The interblink interval I: the relationship between sensation intensity and tear film disruption.

PURPOSE To find the relationship between tear film drying and sensation during the interblink period. METHODS One eye was taped shut, and after a blink the subjects were required to keep the other eye open. Digital video images of the ocular surface (with fluorescein) were obtained using a slit lamp biomicroscope while 23 subjects rated the intensity of the ocular surface sensation by adjusting a one-turn potentiometer to represent the strength of the sensation. They were trained to use the potentiometer before the data were collected. In addition, the characteristics of the sensation as spoken by the subject were recorded. RESULTS The sensation was generally triphasic, with initial constant sensation and a subsequent biphasic period, with intensity increasing slowly followed by a rapid increase before the subjects blinked (correlations were all r > 0.95). Tear film drying dynamics were also biphasic, and drying and sensation were strongly associated, with a correlation of 0.94 between the break in the bilinear functions of sensation and drying. CONCLUSIONS The method provides novel information about the development of ocular sensation during ocular surface drying. As evidenced by the complex functions required to adequately describe the relationships, tear film drying and ocular surface sensations are associated in complex ways.