This is a test that uses orange dye (fluorescein) and a blue light to detect foreign bodies in the eye. This test can also detect damage to the cornea, the outer surface of the eye.
A piece of blotting paper containing the dye will be touched to the surface of your eye. You will be asked to blink. Blinking spreads the dye around and coats the "tear film" covering the surface of the cornea. (The tear film contains water, oil, and mucus to protect and lubricate the eye.)
A blue light is then directed at your eye. Any problems on the surface of the cornea will be stained by the dye and appear green under the blue light.
The health care provider can determine the location and likely cause of the cornea problem depending on the size, location, and shape of the staining.
You will need to remove your contact lenses before the test.
If eyes are extremely dry, the blotting paper may be slightly scratchy. The dye may cause a mild and brief stinging sensation.
This test is useful in identifying superficial scratches or other problems with the surface of the cornea. It can also help reveal foreign bodies on the eye surface. It can be used after contacts are prescribed to determine if there is irritation of the surface of the cornea.
If the test result is normal, the dye remains in the tear film on the surface of the eye and does not adhere to the eye itself.
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
Additional conditions under which the test may be performed:
If the fluorescein touches the skin surface, there may be a slight, brief, discoloration.
This test is very useful for detecting injuries or abnormalities on the surface of the cornea.
Knoop KJ, Dennis WR, Hedges JR. Ophthalmologic procedures. In: Roberts JR, Hedges JR, eds. Clinical Procedures in Emergency Medicine. 4th ed. Philadelphia, Pa: Saunders Elsevier; 2004: chap 64.
Hurwitz JJ. The lacrimal drainage system. In: Yanoff M, Duker JS, Augsburger JJ, Azar DT, eds. Ophthalmology. 2nd ed. Philadelphia, Pa: Mosby Elsevier; 2004: chap 98.