How is the human eye adapted to its function?

K.C.S.E Biology Q & A - MODEL 2005PP1QN19

How is the human eye adapted to its function?

answers

Adaptations of the eye.

The presence of:-

• The sclerotic layer which contains tough connective tissue fibres which helps it to support and protect the other parts of the eye ball.
• The choroids which contain many blood capillaries which supply oxygen and nutrients of the retina and removes metabolic wastes from eye.
• Its highly pigmented, to prevent reflection of light within the posterior chamber of the eye ball.
• The retina which contains photoreceptor cells called cones and rods. It is said to be the light sensitive part of the eye. Cones are adapted for light and colour vision while rods are adapted for dim light vision.
• The vitreous humour-Which is under pressure. It helps to maintain the shape of the posterior chamber of the eye ball. It also plays an important part in the refraction of light rays enabling them to be focused on the retina.
• The cornea, transparent and curved which helps to play an important role in focusing of the image on the retina. It accounts for the largest refraction of light rays.
• The aqueous humour –Contains oxygen and nutrients, which nourish the cornea and the lens. It is under pressure thus helping to maintain the shape of the anterior chambers of the eye. It also plays a part in the refraction of light rays enabling them to be focused on the retina.
• The Iris is heavily is heavily pigment, to prevent entry of light into the eye except through its central aperture called the pupil. It contains circular and radial muscles which constrict or dilate the pupil depending on the intensity of light.
• The Iens is elastic, therefore allows changes in its shape depending on the tension exerted through the suspensory ligaments. This enables it to bring light rays causing from either near or far objects into sharp focus on the forea.
• The ciliary’s body Contains the ciliary muscles whose contraction and relaxation alters the tension exerted on the suspensory ligaments.
• This in turn alters the shape of the lens enabling it to focus for both near and distant objects.
• The eyelids which are movable and opaque structures can be closed through a reflex action to protect the eye from too much light or from foreign objects.
• The eye muscles help to move the eye ball within the orbit. The lateral rectus muscles move the eye up and down whole the oblique muscles the eyeball in its up and down movement.
• The lachrymal gland which continuously secretes a watery, saline and  antiseptic fluid called tears. The tears moisten the cornea and wash foreign particles out of the eye.
• The eyelashes, which are many hairs, protect the eye from the entry of small foreign particles.
• The eyebrows raised portion of the skin above the eye, thickly covered with hair, whose functions are to prevent sweat and dust from entering the eye.