Why are some people born blind?

Blind at birth. While prematurity leading to hyperoxygen retinal degeneration can severely impair vision, there are some other rare conditions that may completely impair vision including hypodevelopment of the eyes, cortical blindness, and various internal eye maldevelopments. You pediatrician can help sort these out and find the proper specialist for help.
Prematurity. Prematurity is a risk factor that can lead to blindness. One important risk factor is birth weight, 1251 grams or less (2 lbs 12 ounces). A landmark study called the early treatment for retinopathy of prematurity, laser decreased incidence of blindness http://www.Nei.Nih.Gov/neitrials/static/study83.Asp.
Lazy eye, amblyopia. The shape of the eye is very important. If the shape of any part of the eye is not adequate then the eye will not function properly. The result is an eye that cannot focus well and will often deviate outwards or inwards. This is often called a "lazy eye" by many non-physicians. The treatment of this condition is to determine etiology: brain vs eye vs muscle, then treat it.
Errors, Infections. Sight is one of the most valued traits humans hold close to their hearts. Some newborns are born blind, because of genetic errors of metabolisms unable to process certain sugars or amino acids. Others succumb to infections such as rubella during gestation, while others are born strictly with eye diseases such as glaucoma or cataracts.