Despite the previous version of the answer, there is no credible
evidence at all for radiation from television, cellphones or
computers causing either temporary or permanent blindness.
Looking at the sun can overwhelm the retinal cells and cause
temporary blindness, but may also very easily cause permanent
damage.
There are a number of causes of temporary blindness, but most
temporary blindness results from sudden temporary changes in blood
pressure, such as aortic dissection, basilar artery or retinal
migraine, cardiac or carotid emboli, choroidal or retinal vascular
spasm, hyperviscosity, severe occlusive carotid disease. Stress
responses (temporary blindness is sometimes seen in soldiers in
conflict) or mild strokes may also have the same effect.
Other causes of temporary blindness may result from chemical or
biochemical poisons such as Pepper Spray, or plants such as daphne
or spurge.
