Visual acuity: Encyclopedia II - Visual acuity - Physiology of visual acuity

Visual acuity - Physiology of visual acuity

Visual acuity is defined as the eye's ability to resolve fine details. To achieve this, the eye's optical system has to project a focused image on the clinical fovea, a region inside the clinical macula having the highest density of cone photoreceptors (the only kind of photoreceptors existing on the fovea), thus having the highest resolution and best color vision. Acuity and color vision, despite of being done by the same cells, are different physiologic functions that don't interrelate. Acuity and color vision can be affected independently without affecting the other function.

Visual cortex is part of the cerebral cortex in the posterior (occipital) part of the brain responsible for processing visual stimuli. The central 10° of field (approximately the extention of the macula) is represented by at least 60% of the visual cortex. Much of this neurons are believed to be involved directly into visual acuity proccesing.

Light travels from the fixation object to the fovea thought an imaginary path called visual axis. The eye's tissues and structures that are in the visual axis (and also the tissues adjacent to it) affect the quality of the image. This structures are: Tear film, cornea, anterior chamber, pupil, lens, vitreous, and finally ending on the retina. The posterior part of the retina, called the Retinal Pigment Epithelium (RPE) is responsible, along many other functions, to absorb light that crosses the retina so it cannot bounce to other parts of the retina.

Adapted from the Wikipedia article "Physiology of visual acuity", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki