Tear film break-up time (TBUT) testing
CONJUNCTIVA, CORNEA
It was done to assess tear film stability (i.e., time needed for tears to be evaporated and diffused after natural blinking). Briefly, sodium fluorescein (1% eye drops; Minims Fluorescein sodium; Baush + Lomb, Kingston-upon-Thames, England) was dropped into the conjunctiva sac. The participants were ordered to blink 3–4 times and then look forward without any blinking. The tear film was examined under the slit-lamp biomicroscope light. The time between the last blink and the emergence of the first break in the tear film (i.e., formation of a dry spot on the cornea) was recorded using a timer [