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 doctor 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
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
Why It Is Done
Routine slit lamp exams are done to find eye problems at an early stage and to guide treatment if
eye problems develop.
A slit lamp exam may be done:
As part of a routine eye exam 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.
detect disorders in the structures in the front of the eye, such as infection
or injury to the cornea,
To monitor complications such as bleeding
after an eye injury.
To monitor complications such as cataract
formation that occur because of
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
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?).
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 center 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
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 eyedrop 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. 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.
The inability to remain still
throughout a slit lamp examination may make it hard for your doctor to check
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. For more information, see the topics
Vision Tests, and
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. For more information, see
How this information was developed to help you make better health decisions.