> ## Documentation Index > Fetch the complete documentation index at: https://docs.getrivet.ca/llms.txt > Use this file to discover all available pages before exploring further. # Photosensitive epilepsy safety > The 2.0 Hz hard cap on bilateral visual stimulation, the first-use warning modal, what to screen for, and what to do mid-set if a client reports symptoms. Bilateral visual stimulation uses a moving stimulus at up to **2.0 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 during a set, **stop the set immediately** and switch to audio or tactile modality. 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. ## 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, and it holds wherever the speed can be set: 1. **The Configure modal** — the slider clamps before anything starts. 2. **The stepper during a running set** — nudging speed mid-set clamps the same way. 3. **Anything stored** — a saved setting above 2.0 is brought back inside the range before it can take effect. You cannot exceed 2.0 Hz through the controls, through browser developer tools, or through a link. ## 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. ## 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 saved in your browser 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. What the modal does not do is screen your client. Rivet shows the warning before the first set; deciding whether photosensitive epilepsy, a recent concussion or a migraine history rules visual BLS out for this person, on this day, is your judgement, exactly as it is in the room. ## 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 the set on sound, with taps in your client's hand if they've paired a phone. The set runs against a calm backdrop with no moving stimulus at all. Neither sound nor taps carry photosensitive seizure risk. ## 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 your client's screen as you do it. 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. ## 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. ## 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. ## Related articles The stimulus parameters, including the 0.3 to 2.0 Hz speed range and the auto-vary toggle. The audio modality — no photosensitive seizure risk; useful when visual is contraindicated. Broader contraindications beyond the photosensitive-epilepsy screening — when EMDR overall is not the right tool.