Everything there is to know about a slit lamp

A slit lamp is an ophthalmology device that, from one side, usually looks like a rack for the head of a patient who sits in front of a doctor's seat. It is equipped with a unique electronic complex and contains a lamp that can focus on a very thin light beam. Attached to it is a biomicroscope.

This apparatus is useful in a vast number of eye examinations of the anterior part of an eyeball, and the posterior segments, including cornea, sclera, iris, conjunctiva, natural crystalline lens, eyelid, and others. They may also be combined with video cameras to obtain more possibilities for routine check-ups and fixation of pathological changes from one ophthalmology clinic visit to another.

A brief history of a slit lamp

This device has a much longer and more in-depth history than can be shown on paper. If we dig very deep, then we can find that the roots of these instruments lie in Ancient Greece, where the first-ever optical enlargement process was discovered. Ancient Greeks were observing different objects through the water surface as they noticed that objects get bigger that way. Centuries passed by, and everyone started to use a glass of water as an enlargement tool. The next step to introducing the slit lamp was an ophthalmoscope created by Hermann von Helmholtz in 1850. After that, in 1911, the first sizable reflection-free ophthalmoscope appeared. And that was, basically, the first-ever known 'grandfather" of our instrument.

A few improvements and engineering enhancements later, in 1965, we got an instrument looking almost like every other modern slit lamp called the Model 100/1. It was created by Littmann, who first redesigned them after World War II. Current versions of this apparatus often include different cameras for videography purposes.

Indications for using a slit lamp

The main indications for the usage of the slit lamp are various types of examinations of the eyes. The patient sits on his side of the tool and puts his or her head into a specific rack, while a doctor observes the patient's eyes. There are in total about six or seven (depending on the apparatus type) possible illuminating options, each of which grants a possibility to observe a different part of an eyeball. Here is the list of those options with the structures possible to see:

  • Sclerotic scatter - entire cornea at a glance
  • Indirect lateral illumination (also known as indirect proximal illumination) - anterior chamber, and cornea
  • Specular reflection -endothelial outline of the cornea, and mid-peripheral corneal epithelium
  • Direct focal illumination - anterior chamber, depth localization, grading cells, and flare
  • Diffuse illumination - adnexa, general surface eye tissue observation
  • Transillumination (also known as retro illumination) - areas behind the crystalline lens

Generally, the number of various pathological processes that can potentially be diagnosed by its use is vast. Among the rare options that can be useful during the slit lamp examinations is video mosaicking, which helps determine a lot of various pathologies. Among those pathologies are: 

  • Cataract
  • Diabetic retinopathy
  • Glaucoma
  • Conjunctivitis
  • Different types of eye tumors
  • Retinitis pigmentosa
  • Macular degeneration
  • Fuchs' dystrophy
  • Corneal injury, e. g., ulcers, and swellings
  • Uveitis
  • Sjögren's syndrome

Other indications for using a slit lamp are present in the toxicology and drug development test industry. By using the tool, the doctor can examine the state of the pupil and their reaction to the light beam. In some cases, it may also be useful for individual drops (usually atrophin) to get the pupils very wide and to look at their reaction and the ocular fundus at one time. That may give much information about the patient's current nerve system.

Complications of use

The biggest group of complications connected with using this type of device is connected with the misuse of the apparatus functions by the doctor and the lack of patient preparation for the procedure, which can lead the doctor to cause serious injuries to a patient's cornea.

The second big group of complications is connected with different malfunctions and brakes of the apparatus itself. Various traumas may occur if, for instance, the doctor breaks the glass of a biomicroscope, and its parts land on the surface of the patient's eyes. The same situation may happen if the patient puts his head on the rack, which breaks due to mechanical instability.

Additional complications might occur if the apparatus is not cleaned and appropriately decontaminated. As a result of this, various infectious diseases may occur. 

General Specifications

These devices usually look and work in a pretty similar way, which is why the general specifications that you will find in the list below will match almost every possible slit lamp, which you may find on the modern medical tool market. We took the main specifications from different lists, summarized them, and got the average indicators. Here are the main specifications:

  • Microscope type - Galilean-type converging binocular
  • Magnification - from 2 x to 20 x
  • Real fields of view - not less than 23 mm x 5,6 mm
  • Interpupillary adjustment - not less than 55 mm x 75 mm
  • Slit width - continuously variable, at least from 0 to 14 mm
  • Slit length - continuously variable, at least from 0 to 14 mm
  • Slit inclination - from 0 to 20°
  • Filters - cobalt blue, red-free, heat-absorbing
  • Input supply - from 200 to 240 Vac, 50 - 60 Hz
  • Motorized table - included
  • Longitudinal movement - not less than 90 mm
  • Lateral movement - not less than 95 mm
  • Vertical movement - not less than 30 mm
  • Chinrest vertical movement - not less than 55 mm
  • Illumination - Halogen or xenon bulbs

In some cases, there are also different additional functions available, e. g., video recording, or photographing, which, understandably, need extra parts, and respectively add some new specifications to the list.

Market Leaders

There are lots of corporations nowadays selling slit lamps across the globe. All of them are pretty much the same. Only the material types and tiny details vary. So, it was pretty hard to find the best manufacturers with the highest quality. Here is our list of the top ten of them:

  • 66 Vision Tech Co
  • Accutome
  • ADC
  • Alcon
  • Carl Zeiss
  • Burton
  • Integra
  • Olympus
  • Stryker
  • Welch Allyn Cogent

Conclusions

A slit lamp is a pretty useful device that finds its place in various types of diagnostic procedures in ophthalmology, eye surgery, neurology, and a few more different medical fields. Nowadays, there is no worthy alternative for those tools in the whole ophthalmology field.

Probably, there are lots of various engineering improvements, and different enhancements waiting for those devices in the future. It is possible that in the future, those apparatuses will also be useful for various treatment procedures that involve light beams.