Abstract
Purpose: :
To determine time courses of retinal structural and functional changes in wild type mice following the induction of ocular hypertension by anterior chamber injection of polystyrene beads.
Methods: :
Induction of ocular hypertension: 6 week old C57BL/6J female mice were anesthetized and had the left eye dilated. A 30 gauge needle was used to puncture the cornea. One of the following mixes was injected over 90 seconds via a glass micropipette attached to a Hamilton syringe and inserted into the anterior chamber through the corneal incision. Mix 1 contained one microliter of a fixed combination of 1 and 6 micron diameter dyed polystyrene beads (Polysciences, Inc.) followed by 3 microliters of Provisc (Alcon, Inc.). Mix 2 contained 2 microliters of the same bead combination followed by 2 microliters of Provisc. Mix 3 contained 2 microliters of PBS followed by 2 microliters of Provisc. The right eye was untreated. IOP was measured with a rebound tonometer (Tonolab) three times a week for 6 weeks.Histology: Six weeks after IOP induction, freshly enucleated eyes were placed optic nerve down in 8% neurobiotin for 20 minutes and washed with oxygenated Ames solution for several light-dark cycles. Retinas were fixed, blocked, incubated with secondary antibody, and whole-mounted. Images were acquired with a confocal microscope and processed in Photoshop.ERGs: Scotopic a- and b- waves and positive and negative scotopic threshold responses (STRs) were measured at 1, 2, 3, 4, and 6 weeks after IOP induction according to previously published protocols.
Results: :
Mix 1 (n = 11) and Mix 2 (n = 18) caused an average increase in cumulative IOP (sum of all measured IOPs) of 35% and 36%, respectively. 28 of 29 animals (97%) had an increased cumulative IOP in the treated eye compared to the untreated eye. Mix 1 and Mix 2 had an average IOP of 12.8mmHg and 12.9mmHg, respectively. Control (untreated) eyes had an average IOP of 9.3mmHg. Only 3 animals (10%) had a measured IOP of 30mmHg or greater at any point. Mix 3 (n = 4) caused an average increase in cumulative IOP of 8% and no animals had an IOP of 30mmHg or greater at any point. Animals that were injected with beads showed a reduction in neurobiotin-positive retinal ganglion cells (RGCs) of 15.7% when compared to untreated control eyes (n = 3). The a- and b-wave amplitudes of bead treated (n = 9), PBS treated (n = 4), and control eyes were essentially the same at all tested light intensities and time points. Analysis of the pSTR and nSTR is currently ongoing.
Conclusions: :
Injection of either volume of polystyrene beads into the mouse anterior chamber results in a reliable, chronic, mild elevation of IOP with a low incidence of IOP spikes. Like human glaucoma, this technique leads to RGC loss without reduction of outer retinal function.
Keywords: intraocular pressure • electroretinography: non-clinical • ganglion cells