Validation of the EYEMATE-SC Suprachoroidal Pressure Transducer for Telemetric Measurement of Intraocular Pressure in Normal Ex Vivo Canine and Equine Globes-Preliminary Results

Abstract

Objective: To determine the accuracy of the EYEMATE-SC suprachoroidal tracer for telemetric tonometry in canine and equine globes.

Procedures: The EYEMATE-SC sensor (7.8 mm × 3.8 mm × 1 mm) was implanted in the suprachoroidal space of four freshly enucleated normal canine and two normal equine eyes. The anterior chambers were cannulated and connected to a reservoir of Plasma-Lyte A and a manometer. Starting at a manometric IOP of 5 mmHg, the pressure was progressively increased to 80 mmHg by raising the reservoir. At each setpoint (5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, and 80 mmHg), triplicate telemetric measurements were taken with the EYEMATE-SC using a portable reading device for telemetric pressure transmission via a radiofrequency band. These measurements were compared to manometric pressure by linear regression analysis.

Results: A strong positive linear regression was observed between EYEMATE-SC and manometry IOPs in both canine and equine eyes (canine: R² = 0.99; equine: R² = 0.99). The EYEMATE-SC was unable to measure pressures > 70 mmHg in either species.

Conclusions: Measuring canine and equine IOPs from the suprachoroidal space using the EYEMATE-SC provided accurate results over an extensive range of pressures in ex vivo globes. This telemetric sensor could assist with long-term, frequent tonometry by pet owners and clinicians following in vivo testing. Although the sensor could not detect pressures above 70 mmHg, this flaw was not considered clinically relevant.

Keywords: dog; glaucoma; horse; intraocular pressure sensor; manometry; ultrasound biomicroscopy (UBM).

FIGURE 1

The EYEMATE‐SC. The implantable suprachoroidal pressure transducer (7.8 mm × 3.8 mm × 1 mm) is embedded in a silicone rubber encasement (A). The ruler on the left shows a millimeter scale (1 mm between two lines). The portable reading device serves for the telemetric pressure transmission via a radio frequency band (B).

FIGURE 2

Suprachoroidal implantation of the EYEMATE‐SC sensor device in a canine globe. (A) A small, 5‐mm incision was made over the pars plana of the ciliary body parallel to the limbus. (B) Following the creation of a suprachoroidal pocket with viscoelastic solution, the EYEMATE‐SC was inserted through the scleral incision, perpendicular to the limbus. (C) The scleral incision was closed with a simple interrupted suture pattern using 8–0 polyglactin 910.

FIGURE 3

Comparison between direct manometry and telemetric measured IOP. Linear regression analysis was performed to compare the EYEMATE‐SC (y‐axis) to direct manometry (x‐axis) in canine (A) and equine (B) eyes. Linear equations and coefficients of determination (R ²) are included in the scatter plots. There was an almost perfect agreement between the dashed regression lines and the solid y = x line.

FIGURE 4

Longitudinal scan using UBM to visualize the EYEMATE‐SC. The transducer (between the two arrowheads) is located in the suprachoroidal space (*), which is locally expanded with viscoelastic solution. The vertical arrow shows the scleral incision through which the implant was inserted into the suprachoroidal space.