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Essentials of Human Anatomy & Physiology Seventh Edition The Eye & Vision Lecture Slides in PowerPoint by Jerry L. Cook Modified by J. Kalinowski 2-04 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Eye and Vision 70 percent of all sensory receptors are in the eyes - only see 1/6th of eye Each eye has over a million nerve fibers Protection for the eye Most of the eye is enclosed in a bony orbit A cushion of fat surrounds most of the eye Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.2 Accessory Structures of the Eye Eyelids – aka. palpebra Meets at medial and lateral canthus Eyelashes Figure 8.1b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.3a Accessory Structures of the Eye Meibomian glands – tarsal glands – modified sebacious glands produce an oily secretion to lubricate the eye Chalazion - inflammation Figure 8.1b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.3b Chalazion Accessory Structures of the Eye Ciliary glands – modified sweat glands between the eyelashes Sty inflammation Figure 8.1b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.3c Conjunctiva Conjunctiva Membrane that lines the eyelids Connects to the surface of the eye Secretes mucus to lubricate the eye Conjunctivitis – inflammation of – sometimes known as “pink eye” Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.4a Conjunctivitis Accessory Structures of the Eye Lacrimal apparatus Lacrimal gland – produces lacrimal fluid Lacrimal canals – drains lacrimal fluid from eyes Figure 8.1a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.4b Accessory Structures of the Eye Lacrimal sac – provides passage of lacrimal fluid towards nasal cavity Figure 8.1a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.4c Accessory Structures of the Eye Nasolacrimal duct – empties lacrimal fluid into the nasal cavity Figure 8.1a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.4d Function of the Lacrimal Apparatus Properties of lacrimal fluid Dilute salt solution (tears) Contains antibodies and lysozyme Protects, moistens, and lubricates the eye Empties into the nasal cavity Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.5 Extrinsic Eye Muscles Six eye muscles attach to the outer surface of the eye Produce gross eye movements Rectus muscles: lateral, medial, superior, inferior Oblique muscles: inferior, superior Need to be able to label on diagram & identify the motions they are responsible for (page 254 of text) Slide 8.6 Figure 8.2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Structure of the Eye The wall is composed of three tunics Fibrous tunic – Outer layer Vascular tunic (uvea) – middle layer Sensory tunic – inside layer Figure 8.3a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.7 The Fibrous Tunic Sclera White connective tissue layer Seen anteriorly as the “white of the eye” Cornea Transparent, central anterior portion Allows for light to pass through Repairs itself easily The only human tissue that can be transplanted without fear of rejection Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.8 Vascular Tunic Choroid – posterior portion Blood-rich nutritive tunic Dark pigment prevents light from scattering Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.9 Vascular Tunic Modified interiorly Ciliary body – anterior smooth muscle Attached to lens Iris Pigmented layer that gives eye color Pupil – rounded opening in the iris for light passage Circular & radial fibers regulate opening Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.9 Sensory Tunic (Retina) Neural layer contains receptor cells (photoreceptors) Rods & Cones Signals pass from photoreceptors via a two-neuron chain Photoreceptors to bipolar neurons Bipolar neurons to ganglion cells Signals leave the retina toward the brain through the optic nerve Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.10 Neurons of the Retina Figure 8.4 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.11 Neurons of the Retina and Vision Rods Most are found towards the edges of the retina Allow dim light vision and peripheral vision Perception is all in gray tones Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.12a Neurons of the Retina and Vision Cones Allow for detailed color vision Densest in the center of the retina Fovea centralis area of the retina with only cones Area of greatest visual acuity Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.12b Optic disk No photoreceptor cells are at the optic disk, or blind spot Site of optic nerve leaving eyeball Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.12b Cone Sensitivity There are three types of cones Different cones are sensitive to different wavelengths Color blindness is the result of lack of one cone type Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.6 Slide 8.13 Lens Biconvex crystal-like structure Held in place by a suspensory ligament attached to the ciliary body Figure 8.3a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.14 Lens Activity of ciliary muscle of ciliary body changes lens thickness to focus light onto retina Cataracts Anterior segment – contains watery aqueous humor Maintains intraocular pressure Glaucoma Fluid circulates over eye and is reabsorbed into the blood stream by canal of Schlemm Posterior segment – contains gel-like vitreous humor Figure 8.3a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.14 Internal Eye Chamber Fluids Aqueous humor in Anterior Segment Watery fluid found in chamber between the lens and cornea Similar to blood plasma Helps maintain intraocular pressure Provides nutrients for the lens and cornea Reabsorbed into venous blood Blocked drainage = glaucoma Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Internal Eye Chamber Fluids Vitreous humor Gel-like substance behind the lens Keeps the eye from collapsing Lasts a lifetime and is not replaced Keeps retina firmly against wall of eyeball Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.15b Vision Light • Light must be refracted (bent) so that it focuses on the retina to form an image. • The cornea, aqueous humor, & vitreous humor have a constant refractory power • The lens is the only refractory structure that can change shape in order to change refractory power. Focus • Distance vision is accomplished by: • Ciliary muscles relaxation • Suspensory ligaments tightening • Results in: • Maximum flattening of lens (decreased convexity) • Decreased refraction Focus • Close vision is accomplished by: • Ciliary muscles tightening • Suspensory ligaments relaxing • Results in: • Lens rounds up (increased convexity) • Increased refraction • Requires continuous muscle contractions • Prolonged periods of close vision can cause eyestrain Lens Accommodation The eye is set for distance vision (over 20 ft away) The lens must change shape to focus for closer objects This ability decreases with age Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.9 Slide 8.16 Real Image Real image is projected on retina: reversed from left to right upside down & smaller Brain adjusts our perception Figure 8.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 8.17 Correcting the Eye • Correct Focus = emmetropia • Nearsightedness = myopia • • • • • • Distant objects are blurry (near objects clear) Focus of light in front of retina Eyeball too long lens too strong – too convex Cornea is too curved – too convex Requires concave lens to correct Emmetropia Myopia Correcting the Eye Farsightedness = hyperopia • Near objects are blurry – distance objects are clear • Focus of light beyond the retina • Short eyeball • lazy lens – lens too weak – too concave • Cornea too flat – too concave • Requires convex lens to correct Hyperopia Astigmatism • Unequal curvatures in cornea & lens • Blurred vision • Specially ground lenses required to compensate irregularities Presbyopia • Decreasing lens elasticity so lens cannot adjust for close vision • Causes difficulty focusing on near objects • Typically age related – corrected with reading glasses, etc. • Near point of accommodation – closest distance at which you can focus on an object