TITLE:
Dynamic Contour Tonometry, Tono-Pen XL®, and Goldmann Applanation Tonometry in Comparison to Intracameral Intraocular Pressure (IOP) Measurements in Patients with Corneal Pathologies
AUTHORS:
Matthias Neuburger, Juliane Großwendt, Sonja Lautebach, Philip Maier, Florian Birnbaum, Daniel Böhringer, Jens Funk, Jens Friedrich Jordan, Thomas Reinhard
KEYWORDS:
Keratoplasty, IOP Measurement, Goldmann Applanation Tonometry, Dynamic Contour Tonometry, Tono-Pen XL®
JOURNAL NAME:
Open Journal of Ophthalmology,
Vol.4 No.2,
May
14,
2014
ABSTRACT: Purpose: The accuracy of Goldmann applanation
tonometry (GAT) has been shown to depend on several biomechanical properties of
the cornea. Newer tonometry devices (e.g., the Dynamic Contour Tonometer
PASCAL? [DCT] and the Tono-Pen? XL [TP]) have been
designed to accurately measure intraocular pressure (IOP) independent of
corneal thickness (CCT) and pathology. This study investigates the influence of
corneal pathologies on the accuracy of these IOP measuring devices, and
compares this accuracy to that of direct intracameral IOP measurement. Methods:
8 eyes of 8 patients suffering from corneal pathologies scheduled for
penetrating keratoplasty, and 10 eyes of 10 patients scheduled for cataract
surgery (control group) were examined. Before surgery, the anterior chamber
was cannulated at the temporal corneal limbus. In a closed system, the
intraocular pressure (IOP) was directly set to 10, 20, and 30 mmHg with a
manometric water column. Intraocular pressure measurements taken by GAT, DCT,
and TP were compared to intracameral measurements obtained by a precision
reference pressure sensor. Results: Control
group: All three methods showed good agreement with the intracameral
readings (mean deviation of all three devices, -0.9 mmHg). Group with corneal pathologies: The TP yielded the most exact IOP
values in the group with corneal pathologies when taking all diagnoses into
account. The mean deviations from the intracameral IOP measurements were -0.9 mmHg ± 3.2 mmHg (mean ± SD) for TP, -2.9 mmHg ± 3.3
mmHg for GAT, and -5.0 mmHg ± 7.9 mmHg for DCT. For bullous keratopathy, the
most exact IOP readings were obtained by the TP (mean deviation -0.2 mmHg ± 3.5
mmHg). The TP and GAT devices underestimated IOP in the patients with Fuchs’
endothelial dystrophy; all 3 devices underestimated adjusted IOP after
keratoplasty. DCT showed the greatest deviations from adjusted IOP in the case
of non-herpetic scars. In the control group, none of the devices showed a
statistically relevant dependency on CCT. Nevertheless, in the group with corneal
pathologies, only TP showed no dependency on CCT. Conclusion: Our results
suggest that the Tono-Pen XL? is the most accurate measurement
device to determine IOP in patients with corneal pathologies, especially in
patients suffering from corneal edema (bullous keratopathy). GAT yielded
surprisingly exact IOP values in patients suffering from irregular corneal
surface. DCT showed a high degree of deviation from the adjusted IOP, and
should not be used to determine IOP in corneas with the disorders listed here.