What is slit lamp biomicroscopy?
A slit lamp is a special microscope combined with a bright, narrow beam of light. It gives your ophthalmologist a magnified, three-dimensional view of the eyelids, conjunctiva, cornea, iris, lens and the front chamber of the eye, and, with special lenses, the retina at the back.
Why it is done
It is the cornerstone of every eye examination, used to detect cataract, corneal disorders, conjunctivitis, dry eye, iris and lens abnormalities and many other conditions early, before they affect your vision.
What to expect
You simply rest your chin and forehead on a support while the doctor examines each eye. The test is quick, completely painless and may include eye drops to widen the pupil for a clearer view.
How a slit lamp works
The 'slit' refers to a narrow, bright beam of light that the instrument shines into the eye. Because the front structures of the eye are transparent, this thin beam creates an illuminated optical cross-section, letting the doctor see each layer in turn. At the same time, a binocular (two-eyepiece) microscope gives a magnified, stereoscopic view with a real sense of depth. The width, height and angle of the beam, as well as different coloured filters, can all be adjusted to highlight particular structures or signs.
What conditions a slit lamp exam can detect
A slit lamp examination helps the doctor detect a wide range of conditions in the front of the eye, including cataract, corneal ulcers and abrasions, conjunctivitis, dry eye, anterior uveitis (inflammation inside the eye), and changes in the iris and lens. With the help of additional hand-held or contact lenses, the same instrument can also be used to examine the retina at the back of the eye. This makes it one of the most versatile tools in a complete eye examination.