The tear film can be thought of as three interactive layers; the outer lipid, middle aqueous and inner mucin layer. All our techniques employed in tear analysis share one commonality in that they are adapted to deal with the minimal sample volumes available; the average tear volume is estimated to be in the region of 7 µl. Currently our interests are focused on the lipid and protein rich aqueous layers. The lipid layer is comprised of both polar and non polar lipids. The lipids of the meibomian gland secretions have been well characterised, but nature and fate of lipids in tears is less well understood – especially during contact lens wear. The aqueous layer is a dilute solution contained dissolved ions and other substances such as proteins. A great and varying number of proteins have been identified in tears. Some of the proteins in tears are indigenously produced tear-specific proteins (e.g. tear lipocalin, lactoferin and lysozyme). Others are plasma derived (e.g. albumin and IgG); thier cncentration in tears varies depending on the intactness adn stability of the blood-tear barrier.
Techniques such as Liquid Chromatography Mass Spectrometry (LCMS), Langmuir and Brewster Angle Microscopy (BAM), Gas Chromatography Mass Spectrometry (GCMS) and Thin Layer Chromatography (TLC) are employed in the analysis of tear lipids. These techniques as well as UV and fluorescence assays are currently being used to analyse patient-to-patient variation and degradation profiles of the tear film lipids in the ocular environment.
The use of non-invasive tear analysis to determine biomarkers in both ocular and systemic disorders is extremely advantageous and the benefits of tear as a diagnostic medium has been gaining momentum in recent years. Furthermore the possibility of using this readily available and easily accessible biological fluid as an alternative to blood based diagnostics holds exciting potential. ELISA, capillary electrophoresis, Lab-on-a-Chip microfluidic technology and immunodiffusion assays include some of the many and varied techniques used in our laboratories to assess protein dynamics in tears.