Orbit Anatomy PDF

 Two symmetrical pyramidal bony cavities or sockets in the skull.  Apex of pyramid is directed posteriorly, medially, and slightly upwards.  Medial walls of the two orbits are parallel to each other and to the sagittal plane while  Lateral wall diverges at an angle of 45 degrees to the medial...

 Two symmetrical pyramidal bony cavities or sockets in the skull.  Apex of pyramid is directed posteriorly, medially, and slightly upwards.  Medial walls of the two orbits are parallel to each other and to the sagittal plane while  Lateral wall diverges at an angle of 45 degrees to the medial wall and 90 degrees to each other.  The orbit comprises seven bones (maxilla, palatine, zygomatic, sphenoid, frontal, ethmoidal, and lacrimal bones). 1 Roof  Formed by the frontal bone and the lesser wing of the sphenoid.  Antero-laterally there is a slight depression termed “lacrimal fossa” for the orbital part of the lacrimal gland. Orbital walls Roof  Antero-medially, there is a small depression for the trochlea of the SO muscle.  The roof separates the orbit from the anterior cranial fossa and frontal lobe of the brain. 2 Lateral wall  The thickest wall of the orbit. It is formed by the zygomatic bone and the greater wing of the sphenoid.  Separated from the roof posteriorly by superior orbital fissure. 3 Floor  Formed by maxillary, zygomatic, and palatine bones.  It is separated from the lateral wall posteriorly by the inferior orbital fissure.  The floor separates the orbit from the maxillary air sinus. 4 Medial wall  The thinnest wall of the orbit.  It is formed by maxilla, lacrimal, ethmoid, and body of sphenoid bones.  The ethmoid is the thinnest bone separating the orbit from the ethmoidal sinus.  Antero-medial lies the lacrimal groove (for the lacrimal sac), continuous inferiorly with the nasolacrimal canal.  Optic canal  4-10 mm long canal that lies close to the apex of the orbit.  It transmits ① Optic nerve ② Meningeal coverings ③ Ophthalmic artery ④ Sympathetic plexus around Artery  lies between the roof and lateral wall connecting the orbit to the middle cranial fossa.  Lies between the roof and lateral wall connecting the orbit to the middle cranial fossa.  The structures passing through are: ① Lacrimal nerve ② Frontal nerve ③ Trochlear nerves ④ Superior division of oculomotor ⑤ Nasociliary ⑥ Inferior division of oculomotor ⑦ Abducent nerves  The first 3 structures passes through common tendinous ring while last 4 objects pass outside CTR in addition to superior ophthalmic vein.  Lies between the floor and medial wall.  It connects the orbit to the pterygopalatine and infratemporal fossae.  It transmits: ① Infraorbital nerve Infraorbital vessels ② Zygomatic nerve ③ Orbital branches of pterygopalatine ganglion ④ Inferior ophthalmic vein. ① Eye ball Extraocular muscles Lacrimal gland ② Orbital vessels ③ Orbital nerves ④ Ciliary ganglion ⑤ Orbital fat The orbit contain no lymph nodes as reactive enlargement of lymph nodes with cause disturbances in orbital volume ① Trauma (Commonest) ② Loss of orbital fat (Elderly) ③ Fracture of orbital floor ④ Horner's Syndrome  High myopia  Contralateral enophthalmos  Ipsilateral lid retraction  Shallow orbits  Using plastic ruler or Hertel’s exophthalmometer to measure globe protrusion anterior to the inter-zygomatic line on axial scans at the level of the lens. ① Normally: up to 20 mm. ② Mild: 21-23 mm ③ Moderate: 24-27 mm ④ Severe: 28 mm or more  Axial  Non-axial  ① ② ① ②  Usually at the upper inner part of the orbit.  Characterized by:  Compressible, pulsating.  Exophthalmos.  Aspiration from it reveals CSF.  Orbital imaging show presence of a defect in orbital bones.  Developmental and metabolic abnormalities of the skull and the orbit.  Paget’s disease.  Osteopetrosis.  Oxycephaly.  Hypertelorism  This may be caused by trauma or during retrobulber injection of anesthesia  Surgical emphysema due to fracture medial wall of the orbit caused by blunt orbital trauma.  It results in axial proptosis which increases with nose- blowing.  The eyelids are swollen with a crepitus sensation on pressure.  Pulsating exophthalmos: traumatic rupture of the internal carotid artery inside the cavernous sinus.  It leads to arterialization of venous drainage of the orbit. The patient usually complains of severe pain and, a rumbling sound.  On examination, there is axial proptosis, lid edema, and telangiectasia at the canthus.  On palpation, pulsations and machinery murmurs can be heard on auscultation. Fundus examination shows dilated tortuous veins.  Definitive diagnosis can be achieved by Angiography.  TTT is by endovascular intervention to occlude fistula.  Suppurative Specific  Orbital celleulitis  Tuberculosis  Cavernous sinus thrombosis  Syphilis  Tenonitis  Sarcoidosis  Perostitis, periostial abscess Inflamatory  Leprosy Non-specific Non-suppurative  Orbital Pseudotumour  The main causative organism is Stapylococcal but may be caused by Streptococcal infection.  Precipitated by sinusitis through direct spread.  Constitutional Symptoms: fever, malaise, leukocytosis, debility.  Unilateral chemosis, pain, and lid edema.  Limitation of eye movements (upward and nasal).  Axial proptosis (downward and lateral).  Ocular: blindness due to central retinal artery occlusion (CRAO) and inflammation of the optic nerve.  Spread of infection: leading to meningitis, brain abscess, and cavernous sinus thrombosis. Orbital Cellulitis  Antibiotics: for children up to 15 years (Ampicillin 200 mg/kg & penicillinase- resistant antibiotic) while in adults, we use penicillin 200,000 IU with a penicillinase- resistant antibiotic.  Surgical: surgical drainage, incision into the area of greatest fluctuation avoiding trochlea and lacrimal gland.   Severe supraorbital pain due to affection of trigeminal nerve.  Proptosis is usually bilateral.  Absent pupillary reflex with complete ophthalmoplegia due to affection of oculomotor, trochlear & abducent nerves.  Fundus examination may reveal bilateral engorged retinal veins and papilledema.  Edema behind the ear due to thrombosis of the mastoid emissary vein  The most common benign orbital tumor is hemangioma while the most common malignant orbital tumor is rhabdomyosarcoma.  Dermoid, lipodermoid, epidermoid, teratoma  Vascular tumors eg. Hemangioma.  Neural tumors eg. Optic nerve glioma.  Muscular tumours eg. Rhabdomyosarcoma.  Lacrimal gland tumors.  Lymphatic tumors.  Either extending from surroundings or metastatic tumors.  Autoimmune inflammatory disorder of the orbit, periorbital tissues, thyroid gland, and skin.  Upper eyelid retraction, lid lag, swelling, redness, and exophthalmos.  Graves’ ophthalmopathy is the most common cause of proptosis either unilateral or bilateral.  It occurs most commonly in individuals with Graves’ disease, and less commonly in individuals with Hashimoto’s thyroiditis. It may affect even euthyroid individuals. IT IS CHARACTERIZED BY INFILTRATION OF:  Eyelid: leading to lid retraction (infiltration of Muller’s muscle), swelling, and upper lid lag (delayed downward lid movement on downgaze)  Periorbital tissues: leading to proptosis and conjunctival chemosis.  Cornea: leading to corneal inflammation, ulceration, and blindness  Extraocular muscles: especially MR and IR with involvement of the fleshy part of the muscle sparing its tendons. It leads to restrictive squint with limitation of outward and upward eye movements.  Optic nerve: leading to infiltrative optic neuropathy that may be complicated with secondary optic atrophy. No physical signs or symptoms Only signs, no symptoms (signs limited to upper lid retraction, stare, lid lag and proptosis up to 22 mm) Soft tissue involvement (symptoms and signs) Proptosis Extraocular muscle involvement Corneal involvement Sight loss (optic nerve involvement) NOSPECS: No signs or symptoms; Only signs; Soft tissue; Proptosis; Extraocular muscle; Cornea; Sight loss.  History and clinical examination to detect symptoms and signs.  Measurement of proptosis using a plastic ruler or exophthalmometer.  Thyroid function tests: T3, T4, TSH.  Anti-thyroglobulin, anti-microsomal, and anti- thyrotropin receptor antibodies.  Orbital imaging: US, CT, or MRI to detect soft tissue swelling, muscle involvement, and optic nerve affection.  Spontaneous remission of symptoms may occur within a year.  Control of thyroid hormone levels is the first step in the treatment.  Topical lubrication of the eye is used to avoid corneal damage.  Corticosteroids are efficient in reducing orbital inflammation, but the benefits cease after its discontinuation.  Radiotherapy is an alternative option to reduce acute orbital inflammation.  Eyelid surgery is the most common surgery performed on Grave’s ophthalmopathy patients.  Surgery may be done to decompress orbit, to improve proptosis, and to address the strabismus causing diplopia. Surgery is performed once the person’s disease has been stable for at least six months  The most common cause of proptosis  Not related to thyroid function  Cumulative  Reversible