In certain epilepsy syndromes, uncommon electroencephalogram (EEG) patterns linked
to oculo-visual responses may yield valuable diagnostic clues. A 16-year-old boy presented
with a history of generalized tonic-clonic seizures spanning 4 years. Birth and developmental
milestones were normal prior to seizure onset. He denied myoclonic jerks but reported
a doubtful history of absences. There was no family history of seizures. He was on
carbamazepine with poor seizure control. EEG showed normal background activity with
generalized, frontally dominant polyspike and wave discharges at a frequency of 3 Hz.
Interestingly, eye closure activated generalized epileptiform discharges, which persisted
until eye opening suggesting eye-closed sensitivity ([Fig. 1A]). Photic stimulation revealed a grade IV photo paroxysmal response at 20 Hz ([Fig. 1B]). Magnetic resonance imaging was normal. A diagnosis of idiopathic generalized epilepsy
(IGE), likely juvenile absence epilepsy (JAE), was made, and he was switched to sodium
valproate, resulting in good seizure control.
Fig. 1 (A) Electroencephalogram (EEG) recorded in an average reference montage demonstrates
posterior dominant spike-and-wave discharges (blue arrow) and generalized spike-and-wave
discharges (red arrow) persisting throughout eye closure. The epileptiform activity
is suppressed upon eye opening and reemerges with eye closure. (Average reference
montage: Time base: 30 mm/sec; Sensitivity: 14 uV/mm; High pass filter: 0.3 s; Low
pass filter: 70 Hz.) (B) EEG recorded in average reference montage demonstrates a reproducible grade IV photoparoxysmal
response elicited by photic stimulation at 20 Hz. (Average reference montage: Time
base: 30 mm/sec; Sensitivity: 40 uV/mm; High pass filter: 0.3 s; Low pass filter:
70 Hz).
Epileptiform EEG patterns triggered by eye closure have been categorized into three
related phenomena: eye closure sensitivity (ECS), eye-closed sensitivity, and the
related term fixation-off sensitivity (FOS). Of these, ECS is more frequent and refers
to brief generalized or occipital epileptiform discharges occurring within 2 to 4 seconds
of eye closure, typically lasting 1 to 4 seconds, and not persisting throughout the
eye-closed state ([Fig. 2]).[1] It has been reported in eyelid myoclonia with absences, idiopathic generalized epilepsies—notably
juvenile myoclonic epilepsy, JAE, childhood absence epilepsy, and idiopathic occipital
epilepsies.[1]
[2]
[3] Studies have associated ECS with poorer seizure control and drug-resistant epilepsy
in IGE.[3]
Fig. 2 Comparative example of eye-closure sensitivity in a 22-year-old patient with idiopathic
generalized epilepsy. Electroencephalogram (EEG) recorded in reference montage reveals
transient generalized epileptiform discharges consistently triggered by eye closure,
lasting approximately 2 seconds post-eye closure. (Average reference montage: Time
base: 30 mm/sec; Sensitivity: 14 uV/mm; High pass filter: 0.3 s; Low pass filter:
70 Hz.)
In contrast, eye-closed sensitivity is a relatively rarer phenomenon, characterized
by epileptiform discharges that begin immediately upon eye closure, persist throughout
the eye-closed state, and cease with eye opening.[1]
[4] Given its link to visual fixation, the term FOS has been used interchangeably.[5] FOS is elicited by eliminating central visual fixation with techniques that include
the use of Frenzel goggles, diffusing filters, or eye closure in dim light—allowing
ambient light while preventing central fixation. Eye-closed sensitivity/FOS typically
manifests as persistent posterior or generalized discharges that begin shortly after
eye closure and persist for the duration of fixation loss, disappearing immediately
upon eye opening or restoration of fixation.[1]
[2]
[5] Eye-closed sensitivity/FOS are classically described in childhood occipital epilepsies
but have been associated with IGE and occipital lesions too.[1]
[2]
[5]
[6] Patients with eye-closed sensitivity have demonstrated a greater persistence of
these abnormalities with advancing age compared to those with ECS.[1] Associated photosensitivity maybe less frequent in eye-closed sensitivity/FOS compared
to ECS.[1]
[6] In rare instances, both ECS and eye-closed sensitivity/FOS have been reported in
patients with IGE.[2] The prognostic implications of eye-closed sensitivity/FOS remain unclear and warrant
further investigation.
Photosensitivity, ECS, and eye-closed sensitivity/FOS represent distinct reflex epileptic
phenomena mediated by occipital hyperexcitability, though they may overlap in clinical
and EEG presentations. A clearer understanding of their appearance and elicitation
techniques can aid accurate EEG interpretation and epilepsy diagnosis.