The retina is the third and inner coat of the eye which is a light-sensitive layer of tissue. The optics of the eye create an image of the visual world on the retina (through the cornea and lens), which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses. These are sent to various visual centres of the brain through the fibres of the optic nerve.
For vision, these are of two types of photoreceptor cells: the rods and cones. Rods function mainly in dim light and provide black-and-white vision while cones support the perception of colour.
The retina has ten distinct layers In adult humans. The entire retina contains about 7 million cones and 75 to 150 million rods. An image is produced by the patterned excitation of the cones and rods in the retina. The cones respond to bright light and mediate high-resolution colour vision during daylight illumination (also called photopic vision). Rods respond to dim light and mediate lower-resolution, monochromatic vision under very low levels of illumination (called scotopic vision/ night vision). The illumination in most office settings falls between these two levels and is called mesopic vision.
What are the major functions of the Retina?
Absorbing photons of light
Converting light into a biochemical message
Converting biochemical message into an electrical impulse
Transmitting electrical impulse to the brain through ganglion cells.
Central retinal artery supplies 15% from inner retinal layer. As per clinical examination of photoreceptors; form and spatial vision, measured by visual acuity and it reflects rod and cone distribution.
Colour vision testing, one of the commonest investigations carried out by ophthalmologists is indicative of cone function and associated processing of the signals and identifies conditions related to colour vision.
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