anatomy

136. • Iris
• The colored anterior part of the eye
• Posses pigment cells; determine eye color
• Form circular curtain with opening at center called pupil
• Regulates the amount of light entering the eye by 2 muscles
• Sphincter pupillae (ring muscle)
• Dilator pupillae (radial muscle)
• Close vision and bright light – pupils constrict
• Distant vision and dim light – pupils dilate
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137. Sensory Tunic: Retina
• A delicate membrane between choroids and vitreous body
• Composed of two layers:
• Pigmented layer – the outer layer that absorbs light and prevents its scattering
• Neural layer – inner layer which contains:
• Photoreceptors that transduce light energy
• Bipolar cells and ganglion cells
• Amacrine and horizontal cells
• Neural layer ends at posterior edge of ciliary body in a wavy border called ora serrata retinae
• Beyond ora serrata it is continued as a non-nervous layer
• Ganglion cell axons: run along the inner surface of the retina and leave the eye as the optic nerve
• The optic disc:
• A circular depression at the site where the optic nerve leaves the eye
• Lacks photoreceptors; it is insensitive to light thus called the blind spot
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138. • Photoreceptors
• Rods:
• Respond to dim light
• Cones:
• Respond to bright light
• Have high-acuity color vision
• Lateral to optic disc at posterior pole is a small oval yellowish area called macula
lutea; at center is depressed area called fovea centralis (site of maximum acuity
of vision)
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139. • Blood Supply to the Retina
• The neural retina receives its blood supply from two sources
• The outer third receives its blood from the choroids
• The inner two-thirds are served by the central artery and
vein (enter eye with optic nerve)
• Small vessels radiate out from the optic disc; can be seen
with an ophthalmoscope
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140. Inner Chambers and Fluids
• The lens separates the internal eye into anterior and posterior segments
• Posterior segment
• Filled with a clear gel called vitreous humor (body)
• Vitreous humor is not replaced continuously
• functions
• Transmits light
• Supports the posterior surface of the lens
• Holds the neural retina firmly against the pigmented layer
• Contributes to intraocular pressure
• Anterior Segment
• Composed of two chambers
• Anterior – between the cornea and the iris
• Posterior – between the iris and the lens
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141. • Aqueous humor
• A plasma like fluid that fills the anterior segment
• Produced by ciliary processes (capillaries)
• Drains at iridocorneal angle via the canal of Schlemm
• Function
• Produce intraocular pressure
• Provide nutrient and removes wastes for cornea and lens
• Interference with drainage results in an increase in intraocular pressure (glaucoma)
which lead to atrophy of retina
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142. 142

143. The Lens
• A biconvex, transparent, flexible, avascular structure
• Allows precise focusing of light onto the retina
• Is composed of epithelium and lens fibers; encapsulated
• Held in position by radially arranged zonular fibers called suspensory
ligament of lens
• Contraction of ciliary muscles relax them and change curvature of lens
• With age, the lens becomes more compact and dense and loses its
elasticity
• Refractive media of the eye
• Light waves pass through cornea, aqueous humor, lens and vitreous body
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144. Muscles of orbit
• Extraocular muscles
• Levator palpebrae superioris
• Elevates upper eye lid
• Origin – roof of orbit
• Insertion – tendon split into superior and inferior lamina
• Superior lamina – insert into skin
• Inferior lamina – contains some smooth muscle fibers (superior tarsal muscle) which insert into tarsal plate
• Innervation
• Superior fibers – oculomotor nerve
• Superior tarsal muscle – fibers from cervical sympathetic trunk
• Applied anatomy
• CN III palsy – upper eye lid cannot be raised voluntarily
• Cervical sympathetic trunk interruption – superior tarsal muscle is paralyzed causing drooping of eye lid
(ptosis)
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145. 145

146. • Recti muscles
• 4 recti: superior, inferior, medial and lateral
• origin – from common tendenous ring surrounding optic canal and middle part of
superior orbital fissure
• insertion – sclera of eye ball posterior to sclerocorneal junction
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147. Oblique muscles
• superior oblique
• origin – body of sphenoid, superomedial to common ring
• insertion – tendon pass through a fibrous pulley (trochlea) and pass downwards and
backwards and insert into sclera at posterosuperior aspect
• inferior oblique
• origin – orbital surface of maxilla
• insertion – pass upwards and backwards and insert below superior oblique
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148. • Nerve supply
• superior oblique – CN IV
• lateral rectus – CN VI
• the rest – CN III
• Actions: rotate eye ball around 3 axes
• superior rectus – elevates and rotates medially
• inferior rectus – depress and rotate medially
• medial rectus – medial rotation (adduct)
• lateral rectus – lateral rotation (abduct)
• superior oblique – downward rotation and laterally
• inferior oblique – upward rotation and laterally
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150. 150

151. 151

152. 152

153. 153

154. 154

155. 155

156. 156

157. Blood vessels of the orbit
• Ophthalmic artery
• Branch of internal carotid artery after leaving the cavernous sinuses; enter the orbit through the
optic canal below the optic nerve; become lateral to the optic nerve; finally positioned above the
nerve
• Branches
• Central artery of the retina – enter optic nerve; at optic disc; divide and spread on retina
• Ciliary arteries - supply the eye ball; anterior groups enter the eye ball at the corneoscleral junction ;
the posterior groups enter around the optic nerve
• Muscular
• Lacrimal artery – supply lacrimal gland, conjunctiva and eye lid
• Anterior and posterior ethmoidal – for nasal mucosa and sinuses
• Supratrochlear and Supraorbital – supply forehead
• Medial palpebral – eye lid
• Dorsal nasal branches – supply upper nose
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158. 158

159. • Ophthalmic veins
• Superior ophthalmic vein
• Accompany the artery, receive tributaries
• Pass through superior orbital fissure and ends in cavernous sinus
• communicate with facial vein
• Inferior ophthalmic vein
• Begins on floor of orbit, receive tributaries
• Ends in superior ophthalmic or cavernous sinus
• communicate with pterygoid venous plexus
• central vein of retina
• ends in cavernous sinus or superior ophthalmic vein
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160. 160

161. • Applied anatomy
• cavernous sinus communicate with veins of the face through superior and inferior
ophthalmic veins; all are valve less thus blood flow in either direction which may
result in spread of infection to cavernous sinus
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162. Nerves of orbit
• Optic nerve (CN II)
• nerve of sight
• made up of axons of cells in ganglionic layer of retina
• emerge from eye ball medial to posterior pole
• runs posteromedially and pass through optic canal to cranial cavity and forms
optic chiasma
• entirely enclosed in meningeal sheaths
• relations
• apex – recti muscles surround it
• ciliary ganglion between it and lateral rectus
• inferomedially – pierced by central artery and vein
• superiorly – ophthalmic artery, vein and nasociliary nerve
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163. • Occulomotor nerve (CN III)
• Course - on the lateral wall of the cavernous sinus and divide into superior and inferior
divisions
• both divisions enter cranial cavity through superior orbital fissure inside the tendinous
ring
• Superior division – supply superior rectus and levator palpebrae
• Inferior division – supply medial rectus, inferior rectus and inferior oblique and gives
branch to ciliary ganglion
• Send parasympathetic preganglionic fiber to ciliary ganglion. The postganglionic fiber
from the ciliary ganglion supply sphincter pupilae and ciliary muscles
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164. 164

165. • Ciliary ganglion
• Parasympathetic ganglion in the course of oculomotor nerve
• Lies at the apex of the orbit between the optic nerve and lateral rectus muscle
• Roots
• Motor root
• From nerve to inferior oblique
• Contains parasympathetic preganglionic fiber originate in the mid brain (Edinger-
westphal nuclei) → oculomotor → nerve to inferior oblique → ciliary ganglion
• Post ganglionic fibers pass through short ciliary nerves and supply sphincter pupilae
and ciliary muscles
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166. • Sensory root
• from nasociliary nerve
• contains sensory fibers from eye ball
• fibers do not relay in the ganglion
• sympathetic root
• from plexus around the internal carotid artery
• contains postganglionic fibers from superior cervical ganglion
• fibers do not relay, pass in short ciliary nerves to supply blood vessels and dilator
pupilae
• Branches – 8 -10 short ciliary nerves, enter sclera around optic nerve
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167. 167

168. • Trochlear nerve (CN IV)
• Course
• lateral wall of the cavernous sinus below CN III
• Enter orbit through superior orbital fissure lateral to the tendinous ring
• Passes in the orbit superior to the levator palpabrae muscle medially and supply the superior
oblique muscle
• Abducent nerve (CN VI)
• Passes inside the cavernous sinus inferolateral to the internal carotid artery
• enter the orbit through the superior orbital fissure inside the tendinous ring
• directs laterally to supply the lateral rectus
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169. 169

170. • Ophthalmic nerve
• The medial and the smallest branch of the CN V
• Purely sensory
• Course: origin from trigeminal ganglion, found on the lateral wall of cavernous sinus below the
trochlear and oculomotor nerve
• Branches - lacrimal, frontal and nasociliary
• Exit through superior orbital fissure to enter orbital cavity
• lacrimal nerve
• Enter the orbit on the lateral part of superior orbital fissure outside the tendinous ring
• moves on the lateral part of the orbit above the lateral rectus muscle
• It passes deep into the lacrimal duct, pierce the orbital septum to the eye lid
• Distribution - lacrimal gland, lateral conjunctiva and lateral part of the upper eye lid
• receive branches from Zygomaticotemporal nerve , a fiber carrying parasympathetic secretomotor
fiber from greater petrosal nerve to lacrimal glands
• its own fibers are sensory to the gland
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171. 171

172. • Frontal nerve
• enter the orbit through the superior orbital fissure on the lateral part of the
orbital wall, out side the tendinous ring, medial to the lacrimal nerve
• Course - superior to the levator palpabrae superioris, below the roof of the orbit.
Before reaching the orbital margin, gives two terminal branches; supratrochlear
and supraorbital.
• Supraorbital nerve – leave to the forehead through supraorbital foramen/notch,
supply skin & conjunctiva of the middle part of superior eye lid and skin of
anterolateral forehead and scalp to vertex
• Supratrochlear nerve – leave the orbit lateral to trochlea and supply skin and
conjunctiva of the medial part of superior eye lid & skin of anteromedial part of
forehead
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173. • Nasociliary nerve
• Enter orbit through superior orbital fissure in the ring
• Course - above CNII, directs anteromedially, b/n superior oblique and medial rectus
• Branches
• Sensory root to the ciliary ganglion and supply the eyeball
• 2 or 3 long ciliary nerves - contain sympathetic fibers from superior cervical ganglion to supply the dilator
papillae
• Posterior ethmoidal nerves - passes through the posterior ethmoidal canal and supply air sinuses in the
sphenoid and ethmoid bones
• Anterior ethmoidal nerves - one of the terminal branch of the nasociliary nerve, enter the cranial cavity
through the anterior ethmoidal canal, and then leaves the cavity through the cribrifom plate of the
ethmoid to enter the nasal cavity
• Internal nasal branch – mucus membrane of the nose
• External nasal branch - leave the nasal cavity b/n the nasal bone and cartilage, supply the lower ½ of the
skin of the nose
• Infratrochlear – 2nd terminal branch, leave the orbit to enter the face above the medial palpebral ligament;
supply medial part of skin and conjunctiva of both eyelids and skin of the upper ½ of the nose
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174. 174

175. • Infra orbital nerve
• Continuation of maxillary nerve, enter orbit through inferior orbital fissure
• Runs on floor of orbit through infraorbital groove and canal
• Emerges on face through infraorbital foramen and divide into palpebral, nasal
and labial branches
• Branches
• Middle superior alveolar nerve – supplies upper premolar
• Anterior superior alveolar nerve – supplies upper incisor and canine teeth and maxillary sinus
• Terminal branches – supply upper lip, nose and lower eye lid
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176. • Zygomatic nerve
• Origin - maxillary nerve in the infratemporal fossa
• Entry to the orbit - inferior orbital fissure
• Course in the orbit - on the lateral wall of the orbit b/n the bone and the
periosteum
• Branches
• Zygomaticotemporal - leave the orbit through a foramen having the same name to join the
temporal fossa. It sends fiber to the lacrimal nerve and lacrimal gland in the orbit. It supplies
skin of anterior ½ of the temple and the adjoining scalp.
• Zygomaticofacial - leave the orbit through zygomaticofacial foramen to the face; supply the
skin of the cheek
• Sympathetic nerve
• Arise from internal carotid plexus
• Enter orbit through nasociliary nerve, plexus around ophthalmic artery, or directly
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