Evaluation of two applanation tonometers in horses

Paul E. Miller From the Section of Ophthalmology, Department of Surgical Sciences, School of Veterinary Medicine (Miller, Pickett), and the Department of Ophthalmology, School of Medicine (Majors), University of Wisconsin, 2015 Linden Dr West, Madison, WI 53706.

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J. Phillip Pickett From the Section of Ophthalmology, Department of Surgical Sciences, School of Veterinary Medicine (Miller, Pickett), and the Department of Ophthalmology, School of Medicine (Majors), University of Wisconsin, 2015 Linden Dr West, Madison, WI 53706.

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Lynda J. Majors From the Section of Ophthalmology, Department of Surgical Sciences, School of Veterinary Medicine (Miller, Pickett), and the Department of Ophthalmology, School of Medicine (Majors), University of Wisconsin, 2015 Linden Dr West, Madison, WI 53706.

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Summary

Comparisons were made of measurements obtained in horses, using 2 applanation tonometers in vivo and in vitro. In vitro comparisons indicated that although neither instrument accurately recorded intraocular pressure (iop), compared with manometric measurements, results of both instruments indicated linear digression from manometric iop values that could readily be corrected, thereby accurately estimating iop in horses. For tonometer 1 (MacKay-Marg), calculated actual lop = 1.48 − 0.9 mm of Hg; and for tonometer 2 (Tono-Pen), calculated actual iop = 1.38 + 2.3 mm of Hg. The coefficients of determination (r2) values were markedly high (0.99 for both equations). In vivo comparisons in clinically normal horses did not reveal significant differences in measured 10P between the 2 instruments, and iop was not altered from baseline after auriculopalpebral nerve block. Mean (± sd) iop in clinically normal horses was 23.5 ± 6.10 mm of Hg and 23.3 ± 6.89 mm of Hg, for tonometers 1 and 2, respectively.

Summary

Comparisons were made of measurements obtained in horses, using 2 applanation tonometers in vivo and in vitro. In vitro comparisons indicated that although neither instrument accurately recorded intraocular pressure (iop), compared with manometric measurements, results of both instruments indicated linear digression from manometric iop values that could readily be corrected, thereby accurately estimating iop in horses. For tonometer 1 (MacKay-Marg), calculated actual lop = 1.48 − 0.9 mm of Hg; and for tonometer 2 (Tono-Pen), calculated actual iop = 1.38 + 2.3 mm of Hg. The coefficients of determination (r2) values were markedly high (0.99 for both equations). In vivo comparisons in clinically normal horses did not reveal significant differences in measured 10P between the 2 instruments, and iop was not altered from baseline after auriculopalpebral nerve block. Mean (± sd) iop in clinically normal horses was 23.5 ± 6.10 mm of Hg and 23.3 ± 6.89 mm of Hg, for tonometers 1 and 2, respectively.

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