Eye examination
An eye examination is a series of tests that measure a person's ocular healthand visual status, to detect abnormalities in the visual system, and to determine how well the person can see. It is performed by an ophthalmologist (M.D. or D.O.--doctor of osteopathy) or an optometrist (O.D.) to determine if there are any pre-existing or potential vision problems. Eye exams may also reveal the presence of many non-eye diseases. The frequency of eye exams differswith age and the health of the person. Eye exams can be performed in infants,and if a problem is noted the infant can be seen by a pediatric ophthalmologist. A child with no symptoms should have an eye exam at age three. Early exams are important because permanent decreases in vision (e.g., amblyopia, alsocalled lazy eye) can occur if not treated early (usually by ages 6-9). Withno symptoms, the second exam should take place before first grade. After first grade, the American Optometric Association recommends that healthy people with no risk factors have an eye exam every two years; for ages 19-40, every two-to-three years; for ages 41-60, every two years; and annually after that.Patients with risk factors for eye disease (e.g., people with diabetes or a family history of eye disease; African Americans, who are at higher risk for glaucoma) and children who have trouble in school, problems with reading, rubtheir eyes when reading, etc. may need more frequent checkups. An eye examination costs about $100 and may or may not be covered by insurance. It includesa patient history, primary tests, and additional specialized tests as needed. Primary tests evaluate the physical state of the eyes and surrounding areasand measure the ability to see.
Most exams will include the following procedures. The eye and medical histories include complaints, past eye disorders, medications, blood relatives witheye disorders, any systemic disorders the patient may have, and hobbies and work conditions. If the patient has glasses, he/she should bring them. The visual acuity examination measures each eye to determine how clearly the patientcan see. An eye chart, usually a Snellen eye chart, is used. These charts are placed at a distance from the person being tested at which people with normal vision can read the 20/20 line; these people are said to have 20/20 vision. For people who can't read the smallest line, the examiner assigns a ratio based on the smallest line they can read. When a patient can't read any line,the chart is moved closer until he/she can read the line with the largest letters. When a patient can't read the chart at all, the examiner may hold up some fingers, move a hand, or use a penlight. In eye movement examination and cover tests, the examiner asks the patient to look up and down, and to the right and left to see if the patient can move the eyes to their full extent. Theexaminer asks the patient to stare at an object, then quickly covers one eyeand notes any movement in the eye that remains uncovered. The doctor may have the patient look at a pen and follow it as it is moved close to the eyes tocheck convergence. The examiner checks the pupil's response to light and views the iris for symmetry and physical appearance. For people whose visual acuity is less than 20/20, the examiner will determine the refractive error andobtain a prescription for corrective lenses. An instrument called a phoropter, which the patient sits behind, is generally used. The examiner tests combinations of corrections to learn which allows the patient to see the eye chartbest. The exam will check vision at distance and near. A prescription for corrective lenses can also be supplied by automated refracting devices or through a hand-held retinoscope. Sometimes drops will be put in the patient's eyesso that the refraction will be more accurate; this is helpful in children andpeople who are farsighted.
Next, the examiner checks the health of the eyes and surrounding areas. Afterdilating the pupils, the examiner uses an ophthalmoscope to view the retina,blood vessels, optic nerve, and other structures. The slit lamp is used to examine the lid and lid margin, cornea, iris, pupil, conjunctiva, sclera, andlens, and in contact lens evaluations. A tonometer may be used to check eye pressure, after using a colored eyedrop. A perimeter measures visual field. Atonometer measures intraocular pressure (IOP). Other tests could include binocular indirect ophthalmoscopy, gonioscopy, color tests, contrast sensitivitytesting, ultasonography, and others.
Seeing clearly does not necessarily mean the eyes are healthy or that the eyes are working together as a team. Regular checkups can detect abnormalities,hopefully before a problem arises. The eye doctor can suggest ways to help protect the eyes and vision (e.g., safety goggles, ultraviolet (UV) coatings onlenses). A person should also have an eye exam if he/she notices a change invision, eyestrain, blur, flashes of light, a sudden onset of floaters (little dots), distortion of objects, double vision, redness, pain, or discharge.
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