Dilation is an essential part of a comprehensive eye examination. It is necessary to diagnose and monitor many medical conditions. Most patients ask why dilation is needed, what are the side effects, and how it works. The intention of this article is to answer the questions patients have about dilation.

Essentially, the main reason eye doctors use dilation drops is that it allows them to examine the eyes posterior segment. More specifically the retina, retinal blood vessels, optic nerve, vitreous, and lens. Common conditions that affect these areas of the eye include diabetes, high blood pressure, high cholesterol, vascular disease, glaucoma, cataracts, macular degeneration, and many more. When a patient complains of blurry vision and cannot be corrected appropriately with glasses, dilation should be used to rule out underlying posterior segment disease. With advancing technology, retinal photography machines can now image the posterior segment. These imaging techniques are great tools to diagnoses and monitor posterior segment disease, but do not replace the need for a dilated exam. Another reason your eye doctor may dilate your eyes is to ensure your eye prescription is accurate. Naturally, our eyes have a muscle that helps us focus the lens of our eye. Farsighted patients use that muscle to see clearly, but over time that muscle can become fatigued thus causing blurry vision and eye strain. To ensure farsighted patients are not over focusing, a dilated (also known as cycloplegic) refraction may be indicated. The last reason your doctor may dilate your eye is for medical treatment. Pharmacologically, dilation drops help to reduce pain from inflammation of the posterior segment (specifically the ciliary body), prevent the iris from sticking to the lens (also known as synechiae during inflammation), and decrease the permeability of an inflamed blood vessel. Uveitis is a common condition where dilation drops are used as medical treatment.

Dilation drops are considered a pharmacologic medication. As with any medications on the market today, there are common and rare side effects associated. There are two main eye drops used for dilation. The first class of dilation drops commonly used are called cholinergic antagonists. The intention of this class of medications to relax the iris sphincter and ciliary muscles. The other main class of eye drops used are an adrenergic agonist, which stimulate the iris dilator muscle. A combination of these two eye drops is used to give optimum dilation results. The physiology of this mechanism involves the parasympathetic nervous system for cholinergic antagonists (muscarinic receptors) and the sympathetic nervous system for adrenergic agonists (alpha receptors). Common ocular side effects of these medications include transient stinging upon instillation, temporary photophobia, and temporary blurred vision, which typically lasts for a few hours. Rare ocular side effects include allergic reactions, dry eye, and angle closure. The main question patients ask is “How long will dilation last?” Answering that questions depend on the number of drops used, the concentration of the drops, type of drops, and the patient ability to metabolize the drops. Typically the common dilation will last about 4-6 hours. Although dilation may have some temporary side effects, it is sometimes necessary to ensure proper ocular health.

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