Wavefront measurements for higher-order aberrations

Currently, most of the doctors change the lenses with different powers in front of the patient and get his response, in order to get the exact prescription. In fact, the result is based on the patient’s subjective feeling. New wavefront technology can automatically identify vision errors from the way light waves travel through the eye, which is objective. Wavefront measurements can also provide more information than conventional eyeglasses or contacts prescription. Actually, wavefront-guided LASIK can provide sharper vision than conventional LASIK. It is estimated that wavefront measurement will replace conventional prescriptions.

A wavefront map consists of the lines perpendicular to the tips of a bundle of light rays, which is perfectly flat under perfect vision and is irregular under an imperfect eye. Wavefront technology evaluates the focus distortions that occur on cornea, so that both lower- and higher-order vision errors can be diagnosed.

Lower-order vision errors such as farsightedness and nearsightedness can be diagnosed by conventional methods, while higher-order aberrations can only be defined by wavefront technology and cured by new kinds of contacts, intraocular lenses and refractive surgery. These aberrations include coma, trefoil and spherical aberration, which receive more concern because they are the sources of LASIK side effects such as halos, ghost images. The mentioned wavefront-guide LASIK can reduce such aberrations and improve visual performance.

The device used to conduct a wavefront measurement is called an aberrometer, which just requires you to rest your chin on its chin rest for a few silent seconds. When you focus your eyes on its light point, the aberrometer firstly measures your pupil diameter, which is used to formulate a theoretically perfect reference wavefront shape. The second step is to draw your actual wavefront with potential distortions. The last job is to compare the two wave-fronts point-to-point, so as to work out your wavefront map.

As mentioned before, the reference wavefront is theoretically perfect, which is also flat and circular plane. In contrast, your wavefront map is three-dimensional and contains distortions, created by imperfections on the cornea and the lens. These irregular components refract and focus light rays abnormally.

Other eye problems include dry eye, cataracts, eye surface scarring, and trauma may also arouse higher-order aberrations and focusing problems.