Ancient Greece & Rome,
Slave traders used a rotating potter's wheel as a provocative medical screening
❶Documentation
-If normal:
>Symmetric posterior driving
>No epileptiform discharges
>No clinical correlate
-If abnormal:
>Type of photoparoxysmal response (PPR)
>Triggering frequency (range)
>Clinical correlate: absent/ present (semiology)
>Persistent beyond stimulation
❷Setup
-Informed consent
-Stop IPS, if discahrges
-Caution in genetic and photosensitive generalized epilepsies, especially JME
-Circular-reflector stimulator, at 30 cm from nasion and 0.7 intensity
❸Protocol
*IPS should be performed 3 min after HV, or before HV
1)Hz: 1→2→8→10→15→18→20→25→40→50→60
2)Eye: closure→closed→open
*Eye closure is the most provocative
3)If PRR occurs, stop ascending sequence
4)Restart from 60 Hz descending to determine range
❹Photic driving
-Occipital/post leads (MC)
-Usually: symmetric, post predominant, and non-epileptiform
-Components: harmonic (2x) and subharmonic (1/2)
E.g.: if 10 Hz stimuli, harmonic is 20 Hz response, and subharmonic 5 Hz
❺Photomyogenic response (PMR)
-Ocular artifact: frontal blinked related deflection
-PMR:
>Time-locked frontotemporal muscle resposne
>Stops when stimulation ends
❻PPR
-Spike-wave or polyspike-wave discharges, often generalized; can persitent beyond stimulation
-PPRs range from post discharges to generalized responses
❼Considerations
ⓐ Does absent photic driving indicate abnormal brain function?→No
-Normal physiological occipital response
-Influenced by: retinal illumination and drowsiness
ⓑWhy IPS w/ eyes open, closure, and closed?→ ≠conditions
-Open→ preserved visual fixation
-Closure→ detect eye-closure sensitivity (ECS) in eyelid myoclonia (Jeavons syndrome)
>brief epileptiform discharges immediately after closing, within 1–3 seconds
-Closed→ fixation-off sensitivity (FOS), mainly in occipital epilepsies