The slit lamp examination uses an instrument that provides a magnified, three-dimensional (3-D) view of the different parts of the eye. During the examination, your doctor can look at the front parts of the eye, including the clear, outer covering (cornea), the lens, the coloured 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.
Fluorescein dye 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
Routine slit lamp examinations are done to find eye problems at an early stage and to guide treatment if eye problems develop.
A slit lamp examination 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.
- 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 doctor 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 doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form ( What is a PDF document? ).
How It Is Done
- The doctor may put one or more types of drops in your eye. Dilating drops may be used to make the opening (pupil) in the centre of the eye bigger. This makes it easier for the doctor to see the structures of your eye. Anesthetic eyedrops may be used to numb your eye if a foreign body is to be removed or if eye pressure is being measured (tonometry). In some cases, fluorescein dye is used.
- You will sit in a chair and rest your chin and forehead against bars on the slit lamp. The lights in the room will be dimmed.
- The slit lamp will be placed in front of your eyes, in line with the doctor's eyes. Focus your eyes in the direction requested by the doctor and try to hold your eyes steady without blinking.
- A narrow beam of bright light from the slit lamp is directed into your eye while the doctor looks through the microscope. In some cases, a camera may be attached to the slit lamp to take photographs of different parts of the eye.
A test called fluorescein staining may be done along with a slit lamp examination.
- During this test, your doctor applies a dye called fluorescein as an eye drop or as a paper strip that is gently touched to the inside of your lower eyelid. The dye dissolves in your tears, coats your cornea, and collects temporarily in any scratches or other abnormal areas. The rest of the dye is washed away by your tears.
- Your doctor shines a light onto your eye. The fluorescein dye shows up under the light, allowing the doctor to see scratches, ulcers, burns, or areas of irritation from an infection or dryness.
A slit lamp examination takes about 5 to 10 minutes.
How It Feels
There normally is no discomfort involved with a slit lamp examination.
Dilating drops may make your eyes sting and cause a medicine taste in your mouth. You will have trouble focusing your eyes for up to 12 hours after your eyes have been dilated. Your distance vision usually is not affected as much as your near vision, though your eyes may be very sensitive to light. Do not drive for several hours after your eyes have been dilated, unless your doctor says it's okay. Wearing sunglasses may make you more comfortable until the effect of the drops wears off.
Anesthetic drops usually wear off in about 30 minutes.
In some people, the dilating or anesthetic eyedrops can cause:
- Brief episodes of nausea, vomiting, dryness of the mouth, flushing, and dizziness.
- An allergic reaction.
- A sudden increase in pressure inside the eyeball (closed-angle glaucoma).
Contact your doctor immediately if you have severe and sudden eye pain, vision problems (halos may appear around light), or loss of vision after the examination.
The slit lamp examination uses an instrument that provides a magnified, three-dimensional (3-D) view of the different parts of the eye.
What Affects the Test
The inability to remain still throughout a slit lamp examination may make it hard for your doctor to check your eyes.
What To Think About
- Other eye tests may be done routinely along with a slit lamp examination, including ophthalmoscopy, vision testing, and tonometry testing for glaucoma.
- A test called gonioscopy may be done during a slit lamp examination to detect certain types of glaucoma. A special contact lens (goniolens) is placed on your eye and a narrow beam of bright light is directed into your eye while the doctor looks through the slit lamp at the drainage angle in your eye. To learn more, see the topic Gonioscopy.
- The doctor may use a high-powered lens to examine the vitreous gel and retina of the eye.
Other Works Consulted
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Current as ofJuly 17, 2018
Author: Healthwise Staff
Medical Review: Kathleen Romito, MD - Family Medicine
Anne C. Poinier, MD - Internal Medicine
Adam Husney, MD - Family Medicine
Christopher Joseph Rudnisky, MD, MPH, FRCSC - Ophthalmology