ballet, gymnastics, marathon running, and cycling) as well as sports that emphasize high-carbohydrate, low-fat diets, may be at an increased risk for iron deficiency. Inadequate intake
A U.S. federal survey of food consumption determined that for women and men over the age of 19, average iron consumption from foods and beverages was 13.1 and 18.0 mg/day, respectively. For women, 16% in the age range 14–50 years consumed less than the Estimated Average Requirement (EAR), for men ages 19 and up, fewer than 3%. Consumption data were updated in a 2014 U.S. government survey and reported that for men and women ages 20 and older the average iron intakes were, respectively, 16.6 and 12.6 mg/day. People in the U.S. usually obtain adequate amounts of iron from their diets. However, subgroups like infants, young children, teenaged girls, pregnant women, and premenopausal women are at risk of obtaining less than the EAR. Socio-economic and racial differences further affect the rates of iron deficiency. Bioavailability
Iron is needed for bacterial growth making its bioavailability an important factor in controlling infection. Blood plasma as a result carries iron tightly bound to transferrin, which is taken up by cells by endocytosing transferrin, thus preventing its access to bacteria. : 30  Between 15 and 20 percent of the protein content in human milk consists of lactoferrin that binds iron. As a comparison, in cows milk, this is only 2 percent. As a result, breast fed babies have fewer infections. Lactoferrin is also concentrated in tears, saliva and at wounds to bind iron to limit bacterial growth.
The test consists of red and green semicircles on a black background with a white round fixation target. The size of the red semicircle is held constant while the green semicircle is varied in size in 1% increments. The patient wears a pair of red/green goggles so that one eye is tested at a time, and the patient attempts to determine when the semicircles are the same size. This is termed the reversal threshold and the size difference between the semicircles is reported as the degree of aniseikonia. A positive value indicates that the object was perceived bigger and thus corresponds to macropsia, and conversely a negative value indicates micropsia. The Aniseikonia Inspector contains an aniseikonia test based on the same principles as the NAT, but the test is run on a computer screen, it is based on a forced choice method, and it can measure the size difference as a function of the size of the objects. The functionality of being able to measure the size difference as function of the size (i.e. field dependent testing) is especially important when the macropsia (or micropsia) has a retinal origin. Treatment
The most common way to treat forms of aniseikonia, including macropsia, is through the use of auxiliary optics to correct for the magnification properties of the eyes. This method includes changing the shape of spectacle lenses, changing the vertex distances with contact lenses, creating a weak telescope system with contact lenses and spectacles, and changing the power of one of the spectacle lenses.