Color blindness (color vision deficiency) is the decreased ability to see color or differences in color. It can impair tasks such as selecting ripe fruit, choosing clothing, and reading traffic lights. Color blindness may make some academic activities more difficult. However, issues are generally minor, and the colorblind automatically develop adaptations and coping mechanisms. People with total color blindness (achromatopsia) may also be uncomfortable in bright environments and have decreased visual acuity. The most common cause of color blindness is an inherited problem or variation in the functionality of one or more of the three classes of cone cells in the retina, which mediate color vision. Males are more likely to be color blind than females, because the genes responsible for the most common forms of color blindness are on the X chromosome. Non-color-blind females can carry genes for color blindness and pass them on to their children. Color blindness can also result from physical or chemical damage to the eye, the optic nerve, or parts of the brain. Screening for color blindness is typically done with the Ishihara color test.There is no cure for color blindness. Diagnosis may allow an individual, or their parents/teachers to actively accommodate the condition. Special lenses such as EnChroma glasses or X-chrom contact lenses may help people with red–green color blindness at some color tasks, but they do not grant the wearer "normal color vision". Mobile apps can help people identify colors.Red–green color blindness is the most common form, followed by blue–yellow color blindness and total color blindness.
Normal tension glaucoma (NTG) is an eye disease, a neuropathy of the optic nerve, that shows all the characteristics of primary open angle glaucoma except one: the elevated intraocular pressure (IOP) - the classic hallmark of glaucoma - is missing. Normal tension glaucoma is in many cases closely associated with general issues of blood circulation and of organ perfusion like arterial hypotension, metabolic syndrome, and Flammer syndrome. Clinical relevance
Over many years, glaucoma has been defined by an intraocular pressure of more than 20 mm Hg. Incompatible with this (now obsolete) definition of glaucoma was the ever larger number of cases that have been reported in medical literature in the 1980s and 1990s who had the typical signs of glaucomatous damage, like optic nerve head excavation and thinning of the retinal nerve fiber layer, while these patients had an IOP that would generally have been regarded as "normal". It is now widely estimated that a larger percentage of patients with primary open-angle glaucoma (POAG) are suffering from normal tension glaucoma. Among Americans of Japanese descent, for instance, the prevalence of NTG is about four times as high as the prevalence of the "classical glaucoma" with an IOP of 22 mm Hg and higher.