Abstract
Purpose: :
The purpose of our study was to determine if there is an optimal anatomical location outside the central cornea to obtain reliable and reproducible intraocular pressure (IOP) measurements using existing tonometry devices.
Methods: :
We cannulated the anterior chamber of human cadaver eyes with a 27 gauge needle placed connected to an isotonic saline manometer resorvoir equipped with an in-line pressure gauge (XP2I Digital Test Gauge, Crystal Engineering, San Luis Obispo, CA). IOP was controlled by raising the reservoir, and masked randomized measurements were recorded at IOPs of 10, 20, 30, and 40 mmHg using the Tono-Pen XL tonometer (Medtronic, Jacksonville, FL) and Schiotz Tonometer (Sklar, New York, NY) with a 7.5gram plunger load applied to the central cornea, temporal corneoscleral limbus, and temporal sclera (3mm posterior to the limbus). We determined and measured precision (n=10 measurements) and accuracy (n=3 measurements) of each tonometer at each specified anatomic site.
Results: :
We included 228 IOP measurements taken 15 seconds apart from two eyes of a single donor. The average coefficient of variation for the Schiotz tonometer at the cornea, limbus, and sclera were 0.06, 0.10, and 0.14 respectively. The coefficient of variation for the Tonopen at the cornea, limbus, and sclera were 0.14, 0.24, and 0.20 respectively. Absolute differences for the Schiotz tonometer compared to manometric IOPs of 10, 20, 30, and 40mmHg were 2.1, 4.6, 16.2, and 22.3 at the limbus and 4.8, 0.6, 4.5, and 1.3 at the sclera respectively. Absolute differences for the Tonopen tonometer compared to manometric IOPs of 10, 20, 30, and 40mmHg were 20.0, 10.2, 23.8, and 3.2 at the limbus and 31.2, 14.7, 24.4, and 29.8 at the sclera respectively.
Conclusions: :
The Schiotz tonometer demonstrated a higher degree of precision compared to the Tonopen tonometer as exhibited by the lower coefficient of variation across all anatomical locations of measurement. Measurement of IOP at the sclera using the Schiotz tonometer demonstrated the highest degree of accuracy compared to manometric IOPs.
Keywords: intraocular pressure • clinical laboratory testing • sclera