In an ideal world, everyone would have perfectly-shaped eyes. The reality, however, is that practically every eye has some form of aberration somewhere in it. These aberrations may or may not cause vision problems, but don't be too surprised if your eye doctor informs you that you are having difficulties due to some such imperfection. In addition to relatively straightforward vision problems such as nearsightedness and farsightedness, it is also possible to suffer higher order aberrations that distort images in a much more complex manner.
What Is an Aberration?
Any deviation from normal refraction of incoming light waves can be considered an aberration, even if that aberration is so minor that it causes no vision problems whatsoever. Any change in the shape, consistency, or functionality of any part of the eye can distort the way light is focused and turned into images by the eye. Nearsightedness and farsightedness involve a simple distortion of the eyeball's shape, while astigmatism usually involves a fairly simple distortion of the cornea. These conditions are thus easy to diagnose and correct.
Causes
Higher order aberrations can be caused by a number of factors. The thickened proteins that create cataracts, for instance, can interfere with proper refraction, as can a lack of tear film in people with chronically dry eyes. Corneal scarring from disease or injury, and irregularities in the lens or vitreous humor (the gelatinous substance inside the eye), can also cause higher order aberrations. These little imperfections in the eye can bend and shift the waveforms of incoming light in all sorts of ways. Eye doctors have learned to recognize these different types of distortion, assigning them such names as trefoil, quadrafoil, coma, defocus, and spherical aberration.
Treatment
Treatment for a higher order aberration involves either correcting the underlying cause, or compensating for the resulting vision problem. If your higher order aberration is the result of cataracts or dry eyes, for instance, your eye care professional can recommend treatments for these disorders that to dramatically improve your vision. The fitting of intraocular lens can resolve not only cataracts but other lens disorders as well.
If your eye's vitreous humor is contributing to the problem, vitrectomy or other procedures can address that issue. You may find that prescription eyewear or refractive laser surgeries such as LASIK can correct your vision adequately. Talk to your eye care professional about which treatments can help your higher order aberrations.