Case report: Prolonged amelioration of mild red-green color vision deficiency following psilocybin mushroom use

This report describes an individual self-experiment by a 35-year-old male with previously diagnosed mild deuteranomaly (red–green CVD). Baseline colour vision had been documented by an optometrist about five years earlier. The subject's prior psychedelic exposures were recorded (including prior psilocybin, LSD, DMT and other agents); at the time of the reported episode he was taking no medications, smoked cannabis once weekly and consumed minimal alcohol. Colour vision was assessed using the Ishihara Test, the commonly used clinical screening tool composed of plates that detect and characterise red–green defects (plates 1–21 identify a defect; plates 22–25 help distinguish protan from deutan defects). The subject self-administered the test immediately before ingesting five grams of dried psilocybin mushrooms, then repeated the test beginning at about 12 hours post-ingestion and periodically over the ensuing four months, only consulting the answer key after approximately four months. The investigators later obtained written informed consent and administered the Ishihara Test themselves at 436 days post-administration. No formal statistical analysis was possible or reported, as this is a single-case behavioural measurement relying on self-reported scores for most timepoints. The authors note ancillary substance exposures that occurred during follow-up (a microdose of LSD on day 16, recreational intranasal esketamine about two months later, and a later 4 g psilocybin use from the same batch prior to the clinician-administered test), and they recorded these as potential confounders. The CARE Case Report Guideline Checklist was completed and is referenced in the supplement.

At baseline (pre-psilocybin), the subject scored 14 on plates 1–21 of the Ishihara Test, consistent with mild red–green CVD; plates 22–25 indicated deuteranomaly. During the acute experience the subject reported intensified colours, but objective change on the Ishihara Test was small at 12 hours post-dose (score 15). By 24 hours post-administration his score rose to 18, exceeding the typical Ishihara cut-off of 17 used to indicate normal colour vision. Scores peaked at 19 on day eight post-administration. At approximately four months post-dose the subject's self-reported score remained elevated at 18. Follow-up testing performed by the investigators at 436 days after the reported psilocybin dose yielded a score of 16 on plates 1–21, higher than the original baseline but still within the mild CVD range. Interpretation of the longer-term trajectory is complicated by intervening substance use: the subject reported a microdose of LSD on day 16 post-psilocybin, recreational intranasal esketamine about two months later, and another 4 g psilocybin use roughly four months prior to the clinician-administered test. Throughout the observation period he continued weekly cannabis use. The subject did not achieve a perfect Ishihara score at any timepoint. No adverse events linked to the experiment are reported in the extracted text.

Barnett and colleagues interpret the data as showing a quantifiable, partial improvement in colour discrimination following a single high-dose psilocybin mushroom self-administration, with peak improvement occurring around one week and measurable enhancement lasting at least 16 days. They emphasise that the subject's improvement was partial—he never scored perfectly—and that this is biologically plausible given the likely genetic basis of his CVD, which would not be corrected by a single pharmacological exposure. The authors discuss possible mechanisms without asserting a definitive cause. Since psychedelics act at multiple levels of the visual system and are known to alter cortical visual processing, they suggest that higher-level changes in visual cortex connectivity or processing might permit an expanded subjective colour spectrum despite unchanged retinal input. Psilocybin-related increases in early visual cortex responses (for example, enhanced P1 amplitude reflecting V1 activity) are noted as a candidate neural correlate of increased brightness perception; the V4 region—implicated in colour processing—is proposed as a plausible site for higher-order changes, though no direct data on V4 and psilocybin are reported. Several limitations are acknowledged. Most of the Ishihara measurements were self-administered and self-reported, raising the possibility of recall or testing effects despite the subject's statement that he did not consult the answer key until four months later. The interpretation of long-term durability is further confounded by subsequent use of other psychoactive substances including LSD, esketamine and later psilocybin from the same batch. The single-case nature of the report, the subject's relatively mild CVD, and the absence of a reported mystical-type experience during the dosing episode also limit generalisability to clinical research populations. The authors recommend future studies employ clinician-administered, blinded measures in larger samples with varying CVD severity, use alternate plate versions to avoid repeated-testing effects, explore different dosages and regimens, and investigate underlying neural mechanisms.

The case report suggests that a single use of psilocybin may induce partial, in some instances prolonged, improvement in red–green colour vision in a person with mild deuteranomaly. The finding raises questions about whether psilocybin can produce durable alterations in visual processing in some individuals. The authors call for systematic research to determine generalisability to more severe CVD, to examine dose–response relationships, and to elucidate the neurobiological mechanisms underlying the observed phenomenon.