Efficacy of New Lenses in Abolishing Photoparoxysmal Responses in Paediatric Patients With Photosensitive Epilepsy (PSE)

1. BACKGROUND

Photosensitive epilepsy (PSE) is the most common of reflex epilepsies and represents approximately 10% of all new cases of epilepsy in the age range 7-19 years (Harding & Jeavons, 1994). Photosensitivity is the nuclear feature of PSE, in which seizures are provoked by light stimuli or visual patterns, such as lines, gratings or checkerboards (Yalçin, Kaymaz, & Forta, 2000)(Fisher, Harding, Erba, Barkley, & Wilkins, 2005). Therefore, usual external triggers of seizures in the daily life of patients with PSE are sunlight and screens, like televisions (TVs), video games and computer displays. Photic/pattern sensitivity can be detected on the electroencephalogram (EEG) by the presence of a specific abnormality, called the 'photoparoxysmal response' (PPR), which is usually evoked by intermittent photic stimulation (IPS) or pattern stimulation, respectively (Quirk et al., 1995). Red color (wavelength around 600-700nm) has been proposed to be the most provocative stimulus among the primary colors to trigger photosensitivity/pattern-sensitivity in these patients (Fisher et al., 2005)(Guerrini & Genton, 2004).

There are certain preventive measures to avoid triggering external stimuli which are particularly useful in PSE patients, but pharmacological treatment is required when seizures are not controlled by preventive measures or when photic or pattern-induced seizures coexist with spontaneous seizures. However, adverse effects of antiepileptic drugs (AEDs) and the relapse percentage after medication withdrawal, which may be nearly 50% (Verrotti et al., 2014), drove investigators to seek other therapeutic alternatives, such as the use of blue lenses that filter out red light. To date, the most extensively investigated lens has been Zeiss Clarlet Z1, which abolished PPRs in 75.9% of 610 patients (Giuseppe Capovilla et al., 2006). This effect was accounted for by the spectroscopic profile of Z1, that shows the minimal transmittance for the spectrum of red color (600-700 nm) (G Capovilla et al., 1999) and a luminous transmittance for the visible spectrum (τν) around 7%.

However, Z1 transmittance characteristics have two main limitations for its use in everyday life: 1) it is a very dark lens and not practical in high-latitude regions, where the number of sunlight hours is reduced; 2) its lack of transmission in the red and yellow parts of the spectrum determines that people using Z1 are almost completely exposed to blue visible light, which has been associated with the appearance of ophthalmological diseases in the long term, such as age-related macular degeneration (AMD) ("blue-light hazard" phenomenon) (Mainster, 2006). 2. RATIONALE

In light of these limitations, we hypothesized that a new type of lenses created by improving some spectral characteristics of Z1 could also be helpful for patients with PSE. This is the reason why we have designed four new lenses at the Aston Brain Center (ABC, Aston University) in collaboration with the Aston University Vision Sciences Department. These new lenses were firstly tested in those patients with PSE referred to the ABC between 2008-2017, when this center was the referral site in West Midlands to perform an EEG with photic/pattern stimulation.