Tests to Diagnose a Cataract

Eye care specialists use several tests to diagnose eye cataracts, such as a simple visual acuity test or pupil dilation. Your optometrist or ophthalmologist will likely need to perform a series of tests to make this diagnosis.

A cataract is a clouding of the eye's natural lens, which lies behind the iris and the pupil. Over time, a cataract may grow larger and cloud a bigger portion of the lens, making it harder for you to see.

This article looks at the tests that help healthcare providers diagnose eye cataracts and determine their severity.

Male patient's eye with mature cataract, Close-up
MedicImage / Getty Images

Who Should Be Tested For Cataracts?

Cataract testing is usually part of a comprehensive eye examination, which assess both your vision and your eye health. All adults should have these exams as recommended by an eye care provider. This becomes even more important as you get older.

If you have symptoms of cataracts or are at risk of developing them, you may need testing sooner than your yearly examination.

Cataracts can cause many symptoms, including:

  • Reduced visual clarity
  • Colors appear faded
  • Seeing halos around lights
  • Requires more light to read or see detail

You are at increased risk of developing cataracts if:

  • You are over the age of 55
  • You have a family history of cataracts
  • You have diabetes
  • You spend a lot of time in the sun without eye protection

Cataracts are common in older people. In the United States, about half of all people age 80 and older have cataracts or have had surgery to remove them. Cataracts aren't always associated with age, though. They can also develop:

  • After an eye injury
  • As a result of another eye disease
  • After using certain medications, including steroids
  • As a result of health problems such as diabetes

Some children are born with cataracts. If you think your child has a vision problem, ask your child's healthcare provider about cataract testing. This can help determine if there is a cataract, what type of cataract it is, and if cataract surgery or another treatment should be prescribed.

Before diagnosing cataracts, your healthcare provider will likely perform a combination of different tests. Your medical history and symptoms will help confirm the diagnosis.

Visual Acuity

A visual acuity test measures your quality of vision at certain distances. Your healthcare provider will ask you to read letters of various sizes from a chart. Your eyes will be tested individually and together. This helps to measure the accuracy of your eyesight at different distances.

The results of this test are recorded as a ratio, such as 20/20 or 20/40. 20/20 vision is considered normal. The ratio of 20/20 means you can see an object that's 20 feet away as clearly as anyone else with normal vision. If you have 20/40 vision, you can see an object that's 20 feet away as clearly as someone with normal vision can see an object that's 40 feet away.

A visual acuity test is an easy, painless, and quick way to evaluate your vision. More tests will be needed, however, to determine if cataracts are the cause of your vision problems.

Contrast Sensitivity

Contrast sensitivity testing is similar to visual acuity testing. The goal of this test is to find out how easy it is for you to separate an object from its background. If it's hard for you to identify an object when it's on a low-contrast background, then you have poor contrast sensitivity.

Cataracts can decrease image contrast. This happens because the cataract can cause light scattering and glare.

Slit Lamp

A slit lamp is a special type of microscope that magnifies your eye. This lets your healthcare provider see the cataract and determine how severe it is.

During this test, you will place your chin on the chin rest of the slit lamp. Your healthcare provider will direct light at your eye and look through the slit lamp.

Pupil Dilation

Pupil dilation is a common test used to diagnose cataracts. When your eye is dilated, the pupil increases in size. This makes it possible for your healthcare provider to see your entire lens. A good view of the whole lens lets your healthcare provider determine if a cataract is affecting your quality of vision.

Potential Acuity Test

A potential acuity test measures how well the eye would see without the cataract. It is typically done before cataract surgery to confirm that the procedure will improve your vision.

During this test, a device called a potential acuity meter (PAM) projects an eye chart onto the eye with a laser. The projection bypasses the cataract. The patient reads the chart just like a normal eye chart on a wall.

If the best measurement is 20/40, the eye will have at least 20/40 vision after the surgery. This test becomes more important when the patient also has another eye disease as well as a cataract.


Several tests can help your healthcare provider diagnose cataracts. A visual acuity test is a gold standard. It measures how well you can see at certain distances. A potential acuity test is similar, but the eye chart is projected onto your eye, bypassing the cataract.

A contrast sensitivity test helps determine how well you can see an object against its background. Your healthcare provider may also perform tests that help visualize your eye and lens.

A Word From Verywell

The good news is, that cataracts are usually easy to treat. The cataract can be removed surgically and replaced with an artificial lens. Cataract surgery is generally considered very safe.

Most people do very well after cataract surgery. Nine out of 10 people who undergo the procedure will have improved vision after recovery.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Optometric Association. Cataract.

  2. Johns Hopkins Medicine. Cataracts.

  3. American Academy of Ophthalmology. What are cataracts?

  4. National Library of Medicine. Visual acuity test.

  5. Shandiz JH, Derakhshan A, Daneshyar A, et al. Effect of cataract type and severity on visual acuity and contrast sensitivity. J Ophthalmic Vis Res. 2011;6(1):26.

  6. National Eye Institute. Get a dilated eye exam.

  7. Klaproth OK, Kohnen T. Potential acuity meter. In: Schmidt-Erfurth U, Kohnen T, eds. Encyclopedia of Ophthalmology. Berlin, Heidelberg: Springer; 2016. doi:10.1007/978-3-642-35951-4_408-3

  8. National Eye Institute. Cataract surgery.

By Troy Bedinghaus, OD
Troy L. Bedinghaus, OD, board-certified optometric physician, owns Lakewood Family Eye Care in Florida. He is an active member of the American Optometric Association.