Ask mr Brain...all will be explained

PUBLISHED : Thursday, 03 June, 1999, 12:00am
UPDATED : Thursday, 03 June, 1999, 12:00am

My vet says my dog has a cataract. Can it be cured? Is it the same as the cataracts humans get? Cataracts in humans and small animals are the same and have similar causes. The lens of the eye, located behind the pupil and iris, helps focus light on to the retina, the light- sensitive tissue which lines the inside of the back of the eyeball.

Normally the lens is transparent, but when it becomes cloudy or opaque - a condition known as a cataract - light is unable to pass through, resulting in impaired vision. Cataracts are one of the leading causes of vision loss in humans.

Cataractous changes of the lens may appear as small dots, white streaks, a 'pearl-like' sheen or a completely white lens. Cataracts are progressive and occur when the chemical composition of the lens changes. They are also associated with diabetes, eye injuries and overexposure to sunlight.

In young people, cataracts are congenital or hereditary; later they are usually the result of degenerative changes brought on by ageing or systemic disease (diabetes). That's why a lot of old people (and old dogs and cats) have cataracts.

Whether in humans or animals, cataracts are treated by surgical removal of the lens.

The same technique is used for humans and animals. A small incision is made in the eye, the lens capsule is carefully opened, and the lens is removed by an instrument which emulsifies the lens into a mulch with ultrasonic waves, and aspirates the remnants.

Why do hawks have acute eyesight? RICHARD Most birds have keen vision to help them catch prey, detect enemies and fly. Owls and other birds of prey have forward-facing eyes which give them a small field of view but a large area of binocular vision, which helps them to judge distances clearly and catch prey.

Birds of prey are called raptors. The bodies of raptors are built for hunting. They have strong and well- developed wings for active flight and soaring, and sharp vision (up to eight times as acute as human eyesight). They can detect movement of a mouse in the grass or a bird in the air as far as two kilometres away! Day-time or diurnal raptors have full-colour vision, while the eyes of nocturnal raptors easily adapt to low light conditions. Since hawks are diurnal raptors, they see better in daylight than at night.

They have hooked bills, large wings and sharp talons which make them great hunters. They hunt a wide range of creatures, which they kill with their powerful feet.

Hawks, falcons, eagles, vultures, owls and condors are all raptors. Vultures are unusual because they feed on the flesh of dead animals rather than killing prey themselves.

Hawks are distinguished from falcons by their broader, rounder wings. The goshawk feeds on small mammals and birds. There is also the destructive chicken hawk.

Raptors are at the top of the food chain. Some eat mice that eat grain. Others eat shrews which eat insects that eat plants. They help to maintain the dynamic balance of the natural world.