Application of a novel interferometric method to investigate the relation between lipid layer thickness and tear film thinning.

PURPOSE The lipid layer of the tear film forms a barrier to evaporation. Evaporation is a major cause of tear thinning between blinks and tear breakup. The purpose of this study was to investigate the relation between tear film thinning and lipid layer thickness before and after instillation of an emulsion eye drop. METHODS Fifty non-contact lens wearers were studied. Spectral interferometry was used to measure the thinning rate of the precorneal tear film for up to 19 seconds after a blink. Simultaneously, lipid layer thickness was measured based on an absolute reflectance spectrum. After a 2-minute recovery, the measurement was repeated. A drop of the lipid emulsion was then instilled; 15 minutes later, two interferometry measurements were performed similarly. RESULTS A histogram of thinning rates was fitted by a bimodal distribution with narrow and broad peaks corresponding to slow and rapid thinning, respectively. The correlation between repeated thinning rate measurements was modest, but repeatability was considerably more significant when analyzed in terms of the slow/rapid dichotomy. Similarly, the correlation between thinning rate and lipid thickness was modest but was more evident when analyzed in terms of the slow/rapid dichotomy. Instillation of an emulsion eye drop significantly increased the thickness of the lipid layer but did not significantly alter the thinning rate. CONCLUSIONS The proposed slow/rapid dichotomy of thinning rates presumably relates to a good/poor barrier to evaporation of the lipid layer. The imperfect correlation between thinning rate and lipid thickness indicates that other factors, such as the composition and structure of the lipid layer, are important (e.g., sufficient polar lipids may be needed to form good interface between nonpolar lipids and the aqueous layer).

[1]  Ewen King-Smith,et al.  The thickness of the tear film , 2004, Current eye research.

[2]  R M Hill,et al.  The thickness of the human precorneal tear film: evidence from reflection spectra. , 2000, Investigative ophthalmology & visual science.

[3]  A. Bron,et al.  Using osmolarity to diagnose dry eye: a compartmental hypothesis and review of our assumptions. , 2002, Advances in experimental medicine and biology.

[4]  Richard J. Braun,et al.  Contributions of Evaporation and Other Mechanisms to Tear Film Thinning and Break-Up , 2008, Optometry and vision science : official publication of the American Academy of Optometry.

[5]  T. Olsen,et al.  Reflectometry of the precorneal film , 1985, Acta ophthalmologica.

[6]  J M Tiffany,et al.  Refractive index of meibomian and other lipids. , 1986, Current eye research.

[7]  R. Rowell,et al.  Physical Chemistry of Surfaces, 6th ed. , 1998 .

[8]  M. Fukuda,et al.  EXPERIMENTAL AND THEORETICAL STUDY OF EVAPORATION OF WATER IN A VESSEL , 1995 .

[9]  F. Holly,et al.  Formation and rupture of the tear film. , 1973, Experimental eye research.

[10]  P. King-Smith,et al.  Three interferometric methods for measuring the thickness of layers of the tear film. , 1999, Optometry and vision science : official publication of the American Academy of Optometry.

[11]  A. Tomlinson,et al.  Refractive Index and Osmolality of Human Tears , 1995, Optometry and vision science : official publication of the American Academy of Optometry.

[12]  Christophe Baudouin,et al.  The definition and classification of dry eye disease: report of the Definition and Classification Subcommittee of the International Dry Eye WorkShop (2007). , 2007, The ocular surface.

[13]  P. King-Smith,et al.  The contribution of lipid layer movement to tear film thinning and breakup. , 2009, Investigative ophthalmology & visual science.

[14]  R. Schiffman,et al.  Reliability and validity of the Ocular Surface Disease Index. , 2000, Archives of ophthalmology.

[15]  A. Adamson.  Physical chemistry of surfaces , 1960 .

[16]  Jason J Nichols,et al.  Thinning rate of the precorneal and prelens tear films. , 2005, Investigative ophthalmology & visual science.

[17]  A. Tomlinson,et al.  Importance of the Lipid Layer in Human Tear Film Stability and Evaporation , 1997, Optometry and vision science : official publication of the American Academy of Optometry.

[18]  J. McCulley,et al.  A compositional based model for the tear film lipid layer. , 1997, Transactions of the American Ophthalmological Society.

[19]  Murat Dogru,et al.  Computer-synthesis of an interference color chart of human tear lipid layer, by a colorimetric approach. , 2003, Investigative ophthalmology & visual science.

[20]  R. Farris,et al.  Tear osmolarity--a new gold standard? , 1994, Advances in experimental medicine and biology.

[21]  D. Maurice,et al.  The oily layer of the tear film and evaporation from the corneal surface. , 1961, Experimental eye research.

[22]  D. Korb,et al.  The Effect of Two Novel Lubricant Eye Drops on Tear Film Lipid Layer Thickness in Subjects With Dry Eye Symptoms , 2005, Optometry and vision science : official publication of the American Academy of Optometry.

[23]  A. Verkman,et al.  Aquaporin-dependent water permeation at the mouse ocular surface: in vivo microfluorimetric measurements in cornea and conjunctiva. , 2004, Investigative ophthalmology & visual science.