The
slit lamp is an instrument consisting of a high-intensity light source that can be focused to shine a thin sheet of light into the eye. It is used in conjunction with a biomicroscope. The lamp facilitates an examination of the
anterior segmentThe anterior segment is the front third of the eye that includes the structures in front of the vitreous humour: the cornea, iris, ciliary body, and lens.Within the anterior segment are two fluid-filled spaces:...
, or frontal structures and
posterior segmentThe posterior segment is the back two-thirds of the eye that includes the anterior hyaloid membrane and all of the optical structures behind it: the vitreous humor, retina, choroid, and optic nerve....
, of the human
eyeEyes are organs that detect light, and send electrical impulses along the optic nerve to the visual and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system...
, which includes the
eyelidAn eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...
,
scleraThe sclera, also known as the white part of the eye, is the opaque , fibrous, protective, outer layer of the eye containing collagen and elastic fiber. It is derived from the neural crest. In children, it is thinner and shows some of the underlying pigment, appearing slightly blue...
,
conjunctivaThe conjunctiva is a clear mucous membrane consisting of cells and underlying basement membrane that covers the sclera and lines the inside of the eyelids...
,
irisThe iris is a membrane in the eye, responsible for controlling the diameter and size of the pupil and the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel...
, natural crystalline lens, and
corneaThe cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43...
. The binocular slit-lamp examination provides stereoscopic magnified view of the eye structures in detail, enabling anatomical diagnoses to be made for a variety of eye conditions.
While a patient is seated in the examination chair, he rests his chin and forehead on a support to steady the head.
The
slit lamp is an instrument consisting of a high-intensity light source that can be focused to shine a thin sheet of light into the eye. It is used in conjunction with a biomicroscope. The lamp facilitates an examination of the
anterior segmentThe anterior segment is the front third of the eye that includes the structures in front of the vitreous humour: the cornea, iris, ciliary body, and lens.Within the anterior segment are two fluid-filled spaces:...
, or frontal structures and
posterior segmentThe posterior segment is the back two-thirds of the eye that includes the anterior hyaloid membrane and all of the optical structures behind it: the vitreous humor, retina, choroid, and optic nerve....
, of the human
eyeEyes are organs that detect light, and send electrical impulses along the optic nerve to the visual and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system...
, which includes the
eyelidAn eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...
,
scleraThe sclera, also known as the white part of the eye, is the opaque , fibrous, protective, outer layer of the eye containing collagen and elastic fiber. It is derived from the neural crest. In children, it is thinner and shows some of the underlying pigment, appearing slightly blue...
,
conjunctivaThe conjunctiva is a clear mucous membrane consisting of cells and underlying basement membrane that covers the sclera and lines the inside of the eyelids...
,
irisThe iris is a membrane in the eye, responsible for controlling the diameter and size of the pupil and the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel...
, natural crystalline lens, and
corneaThe cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43...
. The binocular slit-lamp examination provides stereoscopic magnified view of the eye structures in detail, enabling anatomical diagnoses to be made for a variety of eye conditions.
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 or optometrist then proceeds to examine the patient's eye. A fine strip of paper, stained with
fluoresceinFluorescein is a fluorophore commonly used in microscopy, in a type of dye laser as the gain medium, in forensics and serology to detect latent blood stains, and in dye tracing. Fluorescein has an absorption maximum at 494 nm and emission maximum of 521 nm .Fluorescein also has an isosbestic point ...
, a fluorescent 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
tearsTears are the liquid product of a process of crying to clean and lubricate the eyes. The word lacrimation may also be used in a medical or literary sense to refer to crying. Strong emotions, such as sorrow or elation, may lead to crying. The process of yawning may also result in lacrimation...
.
A subsequent test may involve placing drops in the eye in order to
dilate the pupilsMydriasis is an excessive dilation of the pupil due to disease, trauma or the use of drugs. Normally, the pupil dilates in the dark and constricts in the light to improve vividity at night and to protect the retina from sunlight damage during the day, respectively...
. 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 sensitivityApart from vision, human beings have many physiological and psychological responses to light. In rare individuals an atypical response may result in serious discomfort, disease, or injury. Some drugs have a photosensitizing effect...
for a few hours after this exam, and the dilating drops may also cause increased pressure in the eye, leading to nausea and pain. Patients who experience these rare but serious symptoms are advised to seek medical attention immediately.
Adults need no special preparation for the test; however children may need some preparation, depending on age, previous experiences, and level of trust.
The slit lamp exam may detect many diseases of the eye, including:
- Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
- Conjunctivitis
Conjunctivitis is an inflammation of the conjunctiva , most commonly due to an allergic reaction or an infection...
- Corneal injury
- Fuchs' dystrophy
Fuchs' dystrophy, also known as Fuchs' endothelial dystrophy, is a slowly progressing corneal disease that usually affects both eyes and is slightly more common in women than in men...
- Keratoconus
Keratoconus , is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve....
(Fleischer ringFleischer rings are pigmented rings in the peripheral cornea, resulting from iron deposition in basal epithelial cells, in the form of haemosiderin...
)
- Macular degeneration
Macular degeneration is a medical condition usually of older adults that results in a loss of vision in the center of the visual field because of damage to the retina. It occurs in “dry” and “wet” forms. It is a major cause of visual impairment in the elderly...
- Presbyopia
Presbyopia describes the condition where the eye exhibits a progressively diminished ability to focus on near objects with age...
- Retinal detachment
Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. Initial detachment may be localized, but without rapid treatment the entire retina may detach, leading to vision loss and blindness. It is a medical emergency. The retina is a...
- Retinal vessel occlusion
- Retinitis pigmentosa
Retinitis pigmentosa is a group of genetic eye conditions. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not become legally blind until their 40s or 50s and retain some sight all their lives . Others go...
- Sjögren's syndrome
Sjögren's syndrome is an autoimmune disorder in which immune cells attack and destroy the exocrine glands that produce tears and saliva....
- Uveitis
Uveitis specifically refers to inflammation of the middle layer of the eye, termed the "uvea" but in common usage may refer to any inflammatory process involving the interior of the eye....
- Wilson's disease
Wilson's disease or hepatolenticular degeneration is an autosomal recessive genetic disorder in which copper accumulates in tissues; this manifests as neurological or psychiatric symptoms and liver disease...
(Kayser-Fleischer ringKayser-Fleischer rings are dark rings that appear to encircle the iris of the eye. They are due to copper deposition as a result of particular liver diseases. They are named after Dr Bernhard Kayser and Dr Bruno Fleischer, the German doctors who first described them in 1902 and 1903...
)