The reduction in central corrected visual acuity as a result of destruction of the fovea with a central scotoma requires magnifying vision aids. However, magnification is always associated with a reduction in the size of the visual field. As a result, these vision aids require patience, adaptation, motivation, and dexterity. Cooperation between ophthalmologist and optician is often helpful. The following systems are available in order of magnification.
Increased near-field corrections: The stronger the near-field correction, the shorter the reading distance. Magnification (V) is a function of the refractive power of the near-field correction (D) and is determined by the equation V = D/4.
Example: Eyeglasses with a 10 diopter near-field correction magnify the image two and one-half powers. However, the object must be brought to within 10 cm of the eye.
Magnifying glasses are available in various strengths, with or without illumination.
Monocular and binocular loupes, telescopes, and prism loupes: An optical magnifying system is mounted on one or both eyeglass lenses. The optical system functions on the principle of Galilean or Keplerian optics.
Closed-circuit TV magnifier: This device displays text at up to 45 power magnification.
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