3. Average globe dimensions
– Adult
– Antero-posterior diameter………….24 mm
– Horizontal diameter……………………23.5 mm
– Vertical diameter………………………..23 mm
– Weight………………………………………..7 gm
– Volume……………………………………….7 ml
– Circumference…………………………….75 mm
– Newborn
– Antero-posterior diameter …………….16.4 mm
– Vertical diameter……………………………16 mm
– Horizontal diameter……………………….15.4 mm
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4. Layers (coats) of the eyeball
– Three layers (coats) of the globe
– Outer layer --- Cornea and Sclera
– Middle layer --- Uvea
– Inner layer --- Retina
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5. • Precorneal tear film
– Has a thickness of about 7µm
– Consists of 3 layers
– Lipid layer (outer layer) --- by meibomian glands
– Aqueous layer (middle layer) --- by lacrimal glands
– Mucin layer (inner layer) --- by goblet cells
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6. – Main functions of the tear film include
– Forms a smooth refractive surface on the epithelium
– Carries oxygen to the ocular surface
– Maintains a moist environment for the epithelium
(lubrication)
– Immunity
• Has antibodies --- IgA
• Antibacterial proteins --- E.g., Lysozyme
• Physical barrier --- the mucin layer
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7. • Anatomy of Cornea
– Transparent structure --- forms the anterior 1/6th of globe
– The major refracting surface of the eye --- 43 diopters
– Nutrition --- from limbal capillaries, aqueous, and tear film
– One of the highly innervated tissue in the body --- 300-600x
that of the skin
– Five layers
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8. – Factors for its transparency
– Its avascularity
– Has non-myelinated nerve fibers
– The small, regular diameter of individual collagen fibrils
– Regular arrangement of the collagen fibrils with smaller
interfibrillar spacing
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9. • Limbus
– Transitional zone between the cornea and sclera
– A notable anatomical site
– Site of conjunctival and tenon insertion
– Harbours angle structures internally, and stem cells
externally
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10. • Sclera
– Opaque white --- consists of dense fibrous tissue
– Forms the posterior 5/6th of the external coat of the eye
– Provides an insertion to all EOMs --- except LPS
– Fenestrated with ciliary arteries and nerves, optic nerve,
vortex veins
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11. • Uveal Tract
– The uveal tract is the middle layer of the eyeball
– Consists of 3 structures
– Iris
– Ciliary body
– Choroid
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12. – Pupil
– The central aperture (opening) of the iris
– Size --- average 3-4 mm in diameter
– Regulates the amount of light entering the eye
– An important clinical site of examination for ocular,
CNS, and systemic disorders
– Muscles around pupil --- sphincter pupillae and
dilator pupillae
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13. – Functions of the Uvea
– Regulation of light entering the eye --- pupil
– Aqueous humor production --- ciliary processes
of the ciliary body (CB)
– Controls focusing ability (accommodation) of the
eye --- ciliary muscle in the CB
– Provide nourishment for the outer layers of the
retina --- choroid
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14. • The Retina
– Innermost layer of eyeball --- it is a part of the brain
– The light sensitive part of the eye
– Anatomical sites --- macula, peripheral retina, ora serrata
– Consists of 10 histological layers
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15. – Vascular supply of the retina
– Inner 2/3rd --- by central retinal artery
– Outer 1/3rd --- avascular & gets oxygen & nutrients by
diffusion from the choriocapillaris (choroid)
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16. Segments of the eyeball
– The eyeball is divided into two segments
– Anterior segment --- comprises
• Anterior chamber (AC) --- anterior to the iris
• Posterior chamber (PC) --- posterior to the iris
• The lens
– Posterior segment --- vitreous, and the fundus
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17. • The Lens
– Clear transparent biconvex disc like structure
– Suspended in place by zonular fibers
– Can change its shape --- accommodation
– Has four parts
– Lens capsule, lens epithelium, cortex, and nucleus
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18. – Function of the lens
– Refraction and focusing of light over the retina
– Accommodation
• Change of lens shape so that the refractive
power also changes
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19. • Vitreous
– Jelly, transparent, thick viscous structure
– Fills the largest cavity of eye --- 2/3rd of its volume (4ml)
– Components of the vitreous
– Water --- almost 99%
– Collagens --- important structural protein in vitreous
– Hyaluronic acid --- shock absorber
– Mucopolysaccharide
– Glycoproteins
– Ascorbic acid --- antioxidant
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20. – Functions of vitreous
– Structural --- maintains the shape of the eyeball
– Part of a refractive medium of the eye
– Shock absorber
– Absorbs UV light protecting the retina from damage
– Possesses antioxidants --- serve as a free-radical
scavenger
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22. – Orbital wall is composed of 7 bones
– Frontal – Sphenoid
– Maxilla – Palatine
– Zygoma – Lacrimal
– Ethmoid
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23. – Essential points
– The two medial walls are parallel & 25mm apart
– The angle b/n the two lateral walls is 900
– The angle b/n the medial and lateral walls of a
single orbit is 450
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24. Paranasal Air Sinuses
– Four paranasal air sinuses
>> Ethmoid Sinus
>> Maxillary Sinus
>> Frontal Sinus
>> Sphenoid Sinus
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25. – Clinical importance
– Mucocele may confuse with intra-orbital tumors
– Spread of infection to the orbit from sinusitis
resulting in orbital cellulitis
– Orbital wall fractures may involve sinuses resulting in
subcutaneous emphysema
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26. Lacrimal System
– Lacrimal system comprises two functional categories
– Secretory system
» Main lacrimal gland
» Accessory lacrimal glands
– Drainage system
» Punctum
» Canaliculi
» Nasolacrimal sac
» Nasolacrimal duct
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28. • Innervation of the EOMs
– Innervation of EOM -------------------------- SO4LR6R3
– CN IV (trochlear) --- SO muscle
– CN VI (abducens) --- LR muscle
– CN III (oculomotor) --- all the others
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