Does treatment with bevacizumab (Avastin) in combination with prior or current radiotherapy lead to optic neuropathy?

The investigators research will focus on patients prior to them beginning treatment with bevacizumab (Avastin), by undergoing a baseline visual examination with Visual evoked Potentials testing. This will allow testing of the patient's optic nerve function bilaterally. Patients will then begin their normally scheduled treatment with avastin, and other chemotherapeutic agents, as well any radiation treatments scheduled. Once patients have completed their treatment with avastin for 6-8 weeks, they will then undergo their second Visual Evoked Potential testing, with both studies then being compared for any changes within the optic nerves. Patients will also be recommended to have stringent follow up with an Ophthalmologist to include confrontational visual field testing, external and anterior segment examination, and dilated fundus examination. The investigators main objective is to assess whether or not bevacizumab causes a direct toxic effect on patient's optic nerves leading to an acute/subacute optic neuropathy.

Inclusion Criteria:

• Diagnosed w Glioblastoma grade IV, and scheduled to begin chemo radiotherapy with Avastin

Exclusion Criteria:

• No diagnosis of GBM, not scheduled to begin treatment with avastin in combination with radiotherapy.