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The same water in a smaller bucket looks only slightly cyan, [1] and observing the water at close range makes it appear colorless to the naked eye. The intrinsic color of liquid water may be demonstrated by looking at a white light source through a long pipe that is filled with purified water and closed at both ends with a transparent window.
The irises of human eyes exhibit a wide spectrum of colours. Eye color is a polygenic phenotypic trait determined by two factors: the pigmentation of the eye's iris [1] [2] and the frequency-dependence of the scattering of light by the turbid medium in the stroma of the iris. [3]: 9
Trachoma is an infectious disease caused by bacterium Chlamydia trachomatis. [2] The infection causes a roughening of the inner surface of the eyelids. [2] This roughening can lead to pain in the eyes, breakdown of the outer surface or cornea of the eyes, and eventual blindness. [2]
The pupil of the human eye can range in size from 2 mm to over 8 mm to adapt to the environment. The human eye can detect a luminance from 10 −6 cd/m 2, or one millionth (0.000001) of a candela per square meter to 10 8 cd/m 2 or one hundred million (100,000,000) candelas per square meter.
Trichromatic color vision is the ability of humans and some other animals to see different colors, mediated by interactions among three types of color-sensing cone cells. The trichromatic color theory began in the 18th century, when Thomas Young proposed that color vision was a result of three different photoreceptor cells .
In animal and human hosts, infestation by Thelazia may be asymptomatic, though it frequently causes watery eyes , conjunctivitis, corneal opacity, or corneal ulcers (ulcerative keratitis). [1] Infested humans have also reported "foreign body sensation" – the feeling that something is in the eye.
Eye symptoms provide the common name associated with onchocerciasis, river blindness, and may involve any part of the eye from conjunctiva and cornea to uvea and posterior segment, including the retina and optic nerve. [20] [21] The microfilariae migrate to the surface of the cornea. Punctate keratitis occurs in the infected area. This clears ...
The vertebrate eye is usually either optimised for underwater vision or air vision, as is the case in the human eye. The visual acuity of the air-optimised eye is severely adversely affected by the difference in refractive index between air and water when immersed in direct contact.