Lecture 8 - Contents Of The Orbit PDF

The Orbit CONTENTS: Eyeball and associated muscles Nerves Blood vessels Fat Lacrimal apparatus EYE STRUCTURE The eye contains three layers or tunics: Retina Choroid or Middle (Vascular) Coat External or Fibrous Coat EYE STRUCTURE - Retina  The retina is the innermost tunic of the ey...

The Orbit CONTENTS: Eyeball and associated muscles Nerves Blood vessels Fat Lacrimal apparatus EYE STRUCTURE The eye contains three layers or tunics: Retina Choroid or Middle (Vascular) Coat External or Fibrous Coat EYE STRUCTURE - Retina  The retina is the innermost tunic of the eyeball.  It is a thin, delicate membranous supporting structure covered externally by the choroid and internally by the vitreous body.  The retina is supplied by the central artery of the retina, a branch of the ophthalmic artery, which runs through the optic disc. EYE STRUCTURE - Retina The retina contains two layers: An outer pigment cell layer An inner neural layer which ends anteriorly at the posterior margin of the ciliary body. The outer layer continues past this margin. EYE STRUCTURE - Retina - Contents  The optic papilla disc is the slightly elevated region posterior to the eye, just medial to the posterior pole  Site at which the optic nerve exits. It contains no photoreceptors - it is a “blind spot”  The branches of the central retinal vessels radiate out from the optic papilla.  The retina is most adherent to the optic papilla. EYE STRUCTURE - Retina - Contents  Papilledema is a condition in which the disc is swollen and has indistinct margins.  The optic nerve, which exits at the disc, is covered by the same meningeal layers that cover the brain, therefore increased pressure in the CSF can affect the disc. EYE STRUCTURE - Retina - Contents  Papilledema can occur because of increased intracranial pressure secondary to hemorrhage or a tumor.  On the other hand, increased intraocular pressure (IOP) secondary, for example, to glaucoma, can result in “cupping” of the optic disc. Normal IOP = 10-21 mmHg (average = 16 mmHg) EYE STRUCTURE - Retina - Contents The macula lutea (“yellow spot”) is a small, oval, yellowish area located lateral to the optic papilla. The fovea centralis is the central, depressed part of the macula. It is the area of most acute vision. EYE STRUCTURE  Retinal Detachment  Occurs when the outer pigmented and inner neural layers of the retina separate.  Detachment may occur from direct trauma, or it may have no overt cause at all.  Individuals who are nearsighted, due to a more elliptical eyeball, are at higher risk for detachment because their retina is typically thinned or “stretched” more than that of the normal eye.  Reattachment possible by laser. EYE STRUCTURE  Macular Degeneration (ARMD – Age Related Macular Degeneration)  It is the physical deterioration of the macula lutea.  Leading cause of blindness in developed countries.  Etiologies include:      Aging Diabetes Intraocular infections Heredity Trauma  The first symptom is loss of visual acuity.  Other visual problems include:  Straight lines appear      distorted or wavy Dark, blurry area of vision losing the center of the visual field Diminished color perception “Floaters” Dry eyes Cataracts  At present, there is no cure. Vascular Tunic Choroid Ciliary body Iris EYE STRUCTURE - Choroid (Uvea) This is a highly vascular dark layer located between the sclera and the retina. Capillaries into this layer supply deeper layer of the retina by diffusion. EYE STRUCTURE - Choroid (Uvea)  The ciliary body is the anterior, thickened portion of the choroid.  It is connected to the lens by suspensory ligaments.  It possesses folds on its internal surface called ciliary processes that secrete aqueous humor, a watery fluid that fills the anterior and posterior chambers of the eye. EYE STRUCTURE - Choroid (Uvea)  The ciliary body also contains the ciliary muscle which upon contraction allows the lens to bulge (accommodate) by relaxing the suspensory ligaments.  The ciliary muscle is a smooth muscle innervated by parasympathetic nerves from the oculomotor nerve which synapse in the ciliary ganglion. CN III NUCLEUS PRE-GANGLIONIC FIBERS CILIARY MUSCLE CILIARY GANGLION POST-GANGLIONIC FIBERS EYE STRUCTURE Accommodation  Distant Vision (un-  Near Vision accommodated)  Ciliary muscle is relaxed  Lens is flat because it is stretched by taut suspensory ligaments (accommodated)  Ciliary muscle is contracted  Lens is rounded because tension on the lens is released  Enhanced focus EYE STRUCTURE Accommodation  Presbyopia  Cycloplegia  Age-related inability to read  Paralysis of the ciliary close-up whereby the lens remains flattened in spite relaxation of the suspensory ligaments by ciliary muscle contraction.  In this condition the lens has lost elasticity and can no longer focus on close-by objects (accommodate) body muscle, resulting in loss of accommodation.  May result in accompanying mydriasis. This is especially true due to topical application of muscarinic antagonists such as atropine. ACCOMMODATION Ciliary muscle is contracted Lens is rounded because tension on the lens is released Enhanced focus Near vision UN-ACCOMMODATION Ciliary muscle is relaxed Lens is flat because it is stretched by taut suspensory ligaments Distant vision EYE STRUCTURE - Choroid (Uvea) The iris is the colored circular membrane that lies between the cornea and the lens. Its central opening, the pupil, allows for light to pass through. EYE STRUCTURE - Choroid (Uvea) The iris contains two smooth muscles: The dilator pupillae muscle Dilates the pupil Innervated by sympathetic nerves The sphincter pupillae muscle Constricts the pupil Innervated by parasympathetic nerve fibers from CN III RUBEOSIS IRIDITIS Rubeosis iridis is a medical condition of the iris of the eye in which new abnormal blood vessels (i.e. neovascularization) are found on the surface of the iris. This condition is often associated with diabetes in advanced proliferative diabetic retinopathy. Other conditions causing rubeosis iridis include central retinal vein occlusion, ocular ischemic syndrome, and chronic retinal detachment. EYE STRUCTURE  Cataracts  Small opacities within the lens that, over time, may coalesce to completely obscure the lens.  They are a major cause of blindness worldwide.  Most cases occur as a result of aging, although other factors include diabetes, intraocular infections, excessive UV light exposure, and galucoma. EYE STRUCTURE - Fibrous Coat This outer layer is made up of the sclera and the cornea. The sclera is the white, dense connective tissue portion. The cornea is the anterior, transparent portion. EYE STRUCTURE - Fibrous Coat  The corneal reflex is a protective reflex.  It elicits a bilateral response - touching one side results in blinking both eyes.  The afferent or sensory limb is the trigeminal nerve (ciliary branches of the nasociliary nerve).  The efferent limb is the facial nerve. CORNEAL ABRASIONS FLUORESCEIN STAIN SCLERITIS CHAMBERS OF THE EYE  The internal space of the eye is subdivided by the lens into two separate cavities:  Anterior cavity  Posterior cavity  The anterior cavity is:  the space anterior to the lens and posterior to the cornea  The iris of the eye subdivides the anterior cavity further into two chambers:  Anterior chamber is between the iris and cornea  Posterior chamber is between the lens and the iris CHAMBERS OF THE EYE Aqueous Humor  The anterior cavity contains aqueous humor.  Removes waste products and       helps maintain the chemical environment within the anterior and posterior chambers of the eye Secreted into the posterior chamber It flows through the posterior chamber (1) Goes around lens (1) Down through the pupil (2) Into the anterior chamber (3) Leaves the anterior chamber through the canal of Schlemm (scleral venous sinus) to join the venous blood stream CHAMBERS OF(average THE EYE Normal IOP = 10-21 mmHg = 16 mmHg) Aqueous Humor  Glaucoma  Disease characterized by an increased intracoular pressure (IOP > 22 mmHg).  It results from increased production or diminished reabsorption of aqueous humor.  Fluid buildup causes a posterior dislocation of the lens and substantial increase in pressure in the posterior chamber. CHAMBERS OF THE EYE Vitreous Humor The posterior cavity is posterior to the lens and anterior to the retina. Transparent, gelatinous vitreous body secreted by the ciliary processes of the ciliary body. The vitreous humor completely fills the space between the lens and the retina. MUSCLES OF THE EYEBALL Muscles of the Eyeball  Superior oblique  Lateral rectus  Superior rectus  Inferior rectus  Inferior oblique  Medial rectus NERVE SUPPLY: SO4 – LR6 – R3 Muscles of the Eyeball (Summary) Transverse axis Vertical axis Elevation – SR, IO Abduction – LR Depression – IR, SO Adduction - MR Anteroposterior axis Convergence Intorsion – SO Extorsion - IO MR Muscles of the Eyeball (Summary)  Oblique muscles  Best elevators/depressors when the eye is adducted  Rectus muscles  Best elevators/depressors when the eye is abducted  Therefore, muscles responsible for eye movement in different positions of gaze are: Oblique muscles in adduction Rectus muscles in abduction MUSCLE INNERVATION FUNCTION [MAIN ACTION (S)] SUPERIOR RECTUS CN III ELEVATES EYE INFERIOR RECTUS CN III DEPRESSES EYE INFERIOR OBLIQUE CN III ELEVATION & EXTORSION OF EYE MEDIAL RECTUS CN III ADDUCTS EYE (ONLY) LATERAL RECTUS CN VI ABDUCTS EYE (ONLY) SUPERIOR OBLIQUE CN IV DEPRESSION & INTORSION OF EYE Nerves of the Orbit 1. Optic nerve (CN II): accompanies the ophthalmic artery (ICA). It is a nerve of sight, and it ends in the optic chiasm. 2. Ophthalmic nerve (from V1): sensory nerve. It divides into three branches: Lacrimal nerve = supplies the skin of the lateral upper eyelid 2. Frontal nerve 1. 1. Supraorbital 2. Supratrochlear 3. Nasociliary nerve = enters the orbit via the superior orbital fissure Nerves of the Orbit 3. Oculomotor nerve (CN III): exits the skull via the superior orbital fissure. It divides into: Superior division = superior rectus and levator palpebrae superioris 2. Inferior division = medial and inferior rectus muscles and inferior oblique DAMAGE: - ptosis (paralysis of the levator palpabrae superioris 1. muscle) ( - unopposed action of the lateral rectus and superior oblique muscles (lateral strabismus) - double vision - mydriasis (paralysis of the constrictor pupillae muscle) - inability to accommodate (cycloplegia [paralysis of ciliary muscles]) Trochlear nerve (CN IV): supplies only the superior oblique muscle. It exits via the superior orbital fissure. DAMAGE: patient is asked to look downward with the eye adducted. Limitation of movement indicates paralysis or damage Abducens nerve (CN VI): supplies the lateral rectus muscle. Exits via the superior orbital fissure. DAMAGE: Inability to abduct the eye which results in Medial strabismus Ciliary Ganglion  They are parasympathetic ganglia at the back of the orbit, lateral to the optic nerve, and medial to the lateral rectus muscle.  The occulomotor nerve gives pre-ganglionic parasympathetic fibers to the ciliary ganglion, which then synapse with neurons in the ciliary ganglion, and post-ganglionic fibers go to ciliary muscle and sphincter pupillae by short ciliary nerves.  Sympathetic fibers from the SCG hitch a ride with the internal carotid artery to the ciliary ganglion without synapsing and then by short ciliary nerves go to the dilator pupillae, and palpebral or tarsal muscles. Blood Vessels of the Orbit  Ophthalmic artery: (ICA). Travels in the optic canal inferior to the optic nerve.  BRANCHES:  Central artery of the retina  Posterior ciliary artery  Supraorbital artery  Supratrochlear artery  Dorsal nasal artery  Anterior and posterior ethmoidal arteries  Lacrimal artery- which gives a branch, the recurrent meningeal artery. It anastomoses with the middle meningeal artery.  Ophthalmic veins:  The orbit is drained by the superior and inferior ophthalmic veins. The superior ophthalmic vein joins the facial and drains into the cavernous sinus.