The position of the sun in late spring and early summer can cause a more-severe sunburn. Altitude. At a higher altitude it is easier to become burnt, because there is less of the earths atmosphere to block the sunlight. UV exposure increases about 4% for every 1000 ft (305 m) gain in elevation. Proximity to the equator (latitude). Between the polar and tropical regions, the closer to the equator, the more direct sunlight passes through the atmosphere over the course of a year. For example, the southern United States gets fifty percent more sunlight than the northern United States. Because of variations in the intensity of UV radiation passing through the atmosphere, the risk of sunburn increases with proximity to the tropic latitudes, located between 23.5° north and south latitude. All else being equal (e.g., cloud cover, ozone layer, terrain, etc. ), over the course of a full year, each location within the tropic or polar regions receives approximately the same amount of UV radiation. In the temperate zones between 23.5° and 66.5°, UV radiation varies substantially by latitude and season. The higher the latitude, the lower the intensity of the UV rays. Intensity in the northern hemisphere is greatest during the months of May, June and July—and in the southern hemisphere, November, December and January. On a minute-by-minute basis, the amount of UV radiation is dependent on the angle of the sun.
Anti-vascular endothelial growth factors have been recently used for the treatment of radiation retinopathy. Monitoring of visual acuity in all cases and early referral to the ophthalmologist is warranted. == References ==