However, even if we had the perfect method to correct the optics in the eye, functional vision would still be determined by the retina-brain interaction. This is because vision involves perception (which in turn involves the brain), and not just an optically perfect image. Unfortunately, normal development of the visual cortex (the part of the brain responsible for seeing) requires visual inputs to have been present during the early years of development. Scientists refer to this early period as the ‘critical period’ for vision.
How do we know all this?
Well, from experiments conducted by dark rearing animals. The following links provide examples of some such experiments:
Visual acuity and visual responsiveness in dark-reared monkeys (Macaca nemestrina) [Regal et al., 1976]
Development of visual acuity in infant monkeys (Macaca nemestrina) during the early postnatal weeks [Teller et al., 1978]
Long-term effects of dark rearing on a visually guided reaching movement in cats [Fabre-Thorpe M et al., 1990]
Functional postnatal development of the rat primary visual cortex and the role of visual experience: Dark rearing and monocular deprivation [Fagiolini et al., 1994]
The role of visual experience in the development of columns in cat visual cortex [Crair et al., 1998]
We also see the effects of early sensory deprivation on vision in the case of amblyopia or ‘lazy eye’. In amblyopia, one eye fails to achieve normal visual acuity even with prescription glasses. The reason for this is reduced visual inputs to the affected eye during infancy or early childhood. This can happen for many reasons, cataracts for example. In the absence of visual inputs during the critical period, the visual circuitry of the deprived eye is permanently compromised. The result is normal vision for one eye and blurred vision for the other.
So would this compromised vision be better than no vision at all? I honestly do not know the answer to this. But I find myself veering towards ‘yes’.
Why?
Firstly, because even light perception has some benefit. Secondly, because there may come a time when scientists are able to rewire the brain to its childlike state, thus enabling visual circuits to develop as they normally would in childhood.
Oh wow, what’s this all about?
Well, if you want details, I refer you to an article titled The Power of the Infant Brain. The article is authored by Prof. Takao Hensch of the Center for Brain Science at Harvard University and it was published in the journal Scientific American. Here are the salient points of the article:
- The child brain develops vision and other abilities during “critical periods,” when the brain is primed to undergo lasting change in response to sensory and social stimuli.
- Critical periods open at defined times during the course of childhood and adolescence to allow the molding and shaping of neural connections - a property known as brain plasticity.
- Growing understanding of the molecules that both start and stop critical periods has let scientists gain a measure of control over their timing, restoring plasticity even in adulthood.
- Regulating the biology of early development may one day allow drugs or medical procedures to restart critical periods later in life to correct early developmental problems.
So this is as far as my thinking goes on the subject of vision restoration. As I’m not an expert of any kind, I would like to speak with those who are (ophthalmologists, retina specialists…..), in order to have some clarity on this subject.
If you would like to suggest someone with whom I could speak about what can be done for restoring vision in the case of ND, do get in touch. You can either drop me an email or write a comment at the end of the post.
Till next time then,
Meenu.
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