Astigmatism is a common condition representing an imperfection in the eye’s curvature that affects how light focuses on the retina. Unlike a perfectly spherical eye, an astigmatic eye has a front surface that is irregularly curved, often compared to the shape of a football. This difference in shape, which can occur on the cornea or the lens, prevents light from bending evenly, resulting in blurred or distorted vision at any distance.
Recognizing Common Symptoms
The most frequent symptom is general blurriness, but many describe the distortion as stretched, shadowed, or wavy. This occurs because the uneven curvature causes light rays to focus at multiple points instead of a single, sharp point. This distortion is particularly noticeable when looking at fine details, such as reading small print or observing straight lines that appear slightly tilted.
This constant effort to achieve focus often leads to significant eye strain and fatigue, especially after prolonged periods of visual work like reading or using a computer. The muscles within the eye work harder to compensate for the focusing error, which can manifest as frequent headaches. These headaches often localize around the temples or forehead and tend to worsen late in the day.
Difficulty with night vision is another common sign, as astigmatism can cause lights to appear with noticeable halos, streaks, or glare. Driving at night becomes more challenging because oncoming headlights and streetlights scatter unevenly across the irregular surface of the eye. This scattering effect reduces overall visual clarity in low-light conditions.
Simple At-Home Visual Checks
One widely known self-administered visual check is the Astigmatism Radial or Clock Chart. This test uses a circular design with multiple lines radiating out from the center, similar to the spokes of a wheel. To perform this check, sit a comfortable distance from the chart and cover one eye completely.
If astigmatism is present, the uneven focusing of light causes some lines on the chart to appear darker, bolder, or sharper than others. The lines that appear clearest correspond to the meridian of the eye with the steepest curve. Repeat this process for the other eye to check for astigmatism independently.
These at-home checks are observational tools only. They indicate the potential presence of an irregularity in the eye’s shape but cannot measure the precise amount or axis of the error. A positive result is a strong suggestion that a professional eye examination is necessary to receive a definitive diagnosis.
How Eye Care Professionals Confirm Diagnosis
An eye care professional confirms astigmatism through a comprehensive eye examination using specialized instruments that objectively measure the eye’s refractive properties. One tool is the keratometer, which focuses a light pattern onto the cornea and measures the reflection to determine its curvature. By measuring the steepness of the two principal meridians, the instrument quantifies the extent of corneal astigmatism.
Another objective test is retinoscopy, where the practitioner shines a light into the eye and observes the movement of the light reflex in the pupil. By neutralizing this reflex with different trial lenses, the examiner accurately determines the refractive error, including the cylinder power and axis of astigmatism. This is valuable for young children or individuals who cannot communicate clearly.
The phoropter, the machine with multiple lenses placed in front of your eyes, is used for subjective refraction. This device allows the practitioner to use a technique like cross-cylinder refinement to fine-tune your prescription. The phoropter determines the exact combination of spherical and cylindrical power needed to provide the clearest possible vision. These clinical procedures ensure an objective and precise measurement of the refractive error.