A 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 segment The anterior segment or anterior cavity is the front third of the eye that includes the structures in front of the vitreous humour: the cornea, iris, ciliary body, and lens.Cassin, B. and Solomon, S. ''Dictionary of Eye Terminology''. Gainesvil ...

and

posterior segment The posterior segment or posterior cavity 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.human eye The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows humans to use visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm. ...

, which includes the

eyelid An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eye ...

sclera The sclera, also known as the white of the eye or, in older literature, as the tunica albuginea oculi, is the opaque, fibrous, protective, outer layer of the human eye containing mainly collagen and some crucial elastic fiber. In humans, and so ...

conjunctiva The conjunctiva is a thin mucous membrane that lines the inside of the eyelids and covers the sclera (the white of the eye). It is composed of non-keratinized, stratified squamous epithelium with goblet cells, stratified columnar epithel ...

iris Iris most often refers to: *Iris (anatomy), part of the eye *Iris (mythology), a Greek goddess * ''Iris'' (plant), a genus of flowering plants * Iris (color), an ambiguous color term Iris or IRIS may also refer to: Arts and media Fictional ent ...

, natural

crystalline lens The lens, or crystalline lens, is a transparent biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. By changing shape, it functions to change the focal length of the eye so that it ca ...

, and

cornea The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical ...

. The binocular slit-lamp examination provides a

stereoscopic Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word ''stereoscopy'' derives . Any stereoscopic image is ...

magnified view of the eye structures in detail, enabling anatomical diagnoses to be made for a variety of eye conditions. A second, hand-held lens is used to examine the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...

History

Two conflicting trends emerged in the development of the slit lamp. One trend originated from clinical research and aimed to apply the increasingly complex and advanced technology of the time."Eye Examination with the Slit Lamp"
Carl Zeiss Meditec, AG, p. 33, accessed: February 6, 2011. The second trend originated from ophthalmologic practice and aimed at technical perfection and a restriction to useful methods. The first man credited with developments in this field was

Hermann von Helmholtz Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The Helmholtz Associat ...

(1850) when he invented the

ophthalmoscope Ophthalmoscopy, also called funduscopy, is a test that allows a health professional to see inside the fundus of the eye and other structures using an ophthalmoscope (or funduscope). It is done as part of an eye examination and may be done as part ...

. In

ophthalmology Ophthalmology ( ) is a surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a me ...

and

optometry Optometry is a specialized health care profession that involves examining the eyes and related structures for defects or abnormalities. Optometrists are health care professionals who typically provide comprehensive primary eye care. In the Un ...

, the instrument is called a "slit lamp", although it is more correctly called a "slit lamp instrument"."Eye Examination with the Slit Lamp", Zeiss, p. 34 Today's instrument is a combination of two separate developments, the corneal microscope and the slit lamp itself. The first concept of a slit lamp dates back to 1911 credited to

Allvar Gullstrand Allvar Gullstrand (5 June 1862 – 28 July 1930) was a Swedish ophthalmologist and optician. Life Born at Landskrona, Sweden, Gullstrand was professor (1894–1927) successively of eye therapy and of optics at the University of Uppsala. He ap ...

and his "large reflection-free ophthalmoscope." The instrument was manufactured by

Zeiss Zeiss or Zeiß may refer to: People *Carl Zeiss (1816–1888), German optician and entrepreneur *Emil Zeiß (1833–1910), German Protestant minister and painter Companies *Carl Zeiss AG, German manufacturer of optics, industrial measurem ...

and consisted of a special illuminator connected to a small stand base through a vertical adjustable column. The base was able to move freely on a glass plate. The illuminator employed a Nernst glower which was later converted into a slit through a simple optical system."Eye Examination with the Slit Lamp", Zeiss, p. 35 However, the instrument never received much attention and the term "slit lamp" did not appear in any literature again until 1914. It was not until 1919 that several improvements were made to the Gullstrand slit lamp made by Vogt Henker. First, a mechanical connection was made between lamp and ophthalmoscopic lens. This illumination unit was mounted to the table column with a double articulated arm. The binocular microscope was supported on a small stand and could be moved freely across the tabletop. Later, a cross slide stage was used for this purpose. Vogt introduced

Koehler illumination Koehler is a transliteration of the German surname Köhler, referring to a man making charcoal from wood. Notable people with the surname include: * Ana Luiza Koehler (born 1977), Brazilian comics artist and architect. *Arthur Koehler (1885–19 ...

, and the reddish Nernst glower was replaced with the brighter and whiter

incandescent lamp An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxida ...

. Special mention should be paid to the experiments that followed Henker's improvements in 1919. On his improvements the Nitra lamp was replaced with a

carbon arc An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the first decade of the 1800s, ...

lamp with a liquid filter. At this time the great importance of color temperature and the luminance of the light source for slit lamp examinations were recognized and the basis created for examinations in red-free light. In the year 1926, the slit lamp instrument was redesigned. The vertical arrangement of the projector made it easy to handle. For the first time, the axis through the patient's eye was fixed along a common swiveling axis, although the instrument still lacked a coordinate cross-slide stage for instrument adjustment. The importance of focal illumination had not yet been fully recognized. In 1927,

stereo camera A stereo camera is a type of camera with two or more lenses with a separate image sensor or film frame for each lens. This allows the camera to simulate human binocular vision, and therefore gives it the ability to capture three-dimensional ...

s were developed and added to the slit lamp to further its use and application. In 1930, Rudolf Theil further developed the slit lamp, encouraged by

Hans Goldmann Hans Goldmann (20 November 1899 in Komotau, Kingdom of Bohemia, Austro-Hungarian Empire – 19 November 1991 in Bern) was an Austrian-Swiss ophthalmologist and inventor. Biography Goldmann completed his Gymnasium education in Komotau (now known as ...

. Horizontal and vertical co-ordinate adjustments were performed with three control elements on the cross-slide stage. The common swivel axis for microscope and illumination system was connected to the cross-slide stage, which allowed it to be brought to any part of the eye to be examined. A further improvement was made in 1938. A control lever or

joystick A joystick, sometimes called a flight stick, is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. A joystick, also known as the control column, is the principal cont ...

was used for the first time to allow for horizontal movement. Following

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

the slit lamp was improved again. On this particular improvement the slit projector could be swiveled continuously across the front of the

microscope A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisi ...

. This was improved again in 1950, when a company named Littmann redesigned the slit lamp. They adopted the joystick control from the Goldmann instrument and the illumination path present in the Comberg instrument. Additionally, Littmann added the stereo telescope system with a common objective magnification changer. In 1965, the Model 100/16 Slit Lamp was produced based on the slit lamp by Littmann. This was soon followed by the Model 125/16 Slit Lamp in 1972. The only difference between the two models was their operating distances of 100 mm to 125 mm. With the introduction of the photo slit lamp further advancements were possible. In 1976, the development of the Model 110 Slit Lamp and the 210/211 Photo Slit Lamps were an innovation by which each were constructed from standard modules allowing for a wide range of different configurations."Eye Examination with the Slit Lamp", Zeiss, p. 39 At the same time,

halogen lamp A halogen lamp (also called tungsten halogen, quartz-halogen, and quartz iodine lamp) is an incandescent lamp consisting of a tungsten filament sealed in a compact transparent envelope that is filled with a mixture of an inert gas and a small ...

s replaced the older illumination systems to make them brighter and essentially daylight quality. From 1994 onwards, new slit lamps were introduced which took advantage of new technologies. The last major development was in 1996 in which included new slit lamp optics. See also
From Lateral Illumination to Slit Lamp - An Outline of Medical History
.

General procedure

While a patient is seated in the examination chair, they rest their chin and forehead on a support area to steady the head. Using the biomicroscope, the

ophthalmologist Ophthalmology ( ) is a surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a med ...

optometrist Optometry is a specialized health care profession that involves examining the eyes and related structures for defects or abnormalities. Optometrists are health care professionals who typically provide comprehensive primary eye care. In the Un ...

then proceeds to examine the patient's eye. A fine strip of paper, stained with

fluorescein Fluorescein is an organic compound and dye based on the xanthene tricyclic structural motif, formally belonging to triarylmethine dyes family. It is available as a dark orange/red powder slightly soluble in water and alcohol. It is widely used ...

, 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

tears Tears are a clear liquid secreted by the lacrimal glands (tear gland) found in the eyes of all land mammals. Tears are made up of water, electrolytes, proteins, lipids, and mucins that form layers on the surface of eyes. The different types of ...

. A 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. Patients who experience 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.

Illuminations

Various methods of slitlamp illumination are required to obtain full advantage of slit-lamp biomicroscope. There are mainly six type of illuminating options: # Diffuse illumination, # Direct focal illumination, # Specular reflection, # Transillumination or retroillumination, # Indirect lateral illumination or Indirect proximal illumination and # Sclerotic scatter. Oscillatory Illumination is sometimes considered an illumination technique. Observation with an optical section or direct focal illumination is the most frequently applied method of examination with the slit lamp. With this method, the axes of illuminating and viewing path intersect in the area of the anterior eye media to be examined, for example, the individual corneal layers.

Diffuse illumination

If media, especially that of the cornea, are opaque, optical section images are often impossible depending on severity. In these cases, diffuse illumination may be used to advantage. For this, the slit is opened very wide and a diffuse, attenuated survey illumination is produced by inserting a ground glass screen or diffuser in the illuminating path. "Wide beam" illumination is the only type that has the light source set wide open. Its main purpose is to illuminate as much of the eye and its adnexa at once for general observation.

Direct focal illumination

Observation with an optical section or direct focal illumination is the most frequently applied method. It is achieved by directing a full-height, hairline to medium width, medium-bright beam obliquely into the eye and focusing it on the cornea so that a quadrilateral block of light illuminates the transparent medias of eye. Viewing arm and illuminating arm are kept parfocal. This type of illumination is useful for depth localization. Direct focal illumination is used for grading cells and flare in anterior chamber by shortening height of beam to 2–1 mm.

Specular reflection

Specular reflection, or reflected illumination is just like patches of reflection seen on sunlit lake water surface. To achieve specular reflection, the examiner directs a medium to narrow beam of light (it must be thicker than an optical section) toward the eye from the temporal side. The angle of illumination should be wide (50°-60°) relative to the examiners axis of observation (which should be slightly nasal to the patients visual axis). A bright zone of specular reflection will be evident on the temporal, midperipheral corneal epithelium. It is used to see endothelial outline of cornea.

Transillumination or retroillumination

In certain cases, illumination by optical section does not yield sufficient information or is impossible. This is the case, for example, when larger, extensive zones or spaces of the ocular media are opaque. Then the scattered light that is not very bright normally is absorbed. A similar situation arises when areas behind the crystalline lens are to be observed. In this case the observation beam must pass a number of interfaces that may reflect and attenuate the light.

Indirect illumination

With this method, light enters the eye through a narrow to medium slit (2 to 4 mm) to one side of the area to be examined. The axes of illuminating and viewing path do not intersect at the point of image focus, to achieve this; the illuminating prism is decentered by rotating it about its vertical axis off the normal position. In this way, reflected, indirect light illuminates the area of the anterior chamber or cornea to be examined. The observed corneal area then lies between the incident light section through the cornea and the irradiated area of the iris. Observation is thus against a comparatively dark background."Eye Examination with the Slit Lamp", Zeiss, p. 17

Sclerotic scatter or scattering sclero-corneal illumination

With this type of illumination, a wide light beam is directed onto the limbal region of the cornea at an extremely low angle of incidence and with a laterally de-centered illuminating prism. Adjustment must allow the light beam to transmit through the corneal parenchymal layers according to the principle of total reflection allowing the interface with the cornea to be brightly illuminated. The magnification should be selected so that the entire cornea can be seen at a glance.

Special techniques

Fundus observation and gonioscopy with the slit lamp

Fundus observation is known by the ophthalmic and the use of

fundus camera Fundus photography involves photographing the rear of an eye, also known as the fundus. Specialized fundus cameras consisting of an intricate microscope attached to a flash enabled camera are used in fundus photography. The main structures that ...

s. With the slit lamp, however, direct observation of the fundus is impossible due to the refractive power of the ocular media. In other words: the far point of the eye (punctum remotum) is so distant in front of (

myopia Near-sightedness, also known as myopia and short-sightedness, is an eye disease where light focuses in front of, instead of on, the retina. As a result, distant objects appear blurry while close objects appear normal. Other symptoms may includ ...

) or behind (

hyperopia Far-sightedness, also known as long-sightedness, hypermetropia, or hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blurred effect is due to incoming light being focused behind, i ...

) that the microscope cannot be focused. The use of auxiliary optics - generally as a lens – makes it possible however to bring the far point within the focusing range of the microscope. For this various auxiliary lenses are in use that range in optical properties and practical application.

Light filters

Most slit-lamp use five light filters. Such as # Unfiltered, # Heat absorption- for increased patient comfort # Grey filter, # Red free- for better visualisation of nerve fibre layer and haemorrhages and blood vessels. # Cobalt blue- after staining with fluorescein dye, for seeing corneal ulcers, contact lens fitting, Seidel's test

Cobalt blue light

Slit lamps produce light of the wavelength 450 to 500 nm, known as "cobalt blue". This light is specifically useful for looking for problems in the eye once it has been stained with

Types

There are two distinct slit lamp types based on the location of their illumination system:

Zeiss type

In the Zeiss type slit lamp, the illumination is located below the microscope. This type of slit lamp is named after the manufacturing company

Carl Zeiss Carl Zeiss (; 11 September 1816 – 3 December 1888) was a German scientific instrument maker, optician and businessman. In 1846 he founded his workshop, which is still in business as Carl Zeiss AG. Zeiss gathered a group of gifted practica ...

Haag Streit type

In the Haag Streit type slit lamp, the illumination is located above the microscope. This type of slit lamp is named after the manufacturing company Haag Streit.

Interpretation

The slit lamp exam may detect many diseases of the eye, including: *

Cataract A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble ...

Conjunctivitis Conjunctivitis, also known as pink eye, is inflammation of the outermost layer of the white part of the eye and the inner surface of the eyelid. It makes the eye appear pink or reddish. Pain, burning, scratchiness, or itchiness may occur. Th ...

* Corneal injury such as

corneal ulcer Corneal ulcer is an inflammatory or, more seriously, infective condition of the cornea involving disruption of its epithelial layer with involvement of the corneal stroma. It is a common condition in humans particularly in the tropics and the a ...

or corneal swelling *

Diabetic retinopathy Diabetic retinopathy (also known as diabetic eye disease), is a medical condition in which damage occurs to the retina due to diabetes mellitus. It is a leading cause of blindness in developed countries. Diabetic retinopathy affects up to 80 perc ...

* Fuchs' dystrophy *

Keratoconus Keratoconus (KC) is a disorder of the eye that results in progressive thinning of the cornea. This may result in blurry vision, double vision, nearsightedness, irregular astigmatism, and light sensitivity leading to poor quality-of-life. ...

(

Fleischer ring Fleischer rings are pigmented rings in the peripheral cornea, resulting from iron deposition in basal epithelial cells, in the form of hemosiderin. They are usually yellowish to dark-brown, and may be complete or broken. The rings are best seen usi ...

) *

Macular degeneration Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred or no vision in the center of the visual field. Early on there are often no symptoms. Over time, however, so ...

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 blin ...

* Retinal vessel occlusion *

Retinitis pigmentosa Retinitis pigmentosa (RP) is a genetic disorder of the eyes that causes loss of vision. Symptoms include trouble seeing at night and decreasing peripheral vision (side and upper or lower visual field). As peripheral vision worsens, people may ...

* Sjögren's syndrome *

Toxoplasmosis Toxoplasmosis is a parasitic disease caused by '' Toxoplasma gondii'', an apicomplexan. Infections with toxoplasmosis are associated with a variety of neuropsychiatric and behavioral conditions. Occasionally, people may have a few weeks or mont ...

Uveitis Uveitis () is inflammation of the uvea, the pigmented layer of the eye between the inner retina and the outer fibrous layer composed of the sclera and cornea. The uvea consists of the middle layer of pigmented vascular structures of the eye and in ...

Wilson's disease Wilson's disease is a genetic disorder in which excess copper builds up in the body. Symptoms are typically related to the brain and liver. Liver-related symptoms include vomiting, weakness, fluid build up in the abdomen, swelling of the legs, ...

( Kayser-Fleischer ring) One sign that may be seen in slit lamp examination is a "flare", which is when the slit-lamp beam is seen in the anterior chamber. This occurs when there is breakdown of the blood-aqueous barrier with resultant exudation of protein.Chapter 32 in Classification, Symptoms, and Signs of Uveitis
by DEBRA A. GOLDSTEIN and HOWARD H. TESSLER. 2006 Edition