Tear film dynamics

The pre-ocular tear film is a stratified incompressible fluid which is roughly three micrometers thick. Pathologies of this film or its production are typically responsible for dry eye, which is a common, age-related affliction responsible for considerable disability and days lost through sick leave. It is important to understand how tear film osmolarity varies across the whole ocular surface using empirical indicators of dry eye syndromes, since dry eye-induced tear hyperosmolarity is recognised as a major cause of ocular damage during dry eye. However, relationships between dry eye indicators and corneal surface osmolarity are experimentally inaccessible, highlighting the need for quantitative modelling in this area.

There has been significant work modelling the fluid dynamics of the tear. One study used lubrication theory to study the deposition of the tear film in the up-blink, while another used similar techniques for investigating tear film break-up in the inter-blink and emphasised the importance of evaporation and gravity. These studies, however, have not considered the solute balance within such flows. In a collaboration with Professor Anthony J. Bron and Dr John M. Tiffany (The Nuffield Laboratory of Ophthalmology, University of Oxford), we are pursuing a coupled solute-balance-fluid flow model of the tear film to address such questions. This will encompass currently known data and ideas with a generalisation of current compartmental models to specifically investigate the hyperosmolarity associated with dry eye. This will allow us to approximate and delimit the overall behaviour of solute concentrations within each compartment and to investigate numerous questions of relevance to dry eye, such as whether lacrimal gland secretions of hypotonic fluid can offset the effects of high tear film evaporation rate (due to a deficiency in tear film lipid production).

Please contact Dr Eamonn Gaffney for more details.

Key references in this area

  • A. J. Bron, N. Yokoi, E. A. Gaffney and J. M. Tiffany (2011). A solute gradient in the tear meniscus. I. A hypothesis to explain Marx's line. Ocul. Surf. 9:70-91. (eprints)
  • A. J. Bron, N. Yokoi, E. A. Gaffney and J. M. Tiffany (2011). A solute gradient in the tear meniscus. II. Implications for lid margin disease. Ocul. Surf. 9:92-97. (eprints)
  • E. A. Gaffney, J. M. Tiffany, N. Yokoi and A. J. Bron (2010). A mass and solute balance model for tear volume and osmolarity in the normal and the dry eye. Prog. Retin. Eye Res. 29:59-78. (eprints)