Abstract
Purpose :
To determine the accuracy of elevating IOP by infusing balanced salt solution (BSS) via a Pinport and intraocular microcannula.
Methods :
Brown Norway rats with a head-mounted Pinport leading to an implanted microcannula were connected via a tether to an elevated BSS-containing reservoir and transducer. Animals underwent one or more exposures to awake Controlled Elevation of IOP (aCEI), during which IOP was increased to 45 mmHg for 7 hours with free mobility and access to food and water. Approximately one week after the final aCEI, IOP produced by BSS through the Pinport was directly measured in animal subgroups using a second cannula, placed in the anterior chamber (AC). Intended Pinport pressures were compared to AC cannula and Tonolab pressures.
Results :
In 12 animals (Group 1), AC cannula pressures were within 5 mmHg of the intended Pinport pressure at every IOP level. (Figure) Mean Pinport pressures were not significantly different from the AC cannula (P=0.53) or TonoLab measurements (P=0.48). However, Bland-Altman 95% limits of agreement between the Pinport and AC cannula measurements (2±2 mmHg), were tighter than between Pinport and Tonolab (-1±8 mmHg). AC cannulations in these animals occurred an average of 20 ± 11 (SD) days following Pinport/cannula implantation and 9 ± 2 (SD) days after the final aCEI.
Eight other animals (Group 2), assessed an average of 14 ± 5 (SD) days after the Pinport/cannula implantation and 8 ± 4 (SD) days following final aCEI, showed that AC cannula pressures were more than 5 mmHg below intended Pinport pressures at every level. As an indicator of reliability, Group 1 Tonolab readings at a Pinport pressure of 40 mmHg ranged from 30 – 57 mmHg (mean 41 ± 9 ), while group 2 ranged from 8 – 26 mmHg (mean 19 ± 9).
Conclusions :
Pinport/microcannula implanted eyes can retain good delivery of IOP following awake CEI.
Tonolab response to an initial Pinport pressure of 40 mmHg can identify eyes in which the AC pressure will closely match the intended Pinport IOP.
This system is suitable for studying repeat exposures to known levels of IOP in Brown Norway rats.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.