It’s hard to believe that the definitive book on endogenous visual stress, Stress and Vision authored by Elliott B. Forrest, O.D., is nearing its 30th birthday. Originally published in 1988, the book appeared posthumously thanks to the efforts of Dr. Forrest’s colleague, Dr. Martin Birnbaum.
There is a different approach to visual stress that some have taken emphasizing the exogenous, rooted in the nature of repetitive patterns in the environment. Examples include dashed lines in the road when driving, rows of fluorescence lights, or lines of print when reading. Rather than the primary source of visual stress being maladaptation within the individual’s visual system, it is rooted in the nature of environmental design. This line of investigation has been championed by Arnold Wilkins, a researcher in the U.K., formulated in a book authored in 1995 on Visual Stress.
Wilkins most recently applied this thinking toward visual considerations in architectural design. But reading remains the primary focus of Wilkins’ work, and the approach toward individualized color modifications he and his colleagues have suggested.
Last year, Evans and Allen published a systematic review of controlled trials on visual stress using Intuitive Overlays or the Intuitive Colorimeter. They identify that possible reasons why an individual might prefer a specific color include its effect on visual stress, refractive error, accommodation, decompensated phoria, suggestion or placebo effect. They note the following symptoms and signs that have been used as indicators of visual stress:
One optometrist who spent much of his career unifying the exogenous (environmental) and endogenous (visual system) approaches to visual stress was the recently deceased Dr. Merrill Bowan. He referred to the visual stress experienced by repetitive patterns as visual aliasing, and used the concept of Wilkins’ repetitive grating patterns to probe what he coined as the Bihemispheric Dissonance Test. The patient fixates the center of the pattern, and reports whether the stripes vibrate or that it is simply uncomfortable to view. What the Amsler Grid is to the retinal distortion, the BDT is to cortical hyper-excitability.
When patients reported visual instabilities or discomfort upon viewing this grating pattern, Dr. Bowan suggested using a probe of low power base-in prism (typically 1^ BI each eye). Although this was his preferred method of decreasing or eliminating the visual instabilities or stress, he acknowledged that in some cases the patient responds better to low power plus lenses, or a combination of low power plus lenses together with low power prism. Increasingly, practitioners are considering a differential prescriptive approach to visual stress that considers the relative role of color, plus power, and prism, on an individualized basis.