The dictionary definition of ‘aberration’ is a deviation from the normal or a departure from the usual course. In optometry, it is when light rays are distorted such that they can no longer be brought to a sharp focus on the retina to produce a clear image. This is the basis of most vision problems. First-order (also called low order) aberrations include common problems like nearsightedness, farsightedness, presbyopia and astigmatism. These abnormalities make up 85% of vision problems in people.
Another category of visual defects is called higher-order aberrations. These have less impact on vision and have until recently been largely ignored, partly because they are more complex and could not be treated or even accurately diagnosed.
What are Higher Order Aberrations?
A higher order aberration is a distortion acquired when light passes through an eye with irregularities in the tear film, cornea, aqueous humor, crystalline lens and/or vitreous humor. All eyes have higher order aberrations, but it is the number and extent of them which determines whether or not they will affect your quality of life. Often there are several higher order aberrations in the eye which work together, so it is hard to single out individual symptoms which may point to another diagnosis.
You're probably not familiar with the technical names of higher order aberrations, such as coma, spherical aberration, trefoil and pentafoil, but you might be familiar with their effects. Common symptoms of higher order aberrations include:
Halos and starbursts around light sources are particularly problematic in dim lighting, which can make driving at night very difficult.
Causes of higher order aberrations
In a perfect eye, a wavefront of light would pass through undisturbed and stay smooth, but in nature, rarely is anything perfect. Even small imperfections in the eye’s cornea, lens or other structures can distort the wavefront, giving it a three-dimensional shape, affecting vision quality.
Higher order aberrations can be caused by irregular curves in the lens and cornea, trauma, disease (including cataracts), scarring, dry eyes and large pupils. They are also a common side effect of eye surgeries like LASIK, although over time they may improve for some patients.
Diagnosing and measuring higher order aberrations
While accurate diagnosis of higher order aberrations was a problem in the past, they can now accurately be diagnosed using Wavefront technology. During a Wavefront exam, a special device is used which shines light rays into the eye and measures how they bounce back. A computer program then uses this data to create a 3D map of the eye. Everyone's map is unique, like a fingerprint.
Unlike traditional eye test methods, which rely upon the patient’s subjective response (like saying which lens seems better), a Wavefront diagnosis is objective, very accurate, takes only seconds and requires no patient response.
Treating higher order aberrations
If you believe you are suffering from the effects of higher order aberrations, you should see your eye for a more specific diagnosis. Your treatment options may include:
- Rigid gas permeable contact lenses – because these lenses hold their shape rather than conform to the shape of the cornea, a pool of tears forms underneath which acts as a sort of natural spackle, filling in corneal imperfections. So instead of being distorted by the flawed surface of the cornea, light rays travel through the smooth surface of the contact lens, which results in better vision.
- Wavefront eyeglasses – special, one-of-a-kind eye glass lenses can be made based on the 3D Wavefront map of your eye to give you customized vision correction for your specific needs.
In addition, if you are considering LASIK surgery, you can opt for custom, Wavefront-guided LASIK. This procedure uses Wavefront mapping to tailor the surgery to the specifics of your eye, reducing the risk of complications like higher order aberrations.
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