Glasses are a primary and highly effective method for correcting astigmatism, a common vision problem. This condition is caused by an imperfection in the shape of the cornea, the clear front surface of the eye, or the lens located behind it. Because of this irregularity, the eye does not bend light correctly to achieve a sharp focus. Specialized eyeglass lenses are designed to compensate for this, restoring clear vision.
How Astigmatism Affects Vision
Astigmatism occurs because the light-focusing structures of the eye are not perfectly spherical. A normal cornea is shaped like a perfectly round basketball, but with astigmatism, the cornea or the internal lens is curved more like an American football. This uneven curvature means that light entering the eye is refracted, or bent, more steeply along one axis than the other.
Instead of focusing light rays to a single, sharp point on the retina, the irregular shape causes them to focus at multiple points. This results in images that appear blurred, stretched, or distorted, and this visual impairment is present at nearly all viewing distances. Symptoms of this condition often include eye strain, headaches, and the need to squint to bring objects into focus.
Toric Lenses for Astigmatism Correction
Correcting astigmatism requires a lens that can counteract the eye’s irregular shape, which is why a standard spherical lens is not sufficient. The specialized solution used in glasses for this purpose is called a Toric lens. This type of lens is engineered with different refractive powers and curvatures across its surface, somewhat resembling a section of a cylinder.
The unique geometry of a Toric lens allows it to provide the necessary correction in the exact meridian where the eye needs it most. It essentially bends light more in one direction than the other, precisely compensating for the uneven bending caused by the astigmatic cornea or lens. For the lens to be effective, it must be manufactured and mounted in the eyeglass frame so that the corrective power is aligned perfectly with the orientation of the patient’s astigmatism.
Reading Your Astigmatism Prescription
An eyeglass prescription for astigmatism includes specific measurements beyond the basic correction needed for nearsightedness or farsightedness. The presence of astigmatism is indicated by two extra values on the prescription form: Cylinder (CYL) and Axis. The Cylinder value measures the degree of astigmatism correction required, and a higher number here signifies a more pronounced irregular curvature in the eye.
The Axis measurement is an angular value, expressed in degrees from 1 to 180, that specifies the exact orientation of the astigmatism on the eye. This number dictates the precise alignment of the Toric lens within the frame. When a person first begins wearing new glasses with a significant astigmatism correction, there may be a short adjustment period as the brain adapts to the newly corrected visual input.
Non-Glasses Options for Correction
While glasses are the most common and non-invasive treatment, they are not the only solution available for astigmatism. Specialized contact lenses, often called Toric contact lenses, are a popular alternative that function similarly to their eyeglass counterparts. These lenses feature design elements, such as weighted bases or thin zones, that help them remain stable on the eye to maintain the correct rotational axis for clear vision.
Another non-surgical option is Orthokeratology, commonly referred to as Ortho-K, which involves wearing rigid contact lenses overnight. These custom-designed lenses temporarily reshape the cornea while the person sleeps, allowing for clear vision throughout the following day without glasses or contacts. For a more lasting solution, refractive surgery like LASIK is available, which uses a laser to permanently reshape the cornea and correct the irregular curvature.