What is aberration in optics

Higher order aberrations

Higher order aberrations are optical aberrations in the eye that always occur when the light falling into the eye cannot be bent and refracted correctly. Common aberrations are nearsightedness and farsightedness or astigmatism.

 

Higher-order aberrations (HOA, from the English "higher-order aberrations") are optical aberrations in the eye that are much less noticeable and at the same time more complex than myopia, hyperopia and astigmatism. Because of this, they cannot be corrected with conventional glasses or contact lenses.

If your ophthalmologist has the necessary special equipment to determine optical aberrations (e.g. for wavefront analysis) and it turns out that your eyes are affected to a considerable extent, you may be wondering what exactly this means and what effects it may have on your eyesight .

Higher order aberrations have relatively unknown names - for example coma, spherical aberration or trefoil. They can be the reason that you see worse at night, that you notice glare, a glow around light sources, blurred images, radial patterns or double images.

No eye is perfect; higher order aberrations can be seen in each to some degree. So if you get a diagnosis like this, don't worry at first as long as your vision is not impaired.

What exactly is a higher order optical aberration?

A higher order aberration is a distortion that occurs when a wavefront of light hits irregularities in the refractive apparatus of the eye (e.g. tear film, cornea, anterior chamber, lens and vitreous humor).

Unnatural curvatures of the cornea or lens can add to the distortion caused by the light wavefront. Severe higher-order aberrations can also arise as a result of scars on the cornea after eye surgery, trauma after blunt injuries or eye diseases.

The clouding of the lens of the eye in a cataract can also cause aberrations. And last but not least, they can arise when there is insufficient natural tear film in dry eyes, which normally bends and breaks light rays in such a way that objects are focused and sharply depicted.

Common wavefront shapes

 

This overview shows the more common forms of aberration that occur when a wavefront of light hits eyes with imperfect eyesight. A theoretically perfect eye is represented as an aberration-free, flat surface.

How are optical aberrations determined?

Higher order aberrations are detected by identifying the warps that occur when a wavefront of light hits your eye.

Since no eye is optically perfect, a uniform wavefront of light rays produces very specific three-dimensional distorted shapes on your eye. So far, more than 60 different wavefront shapes have been identified.

To describe the refractive errors of an eye, the aberrations are divided into two categories:

    • To the Low order aberrations Mainly shortsighted and farsightedness as well as astigmatism belong.
    • The Higher order aberrations include many different aberrations. Some have names like coma, trefoil, and spherical aberration.

 

What is the effect of higher order aberrations on eyesight?

The effects of higher order aberrations on eyesight depend on several factors. This also includes the actual cause of the aberration.

People with naturally large pupils are generally more likely to have problems with symptoms that affect vision. Especially when the pupil widens even more in poor lighting conditions. However, people with small or medium-sized pupils can also have significant problems with their vision if the aberrations are caused, for example, by scarring on the cornea or cataracts that cloud the lens of the eye. In addition, some studies have identified specific HOAs that affect the quality of vision in eyes with smaller pupils.

A large number of certain higher-order aberrations can have severe, and in the worst case even disabling effects on vision.

What symptoms are associated with higher order aberrations?

Several different optical aberrations usually work together in one eye. Therefore, it is difficult to relate a particular form of aberration to a specific symptom. Nonetheless, higher order aberrations will also occur

    • Double vision,
    • Blurring,
    • Halos,
    • Radial patterns,
    • decreased contrast vision
    • and poor night vision

connected.

Can higher order aberrations be corrected?

Meanwhile, higher order aberrations are being studied with great care because they can finally be made using the Wavefront technology (aberrometry) be diagnosed. In addition, the aberrations have also been observed more often as a side effect after refractive surgery and have been the subject of greater attention.

Various methods of adaptive optics are currently being developed in order to be able to individually correct higher order aberrations. These include novel spectacle lenses, contact lenses and intraocular lenses, as well as surgical interventions that change the surface of the eye or cornea.

The goal of adaptive optics is vision correction that flattens the shape of the wavefront that appears on the pupil. For this, the actual deformation should be compensated for.

However, adaptive optics may not be able to pinpoint specific physical defects in the refractive apparatus that are the root cause of the deformations.