Fluorescein staining of the cornea

Fluorescein staining is a commonly used eye test in which an orange-yellow dye, fluorescein, is applied to the surface of the eye. The dye binds to damaged or dry areas on the cornea and glows bright green under blue light, usually from a special lamp used by the ophthalmologist or optometrist.

The test is often carried out to detect minor scratches, erosions, infections, dry patches or other corneal abnormalities that are not visible to the naked eye. The test can also be used during the fitting of contact lenses to check whether the lens fits properly and whether any pressure points or irritation are occurring.

Fluorescein is a safe, non-toxic dye that remains on the eye temporarily and is washed away by the tear film after a few minutes to hours. The dye may temporarily turn your tears and contact lenses orange; soft lenses can absorb the dye and are therefore usually removed before the test.

When is the test used?

An ophthalmologist or optometrist carries out a fluorescein staining test in response to symptoms such as pain, redness, a burning sensation, sensitivity to light or the feeling that there is something in your eye. The test helps to assess whether there is superficial damage, dry eye, an infection or a poorly fitting contact lens.

The test is also sometimes used for contact lens wearers to check whether the lens is moving correctly, whether there is sufficient tear exchange and whether the cornea remains healthy.

How is the test carried out?

The ophthalmologist or optometrist applies a drop of fluorescein using a dropper bottle or a moistened paper strip held briefly against the inside of your lower eyelid. You will be asked to blink a few times so that the dye spreads across the surface of the eye.

The optometrist will then examine your eye using a slit lamp and a blue light. Damaged areas glow bright green, whilst healthy tissue remains dark. The test takes just a few minutes and is painless.

What happens after the test?

The fluorescein washes away naturally via your tear film and tear ducts. Your tears may be temporarily orange or yellow in colour, and your skin may become slightly discoloured if you rub your eye. This will disappear within a few hours.

If you wear soft contact lenses, ask your optician or ophthalmologist when you can put them back in; it is usually advised to wait at least an hour or to rinse the lenses thoroughly first.