What is the typical axis of astigmatism?
Jun 29, 2022
Source: Cainiu Health
Dr. Chen You
Introduction
Most astigmatism is regular astigmatism. In myopic astigmatism, the axis is typically 180 degrees, whereas in hyperopic astigmatism, it is usually 90 degrees; the astigmatic meridian lies on the side with higher refractive power. Although irregular astigmatism is rare, it tends to impair vision more significantly. Oblique astigmatism (e.g., axis at 45° or 135°) is particularly problematic—even as little as −0.50 D can affect visual acuity. Nevertheless, regardless of the type, astigmatism invariably impairs vision to some degree.
Astigmatism is actually caused by uneven corneal thickness. When viewing objects, light rays fail to focus precisely on the retina, resulting in blurred or distorted images. Mild astigmatism typically has minimal impact on visual acuity. However, in severe cases, it may cause symptoms such as headache, blurred vision, and diplopia (double vision). So, what is the typical axis of astigmatism?
What Is the Typical Axis of Astigmatism?
Most cases of astigmatism are regular (with-the-rule) astigmatism. In myopic astigmatism, the axis commonly lies at 180 degrees; in hyperopic astigmatism, it typically lies at 90 degrees. The astigmatic axis corresponds to the meridian with higher refractive power. Although irregular astigmatism is relatively rare, it tends to affect vision more significantly. Oblique astigmatism—where the axis falls between 30° and 60° or between 120° and 150°—is particularly impactful; even a low degree of 0.50 D can impair visual function. Regardless of type, astigmatism invariably affects vision to some extent and generally requires optical correction with spectacles. A 0.50 D astigmatic correction may occur at any axis position, depending on age-related or ocular anatomical factors.
The most common type is “with-the-rule” astigmatism, wherein a 0.50 D astigmatic correction occurs along the horizontal meridian (axis 180°). Conversely, “against-the-rule” astigmatism refers to a 0.50 D correction along the vertical meridian (axis 90°). If the axis lies at 45° or 135°, it is termed “oblique astigmatism.” With-the-rule astigmatism of 0.50 D usually causes negligible visual disturbance and often does not require correction.
In daily life, patients should maintain a positive mindset and actively cooperate with their physicians during treatment. Medications should be taken on schedule and in the prescribed dosage, while attention to routine eye care is essential to facilitate prompt clinical improvement. We hope this information proves helpful.
