Let’s focus on the eye of the matter
The choroid layer is thin over the posterior two-thirds of the eye ball, but it becomes thick in the anterior part to form the ciliary body.
Hyderabad: This is in continuation to the last article focusing on sense organs. Today, we will discuss the eyes in detail.
Eye
• Our paired eyes are located in sockets of the skull called orbits.
• The adult human eye ball is nearly a spherical structure.
• The wall of the eye ball is composed of three layers.
• The external layer consists of a dense connective tissue and is called the sclera.
• The anterior portion of this layer is called the cornea.
• The middle layer, choroid, contains many blood vessels and looks bluish in colour.
• The choroid layer is thin over the posterior two-thirds of the eye ball, but it becomes thick in the anterior part to form the ciliary body.
• The ciliary body itself continues forward to form a pigmented and opaque structure called the iris which is the visible coloured portion of the eye.
• The eye ball contains a transparent crystalline lens which is held in place by ligaments attached to the ciliary body.
• In front of the lens, the aperture surrounded by the iris is called the pupil.
• The diameter of the pupil is regulated by the muscle fibres of iris.
• The inner layer is the retina and it contains three layers of neural cells – from inside to outside – ganglion cells, bipolar cells and photoreceptor cells.
• There are two types of photoreceptor cells, namely, rods and cones.
• These cells contain the light-sensitive proteins called the photopigments.
• The daylight (photopic) vision and colour vision are functions of cones and the twilight (scotopic) vision is the function of the rods.
• The rods contain a purplish-red protein called the rhodopsin or visual purple, which contains a derivative of Vitamin A.
• In the human eye, there are three types of cones which possess their own characteristic photopigments that respond to red, green and blue lights.
• The sensations of different colours are produced by various combinations of these cones and their photopigments.
• When these cones are stimulated equally, a sensation of white light is produced.
To be continued…
By
Dr. Modala Mallesh
Subject Expert
Palem, Nakrekal, Nalgonda
9989535675
