Compared with the relatively dark environment within the uterus, the newborn is bombed with visual stimuli of differing light intensity and contours within the first few months of life
This encourages the development of the lateral geniculate nucleus (LGN) and striate cortex
Time where the visual system is still plastic and also susceptible to any interruptions, so the effect of experience on the brain is mainly strong. Beyond this period, disruption to visual function is thought to be permanent.
From 8 years old the response to a sudden change in motor or sensory input may be diplopia rather than adaptations such as suppression, anomalous correspondence or eccentric fixation
More rarely, excessive amblyopia treatment can also produce diplopia when carried out after this age, where it also produces a change in the squint angle, particularly in deep ARC
The eyelids of one eye are sutured shut for a period of time, resulting in light perception but allowing very little patterned image (shape and form are difficult to see) on the retina. However the direction of movement of an object can be detected.
Physiological properties of cells in the lateral geniculate driven by the sutured eye
The arbors of X (fine detail) cells are smaller than normal, and the arbors of Y (movement) cells are smaller than normal. As a result, fewer Y cells are recorded, and the spatial contrast sensitivity of the X cells is reduced.
The four superficial layers have neurons with small cell bodies and are called the parvocellular layers. The two deep layers have neurons with large cell bodies and are called the magnocellular layers.
Because one eye is closed the ocular dominance columns from that eye will not be active and will hence have less metabolic activity. The ocular dominance columns from the other eye will be active and will have greater activity leading to a darker stain in these areas for cytochrome oxidase.
The ocular dominance changes occur in a particular sequence. At the critical period, monocular deprivation produces a saturating ocular dominance shift.
The projections from the lateral geniculate nucleus to the visual cortex from the two eyes overlap each other at birth, then they segregate into eye specific columns around the time that stereopsis develops.
In the case of monocular deprivation, the terminals from the deprived eye retract until they cover a small fraction of the space, and the terminals from the normal eye do not retract.
One can close the left eye until nearly all cells are dominated by the right eye, and then open the left eye and close the right eye until nearly all cells are dominated by the left eye, a process known as reverse suture.
Binocular recovery following monocular deprivation
For full recovery of acuity and binocular vision, one needs monocular vision through the previously deprived eye to bring up the acuity in that eye as well as binocular vision to get the two eyes to work together and prevent vision in the previously non-deprived eye from declining. The ideal procedure is to patch the non deprived eye for one half to three quarters of the time, reflecting clinical experience with infants. Unfortunately, even the best procedure does not yield normal depth perception.
If the left eye is sutured closed, then there is a retraction of terminals in the visual cortex coming from the left eye and an expansion of terminals coming from the right eye.
This is seen in the parvocellular layers, which deal with high spatial frequencies, and not in the magnocellular layers, which deal primarily with movement