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.

Figure 1. Fluorescein staining of a flat-fitting GP lens.

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

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.