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A careful look at all the clues can help the clinician differentiate between dry eye and allergies. The patient history may contain the most important clues for establishing a diagnosis.
Philadelphia-Look carefully at the clues and one can differentiate between dry eye and allergies. The patient history may contain the most important clues to the diagnosis, said Christopher J. Rapuano, MD, professor of ophthalmology, Jefferson Medical College of Thomas Jefferson University, and co-director, Cornea Service, Wills Eye Institute, Philadelphia.
The season is the first helpful clue to the etiology of the ocular symptoms. Allergies are more likely to manifest in the spring and fall, perhaps in summer, but less so in winter. Dry eye can be a seasonal complaint also, and that is especially true in the winter in the presence of dry air outdoors and dry heat indoors and in the summer when wind can cause feelings of dry eye.
"Patients with allergies tend to present with the primary complaint of itchiness, and patients with dry eye tend to present with eyes that they describe as dry, gritty, sandy, dusty, or the feeling of a foreign body sensation," he said.
A caveat to this guideline is that there can be huge overlaps both in the season and the complaints, as well as patients may have both dry eye and allergies.
"Patients with dry eye tend to develop more allergies," he said. "In a normal individual, when an allergen such as pollen gets into the eye the tears will wash it away quickly, before an allergic reaction can occur. However, a patient with dry eye may not have a sufficiently large tear volume to wash the allergen out quickly enough to prevent the symptoms of allergy."
The third clue in these patients is a determination of specific medications that have been helpful to the patients. Patients with ocular symptoms have often tried various treatments. If artificial tears have helped the patient to obtain relief, it is more likely that the patient has dry eye; if anti-allergy treatments have helped, then the patient is likely to have an allergy.
It is also important to determine whether patients are taking anti-allergy pills. These medications can lessen allergy symptoms, but they also dry out the sinuses and the mucous membranes in the body.
"Before treatment, the dry eye symptoms might have been slight, but these medications can worsen dry eye substantially," Dr. Rapuano said. Antihistamine drops can induce a bit of dryness, but the effect is not as great as that seen with antihistamine pills, he said.
Other clues to a diagnosis are the examination findings; however, in patients who do not have severe dry eye or allergies, the disorders can be harder to differentiate on exam.
Severe allergies are often characterized by significant papillae, bumps on the conjunctiva, and a stringy discharge from the eye. However, in mild and moderate disease, the findings may not be as pronounced.
Patients with dry eye tend not to have a significant tear lake, but they do have numerous dry spots (superficial punctate keratitis), and filaments (epithelial strands) on the cornea, he said.
Schirmer's testing may indicate decreased tear production and point toward a diagnosis of dry eye.
In older patients, and especially postmenopausal women who present severe dry eye, a systemic disorder such as Sjögren's syndrome may be present, he added.