I come your way once again with dynamics of vision, as a student optometrist it is my passion to bring to enlighten many about visual healthcare. In our lesson today we would be looking at the areas of the brain that contributes to vision.
Lets have a quick recap of the visual pathway on how light stimulus gets to the brain for interpretation. In our previous lessons we learnt that when we look at an object the light emanating from it enters our eyes with the help of the cornea and the lens which refract and focus it on our retina. The retina converts this by the dynamics of phototransduction into electrical impulses which comes together to form the optic nerve which transmits the impulses to the brain.
Lets look at some basic brain parts to help us appreciate things better. When we take the brain we have the 3 division and the 4 lobes. The divisions been the forebrain, midbrain and hindbrain with the lobes been frontal, parietal, occipital and temporal. The frontal part of the eye is mainly related to actions that we do voluntarily whereas the back does more of things we do not voluntarily act on.
Once impulses leaves the eye socket into the skull it has entered the brain. Primarily light impulses goes to the primary and secondary visual cortices otherwise known as V1, V2, V3, V4 and V5. (In terms of broadmann area, these are 17, 18 and 19)This is where interpretation of of images occur, where we get to see shape, colors etc. These areas are found at the occipital lobe and do not work independent of each other instead impulses may move in between areas depending on what one seeks to interpret or otherwise perceive.
Then there is frontal eye fields. Most people have the general idea that hitting the back of the head might affect vision which goes in line with the primary and secondary visual cortices however vision does not only deal with the occipital lobe. In the frontal lobe there is the area which is denoted as broadmann area 8 otherwise known as the frontal eye fields. What this area does is that it help us to consciously choose where we want to look at or the area we would rather be seeing, So it has a direct relation the muscles in the eye that enable us to move our eyes without moving our head.
In the midbrain is the pretectal nucleus which controls our ability to narrow our pupils thus restricting intense light from entering our eyes and damaging the retina. The superior colliculus also help regulate the circardian rythmn or the sleep pattern. They also help us in bringing our eyes closer together when we are looking at near object or taking taking them further apart when looking at objects further away. The temporal area enable us to recognize faces and damage to this part results in what we call Prosopagnosia otherwise known as facial blindness.
So basically when we talk about vision, it does not end with the eye as we see it. Most of what we call vision and its related functions occurs in the brain, so one is not wrong to say that we see with the brain and not the eye. Aside the transduction of light into the eye and the refraction at the eyeball level all others come from brain hence it is pertinent that we protect our skull and brains from mechanical injuries which may otherwise have detrimental effect on our eyes.
