Table 1.
Summary of published studies evaluating different tonometer types in cats.
| Tonometer Type | Tonometric Principle | IOP in normal cats (mmHg) | Limitations/Comments | Reference |
|---|---|---|---|---|
| Schiotz tonometer | Indentation | 21.6±5 (n=37) | 5.5gm weight;1955 human conversion table | (12) |
| Pneumotonometer (Mentor O & O) | Applanation | Not established | Underestimates IOP >20mmHg, overestimates IOP <15mmHg | (13) |
| Tono-Pen | Applanation | 19.7±5.6 (n=41) | Underestimates higher IOPs | (14) |
| Mackay-Marg | Applanation | 22.6±4 (n=37) | Underestimates higher IOPs | (14) |
| Tono-Pen XL (also Tono-Pen Vet§) | Applanation | 18.4 ±0.6 (SEM) (n=33) | Markedly underestimates higher IOPs | (13, 15-16, 18)§ |
| TonoVet | Induction-Impact (rebound) | 20.74±0.5 (n= 76) | Accurate but less precise at high IOPs. | (16, 18) |
| Perkins | Applanation | 15.1 +/- 1.7 (n=20)* | Upper maximal scale measurement limits IOP readings to approx. = 50mmHg. *Not tested outside normal physiologic range | (17) |
Mean IOP is presented ± standard deviation unless indicated otherwise;
SEM = standard error of mean; n = number of animals used to determine reference range where applicable.
Asterisk indicates data derived after calibration curve correction