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Biology II 07.2 Eye Anatomy: External & Accessory Structures Only about 1/6th of the eye can be seen. The rest is surrounded & protected by fat & the orbit of the skull. Leave ~ 7 – 10 lines for a diagram. Eyelids Protect eye anteriorly Medial and Lateral Canthus Edges of the eye Eyelashes Tarsal glands Modified sebaceous glands Eyelid edges Produce an oily secretion that lubricates the eye Ciliary glands Modified sweat glands Found between the eyelashes ”Cilium” = eyelash Conjunctiva Delicate membrane Lines the eyelids & covers part of the outer surface of the eyeball 07.2 Eye Anatomy: External & Accessory Structures 1 of 3 6/29/2017 Biology II Secretes mucus to lubricate eye Homeostatic Imbalance (p 273): Conjunctivitis Inflammation of the conjunctiva Reddened, irritated eyes Pinkeye, infectious form caused by bacteria or viruses, is highly contagious. LACRIMAL APPARATUS Lacrimal gland Located above the lateral end of each eye. Produces lacrimal fluid o Dilute salt solution (tears) o Contains antibodies & lysosomes (enzymes that destroys bacteria) o Protects, moistens, & lubricates the eye Lacrimal canals Tears flush across the eyeball into this these canals then into the Lacrimal sac which then goes into the Nasolacrimal duct which empties into the nasal cavity. When Lacrimal secretions increase substantially tears spill over the eyelids, fill the nasal cavities and cause “sniffles” o Occurs when eyes are irritated or emotionally upset Homeostatic Imbalance (p 274): A cold or nasal inflammation often causes the lacrimal mucosa to become inflamed and swell. This impairs the drainage of tears from the eye surface, causing “watery” eyes. Leave ~ 7 – 10 lines for a diagram. 07.2 Eye Anatomy: External & Accessory Structures 2 of 3 6/29/2017 Biology II Only 6 muscles move each eye. These muscles are well designed to move the eye, but they are not well suited for keeping it still. 4 rectus muscles arranged in two pairs: Superior/inferior Lateral/medial 2 oblique muscles Superior/inferior TYPES of EYE MOVEMENT Conjuctive Both eyes move in same direction Saccades: very fast & accurate, used to fixate a peripheral target Smooth pursuit: maintains fixation on a moving target Vergence Eyes move in opposite directions Used to track an object moving in depth Closely coordinated with accommodation Remember to: Reduce, Recite, Reflect, & Review! 07.2 Eye Anatomy: External & Accessory Structures 3 of 3 6/29/2017