Research article

Tono-Pen XL tonometry during application of a suction ring in rabbits

Spyridon K Charisis^1* , Harilaos S Ginis^2* , Georgios A Kounis^2* and Miltiadis K Tsilimbaris^1*

¹  University Hospital of Heraklion, Eye Clinic, Heraklion, Crete, Greece

²  Institute of Vision and Optics, University of Crete, Heraklion, Crete, Greece

author email corresponding author email* Contributed equally

BMC Ophthalmology 2008, 8:14doi:10.1186/1471-2415-8-14

Published:	30 July 2008

Abstract

Background

The purpose of this study is to evaluate the use of Tono-Pen XL in measuring IOP during the application of a suction ring in rabbit eyes with manometrically controlled IOP.

Methods

Tono-Pen XL was calibrated against direct manometry in 10 rabbit eyes. A suction ring was then applied in 4 rabbit eyes and the IOP was determined manometrically during suction ring application at 350 mmHg vacuum pressure. Finally, in 6 catheterized rabbit eyes the IOP was measured with Tono-Pen XL during suction ring application at suction vacuum from 350 to 650 mmHg, while keeping actual IOP stable at 30 mmHg and 60 mmHg.

Results

Linear regression analysis revealed that the Tono-pen XL was reliable for IOPs between 10 and 70 mmHg (R² = 0.9855). Direct manometry during suction ring application showed no statistically significant variation of Tono-Pen XL readings when the incanulation manometry intraocular pressure changed from 30 mmHg to 60 mmHg and no statistically significant correlation between suction vacuum and IOP measurements.

Conclusion

Tono-Pen XL measurements are unreliable during the application of a suction ring on living rabbit eyes even when the actual IOP is forced to be within the validated range of Tono-Pen XL measurements. This inaccuracy is probably related to altered corneal and scleral geometry and stress.