Transcript 8-Orbit II
ORBIT II Dr. Mujahid Khan Blood Supply Ophthalmic Artery: • It is a branch of Internal Carotid Artery • Emerges from cavernous sinus • Runs forward lateral to the optic nerve • Reaches the medial wall of the orbit • Gives away several branches Central Artery of Retina • Is a small branch • Pierces the meningeal sheath of optic nerve & gain entrance to the nerve • Enters the eyeball at the centre of optic disc • Divides into 2 branches called end arteries Ciliary Arteries • Can be divided in two groups • Anterior group enters the eyeball near the corneoscleral junction • Posterior group enters the eyeball near the optic nerve Lacrimal Artery • It supplies the lacrimal gland Supratrochlear & Supra orbital Arteries • Are distributed to the skin of the forehead Ophthalmic Veins • Superior ophtalmic vein communicates in front with the facial vein • Inferior ophthalmic vein communicates with the pterygoid plexus through the inferior orbital fissure • Both the veins pass backward through superior orbital fissure & drain into cavernous sinus Lymph vessels • No lymph nodes or vessels are present in the orbital cavity The Eye • Eyeball consists of 3 coats: • The fibrous coat • The vascular pigmented coat • The nervous coat Fibrous Coat • Made up of posterior opaque part, the sclera & anterior tranparent part cornea Sclera • Composed of dense fibrous tissue • Pierced by optic nerve posteriorly and is fused with the dural sheath of the nerve • Lamina Cribrosa is the area of sclera that is pierced by optic nerve fibers • Also pierced by ciliary arteries & nerves • Is continuous in front with the cornea Cornea • Is transparent • Responsible for refraction of light entering the eye • It is in contact with the aqueous humor posteriorly Vascular Pigmented Coat • Consists from behind forward: • Choroid • Ciliary body • Iris Choroid • Is composed of an outer pigmented layer and an inner highly vascular layer Ciliary Body • • Is continuous posteriorly with choroid Anteriorly lies behind the peripheral margin of iris • Composed of: • Ciliary ring Ciliary process Ciliary muscle • • • Ciliary ring is the posterior part of the body, has shallow grooves, Ciliary striae • Ciliary processes are radially arranged folds connects the suspensory ligaments of the lens • Ciliary muscle is composed of meridianal and circular fibers of smooth muscles Iris • Is a thin, contractile, pigmented diaphragm • Has central aperture called pupil • Is suspended in the aqueous humor between the cornea and lens • Its periphery is attached to the anterior surface of the ciliary body • Divides the space between cornea and lens into anterior & posterior chambers Nervous Coat or Retina • Consists of an outer pigmented layer & inner nervous layer • Its outer surface is in contact with choroid • Inner layer in contact with the vitreous body • Posterior three-fourths is the receptor organ • Macula lutea is the oval yellowish area in the center of the posterior part • Fovea centralis is the central depression Retina • Optic nerve leaves the retina to medial side of macula lutea by the optic disc • Optic disc is depressed at its center, where it is pierced by central artery • Optic disc is insensitive to light and referred as blind spot • Optic disc is seen to be pale pink with ophthalmoscope examination Optic Nerve • Enters the orbit from middle cranial fossa by passing through the optic canal • Accompanied by ophthalmic artery • It is surrounded by sheaths of pia, arachnoid and dura maters • It runs forward and laterally within the cone of the recti muscles Optic Nerve • Pierces the sclera at a point medial to the posterior pole • The meninges fuse with the sclera • The subarachnoid space extends forward as far as the eyeball • A rise in pressure of the CSF within the cranial cavity is transmitted to the back of the eyeball Nasociliary Nerve • Arises from the ophthalmic division of the trigeminal nerve in the lateral wall of the cavernous sinus • Enters the orbit through the lower part of the superior orbital fissure • Crosses above the optic nerve with the ophthalmic artery • Ends by dividing into the anterior ethmoidal and infratrochlear nerves Branches of Nasociliary Nerve • Communicating branch to the ciliary ganglion • The long ciliary nerves (2-3 in number) • Posterior ethmoidal nerve • Infratrochlear nerve • Anterior ethmoidal nerve • External nasal nerve Ciliary Ganglion • It is about the size of a pinhead • It is a parasympathetic ganglion • Situated in the posterior part of the orbit on the lateral side of the optic nerve • Receives its preganglionic parasympathetic fibers from the oculomotor nerve via nerve to inferior oblique • The postganglionic fibers leave the ganglion in the short ciliary nerves Contents of the Eyeball • Aqueous Humor • Vitreous body • lens Aqueous Humor • Clear fluid fills the ant. & post. Chambers • Is a secretion from ciliary processes • Drained away through canal of Shlemm • Obstruction to its draining results in glaucoma • Glaucoma causes degenerative changes in the retina Aqueous Humor • Supports the wall of the eyeball • Maintains its optical shape • Nourishes the cornea and lens • Removes the products of metabolism Vitreous Body • Is a tranparent gel • Fills the eyeball behind the lens • Hyaloid canal is a narrow channel runs through it extends from optic disc to posterior surface of the lens • Canal is filled with hyaloid artery in fetus • Contribute in the magnifying power of eye • Supports posterior surface of lens Lens • Is a transparent, biconvex structure • Enclosed in a transparent capsule • Situated behind the iris & in front of vitreous • Encircled by ciliary process • Assumes globular shape due to tense elastic capsule • Its circumference attached to the ciliary process by suspensory ligament Lens • Suspensory ligament keeps the elastic lens flattened • Ciliary muscle contracts to accommodate the eye for close objects • Lens becomes dense & less elastic in advance age resulting in presbyopia • Glasses are used to overcome presbyopia