SOAPBOX

EXPLAINING VISUAL SNOW SYNDROME

BY A/PROF CLARE FRASER

Imagine if your whole visual perception was like a poorly tuned television. This is what patients with visual snow syndrome (VSS), a relatively newly recognised syndrome will describe. Patients will complain of seeing continuous, uncountable, dynamic, tiny dots flickering across their entire visual field. They describe this as being like the static or the ‘snow’ on a poorly tuned analog television – hence the term “visual snow”.

This ‘snow’ is superimposed on the visual scene meaning there is no loss of visual acuity nor visual field defects on routine ophthalmic testing. The static is classically described as being black-andwhite, but can be colored. Patients also describe the presence of other visual phenomena including the persistence of afterimages, trail phenomena, photophobia, nyctalopia, and an increased awareness of normal entoptic phenomena (for example floaters). We found many patients with VSS also experience a highpitched tinnitus and tremor.

Diagnostic criteria for VSS have been published in an effort to capture the spectrum of the condition (Table 1). It has been reported up to 2% of the population in the UK have VSS. Despite this, VSS is a disorder that is frequently overlooked or misdiagnosed. The lack of recognition can make it a challenge for patients as well as clinicians and researchers.

While VSS could be thought of as a hallucination because there is no real-world correlate of the perception, it may be more accurate to consider it an illusion created by disordered visual processing. A syndrome called hallucinogen persisting perception disorder, triggered by LSD and magic mushrooms altering visual perception, can be very similar to the experience of VSS. There are many theories about the origin of the percept of visual snow, which include pathology in the thalamus, visual cortex or the areas involved in higher visual processing. The exact pathophysiology may vary slightly between patients, which could explain the main symptom of visual snow, but could also explain the variety of other entoptic phenomena and indirectly related symptoms such as tinnitus.

The average age of a large cohort of 1,100 VSS patients was 29 years old, though nearly 40% reported having symptoms for as long as they could remember. There was no difference between men and women reported however, in our own cohort of patients in Australia 75% of VSS patients were male. The prevalence of migraine and migraine with typical aura in VSS patients, 50-80%, is high in comparison with the general population. Some patients attributed symptom onset to a severe migraine attack. Others report the onset of symptoms to be associated with certain medication, trauma or infection. In cases where the visual snow was brought on by an inciting event such as concussion, or infection, management of the underlying cause may significantly alleviate the symptoms.

Psychiatric symptoms such as anxiety and depression are highly prevalent in patients with VSS and are associated with increased visual symptom severity and reduced quality of life. Therefore, treatment of psychiatric symptoms can offer an avenue for clinicians to help the patients improve their quality of life and ability to cope with other symptoms. In general, VSS seems to be non-progressive, though it does fluctuate in severity within and between patients. During times of stress and other illness the symptoms can seem worse and treating the underling stressor or illness can help.

There have been no proven medical treatments to alleviate visual snow. Though there are some case reports describing the use of lamotrigine, we have not found this to be helpful for most patients given the side effect profile of the drug. Tinted lenses may reduce how symptomatic the VSS appears to the wearer, but these will not cure the condition. There are some reports of orthoptic exercises being beneficial, but this has not been proven with rigorous scientific methods, and can be expensive.

An explanation, reassurance regarding progress and acknowledging the condition is often the first step to patients feeling less symptomatic. An honest discussion of the current state of research offers clarity and understanding which the patients generally find helpful. Some patients who are more prone to introspection and anxiety can struggle if they become too enmeshed in patientled chat groups, so caution should be advised. However, others find the support of patients experiencing similar symptoms to be helpful. n

Name: A/Prof Clare Fraser Qualifications: MBBS, MMed, FRANZCO Organisation: Save Sight Institute, The University of Sydney Position: Associate Professor of Neuro-ophthalmology Location: Sydney Years in profession: 22 years as a doctor.

Diagnostic criteria for visual snow syndrome

1 Visual snow: dynamic, continuous tiny dots in the entire visual field lasting longer than 3 months

2 Presence of at least two additional visual symptoms from the following: a) Palinopsia: afterimages or trailing of moving objects b) Photophobia c) Nyctalopia (impaired night vision) d) Other persistent positive visual phenomenon including (but not limited to): enhanced entoptic phenomena (excessive floaters or blur field entoptic phenomenon), kaleidoscope type colors with eyes open or closed, spontaneous photopsias

3 Symptoms are not consistent with typical migraine visual aura

4 Symptoms are not better explained by another disorder

Table 1: Proposed criteria for visual snow syndrome. Based on Metzler AI, Robertson CE. Visual Snow Syndrome: Proposed Criteria, Clinical Implications, and Pathophysiology. Curr Neurol Neurosci Rep. 2018:18:52. doi: 10.1007/s11910-018-0854-2. AN EXPLANATION, REASSURANCE REGARDING PROGRESS AND ACKNOWLEDGING THE CONDITION IS OFTEN THE FIRST STEP TO PATIENTS FEELING LESS SYMPTOMATIC.