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  • Author or Editor: Lynda J. Majors x
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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.

Free access
in American Journal of Veterinary Research

SUMMARY

Comparisons of the MacKay-Marg and Tono-Pen applanation tonometers in open and closed in vitro systems were made for the eyes of cats. Both instruments significantly underestimated intraocular pressure (iop) vs direct manometry (P < 0.001), but in readily predictable manner, with high coefficients of determination (r 2 = 0.99). For tonometer 1 (MacKay-Marg), calculated actual iOP = 1.36 × (MacKay-Marg measurement) − 1.67 mm of Hg; and for tonometer 2 (Tono-Pen), calculated actual iop = 1.37 × (Tono-Pen measurement) + 0.8 mm of Hg, using measurements from 11 enucleated eyes. In vivo comparisons were initially made in 81 clinically normal eyes (n = 41 cats) by applying the Tono-Pen first followed by the MacKay-Marg. Compared with the MacKay-Marg, the Tono-Pen significantly (P < 0.001) underestimated iOP in these cats. When the order of tonometer applanation was subsequently reversed in 73 clinically normal eyes (n = 37 cats) the Tono-Pen again significantly (P < 0.001) underestimated iOP, compared with the MacKay-Marg. Alterations in tonometer order did not result in significant differences in measured iOP for the MacKay-Marg when compared with itself, but Tono-Pen measurements were significantly (P < 0.05) less when its use followed, rather than preceded, that of the MacKay-Marg. Mean (± sd) iop in clinically normal cats when each tonometer was used first was 22.6 ± 4.0 mm of Hg (range, 14 to 32 mm of Hg) for the MacKay-Marg and 19.7 ± 5.6 mm of Hg (9 to 31 mm of Hg) for the Tono-Pen. The mean (± sd) absolute value of the differences between MacKay-Marg measurements and those obtained by use of the Tono-Pen was 3.2 ± 3.1 (range, 0 to 13 mm of Hg difference).

Free access
in American Journal of Veterinary Research