A thorough eye examination consists of a variety of standard tests designed to measure visual acuity and other vision faculties, as well as observe the health of the eye and check for common eye diseases. There is no pain or discomfort associated with an exam, and they typically take less than an hour.
General eye exams can diagnose a variety of eye conditions early on and are the best way to preserve good vision. For children, strabismus (crossed eye) and amblyopia (lazy eye) can often be diagnosed and treated in early childhood, avoiding life-long vision impairment. Also, rare eye conditions from birth (like congenital cataracts) can be diagnosed and treated. For all ages, refraction tests can determine whether prescription eyewear would be beneficial, and what power is necessary. Furthermore, many debilitating eye diseases can be diagnosed before noticeable symptoms occur, potentially making the difference between minor damage and major vision loss.
Eye exams are recommended regularly throughout all phases of one’s life. In the first three years, infants should have their vision checked as part of regular pediatric checkups. Between age three and six, an eye exam every year or two is recommended. Throughout childhood and the teenage years, exams should be scheduled as necessary. Adults should have at least one exam in their twenties, at least two in their thirties, and an exam every two to four years after that. Exams are recommended for seniors every one to two years. People with diabetes should have at least one exam per year. Exams are also more frequent for patients monitoring a diagnosed eye condition, or with a hereditary predisposition to an eye disease.
Common tests and evaluations during an eye exam include:
- Introductory interview: The doctor will ask basic questions about a patient’s medical history and eye health history.
- External examination: The doctor inspects all outward visible parts of the eye and surrounding tissue.
- Pupil inspection: The patient’s pupils will be inspected for equal size and regular shape. Then the doctor tests how they react to light and objects at various distances.
- Eye muscle health and mobility: Eye movement is checked in six directions (corresponding to the six extraocular muscles), as well as tracking a moving object (such as a pen).
- Visual field: The patient covers one eye at a time, and with the other eye gazing straight ahead, identifies objects in peripheral vision (often simply the number of fingers the doctor is showing.)
- Visual acuity: A common means of measuring visual acuity is the Snellen chart. This is a large card or projection with progressively smaller horizontal lines of random block letters. The test determines how well a patient can discern detail at a given distance. Patients taking this test will cover one eye and then read aloud the letters of each row, starting from the top. The smallest row that can be accurately read indicates the patient’s visual acuity in that eye.
- Refraction: This test is used to find the best corrected vision, if necessary for prescription eyewear or contacts. The doctor will try various lenses in front of each eye, as the patient focuses on a chart at a distance or up-close, to help determine the best power of correction.
- Color vision: The doctor shows the patient a series of images with symbols embedded in color dots or patterns. Based upon the patient’s ability to identify the symbols, certain types of colorblindness can be diagnosed or ruled out.
- Ophthalmoscopy: This test is often done with an ophthalmoscope, a handheld instrument with light and magnifying lenses. Alternatively, the doctor may use other means, such as a slit lamp, which affords a more three-dimensional view. Ophthalmoscopy aims to inspect the retina and surrounding internal eye. This test can help diagnose problems with the retina or detachment of the retina, and monitor diseases like glaucoma and diabetes. An opacity in the eye can indicate a cataract. Sometimes the doctor will dilate the pupils with eye drops, to gain a wider view of the internal eye.
- Tonometry: This test measures intraocular pressure, which can be a sign of glaucoma if pressure is abnormally high. Internal eye pressure is measured either with a puff of air at the cornea or brief direct contact with the cornea, to measure how easily it is pushed inward.