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| The Surgical Technologist | MARCH 2022 114 but also contains no blood vessels. The lens capsule is a clear, membranous layer that is elastic which contributes to it being under constant tension to assist the lens in assuming a globu- lar shape while the zonules that are also under tension can pull laterally to flatten the capsule and lens. The retina is the inner tunic layer. The retina is a transpar- ent layer of tissue that is continuous with the optic nerve in the posterior of the eye and continues anteriorly as the inner lining of the eyeball ending posteriorly to the margin of the ciliary body. In the center of the retina is a very small yellow- ish-colored area called the macula lutea and in its center is the fovea centralis that represents the area of sharpest vision, providing focus and fine detail. The retina contains the photoreceptors called cones and rods. The photoreceptors are a type of neuron, but each have distinct shapes. The shape of cones are short and blunt, and rods are long, thin projections. The retina contains approxi- mately 3 million cones and 100 million rods. 2 There are key differences between cones and rods. Cones provide the ability to see colors and rods produce black and white vision. Rods are much more sensitive to light, and therefore, provide vision in low light. This explains why dogs can see so much better in the dark as compared to humans; they only have rods to pro- duce black and white images, thus superior vision in low light. However, humans have the advantage of seeing color images. The fovea centralis does not have rods but has thousands of cones. The retinal layers including its blood vessels are located to each side of the fovea centralis that increases the exposure of the cones to incoming light. Therefore, to view an image in detail, a person will adjust the eyes to allow the details of the image to fall upon the fovea centralis. E P I D E M I O L O G Y AMD does not cause blindness, but is the leading cause of vision loss in people over the age of 65. 3,6 The disease causes a loss of central vision by deterioration of the macula lutea. Therefore, it interferes with everyday activities, such as seeing faces, reading, writing, or doing repairs around the house. Estimates of the direct healthcare costs because of AMD in the U.S., Canada, and Cuba combined is approximately $98 billion. 12 The estimate for the global cost is $255 bil- lion in direct healthcare costs. 11 In 2010, 2,069,403 people in the U.S. had AMD. 4,5 It is projected this will increase to 3,664,044 in 2030 and 5,442,265 in 2050. 4,5 Age is the primary risk factor for AMD. 3 Other major risk factors include: • Family history: People who have a family history of AMD are at an increased risk for AMD. 3 • Gender: In 2010, 65% of AMD cases were women compared to 35% in men. 6-8 Two explanations are the longer life expectancy of women compared to men and the use of hormone therapies have a protective effect against the development of AMD. 6-8 • Genetics: Researchers have identified over 20 genes that can affect the risk for developing AMD. However, there are currently no genetic tests that can contribute to a diagnosis of AMD as well as cannot definitively predict who will develop it. The American Academy of Ophthalmology currently does not support genetic testing for AMD. • Race: AMD occurs more often in Caucasians than African Americans, Hispanics, or Latinos. AMD affects more than 14% of Caucasian Americans 80 years of age and older. 6 In 2010, 89% of Americans with AMD were Caucasian and by comparison, the African American and Hispanic American populations accounted for 4% of AMD cases. 6 • Smoking: Research indicates that smoking doubles the risk for developing AMD. S T A G E S O F A M D There are three stages of AMD – early, intermediate, and late. The stage is determined according to the size and num- ber of drusen present. 3 Patients can have AMD in one eye only or both. Additionally, one eye could have a later stage as compared to the contralateral eye. 3 Figure 1: Eye anatomy