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Background
When eyesight is tested, a great deal of emphasis is placed upon the ability to see letters on a chart several metres away and the ability to read from a book. Clearness of vision or “Visual acuity” is then expressed as the smallest size of letter identified on the chart. It is often not comfortable to read at this threshold of vision for long periods.
Vision in the real world is not that simple. More than 40% of the brain is devoted to visual function. To have normal vision is to have the ability to perform a number of visual ‘tasks’. A child often will have difficulties in more than one of these ‘tasks’. The extent of difficulties they have will vary with the eye problem they have and with the child.
To understand the tasks that the eye must perform it helps to think of the eye like camera.
The clear cornea at the front and the lens inside the eye focus like camera lenses.
The retina (light sensitive film) inside the eye is the film that turns the picture into an electrical signal.
The optic nerve brings the signals to the brain much like a cable connecting a camera to a computer.
Normal vision is the ability to carry out the following “tasks”:
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