Binocular vision disorders are prevalent in our patients of all ages, from school-aged children to the elderly. In fact, studies estimate between 21% and 38% of the population has some form of binocular dysfunction or vergence anomaly.^1-2 As optometrists, we can significantly improve a patient’s quality of life by uncovering and treating these issues.

Here, I describe the top three alignment disorders an optometrist will routinely encounter in a primary care setting, how to best treat them, and how to check for them.

CONVERGENCE INSUFFICIENCY

Convergence insufficiency (CI) is the decreased ability to converge the eyes and maintain binocular fusion while focusing on a near target. Symptoms of CI include eye strain, double vision, headaches, blurred vision at near, tension in and around the eyes, print moving on the page, and frequently losing one’s place while reading. Symptoms tend to worsen during prolonged near work, such as reading or electronic device usage. Clinical findings include receded near point of convergence (NPC), decreased base out vergence amplitudes at near, and greater exophoria at near than distance.

CI is the most common binocular vision disorder encountered in the primary care office.³ While seen most frequently in children and young adults, it can occur at any age. Recent literature shows an increased incidence of CI in special populations that optometrists regularly see — 49% of young adults have CI after a concussion, as do nearly 16% of children with ADHD, and 53% of children and adults with Lyme disease.^4-6

Treatment: First, correct any refractive error. Slightly under-correct hyperopia, and fully correct myopia. Extra minus correction will stimulate accommodative convergence. This alone may reduce the angle or frequency of exotropic deviation.

Evidence-based medicine shows the best and most efficacious treatment for CI is office-based, along with home-based optometric vision therapy.³ NIH studies show that this treatment is long-lasting as well.⁷ If your office does not provide vision therapy, consider referring these patients to an optometrist who does. Alternatively, there are several computer-based programs that can be prescribed for home use and can be monitored remotely.

An OD can sometimes prescribe glasses with low amounts of base in prism if conventional CI exercises are unsuccessful or not feasible. Our office finds great success with contoured prism (increased base in prism at near compared to distance). Base in prism works well for adults who cannot schedule time for vision therapy, and for patients who cannot do vision therapy because they are too symptomatic. The optometrist will typically prescribe the least amount of prism necessary to achieve comfortable binocular vision at near.

DECOMPENSATED HETEROPHORIA

Most people who are not strabismic will still exhibit a tendency for the eyes to misalign when dissociated, such as when one eye is covered. This tendency is defined as a heterophoria. Any latent binocular misalignment that becomes symptomatic is considered a decompensated heterophoria.

Several factors can cause a heterophoria to decompensate. If the heterophoria is very large, it may be too much for the motor and sensory fusion to overcome. Working at an abnormally close working distance could also cause the heterophoria to increase to where it is too much to tolerate. If the patient’s fusional reserves are inadequate, they could weaken to where they can no longer overcome the heterophoria if the patient becomes ill. Lastly, any issue that interferes with sensory fusion can cause a heterophoria to decompensate. Examples include working in dim environments, cataracts, visual field loss, and uncorrected refractive error.

A patient with a significant degree of esophoria has a greater risk of decompensating than a patient with exophoria, especially in the case of latent hyperopia. Symptoms of decompensated esophoria may include headache, blurred vision, and intermittent or constant diplopia.

Treatment: Vision therapy has long been advocated as the primary intervention technique for non-strabismic anomalies of binocular vision. Vision therapy can increase the efficiency of the accommodative system to facilitate a more effective interaction between the accommodative and vergence system.⁸ In-office or computerized home therapy could be beneficial for these patients.

In the case where decompensated heterophoria patients failed vision therapy, or could not complete the program, I prescribe spectacle prism. Practitioners can follow Sheard’s or Percival’s criterion for prescribing prism.

The alignment tests we normally use do not provide any natural cues with the measurements since the patient views the targets under artificial viewing conditions. Some researchers suggest practitioners recommend prisms that make the patient feel most comfortable while viewing objects in the real world.⁹ For this reason, I prefer to trial frame prism in the office (see image). I typically start with 1/3 to 1/2 of the measured phoria in the trial frame to see how the patient responds.

Surgery is an option in these patients if vision therapy and/or prism does not provide the desired results. For a decompensated esophoria, the surgeon would perform a medial rectus recession, and for a decompensated exophoria, a lateral rectus recession. Patients should be advised of the risks of consecutive exotropia or esotropia and should follow up with their optometrist on a regular basis to evaluate for double vision.

VERTICAL HETEROPHORIA

Vertical heterophoria is caused by vertical misalignment of the eyes, with misalignments as small as 0.25 prism diopters resulting in significant symptoms. The misalignment can be congenital or acquired from a brain injury/concussion or stroke.

Congenital vertical heterophoria can be due to orbit asymmetry or asymmetry in extraocular muscle innervation or strength. The overuse of the opposing elevator and depressor muscles trying to realign the eyes to avoid vertical diplopia can result in headache and eye pain. The rapid alignment/misalignment cycle is thought to cause a sensation of image vibration, dizziness, and other vestibular symptoms. In addition to that, patients with vertical heterophoria can also experience neck pain, reading/learning difficulties, balance/gait issues, and often have higher levels of anxiety.

A head tilt may also be a sign of vertical heterophoria. Twenty percent of the general population is estimated to have a vertical heterophoria.¹⁰

Treatment: Once a possible vertical heterophoria patient has been identified, a specialized neurovisual evaluation is performed. The optometrist should trial prism in small 0.25 D increments in the office until visual clarity is maximized and symptoms are minimized. Gait and balance testing, along with symptom re-assessment should be repeated along the way. Patients should experience an immediate 50% reduction in symptoms.

The OD should order spectacle lenses that have the specified amount of microprism. Some patients may require multiple prism corrections before the vertical deviation is completely compensated. Increases in prism may be required during the initial adaptation period.¹⁰ Education is important to help the patient understand how the visual and vestibular systems are connected.

For further reading, Debby L. Feinberg, OD, has written on the benefits of prism lenses for vertical heterophoria patients with symptoms such as dizziness, anxiety, and headaches. She has written on this topic for a previous article in Optometric Management,¹¹ as well as in an article co-written with Mark Rosner, MD, published in Optometry & Visual Performance.¹²

HOW TO DETECT BINOCULAR VISION DISORDER

The first step in detecting binocular vision disorders is to ask the right questions. Many of our patients, especially children, do not realize that their symptoms — eyestrain, headaches, losing words on the page — are not normal. Most patients also do not realize their symptoms of dizziness and neck pain could be related to their ocular alignment.

To assess these symptoms, optometrists can use a standardized questionnaire, such as the Convergence Insufficiency Symptom Survey, Brain Injury Vision Symptom Survey, Binocular Vision Dysfunction Questionnaire,¹³ or they can create a customized one. My practice uses a 7-question quantitative survey that is easy for the patient to fill out in-person or can be completed online before they come to the office. The results of a screening survey help the technician or the doctor determine whether further testing beyond the normal comprehensive examination testing is warranted.

Since we started using a symptom survey in fall 2018, we found 50% to 60% of our patients qualify for further binocular vision testing based on their responses. This number has increased since the start of the pandemic, with patients of all ages spending more time in front of screens and doing near work. Additional testing for binocular vision dysfunction in the symptomatic patients should include horizontal and vertical phorias at distance and near, base in and base out vergence testing, and accommodative convergence/accommodation (AC/A) ratio. All patients, even if not deemed “symptomatic,” should have stereopsis, NPC, and a distance and near cover test, in addition to normal entrance tests. In the case where a patient does not understand the survey, or doesn’t realize his or her symptoms, such as headaches and dizziness, could be eye-related (and therefore doesn’t report it), we can still pick up a problem with these simple tests.

Patients with vertical heterophoria will report more dizziness, vestibular symptoms, and anxiety than patients with CI or decompensated phoria. If a vertical heterophoria is suspected, the above testing can be modified. Symptoms usually occur with less than 2 prism diopters of disparity, so the deviation is difficult to assess with a traditional cover test. It may be helpful for the optometrist to look for small eyelid movement rather than looking at the actual eye. To see whether the patient would benefit from small amounts of vertical prism, ODs can ask the patient to tilt their head to whichever side is most comfortable for them visually, and add prism incrementally in 0.25 prism diopters base down to the eye opposite the head tilt. Observation of posture, gait, and balance is also important in these patients.

BINOCULAR VISION DYSFUNCTION ON THE RISE

With our society’s increasing near visual demands, I expect we will see more binocular vision dysfunction in our practices. In addition to increased screen time and electronic device usage, we have more patients diagnosed with Lyme disease, ADHD, and concussion due to increased awareness and better testing methods. Detecting and treating binocular vision disorders provides comprehensive care and differentiates our practices. OM

REFERENCES

1. Hokoda SC. General Binocular Dysfunction in an Urban Optometry Clinic. J Am Optom Assoc. 1985;56:560-563.
2. Montes-Mico R. Prevalence of General Dysfunctions in Binocular Vision. Annals of Ophthalmology, 2001;33:205-208.
3. Scheiman M, Cotter S, Mitchell GL, Convergence Insufficiency Treatment Trial Study Group, et al. Randomized clinical trial of treatments for symptomatic convergence insufficiency in children. Arch Ophthalmol. 2008;126:1336-1349.
4. Master CL, Scheiman M, Gallaway M, Goodman A, et al. Vision diagnoses are common after concussion in adolescents. Clin Pediatric. 2016;55:260-267.
5. Granet D, Gomi CF, Ventura R, Miller-Scholte A. The relationship between convergence insufficiency and ADHD. Strabismus. 2005;13:163-168.
6. Matta NA, Singman EL, McCarus C. Lyme disease and convergence insufficiency: is it a near fit? Am Orthopt J. 2006;56:147-150.
7. Convergence Insufficiency Treatment Trial Study Group. Long-Term effectiveness of treatments for symptomatic convergence insufficiency in children. Optom Vis Sci. 2009;86:1096-1103.
8. Ciuffreda KJ. The scientific basis for and efficacy of optometric vision therapy in nonstrabismic accommodative and vergence disorders. Optometry. 2002;73:735-762.
9. Otto JMN, et al. Do dissociated or associated phobia predict the comfortable prism? Graefes Arch Clin Exp Ophthalmol. 2008;246:631-639.
10. Surdacki M, Wick B. Diagnostic occlusion and clinical management of latent hyperphoria. Optom Vis Sci. 1991;68:261-269.
11. Feinberg D. Practice Profile: Vision Specialists of Michigan. Optometric Management magazine. Oct. 17, 2019. https://www.optometricmanagement.com/issues/2019/october-2019/the-case-for-vertical-heterophoria-care. Accessed Oct. 11, 2022.
12. Feinberg DL, Rosner MS. Vertical Heterophoria Treatment Ameliorates Headache, Dizziness and Anxiety. Optom Vis Perf. 2020;1:24-34.
13. Feinberg DL, Rosner MS, Rosner AJ. Validation of the Binocular Dysfunction Questionnaire (BVDQ). Otol Neutrol. 2021 Jan;42(1):e66-e74.

DR. RICHARD started Spectrum Vision Care in Chalfont, Penn., in 2016. She does primary care, neuro-optometry, and low vision rehabilitation. She is an active member in the AOA and her local society, and is pursuing fellowship in NORA.