Factual error: The type of book that Eli is protecting would actually be just a fragment. The complete Bible, in braille, occupies as many as 18 volumes.
Factual error: Eli uses an apparently moist KFC wetnap to clean himself in an early scene, yet it's been at least 30 years since the apocalyptic event happened. Unopened wipes only stay moist for months, even big packets of baby wipes only stay wet for 2-3 years.
Answer: A large study was done after the atomic blasts in Japan in WW2 after the surrender on the effects to victims' eyesight. Over 70% of the people that indirectly looked at the light were not completely blind. They suffered from cataracts, and out of those studied over 50% could see during the day - mostly shades of black and shadows / silhouettes of people and objects. Those that survived became very keen to see movement as long as they were in bright light, also heightened since of smell and feeling vibrations. This would explain why Eli never traveled at night and was not totally blinded by a nuclear flash, if he was completely blind - night would give him a much larger advantage. You notice he always travels when the sun comes up so he can see silhouettes of people and objects moving. Also when Solara interred his room at Carnegie's hall she said "it's bright in here" Eli had all the lights on so he could see anyone entering the room / cell. Also he wears sunglasses because obviously he does not want his cataracts to get worse. If you watch the movie again there are many tells to support that he is only partially blind and had mild to moderate cataracts. You can also see his eyes on the boat to Alcatraz, showing his cataracts.
He was born blind, at the start he smells the hijackers and moves into the dark to level the playing field.
How would he know where the dark is?
He was not born blind. He was blinded during armageddon, but after finding the Bible was given his sight back in order to complete the task given to him by God. Once his task was completed he once again lost his sight.
Nope! He was given his sight back by God in order to complete the task he was given, only to lose it once again after it was completed.