What Is a Slit Lamp Examination?

Medically Reviewed by Whitney Seltman, OD on May 06, 2021

When you visit your eye doctor, they’re not just checking to see if you can read the third line on the eye chart clearly. They’re also making sure your eyes are healthy.

To do this, many doctors use a “slit lamp.” It’s a special microscope and light that lets your doctor see your eyes in 3-D, both inside and out. They’ll use it along with an ophthalmoscope to look at the back of your eye.

A slit-lamp exam is usually done during a regular checkup with your eye doctor.

What Should I Expect?

The slit lamp is several pieces of equipment combined into one device. It includes a binocular microscope on a base that moves in an arc, an adjustable light source, and a frame to rest your head on and hold it steady during the exam.

Your doctor has a lot of flexibility with the light. They can narrow and widen it, increase its brightness, and filter it with colors. By doing this, your doctor can focus on particular parts of your eyes and face.

If you drive to your appointment, you may want to bring someone along to take you home. Some eye exams include dilating your pupils. Until they return to normal size, the outside world may seem overly and even uncomfortably bright for a few hours. Your vision may be a bit blurry too.

What Is the Doctor Looking At?

Before the exam starts, you’ll be asked to remove your glasses or contact lenses. You’ll put your chin and forehead against the microscope rests to keep your head steady. Your doctor may also put a few drops of dye in your eyes to highlight things they want to look at. They’ll then turn out the room lights and turn on the slit lamp.

During the exam, your doctor will look through the microscope, adjusting the light from the slit lamp to view certain parts of your eyes. Things they’ll look at:

The skin around the eye. Your doctor can check the area for skin diseases and abrasions.

Your eyelids and eyelashes. Styes (oil gland infections), folliculitis (hair follicle infections), and tumors are some of the conditions your doctor will look for.

The surface of the eye. This includes the tissue under your eyelids and over the whites of your eyes. These areas can be swollen or infected. This can be caused by sexually transmitted diseases, allergies, or viruses

The sclera. This is the protective outer layer of the eyeball. Next to the sclera is the episclera, which helps keep it healthy. These areas can get diseases related to allergies, autoimmune disorders (where the body attacks itself), and gout (a type of arthritis).

The cornea. This is the layer of the eye that helps focus your vision. A slit-lamp exam may show your cornea isn’t as clear as it used to be. A number of things can cause your vision to blur.

The iris. This is the colored disc that surrounds the pupil and changes to allow more or less light into your eye. It can be affected by a variety of diseases and conditions, including freckles or melanoma of the iris. 

The lens. Cataracts (a clouding of the lens) are diagnosed by examining this part of the eye. It’s located behind the pupil.

In addition, when the slit lamp is coupled with a special magnifying lens, your doctor will be able to view the retina and the optic nerve located in the back of your eye. Before doing this exam, they’ll dilate your pupils with eye drops.

Looking at the retina and optic nerve can help your doctor figure out if you have glaucoma or if diabetes is affecting your eyes. The examination may also show tumors, blood clots, and hardening of the arteries caused by high blood pressure.

Though eye exams make some people squeamish, the procedures should be pain-free.

The Results

Your doctor should tell you what they learned during your eye exam immediately.

If your exam reveals you may have a disease affecting other parts of your body, your eye doctor may recommend you see your regular doctor. If you have a specific eye condition, they may give you a prescription or suggest further testing.

Show Sources


Mayo Clinic: “Eye exam,” “Slit-lamp examination.”

Ophthalmic Photographers’ Society: “Slit Lamp Biomicrography.”

Weill Cornell Brain and Spine Center, “Orbital Tumors.”

University of Ottawa, “Primary Care Ophthalmology: Slit Lamp: Anterior Segment Exam,” “Primary Care Ophthalmology: Slit Lamp: Part and Functions,” “Primary Care Ophthalmology: Slit Lamp: Preparing the Patient.”

American Academy of Ophthalmology, “Conjunctiva,” “Slit-Lamp Biomicroscopy,” “What to Expect When Your Eyes Are Dilated.”

Palo Alto Medical Foundation, “Eye Health Department: Frequently Asked Questions.”, “What is the structure of the sclera, episclera and Tenons capsule?”

National Eye Institute, “Facts About the Cornea and Corneal Disease.” (American Foundation for the Blind), “Eye Health: Anatomy of the Eye.”

National Eye Institute, “Facts About Cataract.”

Stanford Medicine, “Fundoscopic / Ophthalmoscopic Exam.”

© 2021 WebMD, LLC. All rights reserved. View privacy policy and trust info