The investigators propose using retinal oximetry to assess for abnormalities in regional retinal oxygen consumption in previously- irradiated patients, and relate these abnormalities to changes in regional retinal function (i.e. visual field abnormalities). Since different regions of retina receive different radiation doses, the investigators will assess for a dose response as well.

Radiation therapy (RT) is a common treatment for patients with cancers of the sinonasal area, orbit, skull base, nasopharynx, and brain. Because of the close proximity of these targets to the eyes, the retina is often incidentally and unavoidably irradiated. As a result, some patients develop radiation retinopathy and possibly vision loss. Clinicopathologic studies suggest similar microvascular mechanisms for both radiation- and diabetic retinopathy: small vessel occlusion and ischemia that can lead to neovascularization, increased capillary permeability, and visual loss in the regions of retina perfused by damaged vasculature. UNC has a novel, non-invasive retinal imaging technology called a Retinal Oximeter which measures hemoglobin oxygen saturation of retinal vessels. The difference in oxygen saturation between a retinal arteriole and venule pair reflects the oxygen consumption of the retinal region supplied by that vessel pair.

Inclusion Criteria:

1. ≥ 18 years of age at the time of radiation therapy (no upper age limit)
2. History of radiation therapy delivered at UNC-CH or Rex Hospital to the vicinity of the retina(s) ≥ 2 months prior to enrollment
3. Estimated average dose to at least one quadrant of one retina ≥ 30 Gy

Exclusion Criteria:

1. History of diabetes, retinal vascular occlusions, glaucoma, retinitis pigmentosa, occipital stroke or any other ophthalmologic or systemic problem that may confound visual field results.
2. Residual tumor within the visual pathway: retina, optic nerves, optic chiasm, optic radiations and brain.

Adult patients with a history of radiation therapy for a tumor in the vicinity of the retina(s) at the Department of Radiation Oncology, UNC-CH.