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Meng C. Lin, Andrew D. Graham, Kenneth A. Polse, Robert B. Mandell, Nancy A. McNamara; Measurement of Post–Lens Tear Thickness. Invest. Ophthalmol. Vis. Sci. 1999;40(12):2833-2839.
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purpose. A method to measure the tear film beneath a soft contact lens, referred
to as post–lens tear thickness (PLTT), would have many applications to
contact lens research. In this study a noninvasive technique
for measuring the PLTT is presented.
methods. The feasibility of measuring the tear layer by optical pachometry was
first assessed using a model eye. The baseline corneal thickness (B) of
both eyes of 21 subjects was measured, etafilcon-A ionic
disposable soft contact lenses (58% water) were inserted, and the
total thickness (T) of the cornea, contact lens, and PLTT were
measured. After the pachometry readings the lenses were removed and
their center thickness (C) determined. The PLTT was calculated using
the equation: PLTT = T − (B + C). Two sets of measurements
of T were performed at 15 and 25 minutes after lens insertion. The
entire procedure was repeated at a second visit.
results. The pachometry measurements of the small aqueous reservoir between the
model eye and the lens closely matched those obtained by direct
microscopic measurement. For human PLTT, the mean values (and 95%
confidence intervals) for right eyes on visits 1 and 2 were 11 (8, 13)
and 12 (10, 15) μm, respectively, and for left eyes were 12 (10, 15)
and 11 μm (8, 14) μm, respectively.
conclusions. It is possible to measure the post–lens tear thickness using optical
pachometry. The variability between repeated measurements suggests that
with careful sample size planning, the technique is sufficiently
precise to be useful in group assessments of
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