An Amplifying Cascade of Contact Lens-Related End-of-Day Hyperaemia and Dryness Symptoms.

End-of-day (EOD) symptoms of dryness are too often the cause of poor soft contact lens (SCL) tolerance and abandonment of wear. This review examines an amplifying cascade model for these symptoms, which involve thin tear layers on contact lens (CL) front surfaces being susceptible to evaporation-related short tear breakup (TBU) times. Susceptibility to faster tear loss by evaporation may be exacerbated by other forms of tear instability, such as lipid and mucin deficiencies as well as lens surface soiling. Bulbar and palpebral conjunctival hyperaemia and associated faster evaporation of warmer pre-conjunctival tears could also contribute to evaporative dry eye EOD symptoms. In CL wearers, a cascade of increasing hyperaemia toward the end of day, associated increasing tear temperature and evaporative loss, shortened TBU times (TBUTs) and increased osmolarity, all elevate the risk of higher symptom levels according to progressive amplification of this cascade. Chronic wound healing responses to SCL wear, perhaps related to limbal conjunctival trauma, stem cell deficiency and persistent epitheliopathy, as well as one or more immune responses, may contribute directly or indirectly to inflammation and the amplifying evaporative dryness cascade. A diurnal cycle that culminates in EOD symptoms appears to involve a process of recovery from causal mechanisms after lens removal, which allows lenses to be worn comfortably, at least initially the next day. Possible recovery processes are discussed in this review as are procedures that may help de-amplify an inflammatory, evaporative dryness cascade and alleviate EOD symptoms. Evidence of an accrual of adverse responses over long periods of more or less successful lens wear indicate an incremental failure to recover from EOD hyperaemia. Such incremental failure could help explain how SCL wear too often needs to be abandoned after many years of comfortable wear.