William Ngo, OD, BSc is a clinical researcher at the Centre for Contact Lens Research, in the School of Optometry and Vision Science at the University of Waterloo.
Download the poster (.pdf), which was originally shared at the American Academy of Optometry annual meeting, 2015.
Enhancement of clinical observation of Demodex folliculorum
William Ngo1, Sruthi Srinivasan1, Lyndon Jones1, Etty Bitton2
1Centre for Contact Lens Research, University of Waterloo
2Ecole d ‘Optometrie
PURPOSE: Demodex folliculorum is a common ectoparasite associated with blepharitis. These mites have a body length of less than 400um and are typically found burrowed in eyelash follicles, making them difficult to identify with a standard slit lamp (SL). Currently, definitive diagnosis requires lash epilation and observation of mites under a microscope, which is not typical of clinical instrumentation found in an optometric practice. Consequently, the purpose of this investigation was to explore optical instruments to enhance the viewing of Demodex f. An ideal viewing system would provide a magnified upright image (approx. 400-600x) of the eyelashes, with low optical distortion.
METHOD: Four categories of optical instruments were experimented with: SL modifications, condensing lenses, head mounted magnifiers, and digital devices. The optical properties assessed were magnification/field of view, distortion, working distance (WD), viewing stability, and depth of field. Filters, dyes, and different wavelengths of light, along with their practicality were also evaluated.
RESULTS: SL modifications are a viable option, since the optics are optimized and the patient is stabilized. Magnification can be enhanced through adapters (e.g. 20x oculars) or a high quality SL with superior optics. Head mounted magnifiers (e.g. 8x binoculars) offer freedom of movement, but WD is restrictive. Condensing lenses were able to achieve the desired magnification, but at the cost of distortion, image inversion and stability. Digital devices (smartphones) were user-friendly and accessible, however resolution and stability are limitations. Presently, no ophthalmic dyes or filters have effectively enhanced the visualization of the mite.
CONCLUSION: The main challenge to viewing the base of the eyelash is obtaining sufficiently high magnification with minimal distortion and good stability. The slit lamp appears be the best platform for the development of an optical system for viewing Demodex f.