The sympathetic nervous system is what activates the iris dilator. The Parasympathetic & Sympathetic Nervous SystemsĪs Scientific American writes, the body’s parasympathetic nervous system (which also controls the body’s autonomic processes when the body is at rest) is responsible for triggering the iris sphincter response. These factors can include certain types of drugs (recreational or medicinal), alcoholic beverages, and physiological reactions, such as fear or sexual arousal. Under these conditions, abnormal pupil dilation is known as mydriasis. That is how pupils should normally work, but there are other factors that can cause pupils to dilate. In darker conditions, the pupils get larger (or dilate) to let as much light as possible in. In bright conditions, the pupils get smaller (constrict) to make sure that the eyes are not damaged by too much light. Pupil size is controlled by two muscles in the iris (the iris sphincter and the iris dilator), as well as the amount of light that is directed at the eyes.

When a pupil is dilated, it is larger than it normally should be. Most often, this is caused by concussion, PTSD, head or eye injuries, and substance abuse.Ī combination of corrective surgery, protective lenses, and medication can restore the proper functioning of the pupil. Pupils should return to their normal size when the stimulus passes, but some conditions can keep the pupil stuck in its dilated state, causing pain, dry eyes, and difficulty focusing. This usually occurs to see better in poor conditions, but it can also occur because of excitement, fear, or sexual arousal. Pupil dilation is the result of the two muscles in the iris working in tandem to enlarge the pupil. They also offer some protection from harmful light levels. Prosthetic contact lenses create the appearance of having normal sized pupils, even if the pupils themselves are actually still dilated. They can also help to improve the appearance of the eyes (albeit only cosmetically) for people who have concerns about how their dilated pupils might appear to others.

Alternately, sunglasses with polarized lenses will reduce the glare from bright lights.Ĭustom prosthetic lenses can reduce the sensitivity to light caused by dilated pupils. While there are medications and treatments to address this problem, these patients can also use eyeglasses with photochromic lenses, which automatically darken in bright light conditions to protect the eyes from too much light. People who have dilated pupils will be more sensitive to sunlight (or bright lights in general), since their pupils cannot constrict to protect the eyes from exposure to too much light. If treatment is not received, these can become long-term problems. This can cause a number of undesirable effects, including pain in the eyes, vision problems, headaches, dizziness, confusion, and difficulty balancing and coordinating movement. When the dilation is caused by drugs, alcohol, an injury to the eye or head, or another condition that requires medical assistance, the pupils may not return to their undilated state. It will likely pass when the external stimulus is no longer in the picture. In many cases, pupil dilation is a natural response to poor lighting conditions, fear or shock, or interest (sexual or otherwise). The Parasympathetic & Sympathetic Nervous Systems.Implantable Miniature Telescope Surgery.

Blown pupil causes