**3.1 POAG models**

IOP can be elevated through direct or indirect blockage of the trabecular meshwork via injection of hypertonic saline into episcleral veins, cauterization of the episcleral veins, or photocoagulation with an argon laser, which all block outflow and induce an elevation of IOP [20].

### *3.1.1 Laser photocoagulation*

Laser photocoagulation has been used as an experimental model in non-human primates. This technique damages the trabecular meshwork, which blocks outflow of aqueous humor and elevates IOP [47]. It requires three lasers in a 7-day interval to increase IOP by 60%. This method is expensive and can cause anterior peripheral synechiae, hyphema, and corneal edema. In animals subjected to this procedure, it caused loss of RGCs and thinning of the nerve fiber layer, both phenotypes

#### *An Overview of Glaucoma: Bidirectional Translation between Humans and Pre-Clinical… DOI: http://dx.doi.org/10.5772/intechopen.97145*

associated with glaucomatous damage in humans [17, 48]. An argon laser with the slit lamp can also be used, but only for certain strains of rodents because it can cause pigment affinity and variation in elevation of IOP [49, 50]. If laser photocoagulation is combined with temporary narrowing of the iridiocorneal angle via paracentesis, this results in a sudden, 3-week increase in IOP that is not reflective of glaucoma progression in humans, although more acute changes can be evaluated. It can also cause ischemia and opacity of the central cornea [51]. To create a more chronic elevation of IOP condition, 50 microliters of hypertonic saline solution can be injected into the collecting veins of a rat eye to cause sclerotic damage to the trabecular meshwork and optic nerve. This is accomplished with specialized microneedles and a complex procedure both difficult to execute and to teach. A moderate increase in IOP is seen 7–10 days after the procedure and is recommended for use in studies exploring neuroprotection [52]. In addition, a nylon suture can be used to occlude the vein and cause an increase in IOP [15, 53].
