Slit Lamp Exam

Written by Jaime Herndon
Medically Reviewed by George Krucik, MD

What Is a Slit Lamp Exam?

Diseases of the eye can be difficult to diagnose during a general physical examination. A doctor who specializes in treating eye problems (ophthalmologist) is better able to examine and diagnose these conditions because the tools he or she has are specific to the eyes. When you have an eye check-up, you will likely undergo a slit lamp exam.

A slit lamp exam is typically performed at an optometry or ophthalmology office. It is also called biomicroscopy. This exam allows the doctor to see areas at the front of the eye, including the eyelids, conjunctiva, iris, lens, sclera, and cornea. The retina and optic nerve can also be seen. Using this exam, the doctor can microscopically examine the eye for any abnormalities or problems.

What Happens During a Slit Lamp Exam?

Once you are in the examination chair, the doctor will place an instrument in front of you on which to rest your chin and forehead. This helps steady your head for the exam. Your eye doctor may put drops in your eyes to make and abnormalities on the surface of your cornea more visible. The drops contain a yellow dye (fluorescein, which will wash away your tears.

The doctor will use a low-powered microscope, along with a slit lamp­—a high-intensity light—to look closely at your eyes. Filters can be attached to the slit lamp to get different views of the eyes. Some doctor’s offices may have devices that capture digital images to track changes in the eyes over time.

Drops may also be put in your eyes to allow your pupils to dilate, or get bigger. The exam will be performed again, this time with a different lens that enables the doctor to examine the back of your eye.

You do not have to prepare in advance for a slit lamp exam.

What Does this Exam Help Diagnose?

A slit lamp exam can aid in diagnosing the following:

  • macular degeneration—chronic condition affecting the macula, which is the tissue on the eyeball’s inside back wall
  • detached retina—when the retina, which is an important layer of tissue at the back of the eye, becomes detached from the blood vessels that nourish it
  • cataracts—clouding of the lens that negatively affects the ability to see
  • injury to the cornea—an injury to the tissue that covers the front of the eye
  • blockages of the retinal vessel—obstructions in the eye’s blood vessels that can cause loss of sight

Ask your doctor what he or she is looking for during the exam, and which eye conditions you may be at risk for.

What to Expect After the Exam

Typically, there are no significant side effects of this exam. Your eyes may be sensitive to light for a while afterward, especially if your pupils were dilated. If you start feeling nauseous or have eye pain, return to your doctor’s office as soon as possible. These may be symptoms of increased pressure of the fluid in the eye, which needs to be treated.

What Do Abnormal Results Mean?

If the results of your slit lamp exam are abnormal, a variety of conditions may be present. General vision problems, infections, inflammation, and glaucoma can all be causes of abnormal results. For instance, if macular degeneration is taking place, the doctor may find drusen, which are yellow deposits that can form in the macula early on in age-related macular degeneration. If your doctor suspects a particular cause of vision problems, he or she may recommend further testing to get a more definitive diagnosis.

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