Some vertebrates, including humans, have an area of the central retina adapted for high-acuity vision. Because of this, cephalopods do not have a blind spot.Īlthough the overlying neural tissue is partly transparent, and the accompanying glial cells have been shown to act as fibre-optic channels to transport photons directly to the photoreceptors, light scattering does occur. In contrast, in the cephalopod retina, the photoreceptors are in front, with processing neurons and capillaries behind them. No photoreceptors are in this region, giving rise to the blind spot. The ganglion cells, whose axons form the optic nerve, are at the front of the retina therefore, the optic nerve must cross through the retina en route to the brain. The vertebrate retina is inverted in the sense that the light-sensing cells are in the back of the retina, so that light has to pass through layers of neurons and capillaries before it reaches the photosensitive sections of the rods and cones. Structure Inverted versus non-inverted retina Much like the rest of the brain is isolated from the vasular system via the blood–brain barrier, the retina is similarly protected by the blood–retinal barrier. It is the only part of the CNS that can be visualized noninvasively. In vertebrate embryonic development, the retina and the optic nerve originate as outgrowths of the developing brain, specifically the embryonic diencephalon thus, the retina is considered part of the central nervous system (CNS) and is actually brain tissue. Several important features of visual perception can be traced to the retinal encoding and processing of light. Neural signals from the rods and cones undergo processing by other neurons, whose output takes the form of action potentials in retinal ganglion cells whose axons form the optic nerve. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses that are sent to various visual centres of the brain through the fibres of the optic nerve. A third type of light-sensing cell, the photosensitive ganglion cell, is important for entrainment of circadian rhythms and reflexive responses such as the pupillary light reflex. Cones function in well-lit conditions and are responsible for the perception of colour through the use of a range of opsins, as well as high-acuity vision used for tasks such as reading. Rods function mainly in dim light and provide monochromatic vision. The primary light-sensing cells in the retina are the photoreceptor cells, which are of two types: rods and cones. The neural retina consists of several layers of neurons interconnected by synapses and is supported by an outer layer of pigmented epithelial cells. The retina serves a function which is in many ways analogous to that of the film or image sensor in a camera. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception. The optic nerve then transmits these signals to the visual cortex – the part of the brain that controls our sense of sight.The retina (from Latin: rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The retina acts like an electronic image sensor of a digital camera, converting optical images into electronic signals. Light focused by the cornea and crystalline lens (and limited by the iris and pupil) then reaches the retina – the light-sensitive inner lining of the back of the eye. Process called accommodation, this lens helps the eye automatically focus on near and approaching objects, like an autofocus camera lens. ![]() The eye’s crystalline lens is located directly behind the pupil and further focuses light. ![]() The iris of the eye functions like the diaphragm of a camera, controlling the amount of light reaching the back of the eye by automatically adjusting the size of the pupil (aperture). Light is focused primarily by the cornea – the clear front surface of the eye, which acts like a camera lens. In a number of ways, the human eye works much like a digital camera: Read on for a basic description and explanation of the structure (anatomy) of your eyes and how they work (function) to help you see clearly and interact with your world. ![]() How vision works or health problems that can affect the eye. When surveyed about the five senses - sight, hearing, taste, smell and touch - people consistently report that their eyesight is the mode of perception they value (and fear losing) most.ĭespite this, many people don’t have a good understanding of the anatomy of the eye,
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