structure of eye

Structure of eye

1. STRUCTURE OF EYE

2. INTRODUCTION The eye or the organ of sight is situated in the orbital cavity of the skull It is well protected by bony walls of the orbit Orbit also contains muscles of eyeball, their nerves, blood vessels, and lacrimal gland Each eyeball is similar to a camera and which produces images

3. STRUCTURE OF THE EYEBALL Wall of eye ball Light transmitting media (or) refractive media

4. WALL OF THE EYEBALL : OUTER LAYER (FIBROUS COAT) : SCLERA AND CORNEA MIDDLE LAYER (VASCULAR COAT) : CHOROID ,CILIARY- BODY AND IRIS INNER LAYER (NERVOUS COAT) : RETINA

5. WALL OF EYEBALL OUTER LAYER (TUNICA EXTERNA OR TUNICA FIBROSA) CORNEA SCLERA MIDDLE LAYER (TUNICA MEDIA OR TUNICA VASCULOSA) CHOROID CILIARY BODY IRIS INNER LAYER (TUNICA INTERNA OR TUNICA NERVOSA ) RETINA (LAYERS OF RETINA, ROD,, CONES, LAYER OF NERVE FIBERS Etc .)

6. OUTER LAYER (OR) TUNICA EXTERNA (OR) TUNICA FIBROSA This gives shape of eyeball and contains sclera and cornea

7. MIDDLE LAYER (OR) TUNICA MEDIA (OR) TUNICA VASCULOSA This layer comprises of three structures:, Choroid Ciliary body Iris The choroid , ciliary body and iris together form the uveal tract. This layer contains blood vessels Pupil is the small opening in front of it

8. INNER LAYER (OR) TUNICA INTERNA (OR) TUNICA NERVOSA (OR) RETINA Retina is the light sensitive membrane

9. SCLERA AND CORNEA Sclera or the “white of the eye” forms the outermost layer of the eyeball The anterior one sixth part of the sclera is transparent and is known as cornea. The cornea is described as the “ window of the eye ” Light rays pass through the cornea to reach the retina.

10. FUNCTIONS OF SCLERA It provides protection to the delicate structure within the eye It resists intraocular pressure It maintains shape of the eyeball The smooth external surface allow easy eye movement

11. CHOROID Choroid is a thin pigmented membrane, dark brown in color which is situated in between sclera (externally) and retina (internally)

12. CILIARY BODY Ciliary body is the continuation of choroid consisting of smooth muscle fibers, i.e., the ciliary- muscle

13. Contd…. Ciliary body contains suspensory ligament for attaching the lens in position The ciliary muscles help in accommodation by adjusting the thickness of lens

14. IRIS Iris is the pigmented membrane surrounds the pupil It arises from the margin of ciliary body and forms a dark centered opening called pupil The space between cornea (in front) and the lens (behind) is the anterior segment

15. Contd… It is again divided into two parts by the iris; The space between the iris and cornea is the anterior chamber The space between iris and lens is posterior chamber They are filled with a clear fluid, the aqueous humor

16. RETINA Retina is the inner most layer of the eyeball It is a thin delicate layer continuous posteriorly with optic nerve The outer surface of the retina , formed by pigment cells, is attached to choroid Its inner surface is in contact with the hyaloid membrane of the vitreous The small area of retina where the optic nerve leaves the eye is the optic disc or the blind spot. It has no light sensitive cells (Rods or Cones)

17. The retina has three parts: OPTIC CILIARY IRIDIAL The optic part contains nervous tissue and it is sensitive to light It extends from the optic disc to the ciliary body The thin, non nervous, non sensitive layer covers the ciliary body and iris is called ciliary and iridial part of retina Contd….

18. Contd……. Lateral to the optic disc a depression called macula lutea (due to its yellow color) The center of macula is again depressed to form the fovea centralis It contains cones only and is the site of maximum acuity of vision The rods and cones are the receptors of light and sight These cells contains photosensitive pigments (Rods- Rhodopsin, Cones – Iodopsin) involved in the conversion of light rays into nerve impulses

19. BLOOD SUPPLY Arterial blood is supplied by branches of ophthalmic artery (ciliary arteries &central retinal artery) Venous drainage a number of veins including the central retinal vein

20. LIGHT TRANSMITTING MEDIA (OR) REFRACTIVE MEDIA Aqueous humo r Vitreous humor Lens

21. AQUEOUS HUMOR Aqueous humor is a clear fluid fills the space between cornea and lens It is secreted by capillaries of ciliary process From here the fluid reaches to the anterior chamber which finally reaches to the canal of schlemm

22. Contd….. Interference with drainage of aqueous humor results in an increase of intraocular pressure (glaucoma) (Normal IOP 10 to 20 mmHg) This leads to atrophy of the retina, leading to blindness

23. FUNCTIONS It helps to maintain intraocular pressure and thus maintains the shape of eyeball It is rich in ascorbic acid, glucose and amino acids and nourishes the cornea and lens

24. VITREOUS HUMOR Vitreous humor or vitreous body is a colorless, transparent, jelly- like substance which fills the posterior segment of the eye (i.e., behind the lens). It is enclosed in a delicate hyaloid membrane

25. FUNCTIONS It helps to preserve the spherical shape of the eyeball and to support the retina

26. LENS The lens of the eyeball is crystalline in nature It is situated behind the pupil It is biconvex, transparent, and elastic in structure Lens refracts light rays and helps to focus the image of the object on retina Lens is supported by suspensory ligaments (Zonular fibers) which are attached with ciliary bodies

27. ACCESSORY ORGANS OF THE EYE EYEBROWS EYELIDS & EYELASHES LACRIMAL APPARATUS CONJUNCTIVA

28. CONCLUSION Eye is the organ of the sense of sight, situated in the orbital cavity. It is a delicate organ and which is protected by several structures.