Slit Lamp

Overview

A slit lamp is the central diagnostic instrument of an eye exam. It pairs a stereo microscope with an illuminator that casts a thin, bright slit of light into the eye, so the clinician can look at the cornea, iris, lens, and front of the vitreous as an optical section, almost a living histology slide. By narrowing the slit and tilting the beam, structures that are transparent in flat light throw shadows and reflections that reveal scratches, cataract, inflammation, and depth.

The instrument has two arms that share one pivot. The Stereo Microscope gives the magnified stereo view, and the Illumination Tower tower projects the slit; both swing about the eye so the angle between viewing and lighting can be set freely. The whole optical head rides on a Joystick Base whose joystick aims and focuses it, while the patient is steadied at the right height by the Head Rest. A Control Board dims the LED and reads the controls, and a Power Supply feeds the unit.

How it works

Light begins at the LED Light Source, whose high-CRI emitter is chosen so tissue and fluorescein stain show true color. A Condenser Lens fills the Slit Aperture, a pair of knife-edge jaws plus a height iris, which sets the slit's width, length, and angle. The Projection Lens then images that lit slit sharply onto the cornea, and a Reflecting Mirror turns the beam down the shared pivot axis. A Filter Wheel adds cobalt-blue light for stained corneal defects or red-free light for vessels.

The examiner views through the Stereo Microscope. A single front objective feeds both channels; each carries an erecting Erecting Prism and a 10x eyepiece, so the image is upright and three-dimensional. The Magnification Changer is a detented drum of paired Galilean telescopes that steps magnification through fixed settings in both channels at once. A Beam Splitter taps part of the beam to a Lens Assembly and CMOS Image Sensor for documentation without dimming the oculars. Because illumination and viewing pivot about the same axis, the clinician can swing the slit to any oblique angle and keep the eye sharp throughout.