Question

Explain how the brain preserve the image form on the retina

Answer 1

Because light rays diverge in all directions from their source, the set of rays from each point in space that reach the pupil must be focused. The formation of focused images on the photoreceptors of the retina depends on the refraction (bending) of light by the cornea and the lens (Figure 11.2). The cornea is responsible for most of the necessary refraction, a contribution easily appreciated by considering the hazy out-of-focus images experienced when swimming underwater. Water, unlike air, has a refractive index close to that of the cornea; as a result, immersion in water virtually eliminates the refraction that normally occurs at the air/cornea interface. The lens has considerably less refractive power than the cornea; however, the refraction supplied by the lens is adjustable, allowing objects at various distances from the observer to be brought into sharp focus on the retinal surface.

Answer 2

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• The amount of light entering the eye is controlled by the pupil, which is surrounded by the iris – the coloured part of the eye. Because the front part of the eye is curved, it bends the light, creating an upside down image on the retina. The brain eventually turns the image the right way up.