For example, if each pattern is 1.75 cm wide and is placed at 1 m distance from the eye, it will subtend an angle of 1 degree, so the number of white/black bar pairs on the pattern will be a measure of the cycles per degree of that pattern. The highest such number that the eye can resolve as stripes, or distinguish from a grey block, is then the measurement of visual acuity of the eye. For a human eye with excellent acuity, the maximum theoretical resolution is 50 CPD (1.2 arcminute per line pair, or a 0.35 mm line pair, at 1 m). A rat can resolve only about 1 to 2 CPD. A horse has higher acuity through most of the visual field of its eyes than a human has, but does not match the high acuity of the human eyes central fovea region.Spherical aberration limits the resolution of a 7 mm pupil to about 3 arcminutes per line pair. At a pupil diameter of 3 mm, the spherical aberration is greatly reduced, resulting in an improved resolution of approximately 1.7 arcminutes per line pair. A resolution of 2 arcminutes per line pair, equivalent to a 1 arcminute gap in an optotype, corresponds to 20/20 (normal vision) in humans. However, in the compound eye, the resolution is related to the size of individual ommatidia and the distance between neighbouring ommatidia. Physically these cannot be reduced in size to achieve the acuity seen with single lensed eyes as in mammals.
Stool samples from patients with diarrhea or other GI symptoms should be tested for STEC and the presence of Shiga-toxin. However, a positive identification of Shiga-toxin, which is required to diagnose STEC-HUS, does not rule out aHUS. Nevertheless, in the appropriate clinical setting, a positive identification of Shiga-toxin makes aHUS very unlikely.aHUS patients report a mean timeline of  29 days for  the overall diagnosis process from first noticing symptoms to receiving an aHUS diagnosis. During which time they report their overall health state drops from 88% of patients feeling good to excellent, to 99% feeling good to very poor and a more than halving of their health status index from 3.8 (on a scale of 1 to 5) pre-illness to 1.4 at diagnosis. Treatment
Plasma exchange/infusion
Although plasma exchange/infusion (PE/PI) is frequently used, there are no controlled trials of its safety or efficacy in aHUS. Even though PE/PI often partially controls some of the hematological manifestations of aHUS in some patients, its effectiveness has not been demonstrated in terms of inducing total disease remission. PE/PI is associated with significant safety risks, including risk of infection, allergic reactions, thrombosis, loss of vascular access, and poor quality of life.