To the Editor:
We were very interested to read this article on visual snow syndrome (VSS; ref. [1]). VSS is not widely recognised in the ophthalmic community, despite its primary symptoms being visual in nature.
The authors provide a detailed review of possible associations and point out that certain medications ‘can have a deleterious effect’. However, they seem to overlook a recent report in the literature suggesting that a common group of drugs could potentially be linked to VSS.
We recently published a study on visual problems related to selective serotonin reuptake inhibiting (SSRI) antidepressants (ref. [2]), self-reported by patients to RxISK.org, an international drug safety website. Of 124 cases, we identified 11 meeting the diagnostic criteria for visual snow (VS; n = 5) or VSS (n = 6). Of particular interest was that while some patients developed VSS after starting the SSRI, for others, it began on reducing the dose or even stopping treatment. A consistent and disturbing feature was the persistence of symptoms regardless of reversing any recent changes in drug regimen.
Silva and Puledda describe the similarities between VSS and Hallucinogen Persisting Perception Disorder (HPPD), which is associated with use of recreational hallucinogenics such as lysergic acid diethylamide (LSD). Evidence suggests that LSD causes visual hallucinations by activating serotonergic 5HT2A receptors (ref. [3]). As hypothesised in HPPD, it may be that chronic activation by SSRIs induces excitotoxic damage to GABA-mediated serotonergic-inhibitory interneurons in neural visual pathways, resulting in a lasting structural change that could explain why symptoms continue after the drug is ceased.
Tinnitus is also highlighted as a common comorbidity with VSS. Both conditions are thought to be forms of thalamocortical dysrhythmia, arising from disruption of ‘noise cancellation’ in thalamocortical pathways due to cortical hyperexcitability (ref. [4]). Serotonin is one of the neurotransmitters involved in thalamocortical transmission.
SSRI usage in the UK population is currently at more than 10% and is set to rise further, with prescriptions for SSRIs increasing by 35% over the last 6 years (ref. [5]). It is likely that cases of VSS presenting to ophthalmology clinics will also increase, making a greater awareness of this condition essential amongst ophthalmologists.
Author contributions
HB wrote and edited the manuscript. DH collected the data and reviewed the manuscript. JL conceived the idea and contributed to writing and editing the manuscript.
Competing interests
The authors declare no competing interests.
Footnotes
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References
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