Explaining Your Eye Exam

By May 11, 2015 Optical Care No Comments


Keeping your eyes healthy is essential to maintaining the quality of your eyesight. This is particularly important for children whose eyes are still developing. If you are seeing an optometrist for the first time, it is helpful to know what to expect from an eye exam.

An eye exam is generally performed by an optometrist, who is a healthcare professional trained in primary eye care. The optometrist prescribes glasses and contact lenses and can diagnose eye disease and treat certain visual conditions. An ophthalmologist is a medical doctor who specializes in eye conditions and can perform eye surgery and treat the full range of eye diseases.

There are two parts to a comprehensive eye exam: a measurement to determine whether eyeglasses are required, and an assessment of the overall health of your eyes and vision. Additional tests may be done to assess risk of eye disease. The tests are all painless and take about one hour.

Visual Acuity. An eye chart measures how clear and sharp your vision is. With a tool called a phoropter, you look into an eyepiece which electronically replicates the distance of 20 feet from the chart. Normal vision is 20/20, meaning you can make out letters from a distance of 20 feet away that most people can see. However, if you need to be 20 feet away to read letters that most people can see from 100 feet away, you have 20/100 vision. A test for color blindness is also included.

Refraction. While you look through the eyepiece of the phoropter, the eye doctor will switch from one lens to another, asking which is clearer. This subjective measurement identifies nearsightedness, farsightedness, and level of astigmatism in order to give the best acuity in your prescription. It also reveals the presence of presbyopia, which is the eye’s inability to change focus when an object is near so you can read small print.

Visual Fields (Perimetry). This measures central vision, the area you can see without moving your eyes, and peripheral (side) vision. There are some variations, but generally the test involves covering one eye while focusing straight ahead, noting when an object enters your visual field from the side.

Slit Lamp Exam. A slit lamp, or biomicroscope, magnifies the eye and illuminates it with a bright light to examine the front and back parts of the eye for any evidence of disease or defect. Each part of the eye is reviewed for overall eye health – the cornea, iris, crystalline lens, anterior chamber, eyelids and eyelashes.

Extraocular movements. This test measures the strength of the muscles that control movement of your eyes, using a tracking device to follow the direction of your gaze.

Pupillary tests. A bright light is directed towards your eyes, singly and together, focusing on the way the pupils change. This measures how your pupils dilate and constrict when responding to light and can reveal neurological problems.

Retinoscopy. A light is shone into your eyes while you stare at a large object (usually the big E). Lenses on the phoropter are flipped so the eye doctor can measure how light is reflected from your eyes to determine your prescription.

Cover test. This will assess how well your eyes work together. You will focus on some distant object while the eye doctor covers and uncovers one eye. The test can reveal depth perception problems, or the presence of strabismus (crossed eyes) or amblyopia (lazy eye).

Tonometry. This test requires that the eye be anesthetized and a small amount of fluorescein (yellow eye) is placed into the eye. A device called a tonometer is brought up to touch the cornea, measuring eye pressure. Another version uses a non-contact tonometer which uses a puff of air to measure pressure. Tonometry is the key way to determine risk of developing glaucoma.

Dilated Fundus or Retinal examination. Although this test is not always performed as part of a routine eye exam, it is an important part of a comprehensive eye exam and needs to be done periodically to detect the presence of eye disease. In the test, special drops are administered which dilate the pupils, allowing the doctor a large window into the internal eye. The vitreous, optic nerve, retina, macula, and blood vessels can be examined. Since the pupil remains dilated for several hours after a dilated fundus examination, it can hamper your ability to see for some time after the exam.

In determining your eyeglass or contact lens prescription, the eye doctor uses the results primarily of the refraction test and the visual acuity test. The prescription is written in a standardized format using the headings OD and OS, which are Latin for right eye and left eye. Sometimes OU is used, which refers to both eyes. The number listed in the Sphere column carries a plus or minus sign to indicate farsightedness or nearsightedness. The higher the number, the greater the correction to your vision that is needed. A second number under the Cylinder column refers to level of astigmatism.

There are other symbols that might appear on a prescription to identify more complex corrections. For example, ADD refers to the magnification power that needs to be added to increase vision acuity. Prescriptions for glasses and contact lenses are not the same, so you will need to have a separate fitting for contact lenses.

How often you need to renew your prescription or get a new pair of glasses will depend on how quickly your eye condition changes. Children with vision problems may need an adjustment to their prescription every year or more often, while adults may enjoy stable vision for many years.

If you are healthy, have good eyesight and no history of eye disease, you may only require an eye exam every two or three years. However, modern technology is placing greater stress on our eyesight, and many people are finding that as they get older eye strain and vision loss increases. Even if you’ve never had an eye exam, it is recommended that you do a baseline exam at age 40. For individuals who wear glasses or contact lenses or who have other eye or vision problems, an exam annually or every 18 months is generally recommended.

At Brighton Optical, our opticians are all NYS licensed professionals ready to handle all your eye care needs. Visit us today to browse our extensive designer eyewear collection!

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