Chapter 7 The Sensory Systems 273 When diabetic retinopathy is sufficiently advanced, bleeding occurs, causing the individual to see red spots. Laser surgery typically is effective in treating the condition when it is caught early enough. Vitreous Floaters Vitreous floaters are small, irregularly shaped specks that drift around within your field of vision. Floaters form when tiny chunks of the gel-like vitreous humor break off and float in the aqueous humor in the center of the eyeball. Although sometimes distracting, ordinary eye floaters are common and normally not a cause for alarm. However, the sudden appearance of multiple floaters accompanied by what appear to be flashes of light on the lateral periphery of the eye can be symptoms of a retinal tear or retinal detachment. In such cases, immediate medical attention is required. Check Your Understanding 1. What is another name for nearsightedness? 2. Presbyopia usually affects people in what age group? Explain. 3. Which disease of the eye is highly contagious? 4. What are the signs and symptoms of cataracts? 5. Distinguish between dry macular degeneration and wet macular degeneration. Diabetic Retinopathy Damage to the retina caused by long-term diabetes is called diabetic retinopathy (reht-i-NAHP- a-thee). This condition is becoming increasingly prevalent and is currently the leading cause of blindness in American adults. Diabetic retinopathy involves swelling and leaking of the vessels that supply blood to the retina. Romaset/Shutterstock.com Figure 7.10 Eye disorders and diseases, such as detached retinas, myopia, cataracts, and macular degeneration, can often be treated successfully with laser surgery. cornea a transparent tissue over the anterior center of the eye extrinsic muscles muscles attached to the outer surface of the eye that are responsible for changing the direction of viewing iris the anterior portion of the choroid, which gives the eye its color lacrimal glands tear secretors located above the lateral end of each eye lens a transparent, flexible structure that is curved outward on both sides optic chiasma the point at which the optic nerves cross optic nerve transmitter of visual sensory signals to the occipital lobe of the brain Mini Glossary Make sure that you know the meaning of each key term. aqueous humor the clear, watery fluid that fills the anterior chamber of the eye provides nutrients for the lens and cornea and helps maintain intraocular pressure choroid the middle layer of the wall of the eye ciliary body the structure between the choroid and the iris that anchors the lens in place ciliary glands modified sweat glands located between the eyelashes cones sensory cells in the retina that are sensitive to bright light and provide color vision conjunctiva a delicate external membrane that covers the exposed eyeball and lines the eyelid LESSON 7.1 Review and Assessment Copyright Goodheart-Willcox Co., Inc.