Slit lamps

For examining the cornea and the interior of the eye.

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The slit lamp or biomicroscope, combines two components:

  •     a bright focal source of light shone through a slit of variable width or height
  •     a microscope, usually binocular

Although it began as an instrument more commonly used by ophthalmologists, its development was overseen by several optical physicists and it came to be a staple item of equipment of contact lens opticians.

View of the eye through an illuminated slit lamp
A mid 1970s view of the eye
through an illuminated slit lamp

A slit lamp allows close surface examination of the front of the eye (the 'anterior segment') especially the cornea. With the use of auxiliary lenses such as Goldmann or Volk lenses it can also be used to inspect the interior of the eye (the posterior section, including the retina and the vitreous).
 

Czapski's tomb in Jena

The grave of Czapski
in Jena

Binocular microscopes

The binocular microscope component was the first to be developed in the 1890s. The first corneal binocular microscope can be attributed to Aubert in 1891. Siegfried Czapski's corneal surface microscope with stand was developed by Zeiss in 1899 and he soon added a movable source of illumination.

Allvar Gullstrand

Slit illumination

The first instrument to feature slit illumination appears to have been that developed by Allvar Gullstrand (1862-1930) and demonstrated at Heidelberg in 1911. He focused the image of a red hot rod through the slit.

Erggelet in 1914 was the first to publish any clinical results based on examinations taken with such an instrument.

The development of the Zeiss Slit Lamp in 1916 would help immensely with the nascent practice of contact lens fitting. It combined the slit illumination of Gullstrand with the corneal microscope of Czapski. It consisted of a very powerful binocular microscope coupled, around the same axis, with a bright light source thus allowing different illuminations and magnified views of the layers and structures of the cornea.

Otto Henker medal

Otto Henker
medal

Czapski, who worked at Zeiss, improved on the design of the optics of his microscope and Otto Henker, also a Zeiss employee and Scientific Head of the Ophthalmic Optics Department, combined it with the illumination system and refined the two. Henker also devised an arm to support the focusing loupe. Now practitioners could have their hands free to inspect the cornea in much greater detail. For a short period Czapski would take over the mantle of Ernst Abbe after he retired in 1903. However, his scientific leadership of the company would not last for long as he died in 1907 following complications after an operation for appendicitis.


The slit lamp reaches Great Britain

In the 1920s Ida Mann together with Harrison Butler introduced the use of the slit lamp to England. Mann was newly qualified in the technique and her youthful enthusiasm was crucial to the success of the move. Harrison Butler, himself a slit lamp novice of only one year's standing, taught her the technique at Professor Vogt's clinic in Zurich. As she described it in her memoirs:

This...beautiful instrument utilised the principle of the fluorescence of living transparent tissues in a focused beam of light...it was like cutting a microscopic section through live tissue and many things undreamt of were revealed.

One could see the individual red blood corpuscles circulating in the conjunctival vessels, could detect the meeting of two streams, red and colourless, in the larger veins like the confluence of the Blue and White Nile, could watch individual white cells crawling about like amoebae on the back of the cornea, and to my joy could see the various parts of the vitreous humour which I knew of embryologically but had not been able to see in the living eye. These discoveries were of great importance, as they increased our powers of accurate diagnosis.

Using a slit lamp was time-consuming because the illumination system and the corneal microscope both had to be focused separately. For this reason it remained a rather specialist piece of equipment until, in 1933, Hans Goldmann (1899-1991) at that time working under Professor Siegrist of Bern, came up with a joystick controlled mechanism to focus the two components in a co-ordinated manner. Also in 1933 Comberg designed a solution featuring a vertically mounted  illumination system.

Hamblin slit lamp

Illustrated here is a British slit lamp by Theodore Hamblin Ltd (circa the 1940s?) It was donated to the museum along with the book: Ocular Signs in Slit-Lamp Microscopy (1952) by James Hamilton Doggart.

In 1950 Hans Littmann (1908-1991) combined the Goldmann and Comberg systems. Littmann was a physicist working to re-establish the firm of Zeiss Oberkochen in the newly-partitioned Germany from 1946. You could also swing the illumination system round, a particularly useful feature in contact lens examinations. In Great Britain many Littmann-type instruments remained in use for up to fifty years, with various modifications and the occasional rewiring en route.

Zeiss slit lamp in museum

On the right is a Littmann-type Zeiss slit lamp, serial no 19372, (1960s?) in the BOA Museum. It is fully manoeuvrable by joy-stick and includes a mobile stand on wheels. This one was used until shortly before 2003 at the Queen Elizabeth II Hospital in Welwyn Garden City and includes an applanation tonometer made by the Swiss firm of Haag-Streit.

TS Hand slit lamp

A hand slit lamp was a feature of the Turville-Stewart combined ophthalmoscope, retinoscope and slit lamp introduced in 1926. An example is illustrated to the left.

Hand slit lamps could be combined with inspection probes and often featured two thicknesses of slit and a blue filter.

Hand slit lamp
Hand slit lamp
Unknown maker

Japanese versions, for example by Neitz, were popular with optometrists later in the 20th century.

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