VISUAL SNOW SYNDROME (VSS):

VSS manifests as a continuous, pervasive overlay of small, flickering dots over a patient’s vision, regardless of lighting conditions, although sometimes reported as more distinct in a darker environment. These dots can appear black/grey against light backgrounds, white/grey against dark, and occasionally exhibit distinct, vibrant colours (neon pink, cyan, and bright green are the most frequently reported colours).

This visual ‘noise’ or ‘snow’ is the primary disturbance, but for a diagnosis, at least 2 of the following visual symptoms must also be present:

• AFTERIMAGE ‘STAINING’ & LINGERING TRAILS
  Patient experiences prolonged ‘staining' of an image in their visual field after stimuli is removed. Moving objects may leave ‘ghost-like’ trails.
• HYPER-AWARENESS OF INTERNAL EYE ENVIRONMENT:
  Normal and typically benign ‘floaters’ are prominent to the patient, noticeably moving across the vitreous eye fluid, interfering with perception. Similarly, patients may also notice fast-moving, luminous dots (correlated to normal white blood cell movement in retinal capillaries) which are reported as particularly noticeable against bright, monochromatic backgrounds (e.g., clear blue sky).
• INTERNAL LIGHT FLASHES:
  Perception of brief, unprovoked flashes or bursts of light originating internally, sometimes referred to as ‘self-light’ from the eye. Can also occur with eyes closed.
• LIGHT SENSITIVITY (PHOTOPHOBIA):
  Patient experiences increased sensitivity to light, ranging from discomfort to physical pain, even in normal lighting conditions.
• SIGNIFICANTLY POOR NIGHT VISION:
  Significant visual impairment in low-light or dark environments, exceeding that of typical individuals.

Considerations and medical exclusions:

Migraines, eye abnormalities, drug abuse, use of psychedelics or hallucinogens, or mental conditions with psychotic symptoms should be ruled out. Following this, a PET scan can potentially show areas of the brain that are unusually active, generally in visual processing centres, which can be a sign of VSS. However, the exact neurological mechanism(s) causing VSS require further research.

HALLUCINOGEN PERSISTING PERCEPTION DISORDER (HPPD):

A subject may be diagnosed with HPPD if they experience one or more of these symptoms:

• VISUAL SNOW:
  Patient may see noticeable or bothersome visual static, as described in VSS. Often reported as more intense or disturbing by subjects.
• PERSISTENT VISUAL DISTORTIONS:
  Objects and spaces may appear warped, shimmering, and altered or fluctuating in size.
• INTENSIFIED/SHIFTING COLOURS:
  Colours appear unnaturally vibrant, oversaturated, or shift in hue, often to an overwhelming degree.
• AFTERIMAGE 'STAINING' & LINGERING TRAILS:
  Typically more prolonged and intense than in VSS. Object trails may mimic the patterns or visual effects experienced under the catalyst substance.
• LIGHTING DISTORTIONS, HALOS & AURAS:
  Subjects describe light sources emitting an aura-like bloom, rings or ‘halos’, and long streaks extending from their centre, akin to lens flares.
• GEOMETRIC PATTERN OVERLAY:
  Faint grids, subtle fractals or complex patterns may appear to be superimposed on detailed surfaces (e.g., knitted fabric, skin texture, hair).
• ‘BREATHING’ WALLS: Stationary rooms or surfaces appear to visually shift, undulate, subtly expand and contract. This is sometimes expressed by subjects as walls ‘flowing’ or ‘melting’.

Considerations and medical exclusions: