The eyeball has three concentric layers and is approximately 21-26mm in diameter. It is connected to the brain by the optic nerve and protected by the bony orbit and eyelids. The cornea is transparent and located at the center of the eyeball's anterior surface, comprising 5 layers and measuring approximately 12mm by 11mm. The sclera covers the posterior four-fifths of the eyeball and provides attachment points for the extraocular muscles. Six extraocular muscles control eye movement, with the four recti muscles originating from a common tendinous ring and inserting into the sclera, while the two oblique muscles originate from bones in the orbit.

2. ANATOMY

3. ANATOMY OF EYEBALL
1.THE EYEBALL
2. OCULAR ADNEXA

4. • SIZE- average AP diameter is 21-26mm
• Circumference-72mm
• At birth its approx 16mm and 23mm at the age of 3
yrs
• It reaches its maximum size by 2 yrs of age and very
little growth thereafter.
• It has 3 concentric layers.
• It is connected to the brain by optic nerve
• It is protected by bony orbit and eyelids.

6. CORNEA
• Occupies the centre of the anterior pole of the globe and is made up
of 5 layers
• Size-12mm horizontal,11mm vertical meridian and thickness-1mm.
• It’s a transparent avascular structure with rich nerve supply through
unmyelinated nerve.
• It is the most important refractive surface with 43 diopters of
refractive power.

8. SCLERA
• Covers posterior 4/5th of the surface of the globe and
forms a protective coat for the eyeball.
• It ends anteriorly at the limbus.
• Limbus is the junction between cornea and sclera.it is
2mm wide and forms a surgical landmark in various
intraocular surgeries.
• Posteriorly forms lamina cribrosa for optic nerve..
• Sclera is an opaque structure that provides attachment of
the extrocular muscles..

9. THE BONY ORBIT
• 2 conical bony recess.
• It is the bony cavity in the skull and houses 1. the eyeball
• 2.the extraocular muscles
• 3. the blood vessels and
• 4. the nerves
• Orbital bones have air cells- paranasal sinuses

10. OCULAR ADNEXA
• The bony orbit
• Eyelids
• Conjuctiva
• Lacrimal apparatus
• Extraocular muscles
• The accessory organs of the eye.

11. EXTRAOCULAR MUSCLES
• Six muscles control the eye movements- 4 recti and 2 oblique which
are voluntary muscles.
• The 4 recti arise from a common annular tendon or tendinous ring of
zinn. The ring is attached to the middle part of superior orbital
fissure.
• The lateral rectus has an additonal small tendinous head that arises
from the orbital surface of greater wing of sphenoid.
• The superior oblique arises from the undersurface of lesser wing of
sphenoid whereas the inferior oblique arises from the orbital surface
of maxilla.

13. EOM Contd…..
Insertion of extraocular muscles=
• The recti are inserted into the sclera a little posterior
to the limbus. The average distances of the insertions
from the cornea are: superior 7.7mm, inferior 6.5mm,
medial 5.5mm, lateral 6.9mm.
• The tendon of SO passes through a fibrocartilaginous
pulley attached to the trochlear fossa of the frontal
bone, it is inserted into the sclera behind the equator
of the eyeball between SR AND LR
• The inferior oblique is inserted close to the SO a little
below and posterior to latter..