Exam Overview

Screening for Cataracts: What You Need to Know

If you think you might have a cataract, the only way to know for sure is to have an eye examination. If your eye care professional finds a cataract, he or she can monitor it and advise you about any future treatment you may need. In order to make a cataract diagnosis, your doctor will ask you a number of questions about your medical history and will perform an eye exam. This comprehensive eye exam should include:

Visual Acuity Testing

The “big E” chart measures how well you see at various distances. From a specified distance – usually 20 feet – your eye care professional will ask you to read aloud progressively smaller rows of high-contrast capital letters and numbers. However, your score on the visual acuity test may not reflect functional impairments such as glare sensitivity and reduced contrast sensitivity.

Ophthalmoscope and Slit-Lamp Examination

Cataracts can be seen with an ophthalmoscope, a hand-held, microscope-like viewing instrument. After using special drops to dilate your pupils, your doctor will examine the internal structures of the eye to check for other eye diseases.


A tonometer is a hand-held instrument that measures intraocular pressure (the pressure of fluids inside the eye) after anesthetic drops are used. This test is performed to rule out glaucoma.

Keratometry and A-Testing

To fit you with the intraocular lens of the proper size and magnification, your eye care professional will use a keratometer to measure the curvature of your cornea. Then the length (optical axis) of your eye will be measured using an A-scan – painless ultrasound waves – to determine the correct power of the IOL lens.

Your doctor may do other tests to learn more about the structure and health of your eye.

If you chose to have cataract surgery, pre-op testing may include an A-scan or optical biometry, keratometry, corneal topography, optical coherence tomography and endothelial cell count. These test results are analyzed by your surgeon, using sophisticated computer analysis, to find the best IOL to meet your needs.

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