Dr. Nirajan Neupane

Eye

• Ectomesodermal in origin

• Located inside bony cavity i.e.,orbit

• Diameter = 2.5 cm ( 1.6 cm in newborn babies)

• Weight = 6-8 gram

EyelidsAlso called palpebrae ( opening : palpebral fissure )

• Skin

• Fibers of orbicularis oculi muscle

• Tarsal plate : meibomian glands

• Levator apparatus in upper / superior eyelid

( levator palpebral superiosis) opens eyes supplied by CN III

• Conjunctiva

• At the base of eyelashes : glands of Zeis & gland of moll ( inflammation: stye painful)

• Inflammation of meibomian gland producing tumor or cyst : chalazion painless

ConjunctivaStratified epithelium columnar/ squamous

Nictitating membrane/ third eyelid

• Transparent membrane

• Protects eyes in water ( frog)

• Reduced in rabbit

• Vestigial in human : plica semilunaris

Lacrimal apparatusLacrimal gland / tear gland and duct system

• modified sweat gland)

• supero lateral aspect of orbit

Tear

• Protects cleans lubricates

• Water ,salts ,lysozyme

Eyeball

Tunica fibrosa Complete coat/ outermost/ cornea & sclera

Sclera : inflammation: scleritis

• Dense fibrous CT

• Posterior 5/6th part

• Anteriorly ends at limbus

• Posteriorly : lamina cribrosa for optic nerve

• Provide attachment for EOM

Cornea ( infl : keratitis)Transparent avascular ,rich in nerves

• Anterior 1/6th

• 5 layers

• Max refractive power

• Eye donation / keratoplasty

• Derives O2 from environ ( dissolved in tear)

& nutrition from aqueous humor

Tunica vasculosa / middle / incomplete/ UveaChoroid , Ciliary body & Iris

• Choroid

-Attaches with pigment layer of retina

• Ciliary body

i. Ciliary process : secretes aqueous humor

ii. Suspensory ligament/ zonules : hold the lens

iii. Ciliary muscle : accommodation (reflex that increases the curvature of lens needed for near vision )

• Iris

Iris (rainbow) diaphragm of cameraGives color to eyes - melanin

• Controls the amount of light entering the eye through the pupil

• Pattern unique to every ind.

After death pupil dilates & doesn’t respond to light

Accommodation -convergence of eyeball-constriction of pupil

Tunica nervosa/ innermost/incompleteRetina- ectodermal in origin

Outer Pigmented layer

Inner Neural layer - photoReceptors : rods & cones

Bipolar layer (including horizontal and amacrine,muller cell)

Ganglion cell layer

Histologically 10 layers

Ora serrata : non visual part of retina ( anterior)

Optic nerve - optic chiasm -optic tract - lateral geniculate body ( thalamus) - optic radiation - occipital cortex

But also to ,

1.superior colliculus : visual reflex( reflex gaze)

2. Pretectal area : light reflex

3. Suprachiasmatic nucleus of hypothalamus : circadian rhythm

Rods Cones

120 M 6M

More in periphery More in center, only cones in

fovea

Dim light , night vision Bright light, color vision

High sensitivity but low acquity Low sensitivity but high acquity

Protein : Rhodopsin Idopsin

• Blind spot

• Yellow spot ( macula lutea) : contains fovea centralis (only cones)

Lens : ectodermal in origin

• Transparent , Crystalline enclosed by CT capsule

• Avascular, no nerves

• Elastic , flexible , biconvex

• With advancing age decreased elasticity : presbyopia

• Due to protein deposition : cataract

Aqueous humor Vitreous humor

Transparent watery fluid

(0.3ml)

Transparent jelly like

substance(4.4 ml)

Secreted by ciliary process &

drained through canal of

schlemn To venous system

Formed during embryonic

period

Increased fluid -increased

IOP

Normal IOP =10-20 mmHg

Covered by hyaloid membrane

Nourishes cornea & LensMaintains spherical shape of

eyeball

Disorders of eyes

• Myopia /nearsightedness

• Hypermetropia/ farsightedness

• Astigmatism : irregular curvature

• Presbyopia : hypermetropia with aging

• Cataract

• Glaucoma

• Trachoma

• Vit A deficiency

Vitamin A deficiency

• most common cause of preventable blindness in children

• first symptom ( night blindness/ nyctalopia

• first sign( conjunctival xerosis)

• Bitots spot

• Tapetum lucidium (retroreflector)eg cat

• Rabbit : monocular vision, red iris