Human Eye structure and function Human eye
Anatomical structure
The human eye is the organ of sight which is located in deep depression of skull called as orbits. It is attached to the orbit by 6 muscles that allow eyeball to move. Eyeball is spherical and has three layers. The first two 2 layer are mesodermal and the third ectodermal in origin.
1) Superior rectus muscles or fibrous tunic/The sclera __ this is the outermost, thick and tough, non vascular covering around the eyeball. Over the projecting parts of eyeball, it is transparent, forming the cornea. It lacks blood vessels but it is composed of special type of connective tissue. It is covered externally by a thin transparent membrane called conjuctiva.
2) lnferior rectus muscle__ distracted muscle fibres are inserted into sclera for eyeball movements. The 3rd,4th & 6th cranial nerves control the eyeball movements to observe in different directions. Light passes and refracted through cornea and rays begin to converge.
3) Vitreous gel body __ space between cornea and lens is called aqueous chamber . It is filled with clear watery fluid called aqueous humour , which is a tissue fluid containing glucose, amino acids, respiratory gases, metabolic wastes and ascorbic acid.
This vitreous chamber is filled with viscous, jelly like humour containing 99% water, salt, a a little quantity of mucoproteins and hyaluronic acid.lt is the part between lens and retina.
4)Ciliary body and muscles__ lt is located just behind the junction between the main part if sclera and cornea.lt contains a network of blood vessels supplying food and oxygen to eye. It is deeply pigment and is connected to a thick structure which have blood vessels and muscle fibres that run in circular direction. Contraction and expansion of ciliary muscles bring about increase and decrease in the size of lens
5) Iris__lt is called diaphragm of eye because it regulates the size of pupil .lt is thin circular structure made up of connective tissues and muscles that surrounds the pupil. Iris is the forward segment of ciliary body which is pigmented and opaque.The colour of our eyes is determined by the amount of pigment in the Iris. This part is the visible coloured portion of the eye. Iris are heavily pigmented in people with Brown or black eyes but less pigmented in people with blue eyes.
6) Lens__it is a transparent crystalline structure. It is present anteriorly inside the Iris and is held in position by ligaments of ciliary body.
7) Pupile__the aperture surrounded by the Iris in front of lens is called pupil. The large central aperture of iris is called pupil.The movement of pupil is regulated by muscle fibres of iris..
8) Anterior chamber__ lt is filled with clear watery fluid called aqueous humor .The lacrimal gland is situated in the orbit which secrets water ,salt and bactericidal protein called lysozyme. The function of tears is to bath the front of eye, washing away in a dust, grit and microorganisms.
9)Cornea__lt is transparent anterior circular portion present in front of the sclera . Sclera is the outer layer of dense connective tissue.
10)Retina__ It is innermost layer of eye.It is very delicate layer which is sensitive to light. It receives image. bears light sensitive. lt bears light sensitive photoreceptor cells- rods and cones.
(a)Rods: contain purple coloured photosensitive pigments Rhodopsin which are more responsive to dim light i.e scotopic vision.
(b)Cones:contain violet coloured photosensitive pigments which function in bright light i. e. photopic vision.
Cones are of 3 differnt types.
(i) short wavelength: sensitive blue cons.
(ii) medium wavelength: sensitive green cones.
(iii) long wavelength: sensitive red cones.
They are called at photopigments.
11)Fovea__lt is central pit portion of the retina. It contents only cones but no rods and gives the distinct interpretation of an image.Therefore have greatest visual activity. i.e. resolution . Outside the fovea, processing of visual information can occur within the retina.lateral to fovea ,there is a blind spot which does not contain light sensitive cells.
12)Macula__It is yellowish pigment spot is present lateral to the blind spot.
13)Choroid__it is the middle layer present inside the sclera. which is blue in colour contains network of blood vessels supplying food and oxygen to eye.
Optic nerve __it is sensory in nature and originate from retina of eye and distribution in optic lobes of brain and function is to give vision.
* Common eye defects*
1)Myopia / Near sightedness
Person has difficulty in seeing distant objects clearly.the person can see near objects clearly. Hence it is also called short sight.Engineer site I the eyeball is too long and the retina is too far from the lens. The light rays converge at a a. In front of the retina resulting in a blurred image. Concave lens corrects this condition by bringing the light rays to a focus at a point further back.
2) Hypermetropia/farsightedness
The person has difficulty in seeing near objects. Hypermetropia is just the opposite of myopia. The eyeball is too short and the retina too cloes to the lens. Light rays strike the retina before they have converged again resulting in a blurred image.
convex lenses saraiki far sighted condition by causing the light rays to converge further forward.
3) Astigmatism
It is due to irregular cornea or lens.lt causing the image to be out of focus, producing faulty vision. It is corrected by cylindrical lens. It can be diagnosis by retinoscopy. It is commonly occur in in kids between 5 to 17 years old girls and boys.
4) Presbyopia/Old sight
It is a defect in accommodation occurring in advancing age. Lens becomes elastic and is not able to focus the image of near object while the distant vision is not impaired. It is also called old age long sightedness. This defect is corrected by using convex lens.
5) Strabismus
It is commonly known as Squint.the eyeball is somewhat bent on onto a side in its orbit so that the optic axis cannot be directed to the same object. Some extra ocular muscle becomes longer or shorter than the normal. It can be cure by small surgery.
6) Cataract / Safaid Motia
The lengths loses its transparency and becomes opaque to light and hence vision is impaired.It is corrected by surgical removal of the opaque lens and using biconvex glasses. Intraocular lens implantation is also done. It is commonly occur in old people & known as Motibindu.
7)Glaucoma/Kala Motia
It is also more common in older people. If untreated it leads to blindness. The pressure in the anterior cavity of the earth increases to an abnormal level.lt exerts pressure on the posterior cavity and greatly reduces the blood supply to the retina. Lack of nutrients ultimately damages the Nerve cells of the retina.ek the pressure is due to blockage of the canal of schlemm a new canal can be created surgically.
** common eye defects such as
Myopia / Near sightedness ,Hypermetropia/farsightedness,Astigmatism,Presbyopia/Old sight,Strabismus,Cataract / Safaid Motia,Glaucoma/Kala Motia, Conjuctiva, Nightblindness,Colour blindness. दृष्टीदोष_निकटदृष्टिता , दूरदृष्टी ता, विषमदृष्टी, दृष्टीमांद्य , तिरळेपणा, मोतीबिंदू, काच बिंदू, डोळे येणे, रातांधळेपणा, रंगआंधळेपणा.
