An imperfection in the eye’s shape can cause light to bend unevenly, leading to blurred or distorted vision. This common condition is known as astigmatism, and it affects a significant portion of the population. Understanding different types of astigmatism, such as oblique astigmatism, is helpful for recognizing symptoms and exploring corrective options.
What is Astigmatism?
Astigmatism is a refractive error where the eye’s cornea (the clear front surface) or the lens inside the eye has mismatched curves, rather than a perfectly round shape like a basketball. Instead, it might be shaped more like an American football or the back of a spoon. This irregular curvature causes light rays entering the eye to refract unevenly, preventing them from focusing to a single point on the retina.
With astigmatism, light focuses at two or more different points, or in front of and behind the retina, resulting in blurred or distorted vision. This condition can occur alongside other refractive errors like nearsightedness (myopia) or farsightedness (hyperopia).
Understanding Oblique Astigmatism
Oblique astigmatism is a specific type of regular astigmatism where the two principal meridians of the eye, representing the steepest and flattest curves, are perpendicular to each other. However, they are oriented at an angle significantly different from the horizontal (0 or 180 degrees) or vertical (90 degrees) axes. For instance, these meridians might lie between 30 to 60 degrees or 120 to 150 degrees. This angular orientation gives it the “oblique” designation.
In regular astigmatism, the principal meridians are always 90 degrees apart, but their orientation determines the type. While “with-the-rule” astigmatism has a steeper vertical meridian and “against-the-rule” astigmatism has a steeper horizontal meridian, oblique astigmatism’s tilted axis distinguishes it. This specific tilt impacts how light is focused.
Recognizing Symptoms and Underlying Causes
Individuals with oblique astigmatism frequently experience blurred or distorted vision, often noticeable at certain angles. This can manifest as difficulty seeing fine details, such as reading menu text or road signs. Other common symptoms include eye strain or discomfort, headaches, and sensitivity to glare. Night vision can also be challenging, and some individuals may find themselves squinting for clearer sight.
The primary causes of astigmatism, including oblique astigmatism, are often genetic or developmental. Doctors do not fully understand why the eye’s shape varies, but a familial predisposition is recognized. In some cases, astigmatism can also develop later in life due to eye injury, certain eye diseases, or eye surgery.
Diagnosis and Corrective Measures
Diagnosing oblique astigmatism involves a comprehensive eye examination. This evaluation typically includes tests to determine how the eyes bend light, known as refraction. Common diagnostic tools include an eye chart to test visual acuity, a phoropter where the patient looks through different lenses, and an autorefractor, which objectively measures refractive errors.
A keratometer measures the curvature of the cornea, and a corneal topography scan can create a detailed map of the corneal surface to identify imperfections. Once diagnosed, various corrective measures are available to improve vision clarity. Eyeglasses with cylindrical lenses are a common solution, designed to properly bend light onto the retina. Toric contact lenses, specifically designed with a geometric shape and weighted bottom for stability, also correct astigmatism. For those seeking to reduce their reliance on corrective lenses, refractive surgeries like LASIK (Laser-Assisted In Situ Keratomileusis) or PRK (Photorefractive Keratectomy) can reshape the cornea with a laser beam to correct the refractive error.