Dow University of Health Sciences Institute of Nursing

Human eye

Maghan Das BscN Student 10th September, 2014

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Eye Accessory structures Eye lids

Upper eye lid Lower eye lid

It is also known as Palpebrae Upper is more movable Upper eye is of Composed of levator palpebrae superioris muscle Protect the eye from excessive light and foreign bodies Space between upper and lower eye lid is called palpebral fissure

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Conti…

•Meibomian glands are sebaceous glands that secrete an oily lubricating material into the lids.• In the inner canthus, the caruncle is the small fleshly mass containing sebaceous glands

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Conjunctiva

• It is transparent • Composed of stratified columnar epithelium • Palpebral Conjunctiva lies at inner of eye lids • Bulbar Conjunctiva lies at eye ball• It covers the sclera, not cornea Eye lashes•Which protect the from border of eye lids Eye brows • Protect the eye ball from foreign objects • Sebaceous ciliary glands lies at the base of hair follicles of

eye lashes and release the lubricating fluid in follicles

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Lacrimal apparatus

•Almond shape • lacrimal glands secrete tears which drain into the puncta, then the nasolacrimal sac, then the duct which empties into the inferior meatus of the nose •Parasympathetic fibers of facial nerve VII•Lacrimal fluid contains salts, mucous and lysozyme •Each gland produces 1 ml lacrimal fluid per day

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Eye muscles

Six extrinsic eye muscles • Superior rectus • Inferior rectus • Lateral rectus•Medial rectus• Superior oblique • Inferior oblique

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Eye ball

• It measures about 2.5 cm in diameter •One-sixth is exposed • It is composed of three layers • Fibrous layer •Vascular layer•Nervous layer

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Fibrous layer (outer layer) • Cornea

•Transparent layer •Covers iris •Refract the light • It has three coats

• Outer surface consist of non keratinized stratified epithelium • Middle coat consist of collagen fibers and fibroblast • Inner coat is consist of sqamous epithelium

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Sclera

• It is called white of eye •Composed of dense connective tissues • It covers the eye ball except cornea •Serves as an attachment for the extraocular muscles•Helps maintain the shape of the eyeball• It is rigid and protect the inner structures

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Vascular layer

• Choroid

•Absorb excessive light•Contain network of blood vessels to supply oxygen and nutrients•Nemours blood vessels • It contains melanocytes •Melanin in choroid absorbs stray light rays

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Ciliary Body

•Ciliary processes produce aqueous humor•Attach with zonular fibers with lens •The muscles of the cilliary body control the thickness of the lens.

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Iris Colored portion of eye ball It is suspended between cornea and lens It contains melanocytes and smooth muscle fibers

◦Brown and black eyes --- large amount of melanin◦Blue eyes ----very low melanin ◦Green eyes ------ moderate melanin

The muscles in the iris control pupillary constriction. Stimulation of the parasympathetic branch of CN III causes

constriction◦Contraction ---- circular muscle ◦Dilation ----Radial muscles

Stimulation of the sympathetic branch causes dilation

Divides the anterior chamber and posterior chamber

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Nervous layer (Retina)

• Inner layer • It has two layers • Pigmented layer •Neural layer • Pigmented layer contains melanin which absorbs stray light •Neural layer is consist of three layers • Bi polar layer ---- horizontal cells and amacrine cells •Ganglian cell layer • Photoreceptor layer

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Photoreceptor

•Two types of Photoreceptor Cones •Bright light stimulates cones •Each retina has 6 millions conesRods •Each retina has 120 millions rods •Dim light stimulates rods

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Macula

• Highest concentration of cones• Fovea centralis

• Center of macula• Contains only cones and no rods

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Optic disc (Blind spot)

• It does not contain rods and cones

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•Lens• A transparent crystalline biconvex structure immediately behind the iris• Suspended from ciliary body by threadlike ligaments called zonules• Refracts light• Focuses light on the retina

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•Anterior Compartment• Aqueous Humor

•Fluid that nourishes the lens and epithelial cells•Help refract light onto the retina

•Posterior Compartment• Vitreous Humor

•Clear gel •Helps refract light onto the retina

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•Optic Nerve• Transmits electrical impulses from

the retina to the brain• The blind spot is located at the

optic nerve head or optic disc where there are no photoreceptors

•Retinal Blood Vessels•Arteries transmit oxygen and

nutrients•Veins carry deoxgenated blood

from the eye

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