An eye examination is a series of tests that measure a person's ocular health and visual status, to detect abnormalities in the components of the visual system, and to determine how well the person can see.
"Despite a number of ways for an eye doctor to check how well your eyes work together, a simple cover test is most often used."
What is involved in a comprehensive eye examination? An ophthalmologist or optometrist may use a number of tests and procedures to examine a person's eyes. The tests vary from simple ones, such as having you read an eye chart, to more complex tests such as using a high-powered lens to examine the tiny structures inside of your eyes.
A comprehensive examination of your eyes may take an hour or more depending upon the doctor and the number and complexity of the tests the doctor performs to completely evaluate your vision and the health of your eyes. What follows are eye and vision tests you will most likely experience during a routine comprehensive eye examination.
Visual Acuity Testing: Visual Acuity Tests measure the sharpness of your vision and are commonly performed using a projected eye chart to measure your distance visual acuity, as well as a small, hand-held chart to measure your near vision.
Color Blindness Test: A doctor often uses a screening test to check your color vision early in a comprehensive eye examination to rule out color blindness. Along with detecting hereditary color deficiencies, a color blind test can alert a doctor to potential eye health issues that might affect your color vision.
Aberrometer: An aberrometer uses wavefront technology in order to detect vision errors based on the way light travels through a person's eye. Aberrometers are used mainly for custom or wavefront LASIK vision correction procedures, although many eye doctors are using this form of technology during routine eye examinations as well.
Autorefractor: An eye doctor may use an autorefractor to determine the lens power needed to accurately focus light on your retina. Autorefractors are very useful in some instances, such as when evaluating children who may not sit still, interact with the eye doctor, or pay attention for enough time to perform a manual refraction. Autorefractors are very accurate, take only a few seconds, and reduce the amount of time it takes for a doctor to determine a person's eyeglass prescription.Cover Test: Despite a number of ways for an eye doctor to check how well your eyes work together, a simple cover test is most often used. During a cover test an eye doctor has you focus on a small object across the room and then covers each of your eyes alternately as you stare at the object. As you perform the test, the doctor will assess whether the eye you have uncovered must move to pick up the object you are looking at, something that could indicate strabismus or possibly a more subtle binocular vision issue that may cause amblyopia or eye strain.
Refraction: A refraction test is one your eye doctor uses to determine your exact eyeglass prescription. The doctor will use a, 'phoropter,' to determine your prescription. During the refraction the doctor places the phoropter in front of your eyes and shows you a number of different lens options, asking you which of the lenses appear clearer to you. Depending upon your answers, your doctor will continue to fine-tune the lens power until they reach a final eyeglass prescription. A refraction test also determines your level of myopia, hyperopia, presbyopia, and astigmatism.
Retinoscopy Test: An eye doctor might perform a retinoscopy with the goal of obtaining an approximation of your eyeglass prescription. During a retinoscopy the doctor will dim the lights in the exam room and give you a large target such as the big, 'E,' on the chart to look at. As you look at the, 'E,' the doctor will shine a light at your eye and flip lenses in a machine in front of your eyes. Depending upon the way the light reflects from your eye, the doctor will be able to guess at your prescription. A retinoscopy is particularly useful for children and people who do not have the ability to accurately answer the doctor's questions.
Slit-Lamp Exam: A slit-lamp is an instrument an eye doctor uses to examine the health of your eyes. It allows your eye doctor to view the structures of your eyes close-up and is also referred to as a, 'biomicroscope.' During this exam, your doctor will obtain a magnified view of the structures of your eyes to evaluate the health of them and detect any signs of disease or infection. You place your chin on a chin rest and a lamp shines at your eye while the doctor looks through a set of oculars at each part of your eye. The doctor examines your eye lid, cornea, iris, conjunctiva and other parts of your eye. With a high-powered lens, the doctor then examines the inside of your eye to include your optic nerve, retina, macula and other parts of your eye. An eye doctor can detect a large number of diseases and eye conditions using this test, to include:
There are several variations of glaucoma tests and all of them are designed to measure the pressure inside your eyes. A, 'tonometer,' measures the pressure in your eyes with the goal of helping to determine whether you have glaucoma or not. A glaucoma test is the, 'puff of air,' test which is technically known as, 'non-contact tonometry (NCT).'
With NCT the test starts as you place your chin on the machine's chin rest. As you look at a light inside of the machine, the eye doctor or a trained technician will puff a small amount of air at your open eye, something that is completely painless. The tonometer itself does not touch your eye. The machine calculates your intraocular pressure (IOP) based upon your eye's resistance to the puff of air. If you have high eye pressure you might be at risk for or even have glaucoma.
Another version of the glaucoma test is performed using an instrument referred to as an, 'applanation tonometer.' The more common version of this instrument is mounted on a slit lamp. In this test, an eye doctor will put eye drops in your eyes to numb them, making them feel somewhat heavy. The drops do not dilate your eyes; they are a numbing agent combined with a yellow dye that glows underneath a blue light. The eye doctor will have you stare into the slit lamp as they gently touch the surface of your eye with the tonometer to measure your IOP. As with the NCT, use of an applanation tonometer is painless and takes only a few seconds.
People often times experience no warnings signs at all of glaucoma until they already have significant loss of vision. Due to this, routine eye examinations that include tonometry are crucial to rule out early signs of glaucoma and to protect your eyesight.
Pupil Dilation Testing
Pupil dilation testing involves an eye doctor putting dilating eye drops in your eyes to enlarge your pupils with the goal of getting a better view of the internal structures of your eyes. The dilating drops usually take about twenty or thirty minutes to begin working. After your pupils are dilated you will be sensitive to light because more light will get into your eye and you might notice it is more difficult to focus on objects that are close to you. The effects may last for a number of hours depending on the strength of the dilating eye drops the doctor uses.
After the eye drops have started working, your eye doctor will use some different instruments to look inside your eyes. You should bring a pair of sunglasses with you to your comprehensive eye examination to minimize the glare and light sensitivity you experience on your way back home. If you forget to bring sunglasses, the staff members at the doctor's office can usually give you a disposable pair to use. Pupil dilation testing is very important for people who experience risk factors for eye disease because it provides an eye doctor with the opportunity to thoroughly evaluate the health of the inside of the eyes.
Visual Field and other Tests
At times, an eye doctor may want to check a person for potential blind spots or, 'scotomas,' in their peripheral vision through performance of a visual field test. Blind spots may originate from eye diseases such as glaucoma. An analysis of blind spots might also assist in the identification of specific areas of a person's brain that have been damaged by a tumor or a stroke.
In some instances, and in addition to the common types of testing performed during a comprehensive eye examination, an eye doctor might recommend more specialized types of eye testing. Many times these specialized tests are performed by other eye doctors such as retinal specialists.
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