Astigmatism

Astigmatism is a refractive error in which unequal curvature of the eye’s optical surfaces produces different focus in different meridians.

Cornea: The transparent front surface of the eye that supplies most of its refractive power. Unequal corneal curvature is a common source of astigmatism.
Eyeglasses: Lenses worn before the eyes to correct refractive errors and improve vision. Cylindrical or toric spectacle lenses correct astigmatic power.
Refractive error: A focusing error in which the eye does not bring light to a sharp retinal image. Astigmatism is one form of refractive error.
Keratoconus: A progressive corneal disorder in which the cornea thins and bulges into a cone-like shape. Its changing, irregular curvature can produce substantial astigmatism.
Blurred vision: Reduced clarity of vision in which details appear indistinct. Different focal positions across meridians can blur edges and fine detail.
Crystalline lens: The transparent, flexible structure behind the iris that changes shape to focus light. Unequal lens curvature can contribute to internal astigmatism.
Contact lens: A thin corrective or cosmetic lens placed directly on the eye’s surface. Toric contact lenses correct astigmatism while moving with the eye.
Myopia: A refractive error in which distant objects focus in front of the retina when accommodation is relaxed. Myopia shifts focus by distance; astigmatism produces different focus by meridian.
Against-the-rule astigmatism: A regular astigmatism pattern in which the horizontal meridian is steeper than the vertical meridian. It is one orientation of regular astigmatism.
Eyestrain: Visual discomfort associated with sustained or demanding visual tasks. Uncorrected astigmatism can contribute to eyestrain during close work.

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