A Single-blind, Placebo-controlled, Outpatient Trial to Assess the Effects of Single Oral Tablet Dose of OPC-214870

• Male and female subjects between 18 and 64 years of age, inclusive.
• Body mass index (BMI) between 18 and 40 kg/m\^2, inclusive.
• Subjects with a diagnosis and history of photoparoxysmal response on EEG.
• Subjects must be stable for 1 month prior to screening. Stable is defined as having no change in concomitant therapy and no worsening in the opinion of the investigator.
• Subjects may be treatment-naïve to AEDs or currently treated with up to 3 AEDs.
• Subjects must have a reproducible standardized photosensitivity range on EEG of at least 3 points in at least 1 eye condition.
• Subjects who agree to remain abstinent, or practice double-barrier forms of birth control, from trial to screening through 90 days after the last dose of IMP, OR males and females of non-childbearing potential who are documented as sterile (i.e. male subjects who have undergone bilateral orchidectomy and female subjects who have undergone bilateral oophorectomy, bilateral salpingectomy, or hysterectomy, or who have been postmenopausal for at least 12 months.

Exclusion Criteria:

• History of non-epileptic seizures
• History of status epilepticus in the past 5 years
• An active central nervous system (CNS) infection, demyelinating disease, degenerative neurological disease, or any CNS disease deemed to be progressive during the course of the trial that may confound the interpretation of the trial results.
• Positive urine drug screen for substance of abuse or upon check in to the trial site. Benzodiazepines are excluded as a drug of abuse, but are allowed as rescue medication or when part of subject's stable concomitant medication at enrollment.
• History of drug and/or alcohol abuse within 24 months prior to screening.
• Consumption of grapefruit, grapefruit juice, Seville oranges, or Seville orange juice within 7 days prior to dosing.
• Consumption of more than 1 alcoholic drink within 24 hours prior to dosing. Food and beverages containing methylxanthines (caffeinated coffee, caffeinated tea, caffeinated soda, and chocolate) must remain stable throughout the trial.
• Extreme physical activity within 24 hours before screening and visit
• Females who are breast-feeding and/or who have a positive pregnancy test result prior to receiving IMP
• Subject having taken an investigational drug within 30 days preceding screening.
• Use of over-the-counter drugs, herbal medicines, or vitamin supplements within 14 days or 5 half-lives, whichever is longer, prior to dosing and antibiotics within 30 days prior to dosing.
• Subjects who had neurosurgery in last 6 months.
• Subjects on a ketogenic diet.
• History of significant sleep disorders, or any disorder or activity that causes sleep deprivation.
• Subjects who work "night shifts"
• Subjects with uncontrolled sleep disorders; subjects should be on a stable dose of sleep medications.
• History of, or current hepatitis or acquired immunodeficiency syndrome or carriers of hepatitis B surface antigen (HBsAg), hepatitis C antibodies (anti-HCV), and/or HIV antibodies.