Slit lamp

One trend originated from clinical research and aimed to apply the increasingly complex and advanced technology of the time.

[1] The second trend originated from ophthalmologic practice and aimed at technical perfection and a restriction to useful methods.

[3] 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.

"[3] The instrument was manufactured by Zeiss and consisted of a special illuminator connected to a small stand base through a vertical adjustable column.

The illuminator employed a Nernst glower which was later converted into a slit through a simple optical system.

Vogt introduced Koehler illumination, and the reddish Nernst glower was replaced with the brighter and whiter incandescent lamp.

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.

Additionally, Littmann added the stereo telescope system with a common objective magnification changer.

[9] At the same time, halogen lamps replaced the older illumination systems to make them brighter and essentially daylight quality.

[10] While a patient is seated in the examination chair, they rest their chin and forehead on a support area to steady the head.

A subsequent test may involve placing drops in the eye in order to dilate the pupils.

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.

[11] 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.

[12] If media, especially that of the cornea, are opaque, optical section images are often impossible depending on severity.

Direct focal illumination is used for grading cells and flare in anterior chamber by shortening height of beam to 2–1 mm.

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.

[17] 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.

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.

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.