Astigmatism is a common refractive error causing blurred or distorted vision at any distance. It occurs when the eye’s front surface—either the cornea or the lens—has an imperfect curvature instead of a perfectly spherical shape. This shape is often compared to an American football rather than a basketball, having a steeper curve in one direction. This asymmetrical curvature prevents light rays from bending properly and focusing on a single point on the retina.
Is Astigmatism a Permanent Condition?
Astigmatism is generally considered a permanent structural characteristic of the eye and does not typically disappear on its own. Since it results from an inherent irregularity in the shape of the cornea or lens, the underlying cause is not one that naturally resolves over time.
For adults, the degree of astigmatism often remains relatively stable once the eye has finished developing. Changes that do occur in later life are usually due to new factors, such as the development of cataracts, which can alter the shape of the internal lens and induce or change existing astigmatism. Certain corneal conditions like keratoconus, where the cornea progressively thins and bulges, can also cause significant changes, resulting in irregular astigmatism.
Rare exceptions to this permanence are mainly seen during childhood development. Young children with mild astigmatism may sometimes see an improvement or slight reduction as their eyes grow and mature. A small amount of vertical astigmatism, possibly due to the constant pressure from the eyelids, may also diminish over time, though larger amounts are generally stable.
Quantifying the Irregularity
Eye care professionals use specific measurements to determine the presence and severity of this vision irregularity. This diagnostic process involves refraction, which identifies how the eye bends light, and pinpoints the precise axis and degree of the asymmetrical curve. Astigmatism is measured in diopters, where a perfect eye would have a measurement of zero.
Most people have a small degree of astigmatism, typically between 0.5 to 0.75 diopters, but measurements of 1.5 diopters or higher usually indicate the need for corrective lenses. Tools like a keratometer shine a light onto the cornea and measure its reflection to determine the curve of the front surface. More advanced instruments, such as a corneal topographer, create a detailed, color-coded map of the cornea’s entire surface to detect subtle imperfections.
The prescription for astigmatism involves two main values: the cylinder and the axis. The cylinder measurement, specified in diopters, indicates the power needed to correct the irregular curvature. The axis, measured in degrees from 0 to 180, indicates the exact orientation of the astigmatism on the cornea.
Available Correction Methods
Vision correction focuses on counteracting the uneven curvature to ensure light focuses correctly on the retina. The simplest and most common approach involves non-surgical corrective lenses. Eyeglasses utilize specially designed cylindrical lenses that compensate for the irregular shape of the eye’s surface, bending light appropriately.
Contact lenses for astigmatism are typically toric lenses, which are soft lenses that have different powers in different meridians to correct the specific curvature. These lenses are weighted to ensure they remain in the correct rotational position on the eye, aligning with the measured axis of the astigmatism. Rigid gas-permeable (RGP) lenses may also be used, as their firm structure helps create a smooth, spherical surface over the cornea, which can be effective for mild to moderate astigmatism.
For individuals seeking a more permanent alteration, refractive surgery physically reshapes the cornea. Procedures like Laser-Assisted In Situ Keratomileusis (LASIK) and Photorefractive Keratectomy (PRK) use a precise laser to remove minute amounts of corneal tissue. This sculpting permanently corrects the irregular shape, reducing or eliminating the need for glasses or contact lenses. Orthokeratology (Ortho-K) offers a temporary non-surgical solution, involving the overnight wear of rigid contact lenses that gently reshape the cornea while sleeping.