Anatomy of a dry eye work up

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As the “graying” of the United States continues, healthcare employees may see tasks handed over to support staff by overburdened practitioners. One area in which ophthalmic support staff can be very effective is in the screening and diagnosis of dry eye patients. Many technicians play an important role in helping to collect raw data, and then presenting it to their practitioner for diagnosis.

As the aging demographics of the United States continue to manifest in overflowing offices, ERs, and ORs across the nation, healthcare employees can expect to see growing numbers of tasks being handed over to support staff by practitioners who are simply too busy to handle the kind of details they once did.

One area in which ophthalmic support staff can be very effective is in the screening and diagnosis of dry eye patients. Much of the work-up consists of asking patients routine questions to help build a history. The clinical tests involved are mostly within the skills sets of ophthalmic technicians. Following are highlights of some common events from an average dry eye work-up.

It is important to know at the outset that there is no agreed-upon or gold standard for diagnosing dry eye. It is a professional diagnosis based on combining information from the history and the physical exam, and usually by performing one or more objective tests. Many technicians play an important role in collecting raw data of this kind, and then presenting it to the practitioner for diagnosis.

Tear break-up time

One of the simplest clinical tests for dry eye is the measurement of tear film break-up time (TBUT). This means the time lapse between the instillation of fluorescein and the first appearance of dry spots on the cornea. TBUT should be measured before instillation of any anesthetic eye drops. Moisten a fluorescein strip with saline and apply it to the inferior cul-de-sac. Ask the patient to blink several times, then examine the tear film using a broad beam slit lamp with a cobalt blue filter, which will highlight the first dry spots on the cornea. A TBUT of less than 10 seconds is considered abnormal and at risk for dry eye.

Epithelial staining

At some point every patient seriously suspected of dry eye will undergo one of the three major epithelial staining techniques: rose bengal, lissamine green, or fluorescein. The goal is to highlight under a slit-lamp examination areas of the cornea or conjunctiva damaged by long-term exposure to dry eye conditions. This physical damage and the staining patterns on the eye can be important diagnostic factors.

Sodium fluorescein is a water-soluble dye that does not penetrate healthy epithelial cells but fills intercellular spaces when cell junctions are disrupted. Certain fluorescein staining patterns may correlate with specific conditions.

Interior staining might indicate blepharoconjunctivitis or trichiasis, while intrapalpebral (lying in between the eyelids) might indicate dry eye, photokeratopathy, corneal/epithelial exposure, or inadequate blink.

Rose bengal and lissamine green stain not only dead or devitalized cells but also healthy cells that are protected by an inadequate mucin coating. A linear pattern of inferior conjunctiva and corneal staining by rose bengal is often seen in meibomian gland dysfunction. Early or mild cases of dry eye are generally thought to be better detected by rose bengal than with fluorescein. Of the three stains, lissamine green causes patients the least discomfort, but is less sensitive and therefore more difficult to read under a slit lamp examination, according to experts.

Schirmer testing

Schirmer testing determines whether the eye is producing enough aqueous tears to keep its surface moist. A small strip of filter paper is inserted into the lower eyelid (conjunctival sac). The eye is closed for a set length of time. Then the paper strip is removed, and the amount of moisture on the strip is measured. Depending on the practitioner, the exact procedure may differ. For example, sometimes a topical anesthetic is added to the eye before inserting the paper test strips.

In a 5-minute period, less than 5 mm of wetting is considered abnormal. Five to 10 mm is normal. A younger patient might wet as much as 15 mm of a strip.

The condition most often associated with the Schirmer test is Sjögren’s syndrome, a systemic immune dysfunction characterized by aqueous tear deficiency and dry mouth. Many of these patients may also have rheumatoid arthritis. In addition to an abnormally low Schirmer test result, other indicators of possible Sjögren’s syndrome include objective evidence of low salivary flow, biopsy proven lymphocytic infiltration of the labial salivary glands, and dysfunction of the immune system, indicated by the presence of serum auto-antibodies.

Evaluating tears

It is also possible to evaluate the health of each of the three main tear components: lipid, aqueous, and mucin.

The easiest of these to test is the lipid layer, which is the thin, smooth coating on the outside of tears that prevents them from evaporating. Lipids can be tested during a routine examination by squeezing the eyelid margin to encourage expression from the meibomian gland. If the discharge does not resemble motor oil and puddles at the orifice, the patient may be suffering from meibomian gland dysfunction.

The aqueous component comprises what we think of as the watery part of the tear. It can be tested by measuring tear lysozyme, tear lactoferrin, epidermal growth factor, aquaporin 5, lipocalin, and immunoglobulin A concentrations with enzyme-linked immunosorbent assay techniques, in addition to tear film osmolarity (TFO). TFO has been shown to be elevated in patients with dry eyes but has been criticized for lacking specificity in meibomitis, herpes simplex keratitis, and bacteria conjunctivitis.

Finally, the mucin component, which is a layer of proteins created by the surface of the eye to allow the aqueous to adhere to the otherwise water-repellent cornea, can be assessed by impression cytology or brush cytology techniques. These methods collect goblet cells that are tested for mucin messenger RNA expression. Although impression cytology is a highly sensitive test, it is a difficult test to perform, requiring proper staining and expert evaluation of samples.

No one test dominates the dry eye field. Practitioners tend to pick and choose which test and evaluation works best for them. Certain tests work better in individual hands. But one thing is certain: The ability to help work up dry eye patients will make you more valuable to your employer.ODT

SIDEBAR

Staining to confirm dry eye

To help diagnose patients with suspected aqueous tear deficiency, ocular surface dye staining may be performed using:

•   Rose bengal

•   Lissamine green

•   Fluorescein