Slit Lamp Techniques

Optometrists use a slit lamp to examine various structures of the eye. The slit lamp is composed of a high-intensity light and a binocular microscope. The microscope allows magnification from six to 40 times and the light source is adjustable. Coupling the illuminated beam with the microscope focuses on a single point, although de-coupling is sometimes preferable. The slit lamp examination can detect problems with the eye, including injuries to the cornea, cataracts and retinal detachment.

Direct or Focal Illumination

• For viewing the structures at the front of the eye, this is the most common technique. Focus illumination through the slit and increase magnification to maximum to view detailed areas of interest.

Indirect Illumination

• Once a feature has been located through direct illumination, de-couple the beam and move it to the side. Structures beyond the illuminated patch scatter light and are easier to view without the glare. View corneal nerves and opacities with this technique.

Retro Illumination

• Another form of indirect illumination, retro illumination reflects light off the iris or retina allowing the microscope to study the lens or cornea in the reflected light.

Diffuse Illumination

• A diffuser is required to soften the light of the illuminating system. Open the slit completely and set magnification to six times to enable a large field of view. This technique is good for general observation of the eye and accessory structures such as eyelids and tear ducts.

Specular Reflection

• A monocular technique that reflects the illumination from the slit at a mirror angle, this method allows the light to be reflected from the front or back corneal surface. Use specular reflection to examine the epithelium, endothelium, tear film and crystalline lens.

Sclerotic Scatter

• Use a narrow slit to reflect the light internally within the cornea. The light is scattered by the sclera, or white of the eye, allowing foreign bodies within the eye to be visible.