ASTIGMATISM Meaning and
Definition
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Astigmatism is a common refractive error that affects the way light enters the eye, causing blurred or distorted vision. It is a condition that occurs when the cornea or lens of the eye is irregularly shaped, preventing light rays from focusing correctly onto the retina.
In a normal eye, the cornea and lens have a smooth, evenly curved surface, enabling them to focus light precisely onto the retina, which then sends clear images to the brain. However, in astigmatism, either the cornea or the lens, or sometimes both, have an irregular curvature, resembling the shape of a football rather than a round sphere. This irregular shape causes the light to scatter and focus on multiple points instead of a single, sharp point on the retina.
Astigmatism can cause blurred vision at all distances, as well as visual distortions, eye strain, headaches, and eye discomfort. It often coexists with nearsightedness (myopia) or farsightedness (hyperopia).
The severity of astigmatism varies among individuals, and it can be classified as either regular or irregular. Regular astigmatism occurs when the principal meridians of the cornea are perpendicular to each other, while irregular astigmatism occurs when one or both meridians are not perpendicular. Irregular astigmatism is usually caused by an eye injury, corneal scarring, or certain eye conditions like keratoconus.
Astigmatism is typically diagnosed through a comprehensive eye examination with the measurement of visual acuity and the use of special instruments to quantify the degree and orientation of the irregularities. It is commonly corrected through the use of prescription eyeglasses, contact lenses, or refractive surgery.
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Etymology of ASTIGMATISM
The word "astigmatism" originates from the Greek prefix "a-" meaning "without" or "lack of", and the Greek word "stigma" which refers to a point or dot. In referance to the eye condition, "stigma" is used to mean a point or focus of light. "Astigmatism" is used to describe an eye condition that lacks a single point of focus, meaning the eye does not properly focus light rays onto the retina. The term was introduced in the mid-19th century to describe this irregularity in vision.
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