Slit Lamp Biomicroscopy: What It Is and What It Shows

How a slit lamp works

The instrument has two main parts that share a common pivot: a binocular microscope for the examiner and an illumination arm that projects a bright slit of light into the eye. By narrowing, widening and angling the slit, the examiner creates an optical section through the cornea, lens and other transparent structures, similar to cutting a thin slice of tissue with light. The patient rests their chin and forehead on a support so the eye stays steady.

Stereoscopic optics give depth, so the examiner perceives the thickness and position of lesions. Magnification is usually changed in steps. The A.R.C. Laser PCL5, for instance, has a five-step changer covering magnifications from 6.3x to 40x, a 10° stereo angle and a pupillary distance range of 52 to 78 mm.

What a slit lamp examination shows

With a slit lamp, the examiner can assess the eyelids and lashes, conjunctiva, cornea, anterior chamber, iris, lens and, with an additional lens, the vitreous and retina. It reveals corneal scars and ulcers, cataract, inflammation in the anterior chamber and many other findings. The technique chosen, such as diffuse, direct focal or retroillumination, depends on what is being looked for; see slit lamp illumination techniques.

Adjuncts widen the scope: a contact lens to see the angle of the anterior chamber, a handheld condensing lens for the posterior segment, and an applanation tonometer attached to the instrument to measure eye pressure. Staff interpret findings according to their training, and this page is not a diagnostic guide.

• Eyelids, lashes, conjunctiva and cornea
• Anterior chamber, iris and lens
• Vitreous and retina with an additional lens
• Eye pressure with an attached tonometer
• Laser delivery when coupled with a laser system

Slit lamp versus ophthalmoscope

A direct ophthalmoscope is a handheld device that gives a magnified view of the back of the eye through the pupil. It is portable and useful at the bedside, but it gives a limited field and little depth. The slit lamp, in contrast, provides a stereoscopic, highly magnified view of the front of the eye and, with a lens, the retina. The two instruments complement each other, and neither replaces the other.

For laser work, there is a third option, the indirect ophthalmoscope, which allows retinal treatment without a table-mounted instrument; see laser indirect ophthalmoscope.

Where slit lamps are used

Slit lamps are the basic instrument of every eye clinic and a common item in hospital emergency departments, optometry practices and operating rooms, where a portable version may be used. They are also the delivery platform for many ophthalmic lasers: the PCL5 is the slit lamp platform for A.R.C. lasers, with halogen or LED illumination and an optional head-up display that shows laser parameters and total energy without looking away from the eyepiece.

Learn the parts of the instrument and their functions in our article on slit lamp parts and functions. Understanding the controls helps new staff use the device properly and helps clinics choose between models.

Choosing and sourcing a slit lamp

If you are equipping a clinic, compare magnification range, quality of optics, illumination type, ergonomics, table, imaging options and service support. We cover price drivers in our slit lamp buying guide. Beckfinity supplies the PCL5 slit lamps from A.R.C. Laser in the UAE; contact our team to discuss your clinic.