Typical Cataract eye examinations may include the following:

• Refraction. This test determines the eyeglass prescription that will give the best possible vision without surgery. It is performed by asking you to look through sample lenses that are held in a device called a refractor.

A patient looks through a refractor during an examination (Photo courtesy NEI.)

Visual acuity is not the only factor that determines the need for cataract surgery. Other factors like glare and difficulty seeing in dim light may prevent normal activities under certain lighting conditions that are not duplicated in the ophthalmologist's office. Visual impairment in the presence of bright lights (glare) and difficulty seeing even large objects in dim light (decreased contrast sensitivity) are common in patients with cataracts, even when they can read small letters under standard testing conditions in an ophthalmologist's office.

The effect of visual impairment on lifestyle must also be evaluated when cataract surgery is contemplated. Someone who sees nearly 20/20 in the ophthalmologist's office may experience so much glare that he or she cannot drive safely. On the other hand, someone who can read fewer letters in the office may not notice any limitations because his or her normal daily activities are less visually demanding.

A surgeon's decision to perform cataract surgery is made after a discussion of visual symptoms. Tests for glare disability and decreased contrast sensitivity may be indicated when visual impairment seems to be out of proportion to the visual acuity that is measured with standard techniques.

• Slitlamp. This examination enables assessment of many conditions of the external parts of the eye as well as the cornea, pupil, and lens. It is the principal tool used to assess the severity of a cataract.
  

A patient looks through a refractor during an examination. ( Photo courtesy NEI. )

• Dilated fundus examination. This examination enables assessment of the back of the eye, including the retina and the optic nerve. The pupil must be dilated with drops to allow a good view of structures inside of the eye.

The physician inspects the eye from a distance using a magnifying lens during the dilated fundus exam. (Photo courtesy Jacqueline Griffiths, MD, Reston VA)

• Keratometry. This examination measures the curvature of the cornea - the clear, outermost part of the eye. The corneal curvature is used to calculate the proper power of the intraocular lens that should be implanted in the eye.

The keratometer is used to examine the curvature of the cornea. (Photo courtesy Jacqueline Griffiths, MD, Reston VA)

• A-scan. This instrument measures the length of the eye with ultrasound. This measurement, along with the corneal curvature (see above) are used to select the proper power of the intraocular lens to be implanted in the eye. Another instrument that measures the eye with a laser-like light may be used to gather this information.

During an A-scan exam, the ultrasound instrument momentarily touches the eye's surface. The eye is anesthetized and the exam causes no discomfort. (Photo courtesy Jacqueline Griffiths, MD, Reston VA)