Focusing of eyes
Our eyes cannot focus two scenes simultaneously. Why?
S. HARIHARAN
Morappur, Tamil Nadu
Vision is a brain phenomenon and not an ocular (eye) phenomenon. The brain behaves like a film or a LCD screen in the camera. Even computer chips which can sense vision can stimulate the brain to perceive the vision.
The basic mechanism of vision is binocular, which is the three dimensional construction of the scenes. The depth, length, breadth are all configured by the scenes received by both eyes through optic nerve projections.
The fundamental contribution of the projection of scenes to the brain is by the so called camera the eyes. The eye movements are such that they move like yoked cart or the front wheel of a car. They cannot move independently, provided there is paralysis of the muscles moving the eye, which results in a condition called squint.
This learning of steriognotic vision is from childhood, due to the phenomenon called ocular fixation of the brain. These impressions are fixed in the brain, in the region called occipital cortex, which is in the rear portion of the brain. In persons who have squint congenitally, the ocular fixations are poor and there will not be a complete processing of steriognotic vision.
If there is acute squint due to paralysis of muscles which deviate the eye ball, due to some disease, there will be a double vision and there will be a double scene projection, which will confuse the brain, which cannot integrate the already formed templates of stereogntic vision.
This is called diplopia. Patients with acute diplopia will prefer to close one eye and see through the other eye, since it is so horrid to see two visions of two scenes at the same time.
Added to that the false image will be dull, and true image will be bright, and handling of objects become difficult for them since exact location and depth of the objects and distance will not be appreciated.
So the ultimate reason for not observing two visions at a time, is by the correct eye ball yoked movements to project the same scenes in three dimensions, sending them through the ocular nerve and tract projections to the brain’s cerebral occipital cortex.
DR. NAGARAJAN Professor emeritus in neuro sciences
Tamil Nadu Dr MGR Medical University
Madurai, Tamil Nadu
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