The slit lamp exam uses an instrument that provides a magnified, three-dimensional (3-D) view of the different parts of the eye. During the exam, your health professional can look at the front parts of the eye, including the clear, outer covering (cornea), the lens, the colored part (iris), and the front section of the gel-like fluid (vitreous gel) that fills the large space in the middle of the eye.

Special lenses can be placed between the slit lamp and the cornea (or directly on the cornea) to view deeper structures of the eye, such as the optic nerve, retina, and the area where fluid drains out of the eye (drainage angle). A camera may be attached to the slit lamp to take photographs of different parts of the eye.

See a picture of the structures of the eye.

Fluorescein dye eyedrops may be used during a slit lamp examination to make it easier to detect a foreign body, such as a metal fragment, or an infected or injured area on the cornea.

Why It Is Done

A slit lamp exam may be done:

• As part of a routine eye examination along with other procedures to evaluate the eye, such as ophthalmoscopy, vision testing, or tonometry (to measure pressure in the eye).
• To look at structures in the back of the eye, such as the optic nerve or retina.
• To help detect disorders in the structures in the front of the eye, such as infection or injury to the cornea, cataracts, conjunctivitis, or iritis.
• To help detect and monitor glaucoma or macular degeneration.
• To check for a foreign body, such as a metal fragment, on or in the eye.
• To detect eye problems that may be caused by other diseases, such as diabetes or rheumatoid arthritis. Routine slit lamp examinations are important to detect eye problems at an early stage and to guide treatment if eye problems develop.
• To monitor complications such as bleeding after an eye injury.
• To monitor complications such as cataract formation that occur because of chemotherapy, radiation treatment, or after a bone marrow transplant.

How To Prepare

If you wear glasses or contact lenses, you will need to remove them before the slit lamp examination.

Eyedrops may be used to widen (dilate) your pupils and to numb the surface of your eyes. Before the test, tell your health professional if you have glaucoma or are allergic to dilating or anesthetic eyedrops.

If dilating drops are used, your eyes may be sensitive to light and you will have trouble focusing your eyes for several hours. If you know your eyes will be dilated, you may wish to arrange for someone to drive you home after the test. You also will need to wear sunglasses when you go outside or into a brightly lit room.

Talk to your health professional about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will indicate. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?) .