Ocular Anatomy & Physiology PDF

OCULAR ANATOMY & ( 2) PHYSIOLOGY  TEAR FILM OUTERMOST LIPID LAYER The major functions of the lipids are to: Prevent evaporation of the tears. Provide lubrication so the lids move smoothly over the globe. Contribute to the opti...

OCULAR ANATOMY & ( 2) PHYSIOLOGY  TEAR FILM OUTERMOST LIPID LAYER The major functions of the lipids are to: Prevent evaporation of the tears. Provide lubrication so the lids move smoothly over the globe. Contribute to the optical properties. Cornea Maintain a lipid strip at the lid margin preventing tear overflow by increasing surface tension.  MIDDLE AQUEOUS LAYER The major functions of the aqueous layer are to: Supply oxygen to the avascular Provide an antibacterial environment to the eye Maintain a smooth surface by filling in the irregularities of the anterior surface. Cornea Wash away surface debris towards the puncta. INNERMOST MUCIN LAYER: The major functions of the mucin layer are to: Interact with the lipid layer to stabilize the tear film. Help collect loose cells, foreign particles, and bacteria in the network on the bulbar conjunctiva. Cornea THE STRUCTURE OF THE EYE 1. Accessory structures of the eye (Ocular adnexa) CONJUNCTIVA Thin, transparent mucous membrane lining posterior surfaces of eyelids and covering anterior surface of the eyeball, excluding cornea. Secretes mucus to lubricate the eye 1. Accessory structures of the eye (Ocular adnexa) CONJUNCTIVA The conjunctiva has two parts: Bulbar conjunctiva: covers the sclera on the front part of the eye. This part of the conjunctiva covers some of the sclera, but it does not cover the cornea. Palpebral conjunctiva: covers the inside of the top (upper) and bottom (lower) eyelids Forniceal conjunctiva: transition region between bulbar & palpebral conjunctiva 1. Accessory structures of the eye (Ocular adnexa) EYE MUSCLE Six muscles attach to the outer surface of the eye situated round the eyeball. Four of these are straight & two are oblique. 1. Accessory structures of the eye (Ocular adnexa)  1. Accessory structures of the eye (Ocular adnexa) EYE MUSCLE Superior rectus Medial rectus : Superior rectus: Inferior oblique Lateral rectus: Rotate the Rotate Rotate the eyeball inwards the eye ball eyeball outwards upwards Medial Lateral rectus rectus Superior oblique: Inferior oblique: Inferior rectus: Rotates the Rotate Rotate the eyeball so that the eyeball so Superior eyeball the cornea turns that the cornea oblique downwards in downwards & turns in upwards outwards & outwards Inferior rectus directions. direction Three antagonistic pairs of muscles control eye movements: 1- The lateral and medial rectus muscles. 2- The superior and inferior rectus muscles. 3- The superior and inferior oblique muscles. These muscles are responsible for movements of the eye along three different axes: Horizontal, either toward the nose (adduction) or away from the nose (abduction) Vertical, either elevation or depression Torsional, movements that bring the top of the eye toward the nose (intorsion) or away from the nose (extorsion). Horizontal movements are controlled entirely by the medial and lateral rectus muscles; the medial rectus muscle is responsible for adduction, the lateral rectus muscle for abduction. Vertical movements require the coordinated action of the superior and inferior rectus muscles, as well as the oblique muscles. The relative contribution of the rectus and oblique groups depends on the horizontal position of the eye.  In the primary position (eyes straight ahead), both of these groups contribute to vertical movements. Depression is due to the action of the inferior rectus and superior Elevation is due to the oblique muscles action of the superior rectus and inferior oblique muscles When the eye is abducted, the rectus muscles are the prime vertical movers. Elevation is due to the action of the superior rectus, and depression is due to the action of the inferior rectus. When the eye is adducted, the oblique muscles are the prime vertical movers. Elevation is due to the action of the inferior oblique muscle, while depression is due to the action of the superior oblique muscle. The oblique muscles are also primarily responsible for torsional movements. https://www.ncbi.nlm.nih.gov/books/NBK10793/  THE MOVEMENT OF THE EYE To turn the eye to the side: This muscle will contract At the same time this muscle will relax The opposite muscles contract & relax in the other eye Image Source: Patrick J. Lynch, medical illustrator 2006  THE MOVEMENT OF THE EYE When things go wrong: Turned eye - Strabismus When things go wrong: Turned eye - Strabismus One eye turned inwards - Esotropia Image Source: Patrick J. Lynch, medical illustrator 2006  THE MOVEMENT OF THE EYE When things go wrong: Turned eye - Strabismus One eye turned outwards - Exotropia Image Source: Patrick J. Lynch, medical illustrator 2006