Photosensitive epilepsy safety

This is the most important page in the EMDR section. Read it before running your first BLS set, and re-read it any time you’re working with a new client.

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The 2.0 Hz hard cap

Rivet’s BLS speed control runs from 0.3 Hz to 2.0 Hz. The 2.0 Hz ceiling is not a UI suggestion — it’s a hard cap enforced in three places:

1. On your device — the practitioner’s Configure modal clamps the slider value before sending it over the data channel.
2. On the client’s device — the BLS client renderer clamps every incoming configuration before applying it.
3. On Rivet’s server — the preferences API rejects any persisted value above 2.0 via the clampBlsConfig() function in the BLS types module.

You cannot exceed 2.0 Hz through the UI, through DevTools, through URL parameters, or through a custom request body. The constant is defined once as CLINICAL_BOUNDS.speed_hz.max = 2.0 and every layer routes through it.

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Why 2.0 Hz

Two converging constraints set the ceiling: Clinical norm. Every published EMDR and EMDR 2.0 protocol stays at or below 2 Hz (van Veen 2015, Maxfield 2008, de Jongh / Matthijssen materials). Faster rates aren’t part of the validated protocols. Photosensitive seizure safety. Sustained visual flicker at or above 3 Hz is the threshold associated with photosensitive seizures in susceptible individuals — this is the WCAG flicker guideline and the photic-stimulation literature consensus. 2.0 Hz sits comfortably below that threshold. The cap is where the two constraints meet. It’s the highest rate the clinical literature uses and well below the rate flicker becomes a seizure-risk surface.

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The first-use warning modal

The first time you opt into BLS for a session, a warning modal surfaces before any stimulus runs. The modal copy:

⚠ Photosensitive seizure warning Bilateral visual stimulation uses a moving dot at up to 2 Hz. A small percentage of people may experience seizures triggered by visual flicker or moving patterns, including those with no prior history. Screen for photosensitive epilepsy, recent concussion, active migraine with aura, severe vestibular disorder, or recent eye surgery before starting visual BLS. If your client reports any visual discomfort, headache, dizziness, or unusual sensation, stop the set and switch to audio or tactile modality. I understand — continue

The modal blocks the Workspace until you tap I understand — continue. The acknowledgment is recorded in your browser’s localStorage for your practice so the modal doesn’t reappear session to session — but every practice surfaces it the first time, including new browsers, new devices, and after you clear browser data. Pressing the spacebar or tapping the corner badge while the warning is unacknowledged opens the modal — you can’t bypass it by trying to start the set with a different control.

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What to screen for

Standard photosensitive-epilepsy informed-consent items. None of these are hard contraindications by themselves — clinical judgment applies — but they are the categories the warning copy enumerates and the categories every EMDR training program covers:

• Photosensitive epilepsy — known history of seizures triggered by visual flicker or moving patterns. This is the primary contraindication.
• Recent concussion — within the last 30 days or with ongoing post-concussive symptoms. Visual tracking and bilateral stimulation can exacerbate symptoms during recovery.
• Active migraine with aura — visual aura migraines have shared sensitivities. A client with frequent visual aura should not run visual BLS during an active migraine cycle.
• Severe vestibular disorder — vertigo, Ménière’s disease, benign positional vertigo. Moving visual stimuli can trigger or worsen symptoms.
• Recent eye surgery — within the last 90 days, or as advised by the surgeon. Sustained visual tracking is not appropriate during recovery.

If any apply, switch the visual modality off in the Configure modal and run audio-only or audio + haptic. Audio and haptic do not carry photosensitive seizure risk.

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What to do mid-set if a client reports symptoms

The client reports a headache, dizziness, visual discomfort, an unusual sensation, or just says “this doesn’t feel right.”

1. Stop the set immediately. Press Space, tap the badge, or click End set. The stimulus stops on the client’s canvas within one frame.
2. Check in with the client. Ask what they’re experiencing. Open space for them to describe what shifted.
3. Reconfigure before the next set. Open the Configure modal, switch the visual modality off, and continue with audio or haptic. Lower the rate. Switch the dual-task category. Whatever the clinical read calls for.
4. Document. Note what happened in your session record. If the reaction was significant, document it in your chart and consider whether visual BLS is appropriate for future sessions.

This is standard EMDR clinical practice. The warning modal copy points to it; the Workspace’s controls let you act on it in seconds.

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Why visual specifically

Photosensitive seizure risk is a visual flicker phenomenon. Audio bilateral stimulation does not carry the same risk — there’s no clinical literature linking alternating-pan audio to seizures. Haptic stimulation (phone vibration) likewise does not carry photosensitive seizure risk. If you have any concern about visual BLS for a given client, the audio and haptic modalities run independently. EMDR 2.0 in particular was designed for multimodal stimulation precisely so visual isn’t required — audio + haptic at 1.5 Hz delivers bilateral stimulation without the visual surface.

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Documentation and consent

Rivet’s warning modal is an informed-acknowledgment surface for the practitioner. It is not a substitute for getting the client’s informed consent before EMDR. Your usual consent process — including the visual modality, the rate range, and what to do if symptoms arise — is the clinically authoritative consent layer. The modal is there as a backstop. If your practice uses a written EMDR consent form, the categories above (photosensitive epilepsy, concussion, migraine with aura, vestibular, recent eye surgery) are the typical screening items to include.

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