Eye Care Diagnostic Tests

Regular eye examinations is of vital importance to maintaining proper vision and eye care.  Your eye care professional has many diagnostic tests available when diagnosis the health of your eye and in searching for such eye diseases as macular degeneration, glaucoma and cataracts.  The exact diagnostic test that will be used during your visit to your eye care professional will vary depending on your family history, symptoms and age.  The article contains more about the various eye care diagnostic tests available.

It is important to have regular eye examinations conducted by eye care professionals, especially if you or your family has a history of eye disease such as macular degeneration or glaucoma.  The various diagnostic tests that your eye care doctor may use in diagnosing problems with your vision and eyes will vary and are essential in ensuring proper eye and vision health as you age.  The following are some of the eye care and vision diagnostic tests that your eye care doctor may utilize during your eye examination.The Optical Coherence Tomography Test (OCT)
The Optical Coherence Tomography Test (OCT) is a computerized imaging technique that uses laser light to make a 3-D image of the retina.  It has become one of the most widely used and most accurate diagnostic test used by eye care professionals in determining troubles with your eyes.  It is a simple test to perform.  The pupil must be dilated and then the patient sits in front of a special type of camera.  A series of pictures are taken of the structures inside the eye.  The OCT test is not intrusive and is painless and provides a detailed view of the retina.  It allows eye care professionals to “see” abnormalities that are not apparent on regular clinical examination.  It is particularly useful in diagnosiing macular degeneration.

The Visual Acuity Test
A visual acuity test is a measure of how well you see or the sharpness and clarity of your vision. A basic visual acuity test will be conducted by your eye care doctor.  You will be asked to read letters on a chart while from a distance of 20 feet. A vision chart will have a series of letters ranging from large to small letters.  The smallest letters you are able to read will be recorded as your acuity. Your visual acuity may be written as 20/20 if your vision is considered normal. If your vision is less than 20/20, it might be written similar to 20/100 indicating that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet. 20/80 vision would mean that someone would have to be 20 feet away to see what someone with normal vision could see at 80 feet.

Confrontation Visual Fields
A confrontation visual field is used by your eye care doctor to measure your overall field of vision. A persons vision is actually divided in the brain into four quadrants per eye. Your eye care doctor will administer this test by having you cover one eye and your eye care doctor will sitting approximately an arm’s length away, directly in front of you. The vision in each quadrant is measured by holding either one, two or five fingers up in each quadrant.  The doctor will have you fixate only on their eye and have you identify how many fingers are held up without looking directly at the fingers. The test is then repeated for the other eye. A visual field test also measures your degree of peripheral vision and checks for blind spots, called scotomas. Depending on the quadrants missed, systemic diseases such as strokes, glaucoma, hypertension, brain tumors and other eye diseases may be diagnosed. Occasionally, eye doctors use an automated computerized instrument, called a perimeter, to measure your visual field.

Extraocular Movements
This test measures the muscles that control eye movement. This is usually a simple test conducted by moving a pen or small object in different directions of gaze. Restrictions, weaknesses or poor tracking of visual objects are often uncovered.

Pupillary Tests
Pupillary reactions (the way your pupils dilate and constrict in response to light) can reveal a lot about the health of the eyes and your body. The nerves that control the pupil travel through a long pathway within the body. Therefore, certain pupillary reactions can reveal neurological problems. Serious conditions can be found this way. Your pupil reactions are tested with a very bright light directed toward one or both of your eyes. Your doctor may focus on one eye or swing the light back and forth to study the way your pupils change.

Cover Test
The cover test is performed to measure how well the eyes work together. It is a simple test in which the eye care doctor asks you to fixate on a near or distant object. He covers one eye, pauses, and then uncovers it. He is evaluating your eye as it is uncovered, as it refixates on the target. This test helps to detect crossed eyes, (strabismus) lazy eye, (amblyopia) or a decrease in depth perception.

Retinoscopy is a test that gives your eye doctor a way to measure refraction, or your need for glasses. It is usually performed early in an exam to estimate the patient’s prescription for glasses. In most cases, the doctor will have you look at a very distant object, such as the large “E” on the eye chart. A device called a retinoscope will then be shown into your eyes. A prescription will be determined based on the degree of light reflecting off of the retina, usually fairly accurately. In addition to giving your doctor a starting point, it is also particularly helpful in young children and adults that may not be able to communicate effectively.

Most people remember refraction as the part of an exam in which the doctor asks the patient, “Which lens is better, one or two?” Refraction is a subjective test to measure nearsightedness, farsightedness, astigmatism or presbyopia. The doctor places an instrument, called a phoropter, in front of your eyes. A series of lens comparisons are shown to you. The doctor will ask you which lens is more clear. The results of the refraction test are primarily what the doctor uses to develop your final eyeglass or contact lens prescription.

Slit Lamp Examination
The doctor uses an instrument called a slit lamp, also called a biomicroscope, to examine the front (anterior segment) and back (posterior segment) part of the eye to evaluate the overall health of the eye. The instrument magnifies your eyes many times and uses a bright light to illuminate the eye structures. Each part of the eye, including the eyelids and eyelashes, conjunctiva, cornea, iris, crystalline lens and anterior chamber, is examined in a methodical manner to reveal any defects or diseases. Cataracts can be diagnosed using the slit lamp.

Tonometry is the measurement of the eye’s pressure, better known as IOP – intraocular pressure. Your eye doctor will instill a drop of anesthetic into your eye. He will then place a small amount of fluroscein (yellow dye) into the eye. A small device called a tonometer is moved close to the eye so that it gently touches the cornea, measuring the pressure of the eye. If eye pressure is higher than normal, your risk of developing glaucoma increases. (Some physicians prefer to measure eye pressure with the “air puff” test. A non-contact tonometer (NCT) determines eye pressure with a painless puff of air.)

Dilated Fundus Examination
The dilated fundus examination is usually the last step in a comprehensive eye examination. Your eye doctor will administer special eye drops to dilate your pupils. This increases the size of your pupil, giving the doctor a larger window in which to inspect the internal eye heath. The doctor is able to examine the vitreous, optic nerve, blood vessels, macula and retina. An instrument called a binocular indirect ophthalmoscope is worn on the doctor’s head. This frees the doctor’s hands to use a powerful lens to focus light emitted from the ophthalmoscope into the eye. With this instrument, the image is a bit smaller but the field of view is much larger, allowing the doctor to view the entire retina. The dilated fundus examination is a crucial part of an eye exam, as many eye diseases can be detected during the test.

It is important to remember that because your eye care professional does not use all the diagnostic tests available to them, it does not mean that your eye examination was incomplete.  The diagnostic tests used are based on your eye care history and any symptoms that you may be exhibiting.  Having regular eye examinations is critical to effective eye and vision care.