Zeta potential of tear samples: A tool to explore the effects of wear of contact lenses |
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| Affiliation: | 1. University of Milano Bicocca, Materials Science Department, via R. Cozzi 55, I-20125 Milan, Italy;2. University of Milano Bicocca, Department of Biotechnology and Bioscience, Piazza della Scienza 2, I-20126 Milan, Italy;3. University of Milano Bicocca, COMiB Research Centre, via R. Cozzi 55, I-20125 Milan, Italy;4. School of Life & Health Sciences, Aston University, Aston Triangle, Birmingham, B4 7ET, UK;1. Optometry and Vision Department, Faculty of Optics and Optometry, Complutense University of Madrid, Madrid, Spain;2. Ophthalmology Department, San Carlos University Hospital, Complutense University, Madrid, Spain;3. Department of Biomedical Engineering, Faculty of Fundamental Problems of Technology, Wroclaw University of Science and Technology, Wroclaw, Poland;1. Contact Lens Services, Tej Kohli Cornea Institute, L V Prasad Eye Institute, Hyderabad, India;2. Brien Holden Institute of Optometry and Vision Sciences, L V Prasad Eye Institute, Hyderabad, India;3. Ophthalmic Biophysics, L V Prasad Eye Institute, Hyderabad, India;1. School of Optometry, Tianjin Vocational Institute, China;2. School of Optometry, Nova Southeastern University, The United States;3. College of Optometry, Pacific University, India;1. Schepens Eye Research Institute-Massachusetts Eye and Ear, Harvard Medical School, Boston, Massachusetts;2. Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts;3. Department of Ophthalmology and Visual Sciences, Paulista School of Medicine, Federal University of Sao Paulo-UNIFESP, Sao Paulo, Brazil |
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| Abstract: | PurposeThe aim was to develop a method to assess the electrostatic properties of human tear samples, and to evaluate their modifications induced by the wear of contact lenses (CLs).MethodThe barrier method was developed for the measurement of the isoelectric point (IEP) on relatively small quantities. The method was applied to compare three groups: tears (TNW) of non-wearers, tears (TW_etaf) of regular wearers of etafilcon A CLs, and tears (TW_omaf) of regular wearers of omafilcon A CLs. Zeta potential (ζ) as a function of pH was measured by a Zetasizer Nano ZS90 (Malvern Instruments) on 40%-diluted samples, obtained by mixing 57 μL of tears of different subjects of the same group with 85 μL of HCl aqueous solution. IEP was deduced as the pH at which ζ is zero, i.e. the net electric charge on tear constituents being neutralized.ResultsWithin an error of about 0.05, IEPs were found to be 2.90 (TNW), 2.80 (TW_omaf), and 3.16 (TW_etaf). On average, a lower H+ concentration is needed to neutralize the surface charge of the tear components of etafilcon A wearers, compared to both TNW and TW_omaf.ConclusionIEP measurements on tear samples of wearers of different types of CLs are proposed in order to enhance the knowledge on the modifications of the profile of charged species in tears. The TW_etaf results, compared to those of the other groups, are compatible with an increase, due to the wear of etafilcon A CLs, of the relative concentration of high-IEP proteins. |
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| Keywords: | Tears Zeta potential Isoelectric point Contact lenses Proteins |
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