Astigmatism is a common condition where the eye’s focusing structures, the cornea or the lens, possess an irregular curvature, leading to blurred or distorted vision. Instead of being perfectly spherical like a basketball, the astigmatic eye is shaped more like a football. This irregularity prevents light from focusing correctly onto the retina. Astigmatism changes over time, as the eye undergoes structural shifts throughout life that directly influence this refractive error, following distinct patterns during development, young adulthood, and later years.
The Developmental Years
Most infants are born with some degree of astigmatism. This initial phase of life is dominated by a natural process called emmetropization, where the eye actively adjusts its shape and size to reduce refractive errors. During this period, the eye attempts to grow into a shape that allows light to focus perfectly on the retina, which is why a large percentage of temporary astigmatism resolves on its own.
The amount of astigmatism tends to diminish significantly, often stabilizing by the time a child reaches school age, around five to seven years old. In this early phase, the most common orientation is “with the rule” (WTR) astigmatism, meaning the vertical meridian of the eye is the steepest curve.
Shifts in Adulthood
Following the developmental stabilization period, astigmatism generally remains stable throughout young adulthood, typically from the early twenties through the forties. The degree of astigmatism does not fluctuate significantly during this time. The astigmatism present in this phase is predominantly corneal, caused by the shape of the clear front surface of the eye.
Changes that do occur in this age range are usually the result of acquired factors rather than natural aging. Eye injury, trauma, or certain surgical procedures can alter the corneal shape and induce or worsen astigmatism. Furthermore, a progressive eye disease like keratoconus, which causes the cornea to thin and bulge into a cone shape, results in a noticeable increase in astigmatism. Hormonal changes, such as those experienced during pregnancy or menopause, can also subtly affect the flexibility of the cornea and lens, potentially causing minor, transient shifts.
The Role of Aging Eyes
The primary change in astigmatism occurs as the eyes age, typically starting around the mid-forties and continuing into the senior years. This involves a systematic shift in the axis of astigmatism, moving from the “with the rule” (WTR) type common in youth to “against the rule” (ATR). Against-the-rule astigmatism means the horizontal meridian of the eye becomes the steepest curve.
The shift is driven by two structural changes within the aging eye. One factor is the cornea, which gradually flattens along the vertical meridian and steepens horizontally. This process may be influenced by long-term changes in eyelid tension and the structural integrity of corneal collagen.
The second factor is the eye’s internal lens, which thickens and loses flexibility over time. This process eventually leads to presbyopia and cataracts. This lenticular change introduces its own form of astigmatism, which increasingly contributes to the total refractive error. Corneal astigmatism alone has been observed to shift toward the ATR direction by an average of about 0.25 diopters per decade after the age of 50.
Monitoring and Management
Since astigmatism changes over a lifetime, regular monitoring is necessary to maintain clear vision. Comprehensive eye examinations should be scheduled annually, especially once a person is over 40 and the WTR to ATR shift begins to accelerate. These regular checks allow an eye care professional to track the changes and ensure the vision correction is current.
The management of changing astigmatism involves updating corrective measures to match the eye’s new shape. Common solutions include prescription eyeglasses with cylindrical lenses or toric contact lenses, which are specifically designed to neutralize the irregular curvature. For those undergoing cataract surgery, the natural lens can be replaced with a toric intraocular lens (IOL) to correct the pre-existing astigmatism at the same time. As the eye continues to change, the prescription will need adjustment to counteract the progressive age-related shifts.