Prevalence of photoparoxysmal response and the significance of sex steroid hormones in epilepsy

I read with keen interest the article titled ‘Prevalence of photoparoxysmal response among South Indian epilepsy patients’ published in Seizure1. Although the authors appropriately conclude by saying that methodological issues have to be taken into consideration while designing studies on photoparoxysmal response (PPR), they fail to mention the duration of the photic train while doing intermittent photic stimulation (IPS). In the protocol by Bickford2, flashes at 1, 3, 6, 9, 10, 15, 20 and 30 Hz each are given in trains of 5 s duration, both with eyes open and closed in a dimly illuminated room. Further, in the methods, the authors have performed IPS with a linear pattern placed in front of the patient with eyes open and photic stimulator angled to the pattern. It should be mentioned here that, when IPS is done with eyes open, careful attention has to be given to eye movement and position since a directional change from primary fixation to lateral gaze diminishes the effect of IPS in evoking PCR3, 4. The authors tested for pattern sensitivity (without IPS) by ‘moving in front of the eyes eight different patterns on a white background’. Moving patterns in front of patient’s eyes, I strongly feel, will cause lateral movement of eyes which would definitely diminish the effect in evoking photoconvulsive response (PCR). This may be the reason for none of the PPR cohorts showing pattern sensitivity in the authors’ series. The excitatory effect of patterns on photic driving can be easily demonstrated by placing the pattern on the strobe light when IPS is given to the subject with eyes open. The strobe is covered by a sheet of thin translucent plastic film with a printed pattern (dot, checkerboard, grate etc)5. It would have been better, had the authors used the previously mentioned method for pattern sensitivity. The prevalence rate of PPR (3.5%) reported by the authors showed a distinct male : female ratio of 1 : 4. In the discussion section, the authors do not offer any explanation nor implication of their observations. They conclude by saying that prevalence rates of photosensitivity are influenced by the patient cohort characteristics, such as distribution of age, gender etc.