Modeling glaucoma in rats by sclerosing aqueous outflow pathways to elevate intraocular pressure

Abstract

Injection of hypertonic saline via episcleral veins toward the limbus in laboratory rats can produce elevated intraocular pressure (IOP) by sclerosis of aqueous humor outflow pathways. This article describes important anatomic characteristics of the rat optic nerve head (ONH) that make it an attractive animal model for human glaucoma, along with the anatomy of rat aqueous humor outflow on which this technique is based. The injection technique itself is also described, with the aid of a supplemental movie, including necessary equipment and specific tips to acquire this skill. Outcomes of a successful injection are presented, including IOP elevation and patterns of optic nerve injury. These concepts are then specifically considered in light of the use of this model to assess potential neuroprotective therapies. Advantages of the hypertonic saline model include a delayed and relatively gradual IOP elevation, likely reproduction of scleral and ONH stresses and strains that may be important in producing axonal injury, and its ability to be applied to any rat (and potentially mouse) strain, leaving the unmanipulated fellow eye as an internal control. Challenges include the demanding surgical skill required by the technique itself, a wide range of IOP response, and mild corneal clouding in some animals. However, meticulous application of the principles detailed in this article and practice will allow most researchers to attain this useful skill for studying cellular events of glaucomatous optic nerve damage.

A Period of Controlled Elevation of IOP (CEI) Produces the Specific Gene Expression Responses and Focal Injury Pattern of Experimental Rat Glaucoma

“…Males were chosen to allow comparison of gene expression responses from this new model to our published results with chronic IOP elevation, which were based on male animals, whose docile nature allows reliable measurement of awake IOP. 12 All protocols conformed to the Association for Research in Vision and Ophthalmology Statement for the Use of Animals in Ophthalmic and Vision Research, and were approved by the Oregon Health and Science University Institutional Animal Care and Use Committee.…”

“…For this reason, experimental and genetically-induced outflow obstruction models in rodents have gained increasing popularity as glaucoma models. 5,9,11–17 …”

Role of BDNF/TrkB pathway in the visual system: therapeutic implications for glaucoma

“…A variety of rodent ocular hypertension models are available for modeling glaucoma (for reviews see [161,162]). Methods to raise intraocular pressure include restricting aqueous outflow by damaging venous drainage from the anterior chamber or by blocking the access of aqueous humor to the trabecular meshwork with microbeads.…”

Using genetic mouse models to gain insight into glaucoma: Past results and future possibilities

“…Along with genetic models, there are inducible models of IOP elevation that are being used to study ocular hypertension-induced RGC death, including, microbead injections (Morgan Chapter REF , this issue), episcleral vein and aqueous outflow sclerosis (Morrison et al, 2015, this issue), acute IOP elevation (Crowston et al, 2015, this issue), glucocorticoid-induced IOP elevation (Overby and Clark, 2015, this issue), and viral gene transfer to generate TM cell dysfunction and resulting IOP elevation (Pang et al, 2015, this issue). For instance, the microbead model has been used to test the importance of a variety of molecular pathways in ocular hypertension induced RGC death (Hu et al, 2012; Huang et al, 2011; Ward et al, 2014) and to investigate susceptibility factors involved in response to IOP elevation (Cone et al, 2010; Steinhart et al, 2012).…”