Explain the difference in acuity and sensitivity to light by different parts of the retina

Difference in acuity and sensitivity to light by the different parts of the retina depend on the relative distribution of cones and rods in it.

• The cones are concentrated in a small area in the centre of the retina called fovea centralis. Cones are arranged such that each cell synapses with its bipolar cell, which in turn synapses with its own optic neuron. Being closely packed light form two close points on the object can fall on two separate cones so that these can be visualized as separate. Hence, higher visual acuity.
• Rods are scattered in the periphery of the retina. Several rod cells connected to a single bipolar cell, in a phenomenon of convergence. . Due to this convergence, rods are more sensitive to light than the cones; low intensity of light which cannot stimulate a single rod or cone is able to stimulate the bipolar neuron connected to the rods as a result of summation.

As a result, acuity is greatest at the fovea which is normally at the centre of the field of vision and gradually decreases towards the periphery of the retina which forms edges of our field of vision.

On the other hand, sensitivity is greatest at the periphery of the retina and decreases towards the centre (fovea).