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Application of Scanning Electron Microscopy With Energy-Dispersive X-Ray Spectroscopy for Analyzing Ocular Surface Particles on Schirmer Strips

Avula, Anuroop MD, MPH*; Galor, Anat MD, MSPH†,‡; Blackwelder, Patricia PhD§; Carballosa-Gautam, Melissa PhD; Hackam, Abigail S. PhD; Jeng, Bennie MD; Kumar, Naresh PhD*

doi: 10.1097/ICO.0000000000001173

Purpose: To demonstrate the application of scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM/EDS) for analyzing Schirmer strips for particle concentration, size, morphology, and type distribution.

Methods: A cross-sectional design was used. Patients were prospectively recruited from the Miami Veterans Affairs (VA) Healthcare System eye clinic, and they underwent a complete ocular surface examination. The size, type, and chemical composition of particulate matter on Schirmer strips (from the left eye) were analyzed using SEM/EDS.

Results: Schirmer strips from all 6 patients showed particle loading, ranging from 1 to 33 particles, whereas the blank Schirmer strip that served as a control showed no particle loading. Most particles were coarse, with an average size of 19.7 μm (95% confidence interval 15–24.4 μm). All samples contained organic particles (eg, pollen and mold), and 5 of the 6 samples contained nonorganic particles. The nonorganic particles were composed of silicon, minerals, and metals, including gold and titanium. The size of aluminum and iron particles was ≥62 μm, whereas the size of 2 other metals, zinc and gold, was smaller, that is, <20 μm. Most metal particles were elongated compared with the organic particles, which were round.

Conclusions: Although SEM/EDS has been extensively used in biomedical research, its novel application to assess the size, morphology, and chemical composition of the ocular surface particles offers an unprecedented opportunity to tease out the role of particulate matter exposure in ocular surface disease and disorders.

*Department of Public Health Sciences, University of Miami, Miami, FL;

Miami Veterans Administration Medical Center, Miami, FL;

Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami, Miami, FL;

§Center for Advanced Microscopy, College of Arts and Sciences, University of Miami, Miami, FL;

Miami Project Imaging and Histology Cores, Miami Project to Cure Paralysis, University of Miami, Miami, FL; and

Department of Ophthalmology, School of Medicine, University of Maryland, Baltimore, MD.

Reprints: Naresh Kumar, PhD, Department of Public Health Sciences, University of Miami, Miami, FL 33136 (e-mail:

Supported by the Department of Veterans Affairs, Veterans Health Administration, Office of Research and Development, Clinical Sciences Research (EPID-006-15S), National Institute of Health (EY026174; Center Core Grant P30EY014801), and Research to Prevent Blindness Unrestricted Grant.

The authors have no conflicts of interest to disclose.

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Received November 10, 2016

Received in revised form January 19, 2017

Accepted January 21, 2017

Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.