Kenneth J. Ciuffreda, O.D., Ph.D. (1) , Daniella Rutner, O.D., M.S., M.B.A.
SUNY/College of Optomeüy, Vision Rehabilitation Service, New York, NY 10036
Visual snow syndrome (VSS) has received considerable attention over the past decade (White et al., 2018; Puledda et al., 2018, 2020; Cufreda et al., 2019). However, it was reported as early as 1944 related to digitalis intake for heart problems (Carroll, 1944). Interestingly, the primary etiology of VSS is traumatic brain injury (TBI) (Tannen et al., 2020). VSS presents a constellation of visual and non-visual symptoms, which are listed and defined in Table 1.
Essentially, visual snow (VS) refers to the pixelated dynamic visual “noise” (like a detuned television) that is perceived to be in front of, and overlaying, the entire visual field (Figure 1). Driver Rehabilitation Specialists who suspect that a client may be experiencing visual snow (VS) should refer them to an eye doctor to confirm the diagnosis and prescribe treatment.
Per the current diagnostic criteria for VSS (White et al., 2018; Puledda et al., 2018, 2020), the individual must report VS plus two or more of the following four visual symptoms: palinopsia, photosensitivity, enhanced entoptic imagery, and “nyctalopia” or difficulty seeing at night. In addition, they typically report one or more of the remaining symptoms in Table 1, such as tinnitus and photopsia.
VSS presents with an interesting and unusual range of sensory motor and perceptual, visual and non-visual, symptoms. Hence, it behooves the clinician (e.g., optometrist and/or occupational therapist) to consider the possible effects of these symptoms on driving, especially in certain environments (e.g., night driving). Furthermore, these symptoms and their driving ramifications are compounded by the comorbid condition of TBI and its own constellation of visual.
Driving with VSS and TBI
The majority of symptoms presented in Table 1 (about 75%) have the potential to negatively impact driving in these patients (Table 2, items 1-10). The impact can be either direct or indirect on vision and general sensory processing.
The key symptom of VS may adversely affect one’s driving in a number of ways. First, the pixelated overlay produces two competing and conflicting depth planes, which could result in visual confusion and act as an attentional distractor, impairing depth/distance perception. Additionally, in younger individuals (<40 years of age, pre-presbyopia), VS may increase the eye’s focusing error (i.e., increased accommodative error) at distant points. The result would be slight blur, presenting difficulty in detecting small details in the complex, dynamic distant visual scene. Fortunately, the adverse effects may be reduced with a chromatic tint.
The other four critical diagnostic criteria-based primary visual symptoms could also adversely affect one’s driving performance and hence one’s safety. For example, in the case of palinopsia, the persistent afterimage with or without trailing can exert a disruptive and confusing effect when superimposed on the dynamic driving scene, especially along with the concurrent overlay of VS. Similarly, the presence of photosensitivity can produce a visual/attentional distraction, a sense of annoyance, watering of the eyes, and eyelid “squinting” to reduce the light intensity entering the eye via the pupil. Fortunately, both can be reduced to some extent with a chromatic tint.
Moreover, palinopsia can be further reduced with simple vision therapy saccadic tracking procedures. The enhanced imagery can also act as a visual distraction and annoyance, with its overlay of internal eye debris/structures upon the visual scene, likely contributing to the vague symptom of “nyctalopia” along with the concurrent presence of VS. Unfortunately, there is no treatment for either disturbing visual symptom. However, one may elect to limit driving to daytime hours when these problems may be less evident.
