The “eye axis” refers to the orientation of astigmatism, a common vision imperfection where the eye’s front surface (cornea) or internal lens has mismatched curves. This irregular shape, like a football, causes light to refract unevenly, leading to blurred or distorted vision. The axis measurement, expressed in degrees from 0 to 180, indicates the specific direction of this curvature. The eye axis can change over time.
Understanding Eye Axis
Astigmatism occurs when the cornea or lens is curved more steeply in one direction than another, preventing light from focusing sharply on the retina. This irregular shape causes light to scatter, resulting in blurry vision. The “axis” number on an eyeglass or contact lens prescription specifies the exact orientation of this curvature. For instance, an axis of 90 degrees indicates a vertical orientation, while 180 degrees signifies a horizontal one.
This measurement is crucial because it guides eye care professionals in positioning corrective lenses to counteract the eye’s irregular shape. The axis does not indicate the severity of astigmatism, which is determined by the cylinder value, but rather the angle at which the correction needs to be applied. Understanding the eye’s axis helps in prescribing lenses that effectively bend light to a single focal point on the retina, restoring clearer vision.
Factors Causing Eye Axis Changes
The eye’s axis can shift due to changes in the shape and flexibility of the cornea or lens. Natural aging processes are a common cause, as astigmatism prevalence increases with age. As individuals age, the axis tends to shift from “with-the-rule” astigmatism, common in younger adults, to “against-the-rule” astigmatism. This age-related change is attributed to alterations in corneal curvature and possibly changes in eyelid position and tension.
Certain eye conditions can also influence the eye’s axis. Keratoconus, a progressive disorder where the cornea thins and bulges into a cone shape, can significantly alter astigmatism and its axis. Pterygium, a fleshy growth on the conjunctiva that extends onto the cornea, can pull on the cornea, inducing or changing astigmatism, often along a horizontal axis.
Eye surgeries can also induce or change the axis of astigmatism. Cataract surgery, which replaces the eye’s natural lens, can lead to changes in astigmatism. Surgical incisions made during cataract surgery can affect corneal shape, influencing the astigmatic axis.
LASIK, a refractive surgery, explicitly reshapes the cornea to correct astigmatism to improve vision. Eye trauma or injury can also result in corneal shape changes, altering the astigmatic axis.
Recognizing and Addressing Axis Changes
Changes in the eye’s axis can manifest through visual symptoms. Individuals might experience blurred or distorted vision, particularly at certain angles. Other common indicators include eye strain, headaches, and difficulty seeing clearly at night. These symptoms arise because the brain struggles to interpret the unfocused images received from the eye.
Eye care professionals detect these changes through a comprehensive eye examination, which includes a refraction test. This test uses various lenses to determine the precise spherical, cylindrical, and axis values needed for clear vision. Corneal topography, which maps the cornea’s curvature, also provides information about changes in corneal shape and astigmatism.
Addressing changes in the eye axis often begins with updating corrective lenses. Eyeglasses with a new prescription can accurately compensate for the shifted axis, providing clearer vision. Toric contact lenses are specifically designed to correct astigmatism and are oriented to align with the eye’s axis. In some situations, surgical interventions may be considered. These can include LASIK to reshape the cornea or, in cases of cataract, the implantation of toric intraocular lenses to correct astigmatism.