Fluorescein Slit Lamp Examination for Corneal Scratches
Yes, corneal scratches (epithelial defects) light up bright green under blue cobalt light after fluorescein application because the dye penetrates into areas where the corneal epithelium is disrupted and intercellular junctions are broken. 1, 2
How Fluorescein Staining Works
Fluorescein dye specifically stains areas of the corneal epithelium where there is sufficient disruption of intercellular junctions to allow the dye to permeate into the tissue. 1 This makes it the ideal diagnostic tool for visualizing corneal scratches and abrasions that would otherwise be difficult to see.
- The dye highlights epithelial defects by accumulating in damaged tissue where the protective barrier has been compromised 2
- Normal intact epithelium does not allow fluorescein penetration, creating clear contrast between healthy and damaged areas 1
Proper Examination Technique
The examination must be performed correctly to visualize the scratch:
- Apply fluorescein using a saline-moistened strip to the inferior tarsal conjunctiva (avoid fluorescein-anesthetic combination drops as anesthetics may affect results) 1, 2
- Examine the ocular surface through a slit-lamp biomicroscope using a cobalt blue filter 1, 2
- Wait approximately 2 minutes after application for optimal visualization 1
- Use a yellow filter in conjunction with cobalt blue light for more intense staining visualization 1, 2
What You'll See
- Corneal scratches appear as bright green fluorescent areas against the darker background of normal cornea 2
- The staining pattern reveals the exact size, shape, and location of the epithelial defect 3
- Fluorescein is more easily visualized on the cornea than on the conjunctiva 1, 2
Important Clinical Considerations
Perform fluorescein staining before instilling any other eyedrops and before manipulating the eyelids, as these can produce false results. 1, 2
- Mild fluorescein staining can occur in normal eyes, particularly in the morning, so clinical context matters 1
- Document the size (in millimeters), location, depth, and shape of any epithelial defect identified 3
- Recurrent staining in the same area may indicate localized anterior basement-membrane abnormalities 1, 2