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Contoured Prism Lenses Relieve Headache, Eye Strain, and Dry Eye Sensation

Posted on January 12, 2022

Binocularity and trigeminal dysphoria go hand in hand

By Jeffrey P. Krall, OD

 As digital device use grows, the symptoms associated with it—such as headaches, neck pain, eyestrain, and dry eye sensation—are increasingly relevant to eye care.1 Reducing screen time and minimizing blue light exposure are often recommended to patients who present with some or all of these symptoms. However, 2 decades of my own research and anecdotal experience—coupled with compelling findings from a recent study—suggest that those strategies, although helpful, are insufficient.2 Proprioceptive feedback, which is closely related to eye movement and binocularity, can be the source of these symptoms;3 and contoured prism lenses can be an effective, efficient, and life-changing solution.

Binocularity is a combination of central and peripheral vision. The management of eye movement between central and peripheral vision relies on the proprioceptive system. The proprioceptive system constantly sends signals from the extraocular muscle so the eyes can maintain fusion.3 When a person decides to move their eyes to look at the next target, their peripheral vision calculates how far and how fast to move their eyes so that central vision can examine the details. The proprioceptive system helps manage this movement.

Interestingly, the proprioceptive fibers from the extraocular muscles do not send their signals via the second nerve—which is the optic nerve—or the third, fourth or sixth cranial nerves. The proprioceptive fibers send their signals via the fifth cranial nerve, which is called the trigeminal nerve. The trigeminal nerve is the largest of the cranial nerves and has three divisions: ophthalmic, maxillary, and mandibular. Functions of the trigeminal nerve include corneal sensitivity and pain reception within the sinuses. Coordination of head position is also directly related to the position of the eyes, as documented by the literature.4,5

To achieve image fusion, constant eye realignment increases the intensity and/or frequency of proprioceptive feedback via the trigeminal ganglion.3 This causes an increase in frontal/temporal headaches, dry eye sensation, neck tension, and related asthenopia (eye strain).6 The combination of these symptoms is known as trigeminal dysphoria. The mechanism is further aggravated by excessive up-close focus, such as that used when looking at a smartphone or computer.1 Correcting eye alignment with contoured prism lenses has been shown to resolve these symptoms substantially and often completely.7

Contoured prism lenses were developed after much research and observation that provided pivotal clues. For instance, when we look down and in, there is increased activity of the superior oblique muscle associated with the decreasing effectiveness of the medial rectus muscle.8 This helps to explain why we often measure an increase in exodeviation between eyes when they are focusing up close. Contoured prism allows eyes to compensate for the increase in exodeviation that occurs at near by providing an increased amount of prism that is independent of the amount of prism prescribed for distance. The ability to manage the misalignment at both distance and near has been integral to resolving the symptoms of trigeminal dysphoria.7

Evolution of an Innovation

Over the past 2 decades, these contoured prism lenses have been perfected and patented in collaboration with neurology and eye care professionals, including Vance Thompson, MD, founder of Vance Thompson Vision in Sioux Falls, South Dakota. They are now called Neurolenses and produced by a company of the same name, Neurolens (Coppell, TX), of which I am a co-founder. To date, I have personally fit over 10,000 patents with these contoured prism lenses, and now eyecare providers across the country are recognizing the benefits of the Neurolens and making them available to their patients, as well.

In addition to offering patients these specially designed spectacle lenses, we now can measure their misalignment objectively and accurately. Optimal use of contoured prism Neurolenses relies on precise measurement of the patient’s misalignment. For this, we use the Neurolens Measurement Device, Generation 2 (NMD2), which captures an objective, accurate and repeatable measurement of ocular alignment (Figure 1).

The NMD2 considers the critical elements of binocular fusion, including heterophoria, vergence conditioning, binocular peripheral fusion, fixation disparity, accommodative convergence response, and alternating monocular central fixation. The device provides a simulation of how the eyes work together to see both near (50 centimeters) and far (6 meters, simulating optical infinity), and identifies eye misalignment as small as 0.10 PD. The device’s mission is to attain a measurement called the Neurolens value, which is used to prescribe contoured prism vision correction.

With this device, coordination of central binocular vision is tested first and measured without peripheral stimulation. Two independent central dots viewed at optical infinity are introduced on the viewing screen while the eyes are alternatingly occluded. If there is no imbalance of central fusion, the dot appears stationary during alternating ocular occlusion. If there is an imbalance of central fusion—a phoria—the central dot vibrates as each eye moves to fix on the central dot following alternating occlusion. The device tracks the movement of each eye and quantifies the phoria.

With the central dot visible and aligned with central fusion, peripheral targets are then introduced independently to both the right and left eyes. These independent targets stimulate cortical fusion of peripheral field of vision while allowing central vision to remain monocular. If there is no disparity between the alignment of central vision and the peripheral alignment of the fused binocular images, the central dot remains stationary. If there is disparity between central fusion and the alignment of the peripheral tracking system, the dot vibrates.

This imbalance is then tracked, and the NMD2 automatically relocates the central target to align with the center of peripheral fusion. The deviation is measured, and the procedure is repeated to measure the central and peripheral alignment of objects viewed at near. The device analyzes over 10,000 measurements to arrive upon a misalignment at distance and near, providing a prescriptive range for contoured prism lens prescription.

Chronic Headache Study

We used these Neurolenses, informed by data from an earlier generation of the NMD2, for a study intended to evaluate their impact on patients with daily refractory headaches. We found that we were able to resolve the misalignment that exists in both distance and near to substantially reduce patient symptoms.7 The participants had previously failed to achieve symptom relief after trying most, if not all, other therapeutic modalities. We started with 186 patients, and there were only seven lost to follow-up.

Self-reported efficacy utilizing the Headache Impact Test (HIT-6™), a validated metric for gauging severity of headache symptoms, indicated that after 90 days, 146 of the 179 patients (81.6%) reported a positive response to the treatment (Figure 2). The data further show that patients who suffered from the most severe headache symptoms upon entering the study reported the greatest benefit in terms of symptom relief. Of these patients, 54% reported that their headaches were substantially reduced or gone. Another important finding is that patients stopped taking many of their headache medications within 90 days of wearing the contoured prism lenses. Nearly 30% of the patients stopped needing 90% of their headache medications; 50% stopped taking more than 50% of their headache medications.

HIT-6™ measures the impact that headaches have on a person’s ability to accomplish the activities of daily living. HIT-6™ scoring assigns point values to symptom frequency, which increase proportionally to symptom severity. A change of 6 points in a patient’s score over time is indicative of one lifestyle change.9,10 The Chronic Daily Headache Study demonstrated a mean reduction in HIT-6™ scores of 7.64, which was highly statistically significant. This result suggests that contoured prism lenses are efficacious in a population for whom other conventional headache treatments were ineffective.7

Survey Data

Following the Chronic Daily Headache Study, we surveyed 360 patients fitted with contoured lenses. The survey asked: “Would you recommend this to your friends and family?” More than 90% responded, and 82% said they would recommend the contoured lenses to their friends and family (Figure 3). Participants completed surveys at 90 days and one year after receiving their contoured prism lenses.11


Our patients have always needed relief from the symptoms that culminate in trigeminal dysphoria, but we are hearing about them even more during this time when increased use of digital devices is exacerbating the problem. Contoured prism lenses provide an efficient and efficacious solution, and as eyecare providers become aware of their availability and add the NMD2 to their armamentarium, their patients are the beneficiaries.

Jeffrey P. Krall, OD, Krall Eye Clinic, Mitchell, SD
Contact: [email protected]; Phone: 605-996-2020
Dr Krall discloses he is a co-founder of Neurolens and a paid consultant.


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  8. Carpenter RHS. Movements of the Eyes. 2nd edition. Pion Limited; 1988. 
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  11. Data on file. neurolens, Coppell, TX. Chronic daily headache study patient survey, 2014.