The slit lamp exam is a routine eye test and a part of a comprehensive eye exam. A slit lamp is a medical device that combines a binocular microscope and an adjustable lamp to produce bright light that lets the doctor see the patient’s eyes in 3-D. Doctors use the instrument to have a better view of the patient’s external and internal eye structures, including:

  • Eyelids- They work to keep the eye lubricated and protect the eyeball from foreign matter or injury.
  • Sclera- It is the outer white section of the eye made of tough fibrous tissue. It works to maintain the eye structure and protect the internal parts.
  • Conjunctiva- It is the thin, clear tissue covering the sclera.
  • Cornea- It is the transparent material that covers the iris and pupil. It works as the outer lens and helps to channel and focus light at the back of the eye. It also protects inner eye parts.
  • Iris- It is the colored portion of the eyeball and works to regulate the quantum of light flowing through the pupil by expanding or contracting it.
  • Pupil- It is the black area in the middle of the colored part of the eye. It is the opening that lets light enter and flow to the back of the eye.
  • Lens- It is positioned after the iris and works to focus light onto the retina.
  • Retina- It is the light sensitive spot on the back wall of the eye. It links to the optic nerve that sends the image to the brain.

Eye disorders can be challenging to diagnose in a general physical examination. An eye doctor uses the slit lamp exam to better assess and detect the disorders. 

Also Known As



The slit lamp exam can be conducted at the eye doctor’s office or the eye clinic by: 

  • an optometrist
  • an ophthalmologist

A slit lamp exam can help the doctor to diagnose and treat many eye conditions, including:

  • Injury to the cornea
  • Cataracts which are a clouding or an opacity of the lens and reduce a person’s ability to see clearly
  • Detached retina, an abnormality in which the retina becomes detached from its base
  • Macular degeneration, a chronic condition that affects the area of the eye that deals with central vision
  • Retinal vessel blockages which are obstructions in the blood vessels of the eye. They can result in a gradual or sudden loss of sight.

Preparation & Expectation

A patient doesn’t require any special preparation for the test. However, the doctor may apply eye drops to dilate the pupils during the exam. The patient may experience increased sensitivity to light for some hours following the test. Therefore, the patient should bring sunglasses and come with someone or make arrangements to be taken home after the test.


The patient will sit in front of the slit lamp and place their chin and forehead on the support. The doctor may apply fluorescein, a special dye, after the first look at the eyes. The dye washes away the tears and clears the eyes. It makes it easier for the doctor to examine the surface of the cornea. He/she may apply additional medication to dilate the eyes for a better view of the inner structures. He/she will administer the drug as an eye drop or use a thin paper strip to touch the white of the eye. It will take about 20 minutes for it to work.

The slit lamp is a versatile device that gives the doctor a lot of flexibility with the light. He/she can filter it with colors, widen or narrow it down, and increase or reduce its brightness to get different views of the eyes. By doing so, the doctor can focus on and carefully examine particular structures of the eyes and determine if there are any usual occurrences or abnormalities.

The doctor will begin by examining the front section of the patient’s eye. He/she will look at the skin around the eye for abrasions and skin disease, check to examine the eyelids for signs of infections and tumors, and the eye surface for abnormalities such as swellings and symptoms of illness or infections. Then the doctor will change the lens and conduct the exam again to assess the inner structures, including the retina and the optic nerve at the back of the eye. The doctor may use modern computerized gadgets that capture digital images to be able to track changes in the patient’s eyes over time.


The doctor can detect a range of conditions through the slit lamp exam. For example, if the patient is having macular degeneration or the degeneration of the blood vessels in the eye, the doctor can observe drusen. They are yellow deposits that can occur early on in the macula in age-related eye disease.
Other eye disorders the doctor can diagnose through the test include:

  • Infections
  • Cataracts
  • Inflammation
  • Bleeding in the eye
  • Retinitis pigmentosa
  • Damage to the retina
  • Damage to the sclera
  • Foreign body in the eye
  • Corneal injury or disease
  • Diseases of the optic nerve
  • A detachment of the retina
  • Increased intraocular pressure 
  • Disease or swelling of the middle layer of the eye
  • Retinal vessel occlusion, an abnormality that causes blockage of the small blood vessels close to the retina

The doctor should discuss with the patient the finding of the test immediately. Where the doctor suspects a particular cause of eye problems, he/she may give the patient a prescription or make a recommendation for further examinations to get a more definitive diagnosis. If the test results show that the patient may have a disease affecting other parts of the body, the eye doctor may recommend a medical check-up by a regular doctor.

Risks & Complications

A slit lamp exam is a safe eye test. However, the medications that dilate the pupils may have some side effects, such as increasing the internal eye pressure, which may cause nausea and eye pain. If a patient experiences any of these symptoms, they should see the doctor immediately.