"We know that allergy contributes to contact lens intolerance," said Dr. Dhaliwal, associate professor, department of ophthalmology, University of Pittsburgh School of Medicine. "One reason is that these patients are taking oral antihistamines, which cause dryness, but importantly, there can be implications in refractive outcomes with regard to LASIK and PRK."
Although oral antihistamines are effective, they can be detrimental to the ocular surface. Topical allergy therapy should be used for patients undergoing refractive surgery, recommended Dr. Dhaliwal, who also is director of refractive surgery and cornea services at the university medical center's eye center.
She explained the relationship between allergies and refractive surgery, noting that optimal healing is essential for optimal visual outcome after refractive surgery. In the allergy subpopulation as well as the general population, diffuse lamellar keratitis (DLK) and dry eye are the two conditions most likely to influence healing, Dr. Dhaliwal added.
Although a mild case of DLK is unlikely to cause significant problems and will improve with topical steroids, a more severe case could lead to stromal melting and permanent vision loss. Allergy and DLK were conclusively linked in a 2003 landmark study by Boorstein et al. published in Ophthalmology.
"What they found is that atopy or allergy is a patient-specific risk factor for the development of DLK after primary bilateral LASIK," Dr. Dhaliwal said. "They also found that individuals with atopy benefit from preoperative treatment to minimize the incidence of DLK and the potential for visual loss."
The study outlined the reasons for the increase in DLK, a sequence that begins with the post-LASIK release of proinflammatory cytokines that upregulate the inflammatory and immune responses and initiate wound healing. Patients with atopy have a heightened immune response and, therefore, are more likely to develop DLK due to excessive neutrophil recruitment into the corneal stroma, according to Dr. Dhaliwal.
Patients with atopy can exhibit DLK following an uncomplicated surgical stimulus, such as LASIK, whereas patients without atopy typically require additional stimuli, such as bacterial endotoxin, or a more significant surgical injury, such as a corneal abrasion, that happens at the same time as the LASIK procedure.
Dry eye is the other condition that frequently affects LASIK patients, Dr. Dhaliwal said. Up to 85% of LASIK patients report dry eye symptoms 1 week after surgery, and 43% of PRK patients and 48% of LASIK patients report postoperative dry eye symptoms as long as 6 months after surgery.
Because of their antimuscarinic effect, oral antihistamines diminish the aqueous phase of tear film, she said. A study of loratadine (Claritin, Schering-Plough Health-care Products) in dry eye showed that punctate keratitis, indicated by fluorescein staining, increased by 122%. In addition, Schirmer testing showed a mean decrease of 6.5 mm of wetting; tear break-up time was shortened by 53%. Patients also reported increased ocular discomfort.
"What's very important is that, after PRK, we need an ideal ocular surface for re-epithelialization to occur," Dr. Dhaliwal continued. In the FDA trials for PRK conducted by VISX, it was shown that patients who use loratadine had an increased time to re-epithelialization, she added, noting that three eyes in this study took longer than 7 days to re-epithelialize.
The recommendation emerging from this study was that patients preparing to undergo PRK discontinue loratadine use before surgery, Dr. Dhaliwal said.
Another study linked allergic conjunctivitis to the association of late-onset corneal haze and myopic regression after PRK.
"The hypothesis is that allergic conjunctivitis led to the production of mast cells that activated fibroblasts, inducing increased collagen production or haze," she said. "So there are multiple ways that allergy indeed influences our refractive patients."