At first glance the study is interesting, but upon closer examination serious limitations become apparent. First, the sample size is tiny; with only 24 participants the results are very difficult to generalize to a larger population. Second, the measures studied by Brown and her colleagues were inherently subjective, and not objectively measured. Indeed, the authors admit that "auditory and visual impairments are.... not unaffected by psychosomatic factors."
A double-blind study (that is, one in which neither the researchers nor the patients knew who was prayed for) would have been far more reliable. This would help control for the well-known placebo effect; it is not only possible but likely that those who receive personal, special attention from prayer groups and researchers might genuinely believe that they can see or hear better, at least temporarily-much in the way that a person who takes a placebo pill that they believe to be a pain reliever might experience less pain.
Furthermore, the study did not control for the pre-existing beliefs of the patients. According to the study, "subjects were recruited at Charismatic Protestant meetings... widely reputed among pentecostals globally as ‘specialists' in praying for those with hearing and vision impairments." That is, all the subjects used in the study not only firmly believed in the power of prayer, but that such prayer was especially helpful in treating eye and ear problems. The subjects could have easily been influenced by what scientists call "demand characteristics," or patients telling the researchers (and those who prayed) what they think they want to hear. It would be interesting (and important) to know whether or not maladies in atheists, agnostics, and others who lack a pre-existing belief in the power of prayer would be improved.