Iris makes interesting colour of the eye but more importantly it regulates the amount of the light that enters the eye. The amount of light is determined by the size of the pupil. The pupil is dark, distinguished central spot regulated by iris muscle fibres that are part of autonomic nervous system. When light enters through the pupil, the iris acts like a diaphragm of a camera. In darkness, when light is insufficient to see properly, the iris contracts and allow the pupil to become dilated in order to accept more light. In contrast, in case of bright light the pupil will constrict and less light enters the …show more content…
One of the anatomical defects which affect the perception of colour is colour blindness. Heredity condition is caused by absence of one or more cones from retina. They are located within the fovea in central part of the retina where the light is converted into retina and the sharpest and clearest vision is achieved. The cones contain photopigment, L-cones for red colour and M-cones for a green colour. The wavelength of the reflected light determines what colour we see. L-cones respond to long wavelengths and M-cones detect medium wavelengths. The blue colour is detected by S-cones associate with short wavelength. Colour blindness is caused by the variation in these photopigments. Although, red and green blindness is most common defect, the complete colour blindness is very rare. The exact and effective treatment for colour blindness is not known. Many people can cope quite well. Without any greater difficulties they usually find their own way have to distinguish the colours. The improvement can be achieves by coloured contact lenses or spectacles. However, the results are not always satisfactory.
Except congenital defects there are many disorders what can lead to visual disturbance or total blindness. Diabetes is one of these disorders and is the most common problem. The issue is the damage of the blood vessels which are unable to carry needed oxygen and nutrients