Subjective Visual Disturbances (SVD) — Parameter Reference v1.0 · 2026

$V_{SVD}$ — Eleven Symptom Domains

$$V_{SVD} = [V_{ST},\ V_{CL},\ V_{FL},\ V_{BF},\ V_{LA},\ V_{GE},\ V_{DC},\ V_{DS},\ V_{TI},\ V_{CVD},\ V_{VF}]$$

• $V_{ST}$ — Visual Static
• $V_{CL}$ — Contrast Loss
• $V_{FL}$ — Floaters
• $V_{BF}$ — Blue Field Entoptic
• $V_{LA}$ — Light Anomalies
• $V_{GE}$ — Glowing Edges
• $V_{DC}$ — Difference Clouds
• $V_{DS}$ — Distortions
• $V_{TI}$ — Tinnitus / Auditory
• $V_{CVD}$ — Color Vision Deficiency domain
• $V_{VF}$ — Visual Field Loss domain

Two identifiers per parameter: The Code column (e.g., ST-01) is a stable, language-neutral label for use in research papers and clinical communication — it never changes even if the app is refactored. The JSON field column (e.g., snowIntensity) is the actual field name used in JSON serialization and the app's database. When writing a paper, cite the code. When writing code or JSON, use the JSON field name.

Implementation Guidelines

Systems wishing to align with this specification should:

• Store each parameter using the specified data type (Float32 = IEEE 754 single, Integer, Boolean, Enum, or ARGB Long).
• Clamp or reject values outside the stated [min, max] range at the point of input.
• Use the JSON field names (e.g., snowIntensity) as JSON keys when serializing session data — these match the app's SymptomLog schema exactly. The ISO-style codes (e.g., ST-01) are stable documentation labels for use in research papers and cross-system communication, not serialization keys.
• Not transmit session data to external servers without explicit user consent.

Partial implementation is supported: a system may implement a subset of the eleven domains, as long as it declares which domains are covered. This specification has no formal certification process — alignment is voluntary.

Data Storage & Privacy

The Visual Snow Simulator operates on a Zero-Knowledge Architecture.

• Local Only: All session data, $V_{SVD}$ parameters, and medical history are stored in an isolated local database. No cloud sync.
• No Network Transmission: The application does not have the network permissions required to send symptom data externally.
• Full Deletion: Uninstalling or using "Delete All Data" in the About screen permanently removes all local records.

$V_{ST}$ — Visual Static Domain

Persistent visual noise across the entire visual field — the defining symptom of Visual Snow Syndrome (Schankin et al., 2014). Phenomenologically analogous to noise on an untuned analogue television.

$V_{CL}$ — Contrast Loss Domain

Perceived reduction of luminance dynamic range, reported as washed-out or low-contrast vision. Related to WHO ICF code b21022 (Contrast sensitivity).

$V_{FL}$ — Floater Domain

Distinct opacities within the vitreous or perceptual field. In SVD context includes both true vitreous floaters and cortical/entoptic equivalents. Tracked separately from static because floater burden follows different trigger patterns.

$V_{BF}$ — Blue Field Entoptic Domain

Scheerer's phenomenon — hyper-aware visualization of leukocytes moving through retinal capillaries. Perceived as small bright dots traversing the visual field, most prominent on blue sky or uniform bright backgrounds.

$V_{LA}$ — Light Anomalies Domain

Aberrant interactions with light sources: aura, scotoma, photopsia, glare (starburst), and halo phenomena. These have distinct clinical subtypes and timing profiles from baseline static.

$V_{GE}$ — Glowing Edges Domain

Edge-contour luminance emphasis and bleed; perceived as glowing outlines around objects and high-contrast boundaries.

$V_{DC}$ — Difference Clouds Domain

Non-point, spatial-frequency dynamic haze textures perceived across the visual field; distinct from discrete-particle static.

$V_{DS}$ — Distortions Domain

Temporal and spatial misalignments: diplopia (double vision), palinopsia (afterimages/trailing), visual vibration, oscillopsia, and Charles Bonnet-type hallucinatory phenomena. Clinical palinopsia subtypes per Gersztenkorn & Lee (2015): Hallucinatory is associated with cortical/neurologic pathology; Illusory occurs in VSS without structural lesion.

$V_{TI}$ — Tinnitus / Auditory Domain

Auditory co-symptom overlay. Tinnitus is a recognized concurrent symptom in an estimated 40–60 % of VSS patients in published cohorts.

$V_{CVD}$ — Color Vision Deficiency Domain domain

Simulation of color vision deficiency as a co-occurring or standalone visual impairment. Supports congenital (hereditary) and acquired CVD phenotypes.

$V_{VF}$ — Visual Field Loss Domain domain

Peripheral or hemi-field vision loss patterns. Includes hemianopia (half-field loss following retrochiasmal pathology) and tunnel vision (concentric peripheral constriction).

Session Metadata (Recommended)

The following contextual fields are RECOMMENDED in session snapshots alongside $V_{SVD}$. All are persisted in SymptomLog.

Medical History Context Fields

Optional self-reported checklist items. These are relevance signals for pattern exploration and shall not be interpreted as diagnostic conclusions.

Potential Standardization Path

This is an open specification today. If clinical adoption grows, the path toward formal standardization is described in the full specification document. The immediate priority is research use and community feedback, not standardization itself.

This VSS/SVD-specific vector matrix is the reference implementation feeding into a broader, condition-agnostic effort: the Open Visual Symptom Standard (OVS), published at openvisual.org. Where this page documents the VSS app's concrete parameters, OVS defines the general schema hierarchy (visual noise, field defects, optical aberrations, persistence, hallucination, spatial distortion, entoptic, color perception, auditory) that this domain vector is a profile of.