PURPOSE. To determine whether cerebrospinal fluid (CSF) entry into the optic nerve is altered in glaucoma. METHODS. Fluorescent 10-kDa dextran tracer was injected into the CSF of 2-month-old (n ¼ 9) and 10-month-old DBA/2J glaucoma mice (n ¼ 8) and age-matched controls (C57Bl/6; n ¼ 8 each group). Intraocular pressure (IOP) was measured in all mice before tracer injection into CSF. Tracer distribution was assessed using confocal microscopy of optic nerve cross-sections of mice killed 1 hour after injection. Paravascular tracer distribution in the optic nerve was studied in relation to isolectin-stained blood vessels. Tracer intensity and cross-sectional area in the laminar optic nerve were quantitatively assessed in all four groups and statistically compared. Aquaporin 4 (AQP4) and retinal ganglion cell axonal phosphorylated neurofilament (pNF) were evaluated using immunofluorescence and confocal microscopy. RESULTS. IOP was elevated in 10-month-old glaucoma mice compared with age-matched controls. One hour after tracer injection, controls showed abundant CSF tracer in the optic nerve subarachnoid space and within the nerve in paravascular spaces surrounding isolectinlabeled blood vessels. CSF tracer intensity and signal distribution in the optic nerve were significantly decreased in 10-month-old glaucoma mice compared with age-matched controls (P ¼ 0.0008 and P ¼ 0.0033, respectively). AQP4 immunoreactivity was similar in 10-monthold DBA and age-matched control mice. Half of the 10-month-old DBA mice (n ¼ 4/8) showed a decrease in pNF immunoreactivity compared to controls. Altered pNF staining was seen only in DBA mice lacking CSF tracer at the laminar optic nerve (n ¼ 4/5). CONCLUSIONS. This study provides the first evidence that CSF entry into the optic nerve is impaired in glaucoma. This finding points to a novel CSF-related mechanism that may help to understand optic nerve damage in glaucoma.

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Glaucoma is a neurodegenerative disorder characterized by the progressive functional impairment and degeneration of the retinal ganglion cells (RGCs) and their axons, and is the leading cause of irreversible blindness worldwide. Current management of glaucoma is based on reduction of high intraocular pressure (IOP), one of its most consistent risk factors, but the disease proceeds in almost half of the patients despite such treatments. Several experimental models of glaucoma have been developed in rodents, most of which present shortcomings such as high surgical invasiveness, slow learning curves, damage to the transparency of the optic media which prevents adequate functional assessment, and variable results. Here we describe a novel and simple method to induce ocular hypertension in pigmented rats, based on low-temperature cauterization of the whole circumference of the limbal vascular plexus, a major component of aqueous humor drainage and easily accessible for surgical procedures. This simple, low-cost and efficient method produced a reproducible subacute ocular hypertension with full clinical recovery, followed by a steady loss of retinal ganglion cells and optic axons, accompanied by functional changes detected both by electrophysiological and behavioral methods.