Partial blindness presents an interesting physiological problem. This is because the nerve fibres on the way from the eyes to the brain partially cross over. At about where the pituitary gland is, the nerve fibres from the inner side of the each eyeball switch sides. This creates a situation where, depending on where the damage is, you may have very different kinds of blindness.
For example, if you lose an eyeball, because of the overlapping of the visual fields of each eye, you do not lose half of your vision. The actual amount of loss of the total visual field is only about 25-30%. What is most disturbing about loss of an eye is the loss of binocular perception and consequently, loss of depth perception.
If on the other hand, if there is complete damage to the optic fibres after the crossing has occurred, there will be potentially greater loss of the visual field, up to 50%.
Intuitively however, we are misled to think a person with an eyepatch is more blind (loss ofvisual field) than a person who may appear normal externally but has a lesion of one of the optic tracts or has damage to the visual cortex of the brain.
So there are times the eyes see but the brain is unable to process the information, while at other times, the eye appears not to see but the brain is actually visually aware. There are social equivalents to these kinds of blindness. For example, data and information is available but the brain is quite blind in not being able to perceive the real signals. The recent discordant interpretations of rainfall patterns show a bit of this hemianopsia. The brain has been conditioned to only see no change despite the signals it received. Likewise, the Central Narcotics Bureau last year was caught in the embarrassing situation of having to 'fess up to misreading the data it had collected. Instead of a downward trend in drug addiction, the numbers had actually been trending upwards.
By contrast, there is the other kind of blindness where people can actually see but pretend to be more blind than they actually are. Such was the case with the famous British naval hero Lord Horatio Nelson. He was well known to be blind in one eye. Now we now know that losing one eye only loses about 25-30% of your visual field, but when he was given a visual signal to withdraw during a battle, he famously quipped, "You know, Foley, I have only one eye - and I have a right to be blind sometimes... I really do not see the signal."
So thanks to Lord Nelson, we now have the expression, "turning a blind eye", when we choose not to see something very obvious.
Our vice squad appear to be somewhat guilty of this, when they appear to be blind to the numbers of streetwalkers lined up along the roadside in Geylang. Sometimes the policeman does this when you complain of something illegal happening. The Lord Nelson in him tells you that it never happened unless someone made a official report. Sounds a bit like our Singapore Medical Council. Medical wrong-doings never happened unless someone had officially made a report, even when things were as evident as day.
There are many Lord Nelsons ruling in biomedical research nowadays apparently. Despite detailed evidences of unethical and fraudulent behaviour flagged up in a number of websites such as Retraction Watch and Abnormal Science, journal editors, research institutes and universities continue to feign ignorance while professing to hold high standards of ethical practices. Just ignore the reports from blogs.
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