Fluorescein test

Introduction

• Stains precorneal tear film, tears and exposed corneal stroma (strongly hydrophilic).
• Fluorescein will not penetrate intact cornea (high lipid content).
• Does not stain exposed Descemet's membrane.
• Stains corneal epithelial defects green and conjunctival ulcers yellow-orange, although the value of the latter property is reduced by poor contrast.
• Stains aqueous very bright green.

Uses

• Check integrity of corneal epithelium, eg corneal ulceration .
• Test of nasolacrimal duct patency.
• Intravenous use to detect retinal vascular abnormalities, inflammatory lesions and intra-ocular neoplasms (fluorescein angiography - specialised application).
• Staining enhanced under ultraviolet light.

Advantages

• Easy test to perform (with exception of intravenous use).
• Minimal equipment required.
• Rapid result.
• Provides clinically important information.

Disadvantages

• May obtain false impression of staining if eye is not irrigated with saline after fluorescein is applied.
• False negative results may be seen when testing nasolacrimal drainage in brachycephalic dogs, as duct may open inside mouth. Open mouth and check staining on soft palate.

Requirements

Materials required

Ideal equipment

• Ultraviolet lamp to enhance visibility of stain.

Minimum consumables

• Sterile, single-use fluorescein-impregnanted paper strips or fluorescein vials.
• Sterile physiological saline or artificial tears.
  Do not re-use vials as pseudomonasgrows well in fluorescein.

Sequelae

Reasons for treatment failure

• Poor technique.
• False positive results due to fluorescein-impregnated strips being applied directly to cornea or excess stain not being washed away after application.
• False negative results may be seen when testing nasolacrimal drainage in brachycephalic dogs.