A pair of eyes are organs of sight. Ophthalmology is the study of structure, function and disease of rye. They are located in orbits (bony cavities). Of skull.

Structure:- Eye is round, hollow organ.

The wall of eyeball is composed of 3 layers.

3 layers of eye ball :-

Sclera        

Choroid

Cornea

(1)   External layer of eye ball coat.

(2)   Composed of dense anatine tissues.

(1)   Middle layer of eye ball coat.

(2)   Contain blood vessels and look bluish in color.

(1)   Innermost layer of eye ball coat.

(2)   Thick at inner & thin at outside.  

(1)   Iris :-At the function b/w sclera and cornea. There is a portion of contractile membrane that contain a membrane called pupil. This contractile membrane is Iris. It control the amount of light reaching the retina.

(2)   Pupil :-Iris has an aperture. The spaul hole in the middle of Iris of eye through which light passes is focused on retina.

(3)   Retina :-the thin layer of cells at the back of eyeball where light is connected into neural signals sent to the brain.

 It has further 3 layer of cells :-

(1)Ganglion cells (2)Bipolar cells (3)Photoreceptors cells.

Photoreceptors cells are also of 2 types :-

Rods and Cones difference :-

Rods

Cones

(1)   These cells are sensitive to dim light and give twilight vision.

(2)   All rods cells are same and do not give color vision.

(3)   Their less no. causes light blindness.

(4)   125 million in human eye.

(1)   These cells are sensitive to bright light and give day light vision.

(2)   All cones cells are of 3 types : blue, green and give colored vision.

(3)   Their less no. color blindness.

(4)   6 million in human eye.

 (4)   Lens :-solid and elastic lies behind the Iris. It provide focus of light on retina.

(5)   Cavity of eyeball is divided into 2 chambers :-

Aqueous humour

Vitreous humour

(1)   Occurs in aqueous chamber.

(2)   It is watery fluid.

(3)   It is reformed.

(4)   If its flow is stopped, it may damage retina.

(1)   Occur in vitreous chamber.

(2)   It is fully like substance.

(3)   It cannot reformed.

(4)   It cannot flow.

(6)   Cilia body:- a tissue inside the eye cilia muscles and cilia process. It helps the tens to charge the shape of lens.

(7)    Fovea:-  it is a small pit composed of cone cells. It is responsible for sharp vision during reading, driving etc.

 (8)   Blind spot:- the place where the optic nerve attached to retina cannot detect light

 (9)   Optic nerve:- they carry visual information from retina to the brain.

Mechanism of vision :-

When light rays focuses on retina through cornea then lens generate impulses in rods and cones, each 3 types of cones in retina of eye contains a different types of photosensitive pigment. When light falls on retina. This light is received by photoreceptors – rods and cones On the retina. The absorbed light activates into action potentials in membranes of muscles. Here, light is travels as nervous impulse through rods or cone cells and reach the synaptic knobs. Trough it, nerve impulse passes to bipolar nerve cells, den to ganglions and then to optic nerves. In this way nerve impulse passed to brain and through retina. the information is processed we are able to see the image. The image formed on retina is inverted.

Eye defects:-

(1)   Near sightedness – (myopia), here for away objects appear blurs. Can be corrected by using concave lenses.

(2)   For sightedness – (hypermetropia) here near object appear blurs can be corrected by using convex lenses.

(3)   Presbyopia –inability of eye due to ageing to focus on nearby objects – also called for sightedness. Can be corrected by using convex lenses.

(4)   Astigmatism – a defect where light rays coming from a point do not meet at a focal point so that image is blurred. Corrected by using cylindrical glasses.

(5)   Cataract – eye lens become opaque due to ageing or disease. Leads to blindness. Corrected by only transplant of new cornea.

 

Related Keywords
11    PMT    Biology    Neural Control and Coordination    Eyes concept