Cyclosporine A (CsA) is used for the treatment of dry eye (DE) with good clinical
results, improving tear secretion and decreasing subjective symptoms. These effects
are attributed to the improved tear film dynamics, but there are no data on the effect
of CsA on the abnormal sensory nerve activity characteristic in DE. Our purpose was
to evaluate the CsA effect on the enhanced activity of corneal cold thermoreceptors
in a tear-deficient DE animal model using in vitro extracellular recording of cold
thermoreceptors nerve terminal impulses (NTIs) before and in the presence of CsA.
NTI shape was also analyzed. Blinking frequency and tearing rate were also measured
in awake animals before and after topical CsA. CsA increased the tearing and blinking
of treated animals. CsA significantly decreased the peak response to cold of cold
thermoreceptors. Neither their spontaneous NTIs discharge rate nor their cooling threshold
were modified. CsA also seemed to reverse some of the changes in NTI shape induced
by tear deficiency. These data suggest that, at least in part, the beneficial clinical
effects of CsA in DE can be attributed to a direct effect on sensory nerve endings,
although the precise mechanisms underlying this effect need further studies to be
fully clarified.
