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Sunday, September 18, 2011

The Eye -- Its Anatomy and Physiology III -- Lesson 263

In the recent post you have learned about the rods and cones.An optic nerve is the nerve of which light energy is focued on the retina, a chemical change occurred in the rods and cones initiating nerve impulseswhich travel from the eye to the brain via the optic nerve. The region in the eye where the optic nerve meets the retina is called retina is called the optic disk. This optic disk is otherwise called as the blind spot of the eye. A small oval which is called the macula is yellowish area to the side of the optic disk.

 A central depression which is called fovea centralis is also contained in it. which composed of largely of cones, and is the location of sharpest vision in the eye.  If fovea's portion or macula's portion is damaged, central vision blindness occurs and the vision is reduced. Through the opthalmoscope the fundus of th eye is the posterior and the inner part is visualized. 

The rods and cones in the retina synapse with neurons and leads to the optic nerve fibers. As the optic nerve fibers travel into the brain, the fibers located more medially cross in an area called the optic chiasm. From the right half of each retina nerve fibers form an optic tract, synapsing in the thalamus of the brain and ending in the right visual region of the cerebral cortex. In the same way, fibers from the left half of each retina merge to from the optic tract and pass from the thalamus to the left region of the cerebral cortex. 

The images are fused in the visual area of the cerebral cortex and a single visual sensation with a three-dimensional effect is experienced. This vision is called binocular vision. Loss of vision in the right visual field is caused due to the damage in the left cerebal cortex. This vision loss in the contralateral or opposite side of the visual field is called hemianopsia, in which hemi means half, an means without, opsia means vision.

In the next post we would learn the short definitions related to this topic.


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