The slit lamp is an instrument consisting of a high-intensity light source that can be focused to shine as a slit. It is used in conjunction with a microscope. The lamp facilitates an examination which looks at anterior segment, or frontal structures, of the human eye, which includes the eyelid, sclera, conjunctiva, iris, natural crystalline lens, and cornea. The binocular slit-lamp examination provides stereoscopic magnified view of the eye structures in striking detail, enabling exact anatomical diagnoses to be made for a variety of eye conditions. Combined with special lenses like Goldmann 3-mirror lens, Gonioscopy single-mirror/ Zeiss 4-mirror lens for angle structures and +90D lens, +78D lens, +66D lens & Hruby (-56D) lens, the examination of retinal structures is accomplished in detail.
While a patient is seated in the examination chair, he rests his chin and forehead on a support to steady the head. Using the biomicroscope, the ophthalmologist then proceeds to examine the patient's eye. A fine strip of paper, stained with fluorescein, an orange-colored dye, may be touched to the side of the eye; this stains the tear film on the surface of the eye to aid examination. The dye is naturally rinsed out of the eye by tears.
The subsequent test may involve placing drops in the eye in order to dilate the pupils. The drops take about 15 to 20 minutes to work, after which the examination is repeated, allowing the back of the eye to be examined. Patients will experience some light sensitivity for a few hours after this exam, and the dilating drops may also cause increased pressure in the eye, leading to nausea and pain; although this is very rare, patients experiencing these symptoms are advised to immediately seek medical attention.
The slit lamp exam may detect many diseases of the eye, including:
- Corneal injury
- Fuchs' dystrophy
- Macular degeneration
- Retinal detachment
- Retinal vessel occlusion
- Retinitis pigmentosa
- Sjögren's syndrome
- Wilson's disease (Kayser-Fleischer ring)