Transient Ocular Hypertension Results in Persistent Retinal Structural and Functional Changes in Pigmented Rabbits

Abstract

Purpose: : To characterize retinal structural and functional changes in a rabbit model of ocular hypertension proposed by Xu Y, Chen Z, Song J. "A study of experimental carbomer glaucoma and other experimental glaucoma in rabbits. Zhonghua Yan Ke Za Zhi. 2002 38:172-5".

Methods: : Elevated IOP was induced in OD of 30 male Dutch-Belted rabbits weighing 2-3 kg by injecting 50 µl of 0.3 % Carbopol 934P (BF Goodrich, Specialty Polymers and Chemical Division, Cleveland OH) into the anterior chamber with a 32 gauge needle. IOP was measured weekly for 18 weeks using a 30 Classic pneumatonometer (Mentor O & O, Inc, Norwell, MA). Horizontal cup depth (CD) and retinal nerve fiber layer thickness (RNFLt) 1 mm inferior to the optic nerve head were assessed from raster scans (6 mm x 6 mm, 64 b-scans, 512 a-scans/b-scan) using a Topcon 3D OCT-1000. Spatial (0.025-4 cpd, at 80% contrast) and contrast (2-80% at 0.025 cpd) sweep VEP acuities were generated using the PowerDiva system (Smith Kettlewell, San Francisco, CA). OCT and VEP measures started on week 5, following resolution of corneal cloudiness which was associated with IOPs > 45 mm Hg. All measurements were performed in OU and data are presented as mean ± SD and analyzed with a paired Student’s T test.

Results: : . IOP peaked at week 2 (OD 62.5 ± 4.7 mm Hg vs OS 27.5 ± 2.3 mm Hg, p<0.05) and resolved by week 9. RNFLt and CD at 5 weeks were already altered: RNFLt = OD 20.5 ± 5 um vs OS 34 ± 7 um (p<0.05); CD = OD 1183 ± 264 um vs OS 833 ± 172 um (p<0.05). Likewise, spatial VEP acuity (SA) and contrast sensitivity (1/contrast sweep VEP acuity*100; CS) were affected: SA = OD 2.36 ± 0.6 cpd vs OS 2.74 ± 0.6 cpd (p<0.05); CS = OD 22.7 ± 21 vs OS 45.7 ± 30 (p<0.05). At 13-14 weeks, despite normalized IOP for ~4 weeks, RNFL continued to thin and visual function degenerated further: RNFLt = OD 13 ± 8 um vs OS 33 ± 5 um (p<0.05); SA = OD 1.87 ± 0.8 cpd vs OS 2.86 ± 0.5 cpd (p<0.05).

Conclusions: : Structural and functional changes in the retina continue to progress despite normalization on IOP in the carbopol model of ocular hypertension in rabbits.

Keywords: intraocular pressure • electrophysiology: non-clinical • nerve fiber layer