Components of an Eye Exam

December 11, 2017
Components of an Eye Exam

Each patient’s signs and symptoms, along with your optometrist’s professional judgment, will determine what tests your optometrist conducts. A comprehensive adult eye and vision examination may include, but is not limited to, the following tests.

Patient History

The optometric technician and doctor will ask about any eye or vision problems you are currently having and about your overall health. In addition, a patient history will include when your eye or vision symptoms began, medications you are taking, and any work-related or environmental conditions that may be affecting your vision. You will also be asked about any previous eye or health conditions you and your family members have experienced.

Visual Acuity

Visual acuity measurements evaluate how clearly each eye is seeing. Reading charts are often used to measure visual acuity. As part of the testing, you will read letters on charts at a distance and near.

The results of visual acuity testing are written as a fraction, such as 20/40. The top number in the fraction is the standard distance at which testing is done (20 feet). The bottom number is the smallest letter size you were able to read. A person with 20/40 visual acuity would have to get within 20 feet to see a letter that should be seen clearly at 40 feet. Normal distance visual acuity is 20/20.

Preliminary Tests

An optometrist may first want to look at specific aspects of your visual function and eye health. Preliminary tests can include evaluations of depth perception, color vision, eye muscle movements, peripheral or side vision, and the way your pupils respond to light.


This test measures the curvature of the cornea (the clear outer surface of the eye) by focusing a circle of light on the cornea and measuring its reflection. This measurement is particularly critical in determining the proper fit for contact lenses.


Refraction determines the lens power you need to compensate for any refractive error (nearsightedness, farsightedness or astigmatism). Using an instrument called a phoropter, your optometrist places a series of lenses in front of your eyes. He or she then measures how these lenses focus light using a handheld lighted instrument called a retinoscope. The lens power is then refined based your input on the lenses that give you the clearest vision. During the portion of the exam, the doctor will continuously ask you to choose between two different settings on the phoropter (“Which is better, 1 or 2?”). It is important that you always choose the best option even if the options to not provide clear vision – the doctor uses this information to dial in the spectacle prescription that will provide your best possible vision.

Eye Focusing, Eye Teaming, and Eye Movement Testing

To see a clear, single image, the eyes must effectively change focus, move and work in unison. An assessment of accommodation, ocular motility and binocular vision determines how well your eyes focus, move and work together. This testing will look for problems that keep your eyes from focusing effectively or make using both eyes together difficult.

Slit Lamp Exam

The slit lamp is used to assess the overall health of your eyes. A slit lamp is a binocular microscope (or “biomicroscope”) that your eye doctor uses to examine the structures of your eye under high magnification. It looks somewhat like a large, upright version of a microscope used in a science lab. During the slit lamp exam, you will be asked to place your forehead and chin securely against the rests on the front of the instrument and your doctor will begin by examining the structures of the front of your eyes — including your eyelids, cornea, conjunctiva, iris, and lens. With the help of a hand-held lens, your doctor may also use the slit lamp to examine structures located farther back in the eye, such as the retina and optic nerve. A wide range of eye conditions and diseases can be detected with the slit lamp exam, including cataracts, macular degeneration, corneal ulcers and diabetic retinopathy, etc.

The Glaucoma Test

Testing for glaucoma typically begins with measuring the pressure inside your eyes. A common glaucoma test is the “puff-of-air” test, technically known as non-contact tonometry, or NCT. (This test was immortalized on the hit TV show Friends, when Rachel couldn’t sit still for it.) Most patients genuinely dislike the air puff method of measuring pressure which is why we DO NOT USE THE AIR PUFF TEST in our offices.

To measure the intraocular pressure of our patients, we use applanation tonometry. For this test, your eye doctor will put yellow eye drops in your eye to numb it. Your eyes will feel slightly heavy when the drops start working. This is not a dilating drop — it is a numbing agent combined with a yellow dye that glows under a blue light. Then the doctor will have you stare straight ahead into the slit lamp while he or she gently touches the surface of your eye with the tonometer to measure your IOP. Applanation tonometry is painless. At most, you may feel the tonometer probe touch your eyelashes. The whole test takes just a few seconds.

You typically have no warning signs of glaucoma until you already have significant vision loss. For this reason, routine eye exams that include tonometry are essential to rule out early signs of glaucoma and protect your eyesight.

Pupil Dilation

To obtain a better view of the eye’s internal structures, your eye doctor instills dilating drops to enlarge your pupils. Dilating drops usually take about 20 to 30 minutes to start working. When your pupils are dilated, you will be sensitive to light (because more light is getting into your eye) and you may notice difficulty focusing on objects up close. These effects can last for up to several hours, depending on the strength of the drop used.

Once the drops have taken effect, your eye doctor will use various instruments to look inside your eyes. You should bring sunglasses with you to your eye exam, to minimize glare and light sensitivity on the way home. If you forget to bring sunglasses, our staff will give you a disposable pair. Pupil dilation is very important for people with risk factors for eye disease, because it allows for the most thorough evaluation of the health of the inside of your eyes.

About Contact Lens Fittings

It’s important to understand that a comprehensive eye exam typically does not include a contact lens fitting, and therefore you will not be given a contact lens prescription at the end of a routine eye exam.