The patient who could not scroll: When prism became the practical solution

Introduction

Digital eye strain is common, but not every patient with headaches, difficulty focusing, and screen intolerance has an ocular surface or accommodative problem.^1,2 A patient can have correctable acuity and healthy eyes while still experiencing a symptomatic vergence disorder, because routine acuity, refraction, and ocular health testing are not designed to detect it. This patient's complaint was unusually specific: She could not scroll on her phone without becoming dizzy.

Convergence insufficiency is a common binocular vision disorder characterized by greater exophoria at near, a receded near point of convergence, and, in some patients, reduced positive fusional vergence. Reported prevalence varies considerably because study populations and diagnostic criteria are not consistent across the literature. The case below shows how a young woman with years of normal examinations turned out to have a convergence-insufficiency pattern with a small vertical component, and why a modest prism became the most practical treatment option for her.

Case presentation

A 35-year-old woman, a social worker in a mental health department, came to me with a multiyear history of headaches, dizziness, and difficulty focusing that had clearly worsened since the fall of 2023. Her description was specific: daily headache and tension pain that intensified with near work, a constant sense that her right eye felt heavy and “droopy,” and dizziness or a motion-sickness sensation when she scrolled on her phone or drove. She volunteered that covering or closing the right eye relieved the discomfort, and that taking out both contact lenses, so that her vision simply blurred, also helped. A previous provider had lowered her contact lens power, which had not made a difference. She reported no double vision.

She carried a diagnosis of chronic migraine, managed with a monthly anti–calcitonin gene-related peptide (CGRP) injection (fremanezumab, Ajovy), onabotulinumtoxin A every 3 months, and rizatriptan (Maxalt) as needed. These helped but never fully controlled her symptoms. By the time she saw me, the problem was interfering with her ability to work, and she found driving and using her phone difficult.

Examination findings

Her ocular health did not explain the picture. The anterior segment was normal in both eyes, intraocular pressures and pupils were within normal limits, extraocular motility was full, and the posterior pole and retina were unremarkable. Manifest refraction was –2.50 sphere for the right eye and –2.50 –0.25 x 090 for the left, with best-corrected acuity of 20/20 in each eye. On its own, none of this accounted for a young woman who could not comfortably look at her phone.

The binocular findings were what caught my attention. On cover testing, she was 2Δ exophoric at distance with a 1.0Δ right hyperphoria, and 12Δ exophoric at near. Her near point of convergence broke at 20 cm. The distance exophoria was small and, in my experience, rarely symptomatic on its own. The large near exophoria and the receded near point of convergence gave me a clear convergence-insufficiency pattern that fit her trouble with sustained near work (Table).

The finding I kept returning to was the vertical one. A 1.0Δ right hyperphoria is easy to overlook, but it matched what she had told me: the right-sided heaviness, and the relief she felt when she covered or closed that eye. When a patient reports relief with monocular occlusion, I take that as evidence that binocular interaction is contributing. In this case, the lateralized symptoms made the small vertical component particularly relevant. This is also why a routine sequence missed it for years. Her acuity was correctable, and her eyes looked healthy, and nothing in a standard refraction and fundus examination surfaces a 1.0Δ vertical phoria or a receded near point of convergence unless those specific tests are performed.

Table 1. Documented Clinical Findings

Differential diagnosis

Because her symptoms overlapped with several conditions, I worked through a broad differential, as follows:

• Migraine: This was an established, active diagnosis, but incompletely controlled despite anti-CGRP therapy, botulinum toxin, and a triptan. The persistence of visual symptoms despite this treatment suggested a second, untreated contributor.
• Vestibular causes of dizziness: This was possible, though her dizziness was provoked by specific visual tasks such as scrolling, driving, and near work rather than by positional change. I did not perform a formal vestibular assessment.
• Ocular surface disease: Screen use made this a plausible contributor, but it did not explain the lateralized right-eye heaviness or the relief with monocular occlusion.
• Refractive error: Her acuity was correctable to 20/20 in each eye, and reducing her contact lens power had not helped.
• Neurologic causes: A new vertical deviation in an adult warrants consideration of cranial nerve, orbital, or central causes. Here, the deviation was small, extraocular motility was full, there was no diplopia, and symptoms tracked with visual demand, all of which was reassuring. I did not pursue neuroimaging or a formal neurologic evaluation, and this report does not substitute for one.

Considering all these points, I diagnosed a convergence-insufficiency pattern with an associated small right hyperphoria, superimposed on her migraine disorder. I did not treat the prism as a cure for migraine, but as a way to remove a constant visual stressor that was plausibly aggravating it.

Management

Office-based vergence and accommodative therapy has the strongest evidence for symptomatic convergence insufficiency and was discussed as an option.³ For this patient, it was not realistic. Her schedule and work demands made a structured, weeks-long program unworkable, which is a common situation for working adults. My goal shifted to relieving her symptoms immediately with a correction she could simply wear.

My prism decision came down to a few practical points. The near exophoria and the right hyperphoria were the findings that best matched her symptoms, so those were what I set out to address, while leaving the 2Δ distance exophoria alone. I prescribed a Newton contoured prism lens (the technology formerly branded Neurolens). The contoured design provided no horizontal prism at distance and progressively introduced base-in prism toward the reading zone, allowing the correction to better match her near demand (Figure). For the vertical, I added 0.5Δ base-down OD and 0.5Δ base-up OS, a combined 1.0Δ vertical correction intended to address the measured right hyperphoria.

I keep vertical corrections as small as the patient will accept. Because vertical fusional reserves are limited, even a small vertical misalignment can be clinically meaningful, so it was the component I most wanted to neutralize, while her 2Δ distance exophoria was unlikely to trouble her. Even a fraction of a prism diopter can change how a patient feels, and vergence adaptation means an unnecessarily large prism can drive escalating prescriptions over time.⁴ I prescribed the prism in spectacles to be worn over her contact lenses. She prefers contact lenses day to day, and this arrangement lets her put the glasses on when she needs them while still functioning without them.

Outcome

The response in the office was immediate: With the trial frame in place, she reported instant relief and was able to look at her phone without dizziness for the first time in years. At a telephone follow-up 3 weeks later, she remained very satisfied. She reported that her dizziness had resolved, that she could comfortably view her phone, and that her other symptoms had improved.

Discussion

The literature on prism for these patients has to be read carefully, because the populations differ. For convergence insufficiency, a Cochrane network meta-analysis found office-based vergence therapy to be the most effective option overall. Base-in prism reading glasses were no better than placebo in children, while one randomized trial with adults found that base-in prism near correction reduced symptoms relative to placebo, with a mean Convergence Insufficiency Symptom Survey (CISS) difference of approximately 8.9 points.³ Evidence for prism in vertical heterophoria is more limited and comes largely from a postconcussion population, in which neutralizing prism reduced headache, dizziness, and anxiety.⁵ My patient's vertical deviation was not postconcussive, so I applied that evidence cautiously, as support for the mechanism rather than proof of effect in her particular situation.

What is well established, and directly relevant to how I prescribe, is vergence adaptation: The eyes adapt to prism over time, which is a practical argument for prescribing the smallest amount that relieves symptoms and refining it to the patient's response.⁴ A validated questionnaire such as the CISS can quantify baseline burden and track response. Validation studies identified symptom-score cutoffs of 16 or higher in children aged 9 to younger than 18 years and 21 or higher in adults aged 19 to 30 years.^6,7 I did not administer the CISS at this visit; a baseline and follow-up score would be worth capturing in future cases of this kind.

The practical lesson is one I keep relearning: A normal routine examination does not rule out a disabling binocular problem. The tests that made the diagnosis, cover testing at distance and near, near point of convergence, and a deliberate check for a vertical phoria, are quick, but only if you actually perform them. And for an adult who cannot take on vision therapy, a small, well-chosen prism can be a legitimate and immediately helpful option.

Conclusion

Binocular vision dysfunction deserves a place on the differential for any young adult with headaches, dizziness, and digital visual complaints despite normal routine examinations. In this patient, a convergence-insufficiency pattern with a small right hyperphoria provided a plausible explanation for symptoms that earlier examinations had not captured, and a modest prism restored her ability to use her phone comfortably. Sometimes, a small amount of prism, carefully chosen, is the most practical thing we can offer.

Author note

Patient identifying details have been altered to protect privacy. All clinical values are as recorded at examination.

References

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2. Auffret É, Gomart G, Bourcier T, Gaucher D, Speeg-Schatz C, Sauer A. Digital eye strain: symptoms, prevalence, pathophysiology, and management. Article in French. J Fr Ophtalmol. 2021;44(10):1605-1610. doi:10.1016/j.jfo.2020.10.002

3. Scheiman M, Kulp MT, Cotter SA, Lawrenson JG, Wang L, Li T. Interventions for convergence insufficiency: a network meta-analysis. Cochrane Database Syst Rev. 2020;12(12):CD006768. doi:10.1002/14651858.CD006768.pub3

4. Cooper J. Clinical implications of vergence adaptation. Optom Vis Sci. 1992;69(4):300-307. doi:10.1097/00006324-199204000-00008

5. Rosner MS, Feinberg DL, Doble JE, Rosner AJ. Treatment of vertical heterophoria ameliorates persistent post-concussive symptoms: a retrospective analysis utilizing a multi-faceted assessment battery. Brain Inj. 2016;30(3):311-317. doi:10.3109/02699052.2015.1113564

6. Rouse M, Borsting E, Mitchell GL, et al; Convergence Insufficiency Treatment Trial (CITT) Investigator Group. Validity of the Convergence Insufficiency Symptom Survey: a confirmatory study. Optom Vis Sci. 2009;86(4):357-363. doi:10.1097/OPX.0b013e3181989252