Question

Explain in brief the structure of the retina of the human eye.

Answer 1

Hint: The retina is a thin tissue film that covers the interior of the back of the eye. It is positioned next to the optic nerve. The aim of the retina is to absorb light directed by the lens, translate the light into neural signals, and transmit these signals for visual recognition to the brain.

Complete answer:
The retina is a complex translucent tissue that consists of many layers, only one of which includes photoreceptor cells which are sensitive to light. To meet the photoreceptor cells, which are of two types, rods and cones, light must pass through the overlying membranes, which are structurally distinguished by their characteristic shapes and functionally by their exposure to various kinds of light. Rods predominate in nocturnal species and are more vulnerable to diminished light intensity; they provide night vision and visual awareness assistance in humans. In humans and other species who are involved throughout the day and have a precise vision (as for reading) and colour, cones are more prominent.

The further cones per unit area of the retina, the finer the detail that can be discriminated against by that area in general. Rods are fairly well spread over the whole retina, but cones appear to be clustered at two sites: fovea centralis, a pit at the back of the retina that does not include rods and contains the densest distribution of cones in the eye, and macula lutea, a circular area of yellow-pigmented tissue about 0.2 to 0.24 inches (5 to 6 mm) in diameter.

Note: Rods are in control of vision at low levels of light (scotopic vision). They do not mediate the perception of colour, and they have poor spatial acuity. At higher light levels (photopic vision), cones are involved, are capable of colour vision, and are responsible for high spatial acuity. The central fovea is filled by cones exclusively.