1.anatomy and physiology

ANATOMIC AND PHYSIOLOGIC OVER VIEW*Surgical specialties are exercise in applied

anatomy and physiology1. THE EYE BALL.2. OCULAR ADNEXAL TISSUES.3. ORBIT AND ITS CONTENTS.4. THE AFFERENT AND EFFERENT VISUAL PATHWAYS.

1-4 form the visual system Structural components.

THE EYE BALL (GLOBE)

HAS THREE LAYERS AND CAVITIES1. The three layers (Coats) of eye ball:A) The fibrous (outer) layer-Cornea/sclera.a) Cornea transparentb) Sclera opaque representing the white appearance of the eye ballFunction: -Along with the IOP, maintains the Shape, stability of the eye ball- Optical

B) The vascular (Middle) layer-Iris/Ciliary body/Choroid--------Uveal tissues.-Brown to dark-brown in appearance.

e.g. -The iris represent the brown appearing part behind the transparent cornea.Functions:-Nutrition for the inner layers of the eye ball.-Provide dark environment of the eye ball cavity to avoid image degradation. E.g. film developing

C.Neuro Sensory (inner) layer-Retina/ RPE.Functions:-transducers the electromagnetic form of image to neuronal impulse to be dispatched to the brain.

THE THREE CAVITIES:

A. Anterior chamber-Between the Cornea and anterior face of the Iris filled with the Aqueous-fluid.B. Posterior chamber:- Between the posterior face of the Iris and lens. Is also filled with the aqueous.*A and B communicate through the pupil.C. Vitreous cavity

Between the Lens and retina Filled with Vitreous (jelly fluid)

Significance:

1. Aqueous from the ciliary body------P/C----Pupil----A/C—Drainage channel----Episcleral vein---systemic circulation.2. Balance between secretions and drainage--------Normal intraocular pressure (10-20mmHg)This make the eye ball a pressurized chamberDecreased drainage------Increased intraocular pressure (ocular hypertension) ---- (Resultant damage to optic nerve)----Glaucoma.Aqueous provide nutrient material to the avascular ocular structures such as the lens and the cornea.

OCULAR ADNEXAL STRUCTURES

1. The lids/conjunctiva

2. The lacrimal system

THE LIDS and CONJUNCTIVA:

THE LIDS;A. function:*Protective shield for the eye ball-Prevent contact with foreign material.-Tear film wetting for cornea and conjunctiva-Sense approaching material using the cilia(eye lashes).B. Anatomy 1. Has four layers:-Skin, muscle, tarsus, conjunctiva2. The upper and lower lids

Upper lid elevators are:-Levator muscle-Mullers muscleLower lid elevators:-Inferior rectus facia-Inferior tarsal muscleLid closer:-Orbicularis oculi muscle innervated by CN VII.

3. Palpebral fissure:-The space between the two lids.

-The two lids met at the medial and lateral canthus.

4. Cilia/Eye Lashes:-Located at the outer edge of the lid margin.-Forward and upward directed in the upper lid-Forward and down ward directed in the lower Lid*Sense approaching objects to the eye like antenna.5. Punctum:-Upper peripheral opening of the lacriaml draininage system.-Localized at the medial end of lid margin.

THE CONJUNCTIVA

-Covering the deeper surface of the lids (Palpebral/tarsal conjunctiva) and the anterior surface of the eye ball excluding the cornea (Bulbar conjunctiva).-Transparent mucous membrane.-The area where the bulbar conjunctiva became continuous with palpebral conjunctive is called Conjunctival fornix.-There are a number of mucin secreting goblet cells in the conjunctiva.-Goblet cell damage result in dry eye despite a normal functioning lacrimal gland

THE LACRIMAL SYSTEM

Has secretor and drainage part.1. Secrotary system:Tear film is composed of three layers:-Oily/aqueous/Mucin layera) Mucin: Goblet cells of conjunctiva.b) Oily: sebaceous mebomian gland, gland of zeiss and moli.c) Aqueous: Main lacrimal gland, glands of Kraus and wolfring.Main lacriaml gland is located at the anterior upper temporal aspect of orbit

Tear film function:

Oily part:-Protect tear evaporation. Mucin layer:-Alter the hydrophobic corneal surface to Hydrophilic so that wetting is facilitated.Aqueous Part:

-Provide nutritive and immunologic substances.General function:-Nutrition-Optical-Immunologic-Wash out tiny foreign bodies.

DRAINAGE SYSTEM:

Pumps and drain the tear to nasal cavity.Drainage canal:-Composed of Punctai, canaliculi, lacrimaL sac and NLDa) Puncta:-Small opening at medial end of each lids.b) Canaliculi:-Continuation of the puncta 2 mm vertical and 8mm horizontal coursing to lacriasml sac.c) Lacrimal sac:-Cystic structure on the lateral aspect of nasal bridge.d) Nasolacrimal duct:-cross the nasal bone to nasal cavity

Lacrimal pumping:

Tear fluid drains from the surface of the eye through the draining system to nasal cavity.-depend on the potency of each segments of the drainage channel.-Is aided by a lacriaml pump mechanism.

a) Normal lid apposition to the eye ball.b) Zipp like lid closure (orbicularis oculi

muscle).

Failure lead to;

Epihora: tearing due to drainage system failure.A) Pump failure. E.g. Facial palsy.B) Drainage canal obstruction.-Difference from tearingTearing is due to irritative or emotional secretion of tear.

THE ORBIT AND ITS CONTENTS

-Formed by: the following seven bones.Maxillary, frontal, Zygomatic, ethimoid, nasal, sphenoids-Pear shaped with base and apex.Contents:-Eye ball, EOMs, Blood vessels, Nerves, Adipose tissue (Cushion of eye ball)Surrounded BY:-Para nasal sinus: Maxillary sinus, frontal sinus, sphenoid sinus

Parts:

1. Orbital Walls:-Medial, lateral, floor and roof2. Rims:-Superior, inferior, medial and lateral3. Canals and fissures:-Orbit communicate with the surrounding structures such as the cranial cavity, sinus and nasal cavity

a. Fissures.

1. Supra orbital fissure-connects the orbital cavity with the cranial fossaTransmit:a) Ocular motor nerves III, IV,VIOcular sensory CN V1Ophthalmic sympatheticOrbital venous draining2. Inferior orbital fissure:Transmits: a) Parasympathetic to lacrimal gland. b) Collateral mengial artery.

b. Canals:

1. Optic canal to anterior cranial fossaTransmit optic nerve, ophthalmic artery.2. Nasolacrimal duct:

-Connect the orbital cavity with the nasal cavity

THE AFFERENT AND EFFERENT VISUAL PATHWAYSTHE AFFERENT AND EFFERENT VISUAL PATHWAYS-Visual perception is a function of the brain.

-Humans are binocular and foveated.

-Both eyes forms separate image of the same object but seen singularly.

I AFFERENT VISUAL PATHWAY:

Retina:a) Cells /layers:

-Receptors (rods and cones)-Bipolar cells-Ganglion cells-Nerve fibers bundles

b) Topography:Central---30 degree (Fovea 10 degree).Peripheral-----> 30 degree.DiscImaginary line passing through the foveaTemporal, nasal, upper and lower retina

2. The optic nerve:-Run from the globe to the chiasma.-Myelinated.

3. Chiasma-Where the two optic nerves merge.-Fibers decussate

4. Optic tract:-Run from the chiasma to LGB-Fibers synapses occur.

5. Radiation-From the LGB to primary visual cortex

• 6. Visual association areas-V2, V3, V4-Interconnection• 7. Ventral and dorsal pathways

-To parietal, frontal, occipital lobe-Orientation and recognition.

II. EFFERENT VISUAL PATHWAYS (OCULAR MOTOR SYSTEM)

• Starts at the various levels and regions of the brain.

• Converge to the brain stem where the gaze centers and the ocular motor nuclei are localized.

GAZE CENTERS:

• Two major centers:-HGC and the VGC.e.g. PPRF, MLF

OCULAR MOTOR NUCLEI AND THEIR PERIPHERAL NERVES.

1. Oculomotor nerve (CN III)

2. Abducent nerve (CN VI)

3. Trochlear nerve (CN IV)

Extra ocular muscles:

• Six extra ocular muscles.• peripheral end of the efferent ocular motor system(ocular motility)1. Medial rectus----Adductor

2. Superior rectus---Elevator3. Inferior rectus----Depressor4. Inferior oblique—Extorter5. Superior oblique---Intorter6. Lateral rectus-----Abduction-Muscle 1 to 4 supplied by the oculomotor nerve-Superior oblique supplied by the trochlear nerve.-Lateral rectus supplied by the abducent nerve.