TEMPORAL SEQUENCE OF CHANGES IN TEAR FILM COMPOSITION DURING SLEEP

Overnight eye closure induces a shift in the nature and composition of the tear film, from a dynamic reflex tear-rich to a stagnant secretor y IgA-rich layer. This is accompanied by the induction of a state of s ub-clinical inflammation, as evidenced by increases in albumin levels, plasminogen activation, conversion of complement C3 to C3c, and the r ecruitment of polymorphonuclear (PMN) cells into the tear film. To det ermine the time course and functional relationship between these poten tially interdependent processes, tear samples were collected from ten non-contact lens wearers after 1, 2, 3 and 5 hours of sleep. A subgrou p of 6 subjects also self-collected tear samples after 8 hours of slee p. Tear samples were analysed for albumin by quantitative immunofixati on assay, secretory IgA (sIgA) by radial immunodiffusion assay, plasmi n-like activity using a chromogenic substrate, and complement C3 to C3 c conversion by immunoblot assay. Epithelial and PMN cells in the prec orneal tear film were recovered from corneal washings from the same su bjects after 1, 3, 5 and 8 hours of sleep, and quantified. Results rev ealed that, unlike epithelial cells which exhibited a slow progressive accumulation as a function of the period of sleep, PMN cell concentra tion exhibited a lag phase, with recruitment occurring after between 3 and 5 hours of eye closure. This was preceded by plasminogen activati on, increases in albumin and sIgA levels, and complement C3 to C3c con version, all of which occurred within 1 to 3 hours after eye closure. Plasmin-like activity appeared to plateau after 3 hours and then decre ased. These findings reveal a temporal sequence in the induction of su b-clinical inflammation in the closed eye, and suggest that complement conversion may produce the chemotactic factor(s) responsible for PMN cell recruitment in the closed-eye tear film.