are doing a lot of near or intermediate work. If you do not have the NMD2, you can at least inform them that if they do have a binocular vision disparity, it may have to be addressed postoperatively. We do not have this device, nor do we use it as a screening tool. If someone is symptomatic postoperatively, I refer them to an optometrist who has it so they can perform the necessary measurements to help with the diagnosis and treatment.
It is important for ocular surgeons to recognize the signs of binocular vision disorders and to understand their relevance with respect to the possibility of post-refractive surgery contour prism correction. If there is any suspicion of a binocular vision disorder, the ideal solution is to work with our colleagues in optometry to help all of our patients achieve clear and comfortable vision.
- References:
- Computer vision syndrome. https://www.aoa.org/healthy-eyes/eye-and-vision-conditions/computer-vision-syndrome?sso=y. Accessed Nov. 22, 2021.
- Digre KB. J Neuroophthalmol. 2018;doi:10.1097/WNO.0000000000000660.
- Maples WC, et al. OVD. 2009;doi:40(2):100-106.
- Richter HO, et al. Work. 2011;doi:10.3233/WOR-2011-1152.
- Rosenfield M. Ophthalmic Physiol Opt. 2011;doi:10.1111/j.1475-1313.2011.00834.x.
- Sánchez-González MC, et al. Ann N Y Acad Sci. 2018;doi:10.1111/nyas.13614.
- For more information:
- Vance Thompson, MD, can be reached at Vance Thompson Vision, 3101 W. 57th St., Sioux Falls, SD 57108; email: vance.thompson@vancethompsonvision.com.
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