Comparison of the human and canine Schiotz tonometry conversion tables in clinically normal dogs

Paul E. Miller From the Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Dr West, Madison, WI 53706 (Miller), and the Department of Small Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 (Pickett).

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J. Phillip Pickett From the Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Dr West, Madison, WI 53706 (Miller), and the Department of Small Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 (Pickett).

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Summary

Intraocular pressure (iop) was measured in 114 eyes of 57 clinically normal dogs with 2 applanation tonometers (Tono-Pen and Mackay-Marg) and the Schiotz indentation tonometer, using the 5.5- and 7.5-g weights. Significant differences were not detected between measurements obtained with the Tono-Pen and Mackay-Marg tonometers the Mackay-Marg and Schiotz tonometers using either weight and conversion with the human calibration table, or the Tono-Pen and Schiotz tonometers using the 7.5-g weight and the human calibration table. Values obtained by use of the Tono-Pen tonometer were significantly less (P < 0.005) than values obtained with the Schiotz tonometer when a 5.5-g weight and the human calibration table were used, but the amount was clinically unimportant. Estimates of iop using the Schiotz tonometer and the canine calibration table, and either the 5.5− or 7.5-g weight were clinically and significantly much higher (P < 0.0001) than estimates obtained with the Tono-Pen, Mackay-Marg, or Schiotz tonometers, using the human calibration table and either weight. Sixty to 70% of clinically normal dogs had an iop ≥ 30 mm of Hg when Schiotz scale measurements were converted with the canine conversion table. For clinically normal dogs, the human calibration table was the most clinically useful table for converting Schiotz tonometer measurements to mm of Hg. Normal mean (± sd) canine readings with the Schiotz tonometer and the 5.5-g weight was 4.9 ± 1.5 tonometerscale units (range, 2 to 11; 95% confidence interval, 1.9 to 7.9). Converted means (± sd) for clinically normal dogs with the 5.5-g weight were 18.0 ± 4.1 mm of Hg (range, 6 to 29; 95% confidence interval, 9.8 to 26.2) with the human calibration table, and 30.9 ± 4.7 mm of Hg (range, 17 to 43; 95% confidence interval, 21.5 to 40.3) with the canine conversion table.

Summary

Intraocular pressure (iop) was measured in 114 eyes of 57 clinically normal dogs with 2 applanation tonometers (Tono-Pen and Mackay-Marg) and the Schiotz indentation tonometer, using the 5.5- and 7.5-g weights. Significant differences were not detected between measurements obtained with the Tono-Pen and Mackay-Marg tonometers the Mackay-Marg and Schiotz tonometers using either weight and conversion with the human calibration table, or the Tono-Pen and Schiotz tonometers using the 7.5-g weight and the human calibration table. Values obtained by use of the Tono-Pen tonometer were significantly less (P < 0.005) than values obtained with the Schiotz tonometer when a 5.5-g weight and the human calibration table were used, but the amount was clinically unimportant. Estimates of iop using the Schiotz tonometer and the canine calibration table, and either the 5.5− or 7.5-g weight were clinically and significantly much higher (P < 0.0001) than estimates obtained with the Tono-Pen, Mackay-Marg, or Schiotz tonometers, using the human calibration table and either weight. Sixty to 70% of clinically normal dogs had an iop ≥ 30 mm of Hg when Schiotz scale measurements were converted with the canine conversion table. For clinically normal dogs, the human calibration table was the most clinically useful table for converting Schiotz tonometer measurements to mm of Hg. Normal mean (± sd) canine readings with the Schiotz tonometer and the 5.5-g weight was 4.9 ± 1.5 tonometerscale units (range, 2 to 11; 95% confidence interval, 1.9 to 7.9). Converted means (± sd) for clinically normal dogs with the 5.5-g weight were 18.0 ± 4.1 mm of Hg (range, 6 to 29; 95% confidence interval, 9.8 to 26.2) with the human calibration table, and 30.9 ± 4.7 mm of Hg (range, 17 to 43; 95% confidence interval, 21.5 to 40.3) with the canine conversion table.

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