A Study to Determine if There is a Possible Association Between NAION and Phosphodiesterase Type 5 (PDE5) Inhibitors

Inclusion Criteria:

- Adult male subjects, at least 18 years of age, who are willing to participate in the
study

- Participants who experienced abrupt visual loss in one eye (defined as typically less
than a 1-day period or visual loss noted upon awakening) and presented for an initial
visit within 45 days of onset of NAION symptoms to an ophthalmologist that resulted in
a diagnosis of Suspected NAION by the investigator

Exclusion Criteria:

- Previous history of NAION

- Previous history of arteritis (anywhere in the body) or clinical or diagnostic testing
evidence of temporal arteritis

- History of glaucoma in either one or both eyes

- History of multiple sclerosis or diagnostic testing evidence of optic neuritis

- Have dementia or other reasons for memory impairment in the opinion of the
investigator

- Have participated in other non-observational studies within 3 months of NAION onset