Abstract
Purpose :
Low optic nerve sheath pressure, may be a factor in the development of glaucoma. Using the rat model, this study considers whether optic nerve sheath pressure lowering via fenestration (i) affects \ in vivo tissue response to acute intraocular pressure (IOP) elevation, or (ii) the response of the eye to chronic IOP elevation.
Methods :
Adult male and female Long Evans rats underwent surgery optic nerve sheath fenestration (n=6/group), which were compared with naïve and sham operated eyes. Both treated and control eyes underwent stepwise IOP elevation (from 10 to 80mmHg), with optical coherence tomography (OCT) volume scans taken at each IOP step. In the chronic study, all animals (n=10/group) had one eye implanted with a circumlimbal suture (8/0) to induce ocular hypertensive (OHT). In the ocular hypertension (OHT) control group, treated eyes only had the suture (S-OHT). In the fenestrated and sham groups, the sutured eyes also underwent the fenestration (F-OHT) or the sham-fenestration procedure (SF-OHT). IOP was measured weekly, and OCT and electroretinography (ERG) were conducted at weeks 4 and 8. Data (mean±SEM) were compared across groups in both studies using 2-way repeated measures ANOVA.
Results :
In the acute study, fenestrated eyes showed posterior retinal deformation at baseline IOP (10 mmHg). All groups showed significant retinal compression with stepwise IOP elevation, an effect significantly greater in the fenestrated group (P<0.01). All groups showed similar patterns of retinal and Bruch’s membrane deformation with IOP elevation. In the chronic study, the F-OHT group showed greater (P<0.05) RNFL thinning compared to controls after 4 (controls -2.3±5.5% vs F-OHT -18.3±5.2%) and 8 weeks of IOP elevation (controls -3.3±5.1% vs F-OHT -24.8±6.9%). After 4 weeks of chronic IOP elevation, the ganglion cell positive scotopic threshold response (pSTR, -30.1±10.4%) was affected by chronic IOP elevation, but bipolar cell (b-wave, -1.9±9.8%) and photoreceptoral (a-wave, -2.9±10.5%) responses were not affected in the S-OHT group. Optic nerve fenestration resulted in significantly greater functional deficits with chronic IOP elevation (pSTR -61.8±10.4%, b-wave -29.6±3.6%, a-wave 26.2±4.8%).
Conclusions :
These data provide evidence that low optic nerve sheath pressure exaggerates the biomechanical impact of acute IOP elevation, and greater ganglion cell injury with chronic IOP elevation.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.