Slit-lamp microscopy
Slit-lamp microscopy, also known as biomicroscopy, is a vital diagnostic tool used primarily by ophthalmologists to examine the tissues of the eye. This instrument enables detailed observation of the anterior segment of the eye through various illumination techniques, including diffuse, direct, and retroillumination, which help visualize both normal and abnormal tissues effectively. The slit-lamp microscope features two coaxial arms: one for adjustable illumination and the other for binocular observation, allowing clinicians to assess eye health with high levels of optical magnification.
In addition to direct observation, auxiliary devices can be attached to measure intraocular pressure and corneal thickness, while specialized lenses can facilitate examination of the retina and optic nerve. The use of dyes such as fluorescein enhances the differentiation of tissue types during examinations. Slit-lamp microscopy is integral to routine eye exams, where it aids in the early detection of various ocular conditions. The instrument's design and functionality have evolved significantly since Allvar Gullstrand's Nobel Prize-winning contributions in 1911, which laid the groundwork for modern ophthalmic practices.
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Subject Terms
Slit-lamp microscopy
Also known as: Biomicroscope
Anatomy or system affected: Eyes
Definition: The use of a special instrument to examine the tissues of the eye
Indications and Procedures
The slit-lamp microscope, or biomicroscope, is used to examine and evaluate tissues of the eye with both stereopsis and multiple values of optical magnification. The anterior segment of the eye is observed with several types of illumination: diffuse, direct (both broad and narrow beam, the latter allowing an almost slide like examination of the clear corneal layers), indirect (side illumination), retroillumination (in which abnormalities are back-illuminated with light reflected from more internal structures), specular (in which light is reflected off various layers to show the detail of each surface), and sclerotic scatter (internal illumination). Various dyes (such as fluorescein or rose bengal) may be employed to help differentiate normal from abnormal tissues.
The instrument has two coaxial rotating arms controlled by a joystick level; one arm carries the adjustable slit-lamp illumination system, with attendant filters and optical stops, and the other arm carries the observation optics (a binocular microscope). An adjustable chin and forehead rest positions the subject’s head.
Auxiliary devices allow the measurement of intraocular pressure (tonometer) and corneal thickness (picometer) and the evaluation of the angle between the cornea and iris (gonioscope lens). Cameras, both still and video, may be attached at various sites. High-powered auxiliary optical lenses have also been developed, which allow the clinician to use the slit-lamp microscope to observe the posterior pole of the eye (through the pharmacologically dilated pupil), including the optic nerve and most of the retina. Ophthalmic lasers can also be attached to this system to treat the various structures of the eye as they are observed directly through the same optics, using the principle of the reversibility of the path of light.
Allvar Gullstrand received a Nobel Prize in 1911 for his contributions to optics, and the same year he introduced his refinement of the slit-lamp microscope. Modern instruments and techniques are largely based on his work. When an individual visits their ophthalmologist for a routine eye exam, the eye doctor uses a slit-lamp microscope.
Bibliography
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