Which are the Optimal Tonometers for Different Animal Species?

—Rabbits—

Abstract

Five models of tonometers being used currently in human ophthalmological clinics were tested for applicability in the study with rabbits.

Ten male Japanese white rabbits aged 13 weeks were used. The tonometers tested were 3 models of the contact type (ALCON, TONO-PEN and PERKINS) and 2 models of the non-contact type (TOPCON and KEELER), which the Japanese Society of Comparative Ophthalmology arranged for the cooperative study group headed by Dr. Ueda of JRA.

The intraocular pressure (IOP) was measured on the corneal surface of both eyes, 3 times a day, in the morning, early afternoon and evening for 3 successive days, using each of the 5 tonometers.

All tonometers except PERKINS could be used for measurement of rabbit IOP. From a practical point of view, TONO-PEN and KEELER were the most conveniently handled, while ALCON required much skill to manipulate. TOPCON was of little practical value because of its inconvenient shape.

The results of statistical analyses of IOP data obtained by the 4 useful models of tonometers suggested the existence of a circadian rhythm of IOP in rabbits. The recording with the 3 tonometers other than TONO-PEN showed a circadian rhythm with the same tendency to elevation in the evening during the 3-day observation period. TONO-PEN recorded no consistent pattern during the observation period.

If the circadian rhythm in IOP really exists in rabbits, the irregular recording with TONO-PEN may indicate some problem in reliability of this model. Of the non-contact type tonometers tested, TOPCON and KEELER provided fairly stable data, but lower IOP values than those reported in the literature. In addition, the shape of the TOPCON model and the function of the KEELER model made than inconvenient to use on rabbits.

We concluded that the ALCON model is the best of the tonometers tested in the present experiments from the viewpoint of reliability of data, although it has some problems in operation.