Signs of Higher-Order Aberrations

Aberrations are deviations from normal vision, such as blurring in an image. Most people are familiar with the terms farsightedness, nearsightedness, presbyopia, and astigmatism. These are considered first-order aberrations and make up 85% of the human eye's vision imperfections. However, another category of refractive errors that has not received much attention until recently is higher-order aberrations. All eyes have at least some degree of higher-order aberrations. These aberrations are now more recognized because technology has been developed to diagnose them properly.

The eye often has several different higher-order aberrations working together. It is sometimes hard to single out individual symptoms that may point to another diagnosis. Some higher-order aberrations can, however, produce patient complaints such as:

• Glare
• Halos
• Starburst effect
• Ghost images
• Blurring

The human eye sometimes produces distortions of an image. These distortions are called aberrations. As a ray of light passes through an optical system, it has a wavefront. In a perfect eye, the wavefront is undisturbed and smooth. In an eye with imperfections, the wavefront becomes distorted and has a characteristic three-dimensional shape. Higher-order aberrations may be caused by irregular curvatures in the cornea and lens, trauma, scarring, dry eyes, and very large pupils.

Higher-order aberrations are measured most commonly by a "Shack-Hartmann aberrometer." This device measures the wavefront of the eye and compares it to an eye that has no aberrations. This aberration map is referred to as the eye's "optical fingerprint" because it is unique and unlike any other person’s optical system. Unlike traditional vision measurements, which require subjective input from the patient, an aberrometer takes only seconds to obtain measurements and requires no patient input.

Knowledge of higher-order aberrations has been available for many years. Only in the last few years has wavefront technology been advanced enough, however, to produce accurate measurements and diagnoses. Certain types of new wavefront designed glasses, contact lenses, intraocular lens implants, and wavefront-guided laser vision correction can correct higher-order aberrations. Much more will be heard about the treatment of higher-order aberrations in the next few years, as wavefront technology appears to have many applications in vision correction.