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OBJECTIVES

Objectives

After studying this chapter, the student should be able to:

  • Understand the basic optics of the eye, including the optics of common refractive errors.

  • Understand basic eyelid, orbit, and ocular anatomy, as well as some of the common ocular disorders associated with each tissue.

  • Understand the role of the primary care physician in the treatment and diagnosis of some of the more common ocular pathologies, as well as have a basic understanding of when an ophthalmology consult is recommended.

PREVALENCE & BURDEN

There are >35 million individuals throughout the world who are legally blind and an additional 240 million individuals who are classified as having low vision. In the United States alone, the prevalence of blindness and low vision in middle-aged adults and the elderly is approximately 1 and 3 million people, respectively. Although we often focus on the physical burden the visually impaired experience when trying to function in a world that relies heavily on visual cues, we often fail to consider the full emotional impact of vision loss. When asked, many individuals state that their top health-related fear is loss of vision, above loss of a limb, being diagnosed with cancer, or even death. As one might expect, individuals who experience significant vision loss are at a much greater risk of developing depression. Further, although it is understood that loss of vision will have tremendous impact on the life of a visually impaired individual, it is also important to appreciate the impact on the family members and friends who help with their routine care. In many countries, it is the cultural norm for a family member to assume a full-time caretaking role to assist a visually impaired relative. Depending on the age of the individual with vision loss and the chosen caretaker, 1 or possibly 2 people may be removed from the workforce. Thus, not only are there personal health implications, there are also broad economic impacts of vision loss as well.

OPTICS & REFRACTIVE ERRORS

The eye is a specialized neurosensory organ whose primary purpose is to gather and process light stimuli emerging from the visual field and convert it into an electric signal that can be modified and propagated along the visual pathway to neurons in the brain for higher order processing. The first critical step is to focus the incoming light onto the retinal photoreceptors. The eye has a refractive power of approximately +60 diopters; with two-thirds of the refractive power being generated by the cornea and one-third of the refractive power being generated by the natural lens. If the axial length is matched correctly to the refractive power of the eye, parallel beams of light from a distant object (greater than approximately 20 feet away) will be perfectly focused on the retinal plane, and a clear image should be perceived by the individual. When the refractive power and axial length are ...

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