Introduction to Slit Lamp

Slit lamp: The full name is "slit lamp microscope", which is the most frequently used optical device in ophthalmology. The eyelid, conjunctiva, sclera, cornea, anterior chamber, iris, pupil, lens, and anterior 1/3 of the vitreous can be clearly observed through a slit lamp microscope, and the location, nature, size, and depth of the lesion can be determined. If equipped with accessories, the scope of inspection will be more extensive. Therefore, the slit lamp is not only an important equipment for ophthalmologists to check, but also an instrument that must be mastered by opticians and optometrists.

Slit lamp principle:

Slit lamp: As the name suggests, the light shines through a slit to illuminate the eye. Because it is a narrow slit light source, it is called "light knife". This "light knife" is irradiated on the eyes to form an optical section, and the health status of each part of the eyes can be observed. The principle is to use the "Tyndall phenomenon" of the British physicist Tyndall.

The Tyndall phenomenon is: when a beam of light passes through the colloid, a bright "path" in the colloid can be observed from the vertical direction of the incident light. This phenomenon is called the Tyndall phenomenon, also known as the Tyndall effect.

This phenomenon seen in daily life includes: the light beam of the flashlight at night; the sunlight shining into the house through the window or the crack of the door; the sunlight in the forest and so on. In order to effectively observe the health status of the eyes, the slit lamp must be installed in a room with relatively dark light, and the slit light source illuminates the eyes, and then the examiner observes the health status of various parts of the eyes through a microscope.

Clinical significance of slit lamp:

1. Diffuse lighting method: it can roughly check the anterior tissues such as conjunctiva, cornea and sclera.

2. Direct black spot lighting method: it can carefully observe the lesions in the illuminated area.

3. Posterior illumination method: It is used to examine the anterior tissue of the eye with the light reflected by the posterior tissue, mainly for the examination of transparent tissue.

4. Specular reflection lighting method.

5. Limbal lighting method.

6. Indirect lighting method, etc.

History of the Slit Lamp Lamp:

In 1911, the Swedish ophthalmologist Gullstrand invented the famous ophthalmic examination instrument "Slit lamp". In 1920, Vogt improved it to make its function more perfect and became the blueprint of today's slit lamp.

In 1950, China began to develop the slit lamp, and in 1967, Shanghai Medical Optical Instrument Factory took the lead in successful trial production. In the same year, Suzhou Medical Instrument Factory also successfully designed and manufactured a slit lamp, and became the main manufacturer of slit lamps in China for more than 20 years. During this period, the factory also introduced a 135 film photographic slit lamp. Since the film processing technology cannot be mastered in the ophthalmology department or even the hospital, its production time lags seriously, which restricts the development of film photography slit lamps. It is only used in a small amount in ophthalmology medical research and paper compilation. Clinically, people have been using the inspection mode of eye observation and handwritten reports.

With the rapid development of the market economy, manufacturers of slit lamps sprung up like mushrooms in the 1990s, and the market competition became fiercer. With the rapid development of computer technology and digital imaging technology, the patterns of new photographic slit lamps are constantly refurbished. Among them, the application of digital cameras is highly respected. The picture report and the text diagnosis can be printed on the same report sheet, and the inspection report can be checked immediately. So far the photographic slit lamp has entered the actual clinical application. Chinese slit lamps have already gone abroad, and many manufacturers have a lot of export volume, and the export sales hit new highs every year.

Basic structure of slit lamp

The structure of the slit lamp is mainly composed of two parts, namely the "slit lamp" and the "microscope". In order to facilitate the slit light source to irradiate various parts of the eye from different angles, and the microscope to observe the eye from different angles, both the slit lamp and the microscope are required to have sufficient left and right swing angles mechanically. The light source of the slit lamp requires that the edge of the slit must be very smooth, and the slit must be clearly imaged on the vertical plane of the center of the circle swinging left and right, and the focus of the microscope must also be focused on this vertical plane of the center of the circle.

Slit lighting sources must have:

1. The width of the crack is adjustable within the range of 0 to 14mm;

2. The length of the slit can be adjusted within the range of 1 to 14mm (when the length and width are both 14mm, the slit light is actually a circular spot);

3. The direction of the crack is adjustable. That is to say, the slit light source can be vertical, horizontal, or oblique;

4. The brightness of the light source is adjustable; for digital photography slit lamps, there should also be background lighting with adjustable brightness.

The microscope is a stereo binocular structure and must have:

1. Clear imaging;

2. The focal length of the eyepiece can be adjusted to adapt to different diopters of the operator's eyes;

3. The distance between the two eyepieces can be adjusted to suit the interpupillary distance of different operators; in addition to the above-mentioned left and right swing function, the mechanical structure also has a three-dimensional adjustable mobile worktable; the jaw frame device can fix the patient's head, jaw The jaw support on the frame can be adjusted up and down to adapt to the length of the skull of different patients; the fixation light can prevent the patient's eyes from turning unconsciously.

Slit lamp effect

When the diffuse illumination method is used, the cornea, iris, and crystal can be observed comprehensively by using concentrated light and low power magnification.

When using direct focus lighting, you can observe the curvature and thickness of the cornea, whether there are foreign bodies and posterior corneal deposits (KP), as well as the layers and shapes of lesions such as infiltration and ulcers; when the focus is pushed back, crystals can be observed The turbid part of the body and the lesions in the front 1/3 of the vitreous body; if the cone light is used, the floating particles in the aqueous humor can be checked.

When the mirror reflection method is used, the subtle changes in the front and back of the cornea and the front and back capsules of the lens can be carefully observed, such as exfoliated cells on the tear film, patterns on the corneal endothelium, patterns on the front and back capsules of the lens, and the adult nucleus.

When the posterior reflective irradiation method is used, corneal epithelial or endothelial edema, corneal posterior deposits, new blood vessels, slight scars, and crystal vacuoles can be found.

When using the spectroscopic lighting method of the cornea, you can find very light turbidity on the cornea, such as thin cloud, blisters, perforation, scars and so on.

When using indirect lighting, the pupillary sphincter, iris hemorrhage, iris blood vessels, corneal pannus, etc. can be observed. At the same time, the slit lamp microscope can also be equipped with front mirrors, contact lenses, and three-sided mirrors, etc., to cooperate with the inspection of the peripheral part of the retina, the anterior chamber angle, and the posterior vitreous body. It can also produce stereoscopic vision through binocular observation.

Therefore, through slit-lamp microscopy, the contraindications to wearing soft contact lenses can be identified, and appropriate soft contact lenses can be selected for the wearer.