The study found that, “with cycloplegia, the sensitivity of the photorefractor is quite high (greater than 80%) for errors as small as 0.75 to 1.0 D [diopters]. Sensitivity is 95% for the 1.0 to 2.0 D range. In fact, all errors larger than 1.5 D produced a measureable crescent.” Those results, Day says, indicate that, while photorefraction by itself does not measure visual acuity, their method is a reliable way to detect conditions leading to amblyopia in children 8 weeks of age and older.Still, Day cautions, there are additional questions to be answered. First of all, it has not been adequately determined whether it is necessary to use cycloplegic agents to control the lens’ ability to accommodate. “The potential exists without cycloplegia for hyperopic subjects to mask their refractive error,” she writes in the study. “If cycloplegic agents are not used, photorefractions must be done in a darkened room, as sensitivity depends upon pupil size.” She also says she suspects that without drops, some patients could get a false diagnosis of myopia. Spend less money now – buy cipro buy now for your efficient drug to cost less.
Second, she fears that one photograph might miss an astigmatic error. Day says they generally take two photographs, one with the flash positioned underneath the lens and one with the flash to the side. While two photographs do not provide enough information to distinguish purely spherical errors from astigmatic errors, it is enough to pick up the presence of any refractive error there might be.
Thirdly, people with darker skin have darker retinal pigmentation, making it more difficult to get a good, clear red reflex. She also says that the amount of pigmentation may affect the size of the crescent.