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D (Depth Perception to Dry Eye)

Depth Perception

Wednesday, January 13th, 2010

The unconscious ability to assess the distance you are away from an object or two or more distant objects are away from each other. Requires the use of two eyes working together.

Diabetes

Wednesday, January 13th, 2010

All diabetics, regardless of age, should have regular eye examinations and monitor their blood sugar level to prevent a number of complications such as cataracts or increased optic nerve damage in the case of glaucoma. There may also be a weakening of the retinal blood vessels (diabetic retinopathy) causing them to leak leading to reduced nourishment of the retina or scarring resulting in cloudy or even loss of vision if left untreated.

Diffraction

Wednesday, January 13th, 2010

The scattering of the rays of light as it passes through a substance such as water glass or plastic or strikes an object.

Dioptre/Diopter

Wednesday, January 13th, 2010

An optical unit of power. When preceeded by a plus sign indicates that the patient is longsighted and that the rays of light passing through the lens will converge on a point of focus.The wearer when unaided can see distance but not near. A minus sign indicates being shortsighted which is opposite to the above with the rays diverging as it passes through. One dioptre is equal to one metre of focal length while two dioptres is only half a metre.

Diplopia

Wednesday, January 13th, 2010

Double vision. Caused when the muscles of each eye are not working together leading to two seperate images of a single object instead of one superimposed each upon the other.

Drooping Eyelids

Wednesday, January 13th, 2010

An often hereditary condition where the top eyelid unconrollably sags due to a malfunction of the lid muscle. Requires surgical intervention. See blepharoplasty and blepharospasm.

Druce

Wednesday, January 13th, 2010

Small yellow or white deposits on the head of the optic nerve or the retina. A common early indication of age related macular degeneration. Drusen (plural) on its own does not indicate that the condition is either present or a certainty rather that the eye is at risk.

Dry Eye

Wednesday, January 13th, 2010

Not only caused by the lack of tear production by lacrimal gland (tear gland) but also by its composition. Most common in the elderly. Symptons consist of irritation and redness as well as excessive tearing. Aggravated by air conditioning, smoke, dry climates and wind.