2015 Vision

Example Test QuestionExample Test QuestionRefractive errors

  • HYPEROPIA (far-sightedness; also called hypermetropia): images are focused behind the retina because the axial length (AL) of the eye is less than the focal length (FL) i.e., AL<FL
    • can be caused if the eyeball is too short (AXIAL HYPEROPIA) or if the refractive power of the eye is abnormally weak (REFRACTIVE HYPEROPIA)
    • corrected by convex lenses, whose refractive power is measured in positive diopters

  • MYOPIA (near-sightedness): images are focused in front of the retina
    • can be either AXIAL or REFRACTIVE
    • corrected by concave lenses, whose refractive power is measured in negative diopters
Correction of refractive errors

  • PRESBYOPIA: blurred vision when reduced malleability causes a decrease in the accommodative power of the lens (resulting in a condition similar to hyperopia)
    • occurs during middle age

  • ASTIGMATISM: observed when the curvature of the cornea or lens is not equal in all meridians, causing unequal refraction and making a portion of the image out of focus

  • CATARACTS: opacity of the lens due to physical trauma, radiation, high glucose concentration in aqueous humor of diabetic patients, or age
    • lens is usually removed (resulting in hyperopia and loss of accomodation) and replaced with an artificial lens

Email: Dr. Janet Fitzakerley | ©2015 University of Minnesota Medical School Duluth | Last modified: 12-feb-15 6:05 AM