Subjective sensations reported during the interblink interval reflect different components of ocular surface sensitivity

Abstract

Abstract: : Purpose: To find the relationship between drying of the tear film and subjective sensations reported during the inter–blink period. Methods: Software written using MATLAB sampled a microphone at 10 KHz, a slitlamp video camera at 4Hz and a potentiometer. One eye was taped shut and after a blink, the subjects were required to keep their other eye open. Digital video images of the ocular surface (with fluorescein) were obtained using a slit lamp biomicroscope. Twenty three subjects were trained to use the potentiometer before the data were collected. They rated the intensity of the ocular surface sensation by adjusting a 1–turn potentiometer to represent the strength of the discomfort. The characteristics of the sensation as spoken by the subjects were recorded. The extent of drying (dark pixels) on the cornea was assessed with a macro written in Object–Image 2.08 software. Results: Subjects responses were classified into 3 broad categories mechanical (scratchy, dry), chemical (stinging, burning) and itching. Reports of itching occurred in 29% of the reports during the initial period of the interblink interval. Reports of mechanical discomfort occurred in 39% of reports at the beginning and mid–period of the interblink interval and in only 9% at the end of this period. Chemical discomfort was reported 91% of the time immediately prior to the blink. Conclusions:During the initial phases of tear breakup, mild discomfort, itch and mechanical symptoms are reported most commonly. It appears, though, that the chemical alterations of the tear film become more predominant as extreme burning and stinging almost always occur when extreme discomfort is reported subjectively and the greatest amount of tear film disruption is present, just before subjects blink.

Keywords: anterior segment • cornea: tears/tear film/dry eye • cornea: basic science