Assessment of intraocular pressure in vitrectomized gas-containing eyes. A clinical and manometric comparison of the Tono-Pen to the pneumotonometer
J. I. Lim, N. P. Blair, E. J. Higginbotham, M. D. Farber, W. E. Shaw and B. R. Garretson
Department of Ophthalmology, Eye and Ear Infirmary, University of Illinois, Chicago College of Medicine 60612.
Elevation of intraocular pressure (IOP) in gas-containing eyes occurs not
infrequently, and applanation tonometry in eyes with epithelial
irregularities is not accurate. The pneumotonometer and TonoPen (Oculab, La
Jolla, Calif) are alternative tonometers for use in these eyes, yet the
accuracy of determining IOP with the Tono-Pen has not been determined
manometrically. We performed a clinical and manometric study comparing the
Tono-Pen with the pneumotonometer in gasfilled vitrectomized eyes. In our
clinical study, we measured IOP in 50 eyes of 50 patients with corneal
irregularities following vitrectomy and air/gas-fluid exchange. Tono-Pen
measurements were highly correlated with those of the pneumotonometer.
However, there was a mean difference of 1.4 mm Hg between Tono-Pen and
pneumotonometer IOP readings. A larger percentage of Tono-Pen readings were
lower than those of the pneumotonometer as IOP levels increased. To assess
the accuracy of these tonometers, we compared manometric readings via an
indwelling catheter with Tono-Pen and pneumotonometer IOP readings in 11
eye bank eyes following a lensectomy, vitrectomy, and air-fluid exchange.
Overall, Tono-Pen and pneumotonometer readings were highly correlated with
those of the manometer. However, both machines showed a significant
underestimation of IOP at pressures greater than or equal to 30 mm Hg;
pneumotonometer and Tono-Pen readings averaged 10.2 and 12.1 mm Hg lower,
respectively, than those of the manometer. We conclude that both the
pneumotonometer and the Tono-Pen underestimate IOP at pressures greater
than or equal to 30 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)
