Overview of Basic Eye Exams
A basic eye exam usually begins with the eye care provider taking a medical history and asking questions about the patient's general health and past and current eye problems. During the examination, three areas of eye function are assessed: visual acuity and refraction, binocular vision (how the eyes work together), and eye health.
A refraction test helps determine the extent of a patient's refractive error (nearsightedness, farsightedness, astigmatism), as well as the proper prescription for glasses and contact lenses.
A small handheld instrument called a retinoscope is used to examine light refraction of the eye. The retinoscope shines light into the eye and the physician looks through the instrument and measures refraction by the movement of the light that comes off the retina. At the same time, the patient's eyes are looking through an instrument called a phoropter, which resembles a very large pair of binoculars. Lenses with dioptric power are placed before the eyes until the patient sees as clearly as possible. This final combination of lenses is the patient's prescription.
Because of their eyes' ability to accommodate, children and young adults usually are treated first with eye drops to dilate the pupils. Dilating the eyes prevents accommodation and allows the doctor to obtain a more accurate picture of the patient's visual needs. When dilation is used, the test is sometimes referred to as "wet refraction."
The binocular vision assessment is performed to determine how well the two eyes work together. Coordinated eye movement is necessary for accurate depth perception. The patient is asked to follow the movement of an object or light while keeping the head still. Test booklets can measure stereopsis (i.e., three-dimensional vision).
Simple observation of the patient's eye movements while viewing distant and near objects also helps the eye care provider evaluate binocular vision function.
During the health assessment, the physician examines the retina the blood vessels of the retina, and the optic nerve head using an ophthalmoscope, a small handheld instrument consisting of a light source and a series of lenses. This examination can help detect signs of diabetes, high blood pressure (hypertension), certain types of stroke, and autoimmune diseases (e.g., rheumatoid arthritis, multiple sclerosis, lupus).
To view the external eye and the more anterior inner eye structures, such as the eyelids, cornea, iris, and lens, a slit lamp microscope is used. The patient rests their chin and head onto the instrument while the physician uses different magnification settings and handheld lenses to examine the eye. The retina also can be examined using this instrument.
For the most thorough look at the internal structures of the eye, the pupils are dilated. Special drops are instilled into the eye that enlarge the pupil and prevent it from constricting when light is shone into the eye during the examination. Other tests, such as color vision tests and a pupil check, provide important information about ocular health.