Another way to think of tears: blood, sweat, and... "dacruon"

Eugene Wolff's 1946 concept of an interpalpebral, trilaminar, preocular tear film does not sit comfortably with more recent scientific observations. A film so defined could exist only in the interblink phase and would exclude unshed retropalpebral fluid. A modern, evidence-based, clinically relevant model is needed, one that includes retropalpebral and meniscal fluids and is applicable throughout the blink cycle. The "ocular surface" (OS) concept combines adjacent discrete epithelia into a single continuous mucosal sheet. This "surface" constitutes an integrated organ. The OS concept has revolutionized the understanding and management of ocular pathology and therapeutics. Further practical advances can be expected once Wolff's trilaminar hypothesis is replaced by a new concept that recognizes a duality: a voluminous muco-aqueous pool extending retropalpebrally, separated always from the atmosphere by its accessory lipid sealant. The neologism "dacruon" (pronounced dacroo-on) is introduced for this composite fluid body. The respective differences between the two components--in their origins, structures, thicknesses, chemistries, motilities, secretion rates, turnovers, functions and manners of disposal--support the duality of the dacruon concept. Adoption of this alternative view of tear structure requires new descriptors to encourage precision and consensus in terminology.