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Evaluation of two applanation tonometers in cats

1991; American Veterinary Medical Association; Volume: 52; Issue: 11 Linguagem: Inglês

10.2460/ajvr.1991.52.11.1917

1943-5681

Paul E. Miller, J. Phillip Pickett, Lynda J. Majors, Ilene D. Kurzman,

Glaucoma and retinal disorders

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).