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Eye Exam Tools: How & Why Your Optometrist Uses Them

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Annual eye exams are vital for safeguarding your eye health as well as your overall health. During your eye exam, your optometrist uses a variety of tools to detect eye disease and address refractive errors. These tools help your optometrist determine if you need eyeglasses and diagnose eye disease, helping to ensure you’re seeing to your full potential.

Pre-Testing & Screening Equipment


An autorefractor measures your eye?s refractive error and determines your baseline prescription. Your optometrist uses this data as a starting point when assessing your refractive error.

Refractive errors include nearsightedness, farsightedness, and astigmatism. The autorefractor tool works by measuring how light bends when it enters your eye. 

An autorefractor requires you to take a seat behind the machine and place your chin on a rest. Then, you will be asked to look at an image in the machine, one eye at the time. The image moves in and out of focus as the machine takes readings to determine when the image is projected clearly onto the retina. It then averages out these readings to determine your baseline eyeglasses or contact lens prescription.

Retinal Camera

A retinal camera is a specialized, low focus microscope with a camera attached. It takes a photo of the back of your eye, including the retina, optic disc, macula, and posterior pole. These images are vital for allowing your optometrist to detect and document serious eye conditions including retinal detachment and age-related macular degeneration. Your eyes are usually dilated before the procedure so your optometrist can see as much of the retina as possible. 


Optomap is a specialized retinal camera that gives your optometrist an ultra-wide view of your retina. The wide angle allows your optometrist to view more of your retina than standard retinal cameras.


A tonometer is used to detect signs of glaucoma by measuring the eye’s fluid pressure, often referred to as your intraocular pressure. If the pressure is too high or too low, it could be a sign that a problem is developing. There are two forms of tonometry test: Contact and noncontact tonometry.

  • Contact tonometry involves using a smooth, flat-tipped cone to apply gentle pressure to the surface of your eye, temporarily flattening your cornea and measuring its resistance. Should your optometrist use this method, they may first numb your eye using numbing eye drops.
  • Noncontact tonometry, often called the “air puff test,” uses a puff of air to measure your eye’s internal pressure by gauging its resistance.


Lensometers are used to measure the prescription of your current glasses. This helps your optometrist to determine a benchmark and better understand how your prescription is changing over time.

Visual Field Test

A visual field test measures how wide of an area your eye can see, including your peripheral vision. It?s important for your optometrist to measure your peripheral vision as peripheral vision loss can be a sign of eye disease like glaucoma.

Exam Room & Diagnostic Equipment

The Snellen Chart

The Snellen chart is one of the most easily recognized optometry tools. It’s a simple chart containing letters and often begins with a large capital E at the top. Each row of letters gets progressively smaller.

The optometrist uses this tool to measure your visual acuity, which refers to how clearly you can see objects a distance. Your optometrist may ask you to put a hand over your right or left eye and read out some letters, then switch eyes. This test measures your vision against the standard 20/20 vision.

20/20 vision measures normal vision measured from 20 feet away. People with 20/20 vision can see clearly when 20 feet away from an object or Snellen chart. Someone with 20/100 vision needs to be 20 feet from an object to see what someone with normal vision can see from 100 feet away.


A phoropter is an instrument used to measure refractive errors and determine the correct prescription for your eyeglasses or contacts.

Typically, you will sit, looking through the phoropter at an eye chart. Your optometrist will then cycle through different lenses with different powers. After switching the lenses, your optometrist will ask you for feedback about which ones help you see best. Your optometrist uses this information to determine which glasses prescription will help provide you with the best vision. 


A retinoscope is a device used to shine light into your eyes so that the optometrist can observe its reflection off the retina. The optometrist moves the light back and forth across the pupil, examining how well your eyes are able to focus. This exam is known as a retinoscopy, and it tests how well your eyes work together as a team. 

This test also gives your optometrist insight into any refractive errors that may exist. If your optometrist determines that your eye is not focusing very well, they will use a series of corrective lenses to determine the prescription of your eyeglasses or contact lenses.

Slit Lamp

A slit lamp is a microscope with a slit light source attached to it and is used by your optometrist to inspect your eyelids, iris, cornea, and lens. With special lenses, this device can be used to examine the back of the eye as well, checking for any abnormalities that may indicate a disease or other serious condition is developing. The optometrist may dilate your pupils for this test.

This test helps to diagnose conditions like glaucoma, cataracts, cornea injuries, and retinal detachment.

Binocular Indirect Ophthalmoscope (BIO)

An ophthalmoscope is an instrument that consists of a light and several small lenses.  

This tool is used to check the outer portion of your retina, called the fundus, to detect eye diseases and conditions that affect blood vessels. 

The BIO has a light on the front and is worn by your optometrist like a headband. The optometrist then holds a condensing lens close to your eye and examines your eyes by looking through the lens. Your optometrist may ask you to look in different directions as they check your eyes. 

When you have an eye exam, your optometrist checks the health of your eye and assesses if your vision can be improved with glasses or contacts. Some eye diseases have no signs or symptoms in the early stages, meaning disease can damage your sight without you knowing.

The tools used during regular eye exams are essential to preventing vision damage and ensuring you can see as clearly as possible.

Written by Dr. Catharine Cheon

Dr. Catharine Cheon completed her Bachelor of Science at McGill University before earning her Doctor of Optometry with Honors at the New England College of Optometry. As a native Calgarian, Dr. Cheon enjoys practicing close to her home.
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