Eye Health Exam

Why should I have my eyes dilated?

Most of us have had the experience of trying to find our car keys so we can find our way home after the eye doctor put those drops in our eyes. Is dilation important? Here are some answers to frequently asked questions…

Why does the doctor want to do this?

In an eye examination without pupil dilation the doctor is only able to see a small fraction of your retina. As soon as a bright light shines into your eye, the pupil becomes so small that only a small part of the back of the eye is visible. Pupil dilation is like looking into a room with the door open as opposed to looking through a keyhole. Fortunately, when the patient has no symptoms, it is unusual that a serious eye disease would be discovered in this process. However, routine dilation can uncover serious eye conditions in an early, more treatable stage and before symptoms are present.

What is the doctor looking at?

The doctor will be examining several structures, namely…

*the retina, a delicate, light-receiving tissue made up of millions of photoreceptors.

*the choroid, a blood vessel layer behind the retina which nourishes it.

*the optic nerve, the “wire” that carries the vision message to your brain.

*retinal veins and arteries, which are a visible “sample” of the health of your blood vessels elsewhere.

What types of problems can be found on routine dilation?

The doctor will be looking for…

*any breaks or tears in the retina that could lead to retinal detachment.

*any evidence of the erosion of optic nerve fibers which causes the loss of side vision in glaucoma.

*any abnormal blood vessels which could herald diabetes, hypertension or other vascular disease.

*any changes in the vitreous humor, the “gel” that occupies the space in front of the retina.

*any freckles (called nevi) that should be watched over time as possible precursors to melanoma.

*any changes to the small blood vessels behind the macula, the center vision part of the retina. Macular degeneration can be discovered and addressed in it’s very early stages, before symptoms of vision loss occur.

*any evidence of past or present inflammation or infection, such as histoplasmosis.

*any early or advanced cataract.

How long does it last?

The distance vision will usually not be affected except that you’ll be light sensitive. Most people have no trouble driving afterwards. In certain rare instances the doctor will recommend returning for the dilation with a driver. If you are under 45 years old, your near vision will be blurry for about an hour. If you know that you have been uncomfortable with dilation in the past, please arrange a ride.

Comprehensive Eye and Vision Examination

  • Recommended Eye Examination Schedule for Pediatric Patients and Adults
  • Limitations of Vision Screening Programs

Periodic eye and vision examinations are an important part of preventive health care. Many eye and vision problems have no obvious signs or symptoms. As a result, individuals are often unaware that problems exist. Early diagnosis and treatment of eye and vision problems are important for maintaining good vision and eye health, and when possible, preventing vision loss.

Individual patient signs and symptoms, along with the professional judgment of the doctor, may significantly influence the testing done. A comprehensive adult eye and vision examination may include, but is not limited to, the following tests:

Patient History

A patient history helps to determine any symptoms the individual is experiencing, when they began, the presence of any general heath problems, medications taken and occupational or environmental conditions that may be affecting vision. The doctor will ask about any eye or vision problems you may be having and about your overall health. The doctor will also ask about any previous eye or health conditions of you and your family members.

Visual Acuity

Reading chart

Reading charts are often used to measure visual acuity.

Visual acuity measurements evaluate how clearly each eye is seeing. As part of the testing, you are asked to read letters on distance and near reading charts. The results of visual acuity testing are written as a fraction such as 20/40.

When testing distance vision, the top number in the fraction is the standard distance at which testing is done, twenty feet. The bottom number is the smallest letter size you were able to read. A person with 20/40 visual acuity would have to get within 20 feet of a letter that should be seen at 40 feet in order to see it clearly. Normal distance visual acuity is 20/20.

Preliminary Tests

Preliminary testing may include evaluation of specific aspects of visual function and eye health such as depth perception, color vision, eye muscle movements, peripheral (side vision), and the way your pupils respond to light.


This test measures the curvature of the cornea, the clear outer surface of the eye, by focusing a circle of light on the cornea and measuring its reflection. This measurement is particularly critical in determining the proper fit for contact lenses.


Comprehensive Eye Examination

Determining refractive error with a phoropter and retinoscope

Refraction is conducted to determine the appropriate lens power needed to compensate for any refractive error (nearsightedness, farsightedness, or astigmatism). Using an instrument called a phoropter, your optometrist places a series of lenses in front of your eyes and measures how they focus light using a hand held lighted instrument called a retinoscope. The doctor may choose to use an automated instrument that automatically evaluates the focusing power of the eye. The power is then refined by patient’s responses to determine the lenses that allow the clearest vision.

This testing may be done without the use of eye drops to determine how the eyes respond under normal seeing conditions. In some cases, such as for patients who can’t respond verbally or when some of the eyes focusing power may be hidden, eye drops are used. The drops temporarily keep the eyes from changing focus while testing is done.

Eye Focusing, Eye Teaming, and Eye Movement Testing

Assessment of accommodation, ocular motility and binocular vision determines how well the eyes focus, move and work together. In order to obtain a clear, single image of what is being viewed, the eyes must effectively change focus, move and work in unison. This testing will look for problems that keep your eyes from focusing effectively or make using both eyes together difficult.

Eye Health Evaluation


Tonometry measures eye pressure. Elevated pressure in the eye signals an increased risk for glaucoma.

External examination of the eye includes evaluation of the cornea, eyelids, conjunctiva and surrounding eye tissue using bright light and magnification.

Evaluation of the lens, retina and posterior section of the eye may be done through a dilated pupil to provide a better view of the internal structures of the eye.

Measurement of pressure within the eye (tonometry) is performed. Normal eye pressures range from 10 to 21 millimeters of mercury (mm Hg), averaging about 14 to 16 mm Hg. Anyone with eye pressure greater than 22 mm Hg is at an increased risk of developing glaucoma, although many people with normal pressure also develop glaucoma.

Supplemental testing

Additional testing may be needed based on the results of the previous tests to confirm or rule out possible problems, to clarify uncertain findings, or to provide a more in-depth assessment.

At the completion of the examination, your optometrist will assess and evaluate the results of the testing to determine a diagnosis and develop a treatment plan. He or she will discuss with you the nature of any visual or eye health problems found and explain available treatment options. In some cases, referral for consultation with, or treatment by, another eyecare provider may be indicated.

If you have questions regarding any eye or vision conditions diagnosed, or treatment recommended, don’t hesitate to ask for additional information or explanation from your doctor.

www.aoa.org 10/08