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Participants and methods SUBJECTSThe study group comprised 34 healthy individuals (mean age 58-4 (SD 14-7) years, ranging from 22 to 84 years). Tear turnover was determined in 55 eyes of the subjects. They were examined by slit-lamp microscope without fluorescein to ensure there were no corneal epithelial lesions. Subjects who wore contact lenses, had ocular abnormalities, or systemic diseases related to tear secretion were excluded. Informed consent was obtained from all subjects before the study. INSTRUMENTATIONFluorophotometric measurements were carried out with an FM-500 laser flare meter (Kowa Company Ltd, Japan), consisting of a slit-lamp and a photometric microscope. Light from the fluorescein solution passes through green barrier filters to a photomultiplier whose output can be read on a computerised display. The instrument was adjusted to scan linearly at a 300 angle between the optical axis of the eye and the excitation beam, and at a 600 angle between the optical axis of the eye and the photometric microscope. The tear film meniscus was measured at the centre of the lower lid margin. MEASUREMENT PROCEDUREAutofluorescence of the tear film meniscus was obtained from each eye before fluorophotometry. A 1 ,ul drop of 0 005% sodium fluorescein (50 ,ug/ml) was then instilled into the upper lateral part of the bulbar conjunctiva without touching the eye. The subject was asked to blink with no squeezing so as to homogenise the fluorescein over the tear film. The eye was scanned in a dark room by fluorophotometer every minute for 5 minutes, and subsequently every 1-5 minutes for 12 minutes. The Schirmer test with anaesthesia and the tear clearance rate were administered 1 hour after the fluorophotometric measurement. A 10 ,lI drop of 0-5% fluorescein and 0.40/o oxybuprocaine hydrochloride was instilled into the 1042 on 12 May 2018 by guest. Protected by copyright.

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