Primary health care providers should also be familiar with some ophthalmic procedures and test to assist in completing detailed and thorough history and physical examination in order to assist them in confirming a diagnosis of ocular allergy. More importantly, these various tests help to differentiate between the many disorders that mimic allergic disorders of the eye.
The Schirmer's tear test is the most commonly used and easily performed test for the evaluation of dry eye. Tear production is assessed by the amount of wetting seen on a folded strip of sterile filter paper after it is placed into the conjunctival sac. The patient is seated with the room lights dimmed and is then asked to "look up" as the lower eyelid is gently pulled downward. Excess moisture and tears are dried along the eyelid margin and conjunctiva with a sterile cotton-tipped applicator. The rounded end of the test strip is bent at the notch approx 90-120 degrees and is hooked into the conjunctival sac at the junction of the middle and lateral one-third of the lower eyelid margin. The patient's eyes remain closed throughout the examination. The test strips are removed after 5 min. The length of the moistened area from the notch to the flat end of the sterile strip is measured using a millimeter ruler or the scale imprinted on the test-strip package. Some of the test strips have a leading edge of tear film that changes color, thus improving the reading of the results. The Schirmer's I test (without anesthesia) measures both basal and reflex tearing, whereas the Schirmer's II test (with anesthesia) measures only the basal secretion of tearing and is performed as outlined previously, but with topical anesthesia instilled.
Fluorescein is a water-soluble dye used to examine the cornea and conjunctival surfaces. It stains the denuded epithelium. It is placed into the eye either with a sterile fluorescein sodium ophthalmic strip (Fluor-l-Strip) or with a dropper in liquid form. A cobalt blue filter is needed to best appreciate the fluorescein-staining pattern of the conjunctiva and cornea. This filter produces a blue hue against the intense green color of the fluorescein dye. The patient is asked to blink several times to spread the fluorescein uniformly and evenly over the entire corneal and conjunctival surface. Soft contact lenses must be removed prior to fluorescein instillation to prevent their permanent staining. At least 1 h must pass after completion of the examination before the soft contact lenses can be replaced in the eyes.
Conjunctival scraping can also assist in differentiating various forms of red eye. After the administration of a topical local anesthetic, the palpebral conjunctiva (under the upper lid) is gently scraped several times with a spatula for cytological examination. The sample is spread on a slide and stained with May-Grunwald, Giemsa, or another or-thochromatic stain to identify eosinophils or neutrophils. The absence of inflammatory cells does not rule out the diagnosis of AC, but the presence of eosinophils strongly suggests it.
Conjunctival and eyelid cultures are obtained using a sterile cotton-tipped applicator moistened in thioglycolate broth. The lower palpebral conjunctiva is lightly wiped with the applicator stick for 5 s as the patient is asked to look up. Moistened swabs are preferred because they pick up and release bacteria better than do dry swabs. The sample is then placed into the transport medium.
Ocular provocation testing can be likened to "skin testing" of the eye. Known quantities of specific allergen are instilled onto the ocular surface, and the resulting allergic response is measured. This technique is commonly performed by allergists in a research study, especially in the assessment of new drugs against ocular allergies.
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