Effects of opiates and opioids on intraocular pressure of rabbits and humans

Acute intraocular injection of morphine or D-Ala-met-enkephalinamide (D-Ala-E) in rabbits caused a sustained decrease in intraocular pressure. Conjunctival instillation of naloxone solution prevented the lowering effect of morphine or D-Ala-E on intraocular pressure. Aqueous outflow facility appeared to be significantly higher in patients addicted to morphine or heroin than in healthy volunteers. Intraocular pressure was significantly lower in addicted patients than in control subjects. Conjunctival instillation of naloxone solution decreased aqueous outflow facility and increased intraocular pressure in addicted patients. Patients with chronic open angle glaucoma showed a significant decrease in intraocular pressure after conjunctival instillation of morphine solution. It is concluded that intraocular opiate receptors are involved in the regulation of intraocular pressure in animals and humans.