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