All about the mechanism of vision

The optic nerves leave the eye and the retinal blood vessels enter it at a point medial to and slightly above the posterior pole of the eye ball.

Hyderabad: This is in continuation to the last article focusing on sense organs. Today, we will continue discussion on eye and the mechanism of vision.

Eye
• The optic nerves leave the eye and the retinal blood vessels enter it at a point medial to and slightly above the posterior pole of the eye ball.
• Photoreceptor cells are not present in that region and hence it is called the blind spot.
• At the posterior pole of the eye lateral to the blind spot, there is a yellowish pigmented spot called macula lutea with a central pit called the fovea.
• The fovea is a thinned-out portion of the retina where only the cones are densely packed.

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• It is the point where the visual acuity (resolution) is the greatest.

• The space between the cornea and the lens is called the aqueous chamber and contains a thin watery fluid called aqueous humour.

• The space between the lens and the retina is called the vitreous chamber and is filled with a transparent gel called vitreous humour.

Mechanism of vision

• The light rays in visible wavelength focused on the retina through the cornea and lens generate potentials (impulses) in rods and cones.

• As mentioned earlier, the photosensitive compounds (photopigments) in the human eyes are composed of opsin (a protein) and retinal (an aldehyde of vitamin A).

• Light induces dissociation of the retinal from opsin resulting in changes in the structure of the opsin.
• This causes membrane permeability changes. As a result, potential differences are generated in the photoreceptor cells.

• This produces a signal that generates action potentials in the ganglion cells through the bipolar cells.

• These action potentials (impulses) are transmitted by the optic nerves to the visual cortex area of the brain, where the neural impulses are analysed and the image formed on the retina is recognised based on earlier memory and experience.

To be continued…

By

Dr. Modala Mallesh

Subject Expert
Palem, Nakrekal, Nalgonda
9989535675