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M. C. Acosta, J. Gallar, C. Belmonte; Mechanical, Chemical, and Thermal Sensitivity of the Cornea After Topical Application of Sodium Hyaluronate Eye Drops. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1954.
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The changes in threshold, intensity and components of the sensation evoked by selective mechanical, chemical and thermal stimulation of the cornea induced by topical application of 0.1% sodium hyaluronate (NaH) have been studied in human subjects.
Corneal sensitivity was measured in 10 volunteers of both sexes using the Belmonte gas esthesiometer (original instrument). Mechanical (air at 0-230 ml/min flow), chemical (0%-80% CO2 in air at subthreshold flow) and cold stimuli (air at subthreshold flow and variable temperatures inducing corneal temperature changes between 0ºC and -4.5ºC) were applied to the center of the cornea. The intensity and perceived magnitude of several psychophysical attributes of the evoked sensation were scored at the end of each pulse, using separate 10cm visual analogue scales (VAS). Threshold for sensation parameters was taken as the stimulus intensity that evoked a VAS score >0.5. Control sensitivity was measured in both eyes of each subject. In a separate session, corneal sensitivity was again measured in both eyes, one without treatment and the other 30 minutes after topical application of a drop of a commercial 0.1% NaH solution or of balanced saline solution.
All the volunteers reported sensation of ocular comfort during at least 30 min after NaH instillation and no changes in ocular comfort after saline solution. Transient blurred vision was reported by 3 subjects immediately after NaH treatment. In the case of mechanical and chemical stimulation, the intensity of the evoked sensation was modestly reduced after NaH, while significantly lower VAS values were given to the irritation sensation and its burning and pricking components. The subjective intensity evoked by thermal cold stimuli remained unaltered after NaH, while the small irritative component of the sensation evoked by cold, even at lowest temperatures, almost vanished. No significant changes of sensitivity were obtained after saline treatment.
NaH reduced the irritative components of the sensation evoked by selective mechanical, chemical and cold stimulation of the cornea without affecting the ability of subjects to identify the intensity of the stimuli, thus supporting the usefulness of NaH eye drops as valuable agents in the management of ocular dryness sensations without disturbing the protective role or corneal neural input.
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