Role of water wettability, water transport, and adhesion in vision

Water plays an important role in life processes, although the specifics are not always known. In the past 25 years, major progress has been made in vision science by applying the principles and techniques of interface science to tear film physiology and pathophysiology, to novel surgical techniques, and to contact lens wear. In this paper, the role and structure of the preocular tear film are discussed, as well as the factors affecting its stability. This double-layered fluid film plays an important role not only in vision and the health of the exposed ocular tissues, but also in deciding contact lens tolerance and functioning. The little-known, misunderstood, and often misdiagnosed dry eye syndrome that is effected by the compromised stability of the tear film is also discussed. A newly recognized role of water as a bioabhesive in ocular tissue adhesion and its failure in terms of disjoining pressure and weak boundary layer are examined in the vision-threatening and painful adhesion failure of corneal epithelium and epithelial trauma during routine ophthalmic procedures such as tonography. The modalities to prevent undesirable contact adhesion in intraocular surgery that could result in surgical complications arc explored. Retinal tears are thought to result from the adhesion failure of the retina to the underlying tissues. A concentric double membrane model of retinal adhesion is proposed that analyzes the role of certain biophysical factors such as elasticity and hydraulic conductivity in promoting or diminishing the adhesion of retina to the choroid.