4 mind-blowing facts about Human Eye | structure ,mechanism of vision , disorders of eye
The human eye is a unique organ. today I’m going to talk about the 4 mind-blowing facts about Eye. It is the window to the world, enabling us to see the forms and colours of the world around us. The eye is one of the five sense organs of the human body. A pair of eyes is present on the head which allows us to see. But how does the eye see?
These are a pair of organ for sight. They are situated in the deep protecting bony cavities of skull called orbits or eye sockets. Eyes are supplied with optic nerve.
facts about Human eye ( Structure ) :-
The wall of the eyeball consists of following three layers :-
1.External layer or Sclerotia :-
This layer is composed of a dense connective tissue called the sclera. It maintains the shape of eye and protects it. The anterior portion of this layer is called cornea. Cornea has no blood vessels and is refractory in function.
2.Middle layer or Choroid :-
This layer contains many blood vessels and appears bluish in colour. It becomes thick in the anterior part to form the ciliary body.
Attached to the ciliary body are the suspensory ligaments. These ligaments are in turn attached to the capsule surrounding the eye lens. The capsule and ligaments, together with the ciliary body, hold the lens in place and control its focal length.
The ciliary body itself continues forward to form a pigmented and opaque structure called the iris. It is the visible coloured portion of the eye. The eyeball Possesses a transparent biconvex crystalline lens held In place by the ciliary body with a central aperture called pupil. Pupil helps in controlling the quantity of light entering the eye.
3.Inner layer :-
The inner layer of eye is called retina. It consists of ganglion cells, bipolar cells and photoreceptor cells, i.e. rods and cones. Both of these contain the light sensitive pigments called the photopigments. The daylight and coloured vision are the functions of cones. The twilight or scotopic or dim light vision is function of the rods.
The rods contain a protein called rhodopsin or visual purple, which contains a derivative of vitamin-A. The cone cells contain erythropsin, iodopsin and cyanopsin containing photopsin protein.
The optic nerves leave the eye from a point called blind spot. At this spot the photoreceptor cells are not present. Thus, it is not involved in vision.
A yellowish pigmented spot called macula lutea with a central pit called fovea centralis is present at the posterior pole of the eye a bit lateral to the blind spot. Fovea is the point where the visual resolution is maximum, i.e. it is the point where brightest and most clear image of object is formed. Lens, ciliary body and suspensory ligament divides the eye ball into two chambers namely aqueous and vitreous chamber.
Aqueous chamber is the space between the cornea and the lens. It contains a thin watery fluid, which is secreted by the veins of ciliary body. It nourishes the lens and cornea and excess is drained into the blood by canal of Schlemm. Vitreous chamber is the space between the lens and the retina. It is filled with a transparent gel called vitreous humour. It regulates eye shape and pressure to keep eye lens in position.
Accessory organs of the eye :-
The eyeball is associated with certain other structures which help in the functioning of the eye. These are :-
It is a skin covering over the supraorbital process of frontal bone. They contain hair which protect anterior aspect of eyeball from sweat and dust.
These are two movable folds of the tissue situated above and below, in front of each eye. On their free edges, there are present short curved hairs called as eyelashes. The inner eyelids contain a transparent mucous membrane called conjunctiva that provides protection to the eyeball and keeps it moist.
There are four glands associated with the eye, i.e meibomian glands (sebaceous glands which help in lubrication), glands of moll (sweat glands), glands of zeis (sebaceous glands) and lacrimal glands (tear glands).
Tears secreted by lacrimal gland help to keep the cornea moist and transparent. Tears also contain lysozymes to prevent microbial infection.
4 mind-blowing facts about Eye, Mechanism of vision :-
▪️Light rays in visible wavelength focussed on the retina
▪️Eye lens generates impulse on the photopigment of rods and cones for their activation
▪️Light induces dissociation of the retinal pigment opsin resulting to the changes in the structure of opsin
▪️Membrane permeability of rods and cones changes
▪️ Potential difference generated in the photoreceptor cells
▪️It generates action potential in the ganglionic cells through the bipolar cells
▪️ Action potential are transmitted by the optic nerve to the visual cortex of brain
▪️ Image formed on the retina is recognised based on earlier memory and experience.
4 mind-blowing facts about Disorders of Eye :-
1.Myopia :- It is also called short-sightedness. The person with this defect can see nearby objects clearly, but not far away objects. It occurs due to increase in convexity of lens or anterio-posterior elongation of the eye ball due to which image being formed in front of the retina. It can be corrected by using concave glasses.
2.Hypermetropia :- It is also called long-sightedness. The person with this defect can see distant objects clearly , closer objects are not clear. In this, the image is formed beyond the retina due to shortening of eye ball or lens being flattened. It can be corrected by wearing convex or convergent lenses. Sometimes in old age this defect occurs due to reduction of the flexibility of lens, then it is called presbyopia.
3.Cataract :- In this disease the lens of eye becomes opaque thereby reducing its visibility. It can be treated by replacing opaque eye lens with artificial intraocular lens or by laser treatment.
4.Astigmatism :- In this, the curvature of cornea becomes irregular and image is not clearly formed. This defect can be corrected by using cylindrical glasses.
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