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Comparison of two handheld applanation tonometers and the association of central corneal thickness, age, and intraocular pressure in normal and diseased canine eyes




To compare the intraocular pressure (IOP) measurements from two applanation tonometers (Tono-Pen XL® and AccuPen®) in normal and diseased canine eyes (including corneal disease, cataract, glaucoma, uveitis, and noninflammatory intraocular disease) and evaluate the associations among the central corneal thickness (CCT), IOP measurements, and age.

Animals studied

Sixty-eight normal and 191 diseased eyes.


A topical anesthetic agent was applied to each eye. One minute later, IOP was measured with the Tono-Pen XL® and then the AccuPen®, and then CCT was measured with an ultrasonic pachymeter. Measurements for the right eye were always taken first.


The Tono-Pen XL® successfully measured IOP in all eyes, whereas the AccuPen® registered measurements in only 98.4% of diseased eyes. The AccuPen® measurements were significantly lower than the Tono-Pen XL® measurements in both normal and diseased eyes. The CCT did not affect the Tono-Pen XL® or AccuPen® measurements in normal or diseased eyes. Spearman's correlation coefficient by rank analysis of CCT and IOP yielded correlation coefficients (r) of 0.144 and 0.101 for the Tono-Pen XL®, and 0.108 and 0.175 for the AccuPen® in normal and diseased eyes, respectively. In normal canine eyes, age correlated inversely with the CCT (r = −0.128) and IOP as measured using the Tono-Pen XL® (r = −0.446) and AccuPen® (r = −0.427).


The AccuPen® measurements were slightly but significantly lower than the Tono-Pen XL® measurements in both normal and diseased canine eyes. The CCT affected the results of neither tonometer regardless of disease, while both IOP and CCT tended to decrease with age in normal eyes.