Many problems can arise when the eyes form an image of what they see. Ideally, light received by the eye will be properly focused on the retina. In reality, the light is sometimes distorted by imperfections in the cornea and lens. These distortions are called aberrations, and an aberrometer is used to measure them.
Light can be thought of as a collection of lines, or rays. Drawing a line that connects the tip of each ray produces a wavefront. A wavefront can be thought of as a picture that represents how perfect the light is.
An aberrometer works by measuring the wavefront as it passes through the eyes. For this reason, it is sometimes referred to as wavefront technology, or a wavefront aberrometer. In an eye with no aberrations, the wavefront will be flat, like a piece of paper. In an eye with imperfections, it will be bent and distorted.
To have aberrometry performed, the patient will look into the aberrometer and focus on a point of light. The aberrometer will send a low-level laser beam into the eye and measure the reflection, or wavefront. The measurement can be done when the light hits the retina, when it reflects off the retina and exits the eye, or at both times.
While the results only take seconds to capture, it takes several minutes for the wavefront map — a picture of the wavefront — to be produced. The wavefront map is unique to each patient. Some compare it to a fingerprint, because no two patients will share the same wavefront map.
Aberrations can be lower order or higher order. Lower-order aberrations are conditions that are well known by most people: astigmatism, nearsightedness and farsightedness, to name a few. The vast majority of people with vision problems will have lower-order aberrations.
Higher-order aberrations are less well known and cause problems such as double vision or blurry vision. Before aberrometry, these were more difficult to treat and were often left undiagnosed. With the wavefront map produced by an aberrometer, both higher- and lower-order aberrations can be easily diagnosed and treated. In addition, by using a wavefront map in refractive surgeries such as LASIK, some higher-order aberrations can be permanently corrected.
Most aberrometers are based on technology invented by Johannes Hartmann and modified by Roland Shack. A high-end aberrometer, not based on Hartmann-Shack technology, was designed by the Ophthonix Corporation. Called the Z-View® aberrometer, it can produce wavefront images with 10 times the resolution of Hartman-Shack-based aberrometers in approximately one minute. Ophthonix uses the higher-resolution pictures to produce its iZon® wavefront-guided lenses, which the company claims outperforms traditional glasses.