The pupil of the eye is the opening of the eye through which light enters the eye. Without dilatation, the specialist will see only a small area of the retina, especially in the elderly [because pupil size decreases with age]. Dilating drops are instilled to dilate the pupil to facilitate a more thorough examination of the peripheral part of the retina, lens and vitreous humour. A thorough retinal examination not only provides clues about your retinal health but also about your overall health and signals evidence of many systemic diseases before their symptoms show up elsewhere in your body.
This opacification of the normally clear lens of the eye mainly forms in older adults, but anyone is susceptible. A dilated exam can aid the evaluation of cataracts. By increasing the pupillary diameter, patients with centrally located cataracts may experience significant improvement in visual acuity. Daily use of dilating drops may forestall the need for cataract extraction in patients at surgical risk.
Retinal Tears and Detachment
A detached retina usually occurs when there is a tear or a hole in the retina, allowing fluid to diffuse behind it and push the retina away from the wall of the eye. Good outcomes are dependent on early detection and repair. A dilated eye exam may be the only means of detection in many cases.
Optic Nerve Disease
The optic nerve is the bundle of nerves that transmits signals from the retina to the brain. When it becomes damaged or swollen from disease, sight is lost because the brain may not receive all of the necessary signals. The optic nerve can be better observed through the dilated pupil and evaluated for its health.
Annual eye examinations including a dilated fundus evaluation are a critical component of diabetic care. Diabetes causes changes in the vascular system: producing blood and fluid leakage into body tissues, including the retina. Without dilatation of the pupil, early stages of diabetic retinopathy may be missed. Through a dilated fundus evaluation, the changes that occur in retinopathy can be seen and monitored sooner. Retinal photography including fluorescein angiography [a technique using injected fluorescein dye to visualise the retinal blood supply] and retinal photocoagulation [laser treatment of the retina], keystones in diabetic eye treatment require very well dilated pupils.
Risk factors for other diseases, including hypertension, are often identifiable in the eyes as well. Hypertension produces a narrowing of the arteries when blood pressure is significantly elevated.
Neurological disorders, such as multiple sclerosis and tumors in the brain often cause swelling of the optic disc. Early detection and effective management of these potentially life threatening conditions can be facilitated through a thorough eye examination.
Pupillary dilatation is also required in uveitis [inflammation within the eye] to prevent sticking between the pupil margin and the front surface of the lens lying behind it. Adhesions are less likely to develop when the pupil is fully dilated because of reduced contact between the iris and lens.
In order to undergo surgical procedures that require the visualisation of structures behind the pupil, such as cataract extraction, vitrectomy and retinal detachment surgery, the pupil must be adequately dilated before surgery.
Examination in children
When assessing refractive errors in children, the ciliary muscles of the child are paralysed using certain dilating drops to give a true objective reading while determining the prescription. Without use of the drops, accommodation by the child would give a false reading.
Treatment of lazy eye
Amblyopia is a dimness of vision that is commonly known as "lazy eye". Use of a dilating drop known as atropine can be an alternative to patching of the normal eye while treating amblyopia. The resultant blurry vision in the normal eye forces use of the amblyopic eye.
Dilating drops are also used as an immediate treatment following corneal abrasion to relax the eye muscles and therefore reduce the pain in this extremely painful disorder.