corneal
assessment
A
Review of Corneal and Conjunctival Stains
BY
MARJORIE J. RAH, OD, PHD
We routinely
use stains to evaluate the integrity of the corneal epithelium and the conjunctiva.
The three most common stains are sodium fluorescein, rose bengal and lissamine green.
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Figure
1. Fluorescein staining of a flat-fitting GP lens.
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Fluorescein
Sodium fluorescein is a water-soluble dye that doesn't penetrate
intact epithelial cells. It fills intercellular spaces when cell junctions are disrupted
and stains damaged epithelial cells. The dye fluoresces under cobalt blue illumination.
A Wratten filter can enhance its visibility. We use fluorescein to assess tear film
stability (tear breakup time), to evaluate GP contact lens-to-cornea fitting relationships
or to detect aqueous humor leakage and epithelial permeability.
Characteristic
fluorescein staining patterns may also help in diagnosing and managing corneal conditions.
For instance, inferior staining can indicate a bacterial source, blepharoconjunctivitis
or trichiasis. Interpalpebral staining often indicates dry eye, photokeratopathy,
exposure or inadequate blink. Superior staining can be a sign of superior limbic
keratitis or vernal conjunctivitis, and overall diffuse staining often occurs in
cases of viral conjunctivitis or medicamentosus.
Fluorescein staining can also occur in contact lens patients because
of sensitivities to lens solutions or due to interactions between certain lens materials
and lens solutions (Figure 1).
It's also important to differentiate between fluorescein staining
on the cornea and fluorescein pooling. If there's a depression in the cornea but
the epithelial cells are intact, the fluorescein will pool in the depressed area.
A classic example of this is dimple veiling, in which small bubbles trapped under
a GP lens make several round impressions in the cornea that fill with fluorescein.
Staining for Dry Eye
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Figure
2. Mild rose bengal staining in the conjunctiva of a dry eye patient. |
We also routinely use rose bengal and lissamine green in evaluating
the cornea, conjunctiva and eyelid margins, especially for evaluating dry eye patients.
A healthy pre-ocular tear film will block rose bengal staining, making it a good
choice for dry eye patients who have poor-quality pre-ocular tear films (Figure
2). Rose bengal is also good for staining Herpes simplex dendrites or neoplastic
lesions.
Both rose bengal and lissamine green stain dead or devitalized
cells and mucus. You don't need a filter to view the stain but, especially for rose
bengal, a red-free (green) filter may enhance the staining pattern. Lissamine green
is becoming more popular than rose bengal because it's typically more comfortable
for patients.
Apply with Care
When using any corneal stain, the same advice applies: Don't paint
the cornea, less is more. You can always add more, but too much dye can obstruct
the view of subtle staining patterns.
To obtain references for this article, please visit
http://www.clspectrum.com/references.asp
and click on document #133.
Dr. Rah is an assistant
professor at the New England College of Optometry where she works primarily in the
Cornea and Contact Lens Service in patient care, teaching and research.
Contact Lens Spectrum, Issue: December 2006