Vision without Sight?
by John MacDebs
“I see no ships” he said, putting his telescope to his blind eye and leading his squadron on to victory. Famously, Nelson was able to be blind or sighted as it suited him and every parent knows that sometimes it’s best not to notice a minor transgression—to turn a blind eye to it.
Blindness is, however, a significant handicap (which assertion should get me a prize for stating the obvious) and poor eyesight makes much of life more challenging.
When we moved to Blackheath we brought with us an enormous old television that Granny no longer had a use for. This monstrosity dominated our living room for years until, finally, its wiring packed up just before Christmas. Granny had bought it when her eyesight started to fail and she found she could no longer see the pictures on a regular sized screen. It came our way when she found she could no longer see the pictures from her chair two feet away. She now owns an even larger television.
Losing your sight is not an uncommon part of aging but I think it must be one of the most difficult challenges to come to terms with. Respectable, solitary, undemanding pastimes such as watching the television or reading become difficult or impossible, and even shopping can be a problem if you can’t identify your change (a problem that I’ve always thought must be more difficult in the USA where all banknotes look the same).
Complete blindness is one step further and yet people manage: responding to challenges with solutions and to adversity with determination. David Blunkett is an inspiring example, taking his guide dog to the House of Commons and proving that the handicap need be no obstacle to success, even in a profession in which reading reports and papers must be a significant activity.
So, sight is an important sense, vision an important aspect of our lives but how does it work? Well, I’ve done some research, visited the loft and extracted my GCSE textbooks and am able to refresh your memories. Light enters the eyeball through the pupil. It passes through a lens which focuses the image onto the retina at the back of the eyeball. Here, light-sensitive cells react by transmitting electrical pulses which pass along nerve cells to the brain where they are interpreted as the sensation we call sight.
This process can go wrong in a number of different ways; if the lens is damaged then the image will not be focussed clearly, if the retina is damaged then it will fail to register the image; if the optical nerve is broken then the images will fail to reach the brain and if the brain itself is abnormal then it’s possible that it will be unable to interpret the messages in a coherent way.
A common problem of old age is a cataract where the lens becomes cloudy and, instead of focussing a clear image, scatters the light passing into the eye. I was unable to discover what caused David Blunkett to be born blind but one possibility is that an viral infection such as rubella caused his retinas to be damaged as they developed. Nelson, of course, proved that trauma (in his case a shard of flying stone) can very effectively damage many parts of the eye.
Sight allows you to see where you’re going. Maybe vision is the ability to know what you’re aiming for. Some people have clear goals and know exactly in which direction they’re headed—some lack this ability and wander aimlessly through life. How does vision work? Is a lack of vision a disability? Unfortunately my textbooks are unable to answer these questions—apparently this is not covered by the GCSE biology syllabus.
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