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

and

optometry Optometry is the healthcare practice concerned with examining the eyes for visual defects, prescribing corrective lenses, and detecting eye abnormalities. In the United States and Canada, optometrists are those that hold a post-baccalaureate f ...

, 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 A lens is a transmissive optical device that focuses or dispers ...

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 in the visual system that reacts to light, visible light allowing eyesight. Other functions include maintaining the circadian rhythm, and Balance (ability), keeping balance. The eye can be considered as a living ...

, 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. "Palpebral ...

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 eye containing mainly collagen and some crucial elastic fiber. In the development of t ...

conjunctiva In the anatomy of the eye, the conjunctiva (: conjunctivae) 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 gobl ...

, iris, natural crystalline lens, and

cornea The cornea is the transparency (optics), transparent front part of the eyeball which covers the Iris (anatomy), iris, pupil, and Anterior chamber of eyeball, anterior chamber. Along with the anterior chamber and Lens (anatomy), lens, the cornea ...

. 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 (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

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; "von" since 1883) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The ...

(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

and

, 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 and his "large reflection-free ophthalmoscope." The instrument was manufactured by Zeiss 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, and the reddish Nernst glower was replaced with the brighter and whiter

incandescent lamp An incandescent light bulb, also known as an incandescent lamp or incandescent light globe, is an electric light that produces illumination by Joule heating a filament until it glows. The filament is enclosed in a glass bulb that is eith ...

. 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 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 cameras 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."Slitlamp"
Haag-Streit, AG, accessed: January 25, 2024. 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. Also known as the control column, it is the principal control devic ...

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

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

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 equipment, 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 ...

. 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 the branch of medicine that deals with the diagnosis, treatment, and surgery of eye diseases and disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a ...

optometrist Optometry is the healthcare practice concerned with examining the eyes for visual defects, prescribing corrective lenses, and detecting eye abnormalities. In the United States and Canada, optometrists are those that hold a post-baccalaureate f ...

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 Triarylmethane dye, triarylmethine dyes family. It is available as a dark orange/red powder slightly soluble in water and alcohol. ...

, 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 generally performed via

ophthalmoscopy 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 ...

, where the observer ( fundus camera or observing eye) is focused to infinity, which brings the subject's fundus into focus due to the refractive power of the subject's optical media. In contrast, the microscope in slit lamp biomicroscopy is focused to the anterior segments of the eye, such that direct observation of the fundus is impossible due to the subject's refractive power. However, with the use of auxiliary optics, the fundus can be brought within the focusing range of the microscope. These optics usually take the form of a lens placed on or near the subject's cornea, which range in optical properties and practical application. Watzke–Allen test is a test used in diagnosis of a full thickness macular hole and also to assess retinal function after surgical closure of the hole, with the help of slit lamp.

Light filters

Most slit-lamps have five light filters options: # 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 Zeiss (company), Zeiss. Zeiss gathered a group of gifted p ...

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 (anatomy), lens of the eye that leads to a visual impairment, decrease in vision of the eye. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colours, blurry or ...

Conjunctivitis Conjunctivitis, also known as pink eye or Madras eye, is inflammation of the conjunctiva, the thin, clear layer that covers the white surface of the eye and the inner eyelid. It makes the eye appear pink or reddish. Pain, burning, scratchiness ...

* Corneal injury such as

corneal ulcer Corneal ulcer, often resulting from keratitis 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 part ...

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. It is a leading cause of blindness in developed countries and one of the lead causes of sight loss in the wor ...

* Fuchs' dystrophy *

Keratoconus Keratoconus is an eye disorder in which the cornea, the transparent front part of the eye, gradually thins and bulges outward into a cone shape. This causes distorted vision, including blurry vision, double vision, increased nearsightedness, ...

( Fleischer ring) *

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

Retinal detachment Retinal detachment is a condition where the retina pulls away from the tissue underneath it. It may start in a small area, but without quick treatment, it can spread across the entire retina, leading to serious vision loss and possibly blindness. ...

* Retinal vessel occlusion * Retinitis pigmentosa * 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 month ...

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 ...

Wilson's disease Wilson's disease (also called hepatolenticular degeneration) is a genetic disorder characterized by the excess build-up of copper in the body. Symptoms are typically related to the brain and liver. Liver-related symptoms include vomiting, wea ...

(

Kayser–Fleischer ring Kayser–Fleischer rings (KF rings) are dark rings that appear to encircle the cornea of the human eye, eye. They are due to copper deposition in the Descemet's membrane as a result of particular liver diseases. They are named after Germany, Germa ...

) A sign that may be seen in slit lamp examination is a "flare", which is when the slit-lamp beam is visible 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