Prism lenses may be the answer for patients with phorias
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A phoria is a misalignment or deviation in binocular vision that is often difficult to detect, because the eyes compensate for the difference.
Although some patients have what are considered “normal” phorias, others suffer from more distinct misalignment, which, if left untreated, can severely affect productivity and lifestyle. Such phorias may be associated with noticeable eyestrain, headache or fatigue that result from the eyes constantly compensating for the misalignment. For eyes trying to maintain binocular vision, the effort is like continuous weightlifting without breaks between sets: At some point, the muscle’s output drops due to overexertion.
Optometrists have identified and treated large phorias, in part due to distinct symptoms such as sustained diplopia. But eyes with smaller phorias (about 0.3 base in or base out) that are constantly working to maintain single vision are not generally treated.
For patients with milder prescriptions, I conduct a test in my office in which I introduce a little prism for different distances of focus. Once the eyes feel more relaxed, and the patient experiences how easily their strain can be relieved, that’s an “a-ha!” moment for them.
Ubiquity of phorias
Regardless of vision correction, people from all age groups can be affected by phorias, and certain lifestyles can especially be affected. More often, I see younger patients spending longer periods with digital screens, and they experience many symptoms, from phoria-related strain to increased myopia.
The academic performance of one of my teenage patients recently had been suffering. She reported headaches, neck pain and occasional dizziness, yet her prescription was only 0.25 D of cylinder. I proposed a new lens, and, a month later, her mom visited the office to inform me that her daughter’s grades had already improved. She saw better, felt better and was more productive in class.
That intervention was a low prescription for Neurolenses, and although it was a subtle change of prism, the lenses relieved her eyes from daily strain. When patients report symptoms of digital vision syndrome or chronic headaches, the cause can be overexertion of eye muscles and the nerves that innervate them.
Discussing contoured prism lenses with patients
I approach discussions with patients about vision alignment by starting with a simple questionnaire about symptom frequency as part of my standard patient history. During my exam, I discuss symptoms related to alignment, and I mention that there is new technology that may improve their symptoms.
During a cover test, I ask the patient if the target is moving. If the answer is yes, I take the opportunity to discuss what happened in that moment. Toward the end of the exam, once I’ve done the refraction, I’ll introduce a little prism and ask if the patient notices a difference. Many of my patients have mentioned feeling that they were given a massage, and that is a key indication of potential benefit from wearing contoured prism lenses. Not every patient will receive that same benefit, so it’s important to identify true candidates.
Ironically, many of my patients who insist that they won’t succeed with a progressive lens easily adapt to a prism progressive. My neighbor in her early 50s had forever described the classic symptoms of misalignment. She was a non-adapt with a previous progressive, so she was hesitant to try contoured prism lenses. Upon first use in a blinded clinical study, she said that she could instantly identify her treatment group based on her headaches subsiding and increased productivity during the day.
I believe that non-adaptation relates to not treating the phoria. As a result of her experience, I discuss previous progressive non-adaptation with all my patients in multifocals.
Implications for productivity
Neurolens recently investigated productivity improvement in a double-masked clinical study that enrolled 60 young adults and tested their reading speed using the Wilkins Rate of Reading Test. Each participant was randomly selected to wear either contoured prism lenses or a premium single vision lens based on their best corrected vision.
Analysis showed that the group that wore the contoured prism lenses demonstrated a statistically significant improvement in reading speed compared with the control group (P = 0.03).
This study’s data has helped validate the lenses to many of my patients who are candidates for contoured prism lenses. While the initial conversation has centered around symptoms and how a new lens can potentially provide relief, I’ve found that during follow-ups, the discussion evolves to how their productivity and daily lives have been enhanced.
For instance, I’ve had many patients report tearing while working (even with eyedrops), a symptom possibly from nerve stimulation related to phorias. For those applicable cases, the potential to do more work is a strong benefit.
Impact of Neurolenses
One of my patients in her 60s with keratoconus and a macular hole visited me, seeking a solution that didn’t require wearing contact lenses. When she began wearing the contoured prism lenses I’d prescribed, the difference to her life was made obvious at the grocery store one day. While shopping with her husband, she noticed she was alone. She called out to him and found him, saying, “Oh, you’re in the coffee aisle!”
He stared in disbelief because she had read the sign. She was in my office the next day in tears of gratitude. The prism lenses improved her vision to the best it has been since the onset of two ocular diseases. Confident in her vision, she had become more active. Her life was changed.
Reference:
- Neurolenses have significant impact on reading speed. https://www.prnewswire.com/news-releases/neurolenses-have-significant-impact-on-reading-speed-301600992.html. Published Aug. 8, 2022. Accessed Jan. 11, 2023.
For more information:
Michelle Jhagroo, OD, practices at Weston Family Eyecare in Davie, Florida. She is also affiliated with the Florida Heiken Children’s Vision Program, a subsidiary of the Miami Lighthouse for the Blind and Visually Impaired.
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