![]() The eyes sit in bony cavities called the orbits, in the skull. Humans have two eyes, situated on the left and the right of the face. Structure A detailed depiction of eye using a 3D medical illustration MRI scan of the human eye Three types of cells in the retina convert light energy into electrical energy used by the nervous system: rods respond to low intensity light and contribute to perception of low-resolution, black-and-white images cones respond to high intensity light and contribute to perception of high-resolution, coloured images and the recently discovered photosensitive ganglion cells respond to a full range of light intensities and contribute to adjusting the amount of light reaching the retina, to regulating and suppressing the hormone melatonin, and to entraining circadian rhythm. The remaining components of the eye keep it in its required shape, nourish and maintain it, and protect it. The retina makes a connection to the brain via the optic nerve. ![]() In order, along the optic axis, the optical components consist of a first lens (the cornea-the clear part of the eye) that accounts for most of the optical power of the eye and accomplishes most of the focusing of light from the outside world then an aperture (the pupil) in a diaphragm (the iris-the coloured part of the eye) that controls the amount of light entering the interior of the eye then another lens (the crystalline lens) that accomplishes the remaining focusing of light into images and finally a light-sensitive part of the eye (the retina), where the images fall and are processed. It is approximately spherical in shape, with its outer layers, such as the outermost, white part of the eye (the sclera) and one of its inner layers (the pigmented choroid) keeping the eye essentially light tight except on the eye's optic axis. The eye can be considered as a living optical device. Clinical and Experimental Optometry © 2016 Optometry Australia.The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows humans to use visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm.Īrizona Eye Model. ![]() This review is interwoven with historical developments, highlighting the important people who have contributed so richly to our understanding of visual optics.įinite models optical models paraxial models schematic eyes visual optics. We provide a glimpse into the future of optical models of the human eye. We consider which optical model should be used for a particular purpose, adhering to the principle that the best model is the simplest fit for the task. They can also be customised for the individual when extensive ocular biometry and optical performance data are available. Many optical model eyes are population averages and must become adaptable to account for age, gender, ethnicity, refractive error and accommodation. If aberrations and image quality are important to consider, such 'paraxial' model eyes must be replaced by 'finite model' eyes incorporating features such as aspheric surfaces, tilts and decentrations, wavelength-dependent media and curved retinas. Many optical eye models give accurate predictions only for small angles and small fields of view. ![]() We cover the models with lens structure in the form of nested shells and gradient index. We discuss many of the theoretical types of optical models (also schematic eyes) of varying anatomical accuracy, including single, three and four refracting surface variants. An extensive list of purposes of models is provided. We address the issue of what is understood by optical model eyes, discussing the 'encyclopaedia' and 'toy train' approaches to modelling. Optical models of the human eye have been used in visual science for purposes such as providing a framework for explaining optical phenomena in vision, for predicting how refraction and aberrations are affected by change in ocular biometry and as computational tools for exploring the limitations imposed on vision by the optical system of the eye.
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