2010 EYE + ACCOMODATION Complete +lab - THE EYE Judianne...

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THE EYE Judianne Kellaway, MD Reading: Gartner and Hiatt, Chapter 19; Klein and McKenzie, pp311-318 Learning Objectives : Label anatomical components of the eye Know how components regulate light into the eye Know how components regulate focus Know layers and functions of cornea, iris, ciliary body, and retina Key Words: Cornea, limbus, iris, ciliary body, choroids, retina, pigmented retinal epithelium, lens, accommodation and eyelids I. INTRODUCTION The eye is a complex photosensitive organ, which conveys the form, light intensity, and color of an environmental image to a photoreceptive layer, the retina, which transmits a corresponding electrical image to the brain. II. MAJOR ANATOMIC COMPARTMENTS OF THE EYE Anterior segment -Anterior chamber -Posterior chamber Posterior segment -Vitreous body [N.B. Terminology: Outer refers to structures nearer the surface of the eyeball, while inner refers to a structure nearer the midpoint of the globe.]
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A. Tunics 1. Fibrous tunic (tunica fibrosa)-outermost layer a. Cornea Transparent, very tough, can withstand force of 5 kg/cm 2 ~ 12mm in diameter Thickness ranges between 0.8-0.9mm centrally to 1.1mm peripherally Refractive power twice as high as lens Five layers Epithelium ~10% of corneal thickness (~50µm) avascular stratified squamous epithelium, nonkeratinizing 5-7 cell layers thick very smooth, bathed in lacrimal fluid Bowman’s layer 8-14 µm thick Condensation of anterior stroma Mostly collagen fibers, randomly disposed Stroma or substantia propria 90% of corneal thickness (~500 µm) collagen fibrils arranged in lamellae 200-250 lamellae in regular layers collagen turnover slow, ~12 months Descemet’s membrane basement membrane of corneal endothelium ~10 µm thick increasing thickness with age Endothelium monolayer of squamous epithelium facing the anterior chamber Critical pump function. Na, K ATPase to dehydrate cornea b. Sclera Posterior five-sixths of globe Thickness ranging from 0.3mm at equator to 1mm posteriorly
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Lamina cribosa posteriorly at site of optic nerve exit Primarily collagen in highly complex orientation Terminates at limbus At optic nerve, outer ½ of sclera is continuous with the dural sheath c. Limbus Narrow (~1 ½ mm) zone between sclera and cornea Provides nourishment for peripheral cornea and removes aqueous humor Aqueous humor passes through trabecular meshwork into Schlemm’s canal, then into episcleral veins Mean intraocular pressure ~20mm Hg Episcleral venous pressure ~10mm Hg Limbus Components Conjunctiva 1. Epithelium 2. Stroma Ciliary muscle Schlemm’s canal Internal trabecular meshwork (spaces of Fontana) Uveal meshwork Iris Anterior chamber Posterior chamber 2. Vascular tunic (tunica vasculosa or uvea) – middle layer a. Iris Circular diaphragm anterior to lens Central aperture = pupil Peripheral border = ciliary border
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2010 EYE + ACCOMODATION Complete +lab - THE EYE Judianne...

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