Question

write a short note on retina it's urgent tomorrow is my test

Answer 1

The retina is the innermost, light-sensitivelayer, or "coat", of shell tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which translates that image into electrical neural impulses to the brain to create visual perception, the retina serving much the same function as film or a CCD in a camera.

The retina consists of several layers of neurons interconnected by synapses. The neural retina refers to the three layers of neural cells (photo receptor cells, bipolar cells, and ganglion cells) within the retina, which in its entirety comprises ten distinct layers, including an outer layer of pigmented epithelial cells. The only neural cells that are directly sensitive to light are the photoreceptor cells, which are of two types: rods and cones. Rods function mainly in dim light and provide black-and-white vision while cones are responsible for the perception of colour. A third type of photoreceptor, the photosensitive ganglion cells, is important for entrainment and reflexive responses to the brightness of light.

Answer 2

The retina is the light-sensitive tissue lining the back of our eye. Light rays are focused onto the retina through our cornea, pupil and lens. The retina converts the light rays into impulses that travel through the optic nerve to our brain, where they are interpreted as the images we see.