Enjoying a sunny day can improve your eyesight and brain function. Staring into direct sunlight is not good for your eyes, but natural outdoor light exposure helps the brain to function brilliantly. It also stimulates your eyes' photosensitive cells.
The intense ultraviolet (UV) rays of the sun damage sensitive cells in the eyes, eventually affecting vision. However, a number of studies have shown that the effects build up and may increase the chance of developing eye problems later in life. These may include cataracts, a clouding of the lens of the eye.
The sun's damage to the eyes does not stop with cataracts. Exposure to both visible light and UV radiation is also a factor in the gradual degeneration of the retina, damage to the cornea, and pterygium (an overgrowth of the conjunctiva).
Permanent damage to the retina has been shown to occur in ~100 seconds, but the exact time before damage occurs will vary with the intensity of the sun on a particular day (clouds and haze can weaken the sun's rays) and with how much the viewer's pupil is dilated (decongestants and other drugs will dilate pupils).
That's because looking directly at the sun, even for a short period, can cause damage to the eyes' retina — a condition known as solar retinopathy. ... A central blind spot in one or both eyes. Increased sensitivity to light. Distorted vision.