Intraocular Pressure Measurement with Perkins Handheld Applanation Tonometer in Cats
Support by UNOESTE (Process #n.135/07).
The glaucoma is characterized by increase of the intraocular pressure (IOP) incompatible with the normal functions of the eye. In cats, glaucoma is usually secondary, as a consequence of inflammations or neoplasias. Early measurement of the increase in the IOP is fundamental to the diagnosis and a better prognosis of glaucoma. In Veterinary, the IOP is measured mainly by the applanation method and the Tonopen is the portable electronic applanation tonometer more used. Unhappily the cost of this instrument is very high what limits his acquisition. In the Medicine, the more popular portable applanation tonometer is the Perkins that uses the Goldman's methodology that consists of the instillation of anesthetic eye drops, because the contact of the instrument in the cornea, and of fluorescein eye drops for the formation of semicircles. This tonometer has a cost on average five times smaller than Tonopen, and this could be an interesting alternative for the IOP exam in the Veterinary, however until the present moment there is few studies of the use of this tonometer in cats. The objective was to evaluate and to validate the accuracy of the Perkins handheld applanation tonometer in the measurement of intraocular pressure (IOP) in cats. Both eyes from ten cats, immediately post mortem, were used for the in situ study and both eyes, from ten clinically normal and anesthetized cats, were used for the in vivo study. Readings of the IOP in situ and in vivo studies were correlated with manometry (by a mercury column manometer) and tonometry (by the Perkins handheld applanation tonometer). The manometry data was measured by the cannulation of the anterior chamber with a 25-gauge needle. The calibration manometry versus tonometry curve was determined by raising the IOP artificially from 5 to 50 mmHg in 5 mmHg steps (5-50 mmHg). Linear regression analysis was performed on the manometry vs. tonometry IOP measurements, and the correlation coefficient (r2) was calculated. The correlation coefficient (r2) between the manometry and the Perkins tonometer was 0.988, and the corresponding linear regression equation was y = 0.0899x + 0.1145 in the in situ study. The mean IOP readings were 15.0±1.7 mmHg (range 13.0-18.0 mmHg) with the manometer and 1.6±0.2 (range 1.3-2.0) mmHg with the Perkins tonometer and were 16.4±2.6 mmHg (range 13.1-20.9 mmHg) after calibration curve correction. The Perkins tonometer was shown to be a practical and accurate method for IOP measurement in cats.