Question

Make a labelled diagram of a vertical section of a mammalian eye. Describe what happens when one looks from a distant object to a near one. Explain the functions of rods and cones

Answer 1

In normal conditions, the suspensory ligaments are kept under tension and the lens is correspondingly flattened. However, contraction of the ciliary muscles attached to these suspensory ligaments relaxes them and permits the lens to take on a more or less spherical shape. These changes in the lens shape enable the eye to shift its focus from far objects to the near objects. This process of adjustment of the lens to focus is called accommodation.

Rods and cones are the photoreceptors present in the retina of the eye. Rods are used for the vision in dim light. The rhodopsin pigment present in the rods is used for light absorption.

Cones are used for the vision in bright light. The pigments present in the cones are erythropsin (sensitive to red), chloropsin (sensitive to green) and cyanopsin (sensitive to blue).