Mushroom eye When it comes to substance abuse, the adage “the eyes are windows to the soul,” rings especially true. When a person is under the influence, several changes in the eyes can be observed: they’d appear bloodshot and dilated, with the pupils moving rapidly and involuntarily. what happens to eyes on shrooms as well as other substances to help you detect signs of addiction. Marijuana Marijuana, also known as cannabis, contains a psychoactive constituent called tetrahydrocannabinol  THC lowers blood pressure, triggering the increase of blood flow and the dilation of blood vessels. Lowered blood pressure causes the blood vessels in the eyes to expand, leading to redness or bloodshot eyes. Marijuana also slows down the brain’s image-processing function. Under the influence of marijuana, hand-eye reflexes are reduced and spatial perception is disrupted. Pupil dilation provoked by cannabis can create imbalances and dazzlements between far vision and near vision. This effect is especially apparent among those who wear multifocal contact lenses, and those who have had laser surgery such as Lasik, PRK, Lasik, Relex, or Smile.