The diagnosis of dry eyes requires examination of the surface of the eye (ocular surface) with a biomicroscope (also called a slit lamp). This optical instrument provides a magnified image of the tear film, the ocular surface, and the eyelids, and allows careful examination of the anterior portions of the eye, including the anterior chamber and iris. The application of non-toxic stains to the ocular surface (in the form of eye drops) can facilitate evaluation of the tear film and demonstrate areas of damage on the ocular surface. Lissamine green is used to demonstrate ocular surface changes associated with insufficient tear flow and excessive dryness. Devitalized cells and strands of devitalized surface tissue (filaments) can be visualized with this stain. A scoring system has been developed to rate the severity of these changes and is useful for monitoring dry eye treatment over time. Fluorescein is a second dye which disperses in tear film. The longer the duration in which the fluorescein dye remains evenly dispersed in the tear film, the better the quality of the tear film. The time that it takes for this tear film to “break up” is an important measure of tear film integrity. Fluorescein also allows detection of small areas on the cornea where the lining cells have been lost due to dryness or other forms of damage.
The fluorescein and lissamine green dyes used for ocular staining may cause some mild irritation. A green stain on the surface of the eyes may be present for several hours.
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