Author: Michael Sauer, MS4, University of Utah School of Medicine
Author Email: email@example.com
Photographer: James Gilman, CRA, FOPS
Keywords/Main Subjects: Fluorescein, Fluorescein Angiography
The use of simple yellow or white light with the slit lamp and indirect ophthalmoscope can provide crucial information when investigating a diagnosis and treatment plan for a patient’s condition. However, many important subtleties may go unappreciated or completely unnoticed unless additional contrast is added to enhance certain details of a patient’s eye exam. For more than a century (1), fluorescein has secured a critical role in the ophthalmology clinic to unveil a variety of ocular abnormalities. Its use is so established that it has been placed on the World Health Organization’s List of Essential Medicines (2).
Fluorescein is an orange powder with fluorescent properties, meaning that when it absorbs light of a certain wavelength it emits light of a different wavelength. In the case of fluorescein, shining blue light (494 nm) on the chemical will result in the emission of a bright green light (521 nm). This makes it very useful for a number of uses in examining the eyes.
Among the most common applications of fluorescein in ophthalmology are investigation of the following features of an eye:
- Corneal damage (including dry eye)
- Leakage of intraocular fluid or an open globe (Seidel test)
- Nasolacrimal duct obstruction (including Jones I Test)
- Retinal vasculature abnormalities
Perhaps the most common ophthalmological application of fluorescein is in assessing corneal damage. When fluorescein is applied to the external tear film, it preferentially accumulates in areas of corneal damage, causing these areas to appear green under the slit lamp’s blue light filter. This makes fluorescein especially useful for detecting damage secondary to dry eye, corneal abrasions, ulcers, and herpetic damage (Image 1).
The mechanism by which fluorescein preferentially accumulates in areas of damage is thought to be due to a compromise in epithelial permeability associated with the corneal injury (3). When a corneal abrasion occurs, the intercellular tight junctions and surface glycocalyx that normally provide a tight seal to the epithelium lose their integrity. While a healthy cell is only minimally permeable to fluorescein, a damaged epithelium is not able to prevent fluorescein from seeping into the injured epithelium and diffusing its way through the paracellular space into the deeper epithelial layers. Because of this, fluorescein does not wash away with blinking and tear flow as easily as the healthy, smooth, and tight regions of adjacent cornea.
Another important physical exam technique that utilizes fluorescein is the Seidel test, which helps identify leakage of the internal eye aqueous onto the external ocular surface, as would be seen in a post-surgical leaking wound or an open globe injury.
To perform the Seidel test, a slightly wet fluorescein strip is painted across the surface of the suspected leak. With the blue filter on the slit lamp, the area is examined for a leak that dilutes the fluorescein and creates a waterfall-like stream of non-fluorescent fluid onto the surface of eye (Image 2).
Nasolacrimal Duct Obstruction
If a patient’s nasolacrimal ducts are obstructed, fluid is unable to flow from the ocular surface to the nasal cavity. To investigate this, fluorescein is applied to both eyes and the tear meniscus is immediately observed. After 2 minutes, each eye is reexamined to observe for changes in the intensity of fluorescein in the tear meniscus. If nasolacrimal duct obstruction is present, the affected eye should show a greater intensity of fluorescein in the tear meniscus at the end of the test relative to the unaffected eye.
In the Jones I test, a cotton swab is placed in a patient’s nostril and fluorescein is applied to the ipsilateral eye. After waiting several minutes for the fluorescein to travel through the canaliculi and ducts, the cotton swab is removed from the patient’s nostril for inspection (as an alternative to a cotton swab, the patient may simply blow his or her nose onto a white tissue paper). If the nasolacrimal ducts are patent, then the orange fluorescein should be visible on the cotton swab or tissue paper. Absence of fluorescein in the nasal cavity makes nasolacrimal duct obstruction more likely.
In addition to applying fluorescein to the external eye, fluorescein can also be injected intravenously to examine the retinal arteries in a technique called fluorescein angiography. When fluorescein is injected into a patient’s vein, it will quickly distribute throughout the body, including the blood vessels of the eye. Blue light is shined onto the retina after injection of the fluorescein, which makes it possible to visualize the retinal vasculature (Images 3 – 4). Besides providing direct imaging of the retina and its vessels, the “arm-to-eye time” (i.e. the time it takes for fluorescein to travel from the injection site to the eye) can also be helpful for ruling out cardiovascular issues such as peripheral vascular disease or heart failure. Fluorescein angiography is generally used to investigate occlusions of the retinal vasculature (e.g. CRAO, BRAO, or BRVO), diabetic retinopathy, or abnormalities of the retinal surface including macular degeneration and macular edema.
Summary of the Case: The unique chemical properties of fluorescein make it an extremely useful and safe tool for investigating a wide variety of ophthalmic abnormalities.
- Straub M. Fluoresceinlösung als ein diagnostisches Hilfsmittel fur Hornhauterkrankungen. Centralbl Augenheilkd 1888;12:75-77
- World Health Organization Model List of Essential Medicines. 21st list, World Health Organization, 2019
- Bron AJ, Argüeso P, Irkec M, Bright FV. Clinical staining of the ocular surface: Mechanisms and interpretations. Prog Retin 2015;44:36-61
Faculty Approval by: Griffin Jardine, MD
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