Optometrists use a variety of tests and procedures to examine your eyes, ranging from simple to complex.  From having you read an eye chart to using a high powered retinal camera to visualize the tiny structures inside of your eyes, all of these tests are important to the process of accurately evaluationg the health of your eyes and recomending an accurate prescription.

In order to fully evaluate your vision and the health of your eyes, you should expect to spend about an hour with your optometrist.

Here are some of the tests that you are likely to participate in during a routine comprehensive eye exam:

Visual Acuity Tests

A visual acuity test, that measures the sharpness of your vision, is often one of the first tests performed during an eye exam.  To measure your distance visual acuity, the doctor may ask you what the smallest line you can read is on an eye chart projected on a screen, mirror or TV.  A similar test is performed for your near vision, typically using a small, hand-held acuity chart.

Normal visual acuity is written as 20/20.  If you have reduced vision, it will be recorded as less than 20/20, such as 20/400.

If you have 20/400 vision, it means that an object that you can see from 20 feet away, a normal 20/20 sighted person can see from 400 feet away. 

Cover Test

There are many ways for your eye doctor to check how your eyes work together, however, the cover test is the simplest and most common.

While doing this, your eye doctor will assess whether the uncovered eye must move to pick up the fixation target, which could indicate vision problems such as strabismus or amblyopia. 

Visual Field Test

In order to check for the possible presence of blind spots (scotomas) in your peripheral vision, the eye doctor will perform a visual field test. 

The doctor will ask you to place your forehead against the machine and to hold a button in your hand.  You will see a white screen inside with a black dot at the center.  While focusing on the black dot, you will see a series of squiggly lines pop up in different quadrants of the white screen.  Each time you see one of thes squiggly lines, you will click the button inyour hand.

Blind spots in your vision can help the optometrist to diagnose important health issues. 

The Glaucoma Test

The glaucoma test, a.k.a.  the “puff-of-air” test, technically known as non-contact tonometry, or NCT, is designed to measure the pressure inside of your eye and is often percieved to be the most difficult part of an eye exam. 

Once again you will be asked to put your chin on the machine’s chin rest, this time looking at a light inside the machine.  The machine will puff a small burst of air at your open eye and based on your eye’s resistance to the puff of air will produce a number that indicates your intraocular pressure (IOP).  It is completely painless, and the tonometer does not touch your eye.

If your IOP number is high, this is an indicator that you could be at risk for glaucoma.

Other than an elevated IOP, there are no warning signs of glaucoma until you start to have vision loss.  This is just one reason  that routine eye exams are essential to protecting your eyesight and overall health. 

Autorefractors

The optometrist will most likely use an autorefractor as a starting point in determining your prescription.  With this piece of equipment, you will be asked to rest your face in a chin rest and focus on a distant image inside of the machine.  

An autorefractor determines the lens power required by your eye to accurately focus light on your retina, giving the doctor a baseline prescription in an accurate & time saving manner.  This is especially useful in certain cases where a patient can not sit still, pay attention or interact with the eye doctor adequately for the amount of time necessary for a manual refraction.

The autorefraction machine can produce an accurate baseline prescription in only a few seconds!

Refraction

This is the test that your eye doctor uses to determine your exact eyeglass prescription.

During a manual refraction, the doctor puts an instrument called a phoropter in front of your eyes.  You will be asked to view an eye chart or other testable image through a series of lenses.  The doctor will ask you about how you percieve the images through each lens.  Based on your answers, the doctor will be able to fine tune the lens power until a final prescription is reached.

The refraction determines your prescription for whichever accomodation disorder you may be experiencing: hyperopia (farsightedness), myopia (nearsightedness), astigmatism or presbyopia. 

Slit-Lamp Examination

When it comes time to examine the health of your eyes, the eye doctor typically uses a slit lamp, also known as a biomicroscope, to get a highly magnified view of the structures of your eye, allowing him or her to detect any signs of infection or disease.

While you have your chin on the chin rest of the slit lamp, the doctor will shine a light at your eye.  The doctor looks through a set of oculars (similar to a microscope) and examines each part of your eye, starting with the front of your eye (conjunctiva, lids, iris, cornea).  In some cases, the doctor will also view the inside of your eye (optic nerve, retina, macula) with the slit lamp.  However, most doctors prefer to perform a dilation or retinal photography (see below) to get an even better view of the inside of the eye than the slit-lamp can provide. 

Optometrists are often the first to detect a wide range of eye conditions with use of the slit-lamp examination, including macular degeneration, cataracts,  corneal ulcers, diabetic retinopathy, and more. 

Pupil Dilation

To obtain a better view of the eye’s internal structures, your eye doctor may need to enlarge your pupils with the use of dilating drops.  The drops usually take about 20 to 30 minutes to start working.  Once they do, the doctor will be able to use a variety of instruments to look through your enlarged pupil.

As a result of pupil dilation, which usually lasts for 4-6 hours afterwards, you may experience sensititivity to light and reduced visual clarity at near.  It is recomended that you bring sunglasses to wear afterwards and don’t plan on doing any up close work after your dilation.

Retinal Photography

In lieu of dilation, you may have the option of having the inside of your eyes viewed using a retinal camera. 

Using a high powered camera lens, the retinal camera can capture a photo of the inside of your eye.  This photo is then loaded into your electronic medical records and serves as a baseline record of the health of your eyes.  At future examinations, subsequent photographs will allow the doctor, by comaprison, to see how the internal structures of your eyes are changing.

Most insurance plans do not cover retinal photogrpahy as part of a comprehensive eye examination, therefore, you may be charged an additional fee for this test.

Other Eye Tests

In some cases your eye doctor may recommend other, more specialized eye tests.

Color Blindness Test

If you suspect that you may have a problem with viewing colors accurately, a color blindness test can be performed.  In addition to detecting color vision deficiencies, color blindness tests can alert your eye doctor to possible eye health problems that may affect your color vision.