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Study finds increased blink rate correlates with decreased corneal sensitivity
Nerve changes in dry eye may be more of a neuropathic complication.
Classifying tear dysfunction groups is important because there are meaningful differences in corneal sensitivity and blink rate among several subcategories, according to a study.
“We wanted to compare the standard method for checking corneal sensitivity, which is with a nylon thread (contact method), to a noncontact method (air jet esthesiometer),” co-author Stephen C. Pflugfelder, MD, a professor and director of the Ocular Surface Center in the Department of Ophthalmology at Baylor College of Medicine in Houston, said.
A second objective was to compare corneal sensitivity to blink rate in a variety of conditions associated with tear dysfunction.
“Most previous studies have consisted of patients with aqueous tear deficiency, particularly Sjögren’s syndrome,” Pflugfelder told Ocular Surgery News. “There has not been a survey among people with other types of tear dysfunction, such as meibomian gland disease and conjunctivochalasis, both of which are probably more prevalent than aqueous deficiency.”
Paradoxical finding
Pflugfelder said a frequent complaint of people with tear dysfunction is that they either blink more rapidly or they close their eyes and have difficulty reopening.
“It seems reasonable that if the eye was more sensitive, then people would blink more,” he said. “But that is not exactly what we found. We actually found that an increased blink rate was correlated with a reduction in corneal sensitivity. This was a surprise and a paradoxical finding.”
However, as more information emerges about what occurs to the corneal nerves in dry eye in these tear dysfunction conditions, “our finding began to make more sense,” Pflugfelder said.
The study, which appeared in the American Journal of Ophthalmology, consisted of 10 normal subjects and 33 subjects with tear dysfunction.
Corneal sensitivity among 10 subjects with aqueous tear deficiency using the contact method was reduced by about 40% compared with controls, whereas it was not reduced in 11 subjects with meibomian gland disease and 12 subjects with conjunctivochalasis.
Sensitivity results were comparable when using the noncontact method for the three tear dysfunction conditions, although for aqueous tear deficiency, sensitivity was further reduced with the noncontact method, according to Pflugfelder.
“Overall, though, there was a significant correlation between the contact and noncontact method, with an R of about 0.54,” Pflugfelder said.
Among all subjects, a reduction in corneal sensitivity detected by the noncontact method significantly correlated with tear breakup time, symptom severity and blink rate.
Carlos Belmonte, MD, PhD, a neurophysiologist from Spain, has found that corneal nerves appear to be “wounded” in dry eye and “may fire spontaneously,” according to Pflugfelder. Therefore, nerve changes in dry eye may be more indicative of a neuropathic type of problem.
“In other words, treating the surface of the eye may not necessarily get rid of the pain, if the nerves themselves are already firing,” Pflugfelder said.
Future research
Based on the current study, “more attention in the future probably has to be given to the corneal nerves and perhaps treatment of the nerve-related pain,” Pflugfelder said, noting that he will incorporate the study’s information and testing in future dry eye clinical trials. “This is important in trying to determine the effectiveness of treatments.” – by Bob Kronemyer
- Reference:
- Rahman EZ, et al. Am J Ophthalmol. 2015;doi:10.1016/j.ajo.2015.08.005.
- For more information:
- Stephen C. Pflugfelder, MD, can be reached at Cullen Eye Institute, Baylor College of Medicine, 6565 Fannin St., NC 205, Houston, TX 77030; email: stevenp@bcm.edu.
Disclosure: Pflugfelder reports no relevant financial disclosures.