The photoparoxysmal response (PPR) is an epileptiform electroencephalographic (EEG) phenomenon triggered by intermittent photic stimulation. It is used to assess photosensitivity in individuals with epilepsy. However, wide variations in interpretation and inconsistent methodological practices have led to unreliable detection and classification of PPR, potentially affecting the management of photosensitive epilepsy. In regions with limited resources, the lack of standardized protocols, challenges with EEG equipment, and restricted access to specialized training further exacerbate diagnostic uncertainty.

Despite multiple efforts to create guidelines for intermittent photic stimulation, the interpretation of PPR remains highly subjective, with only fair to moderate interrater agreement even among experienced specialists. One principal point of contention is differentiating truly stimulus-evoked activity from spontaneous epileptiform discharges. This ambiguity is clinically significant because determining photosensitivity influences lifestyle recommendations and treatment choices. Current classification systems for PPR establish broad categories of abnormal EEG activity, but they lack detailed operational criteria. There is no universal rule for the minimal duration of an abnormal discharge or the acceptable delay from stimulus onset. Additionally, narrowly incrementing photic stimulation frequencies may not always clarify borderline discharges. As a result, technicians and clinicians may prematurely terminate stimulation or misinterpret ambiguous findings, leading to inconsistent diagnoses. Operational criteria focusing on morphology, amplitude, duration, time lag from stimulus onset, and repetition across multiple frequencies could offer a more objective framework. This approach parallels other EEG elements that have benefited from standardized definitions, illustrating the potential to improve interrater reliability through uniform guidelines.

Establishing clear operational criteria for PPR interpretation is vital for consistent diagnosis, research comparability, and optimized clinical care. A concerted effort from the epilepsy community to implement and refine these criteria would help resolve the current variability, ensuring that individuals with potential photosensitivity receive accurate assessment and appropriate management.

A.G.A.: Conceptualization, supervision, and writing - original draft preparation. F.V.V.V., I.M.M.R., J.M.B., and F.J.T.A.: Resources and writing - reviewing and editing. A.E.Z.: Writing- reviewing and editing. All authors commented on the manuscript and approved it.

Article published online:
18 March 2026

© 2026. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. (https://creativecommons.org/licenses/by/4.0/)

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