Eye Dictionary - H

A B C D E F G H I K L M N O P R S T U V W Y

hard contact lens

Hard contact lenses are manufactured using rigid materials that essentially provide a new front surface for the eye. These lenses help in the correction of astigmatism because the tear film of the eye fills in the gap between the lens and the irregularly shaped cornea.

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heterophobia

A constant tendency of one eye to deviate in one or another direction due to imperfect balance of ocular muscles.

high index lenses

Eyeglass lens manufactured from a special plastic material that allows the lens thickness to be reduced substantially while maintaining the optical properties.
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histoplasmosis

Disease caused when airborne spores of the fungus Histoplasma Capsulatum are inhaled into the lungs. This fungus is found throughout the world where bird or bat droppings accumulate. Initial symptoms are usually mild, similar to a common cold. Even mild cases can later cause a serious eye disease called ocular histoplasmosis syndrome, a leading cause of vision loss in Americans ages 20 to 40. Although most people infected with the fungus never develop the disease, people who have lived in an area with a high rate of histoplasmosis should have their eyes examined regularly.
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Holmium laser

Infrared (thermal) laser developed in the late 1980s. The laser’s beam is cool and can remove small areas of tissue without affecting surrounding tissue. In a refractive surgery procedure called Laser Thermal Keratoplasty (LTK), the Holmium laser is used to shrink the peripheral area of the cornea in order to make its shape steeper and correct mild to moderate cases of farsightedness. The laser works when moisture in the cornea absorbs energy from the laser pulses causing corneal tissue to heat up and shrink.
See Refractive Surgery in Eye Care Encyclopedia.

horopter

For a given fixation point, the set of points on the retina that are perceived to have zero retinal disparity. The points sweep out an arc in space that intersects a fixated point in space.

hue

The perception of color as red, yellow, green, blu, or any intermediate shade.

hyperopia (farsightedness)

Vision that results when there is too short a distance from the cornea to the retina. This can be caused by an eye that has a vertical oval shape or a cornea that is flatter than normal. In either case, a person who is farsighted sees well at a distance but has poor reading vision. Those who are farsighted are usually born with the disorder.
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