Structure And Functions Of Human Eye - Practice Questions & MCQ

The Eye :

The human eye is one of the most sensitive sense organs of sight which enables us to see the wonderful world of light and color around us. The eye is essentially a closed sphere into which light passes through a lens and strikes a light-sensitive surface. 

Structure of the human eye: 

• Sclera: It is the outer covering, a protective tough white layer called the sclera (white part of the eye).
• Cornea: The front transparent part of the sclera is called cornea. Light enters the eye through the cornea.
• Iris: A dark muscular tissue and ring-like structure behind the cornea are known as the iris. The color of iris actually indicates the color of the eye. The iris also helps regulate or adjust exposure by adjusting the iris.
• Pupil: A small opening in the iris is known as a pupil. Its size is controlled by the help of iris. It controls the amount of light that enters the eye.
• Lens: Behind the pupil, there is a transparent structure called a lens. By the action of ciliary muscles, it changes its shape to focus light on the retina. It becomes thinner to focus distant objects and becomes thicker to focus nearby objects.
• Retina: It is a light-sensitive layer that consists of numerous nerve cells. It converts images formed by the lens into electrical impulses. These electrical impulses are then transmitted to the brain through optic nerves.
• Optic nerves: Optic nerves are of two types. These include cones and rods.

1. Cones: Cones are the nerve cells that are more sensitive to bright light. They help in detailed central and color vision.
2. Rods: Rods are the optic nerve cells that are more sensitive to dim lights. They help in peripheral vision.

Functioning of the human eye: Much like the electronic device, the human eye also focuses and lets in light to produce images. So basically, light rays that are deflected from or by distant objects land on the retina after they pass through various mediums like the cornea, crystalline lens, aqueous humour, the lens, and vitreous humour

As the light rays move through the various mediums, they experience refraction of light. The light rays are received and focused on the retina. The retina contains photoreceptor cells called rods and cones and these basically detect the intensity and the frequency of the light. Further, the image that is formed is processed by millions of these cells and they also relay the signal or nerve impulses to the brain via the optic nerve. The image formed is usually inverted but the brain corrects this phenomenon. This process is also similar to that of a convex lens.

Visual Angle: The visual angle of an object is a measure of the size of the object's image on the retina. The visual angle depends on the distance between the object and the observer. Larger distances lead to smaller visual angles. The visual angle also depends on the object's size. Larger objects lead to larger visual angles. 

Visual angle $(\phi)=\frac{h}{d}$ where 'h' is the height of the object and' is the distance from the lens.