Higher-order aberration diagnosis

In the world of eye care, an aberration is defined as a deviation from normal vision. A typical example is experiencing a blurring image. In fact, there are many ocular conditions that describe this concept. A majority of people are quite familiar with vision problems like myopia, hyperopia, presbyopia and astigmatism. But the number of people who know further that these conditions belong to lower-order aberrations is quite limited.

What are higher-order aberrations?

It is less well-known that nearsightedness, farsightedness and astigmatism all belong to lower-order aberrations, which make up 85% of all cases of vision imperfections. And there are also higher-order aberrations such as coma, spherical aberration and trefoil. In general, this category of ocular problem has not received much attention from the public. Higher-order aberrations may cause symptoms such as poor night vision, glare, halos, blurring, starburst patterns, double vision and loss of visual contrast. In most cases, slight higher-order aberrations are common and safe. It is proven that nearly all eyes have at least a certain degree of higher-order aberrations.

Use wavefront technology to diagnose higher-order aberrations

As a distortion, higher-order aberration can be diagnosed by a light wavefront, which records the way in which the light passes through the eye’s refractive components. The distortion of a light wavefront can reflect various potential abnormalities, such as irregularities of the refractive components, abnormal corneal curvature, surgery-caused corneal scarring, trauma, cataracts and so on.

An acquired wavefront map will be compared with a reference one

The diagnosis of higher-order aberrations involves two wavefront maps, a reference one from a theoretically perfect eye and an actual one from a real eye. The wavefront map is created by drawing lines perpendicular to each tip of light rays in bundles, as they pass through the eye. The difference between two wavefront maps represents the amount of aberration the eye has. Until now, more than 60 different shapes of wavefront have been identified, with each reflecting one kind of higher-order aberration. The more complex the wavefront shape, the higher the order of aberration.

Some factors that may contribute to higher-order aberrations

Higher-order aberrations affect people’s vision in a significantly different way, but individuals with larger pupil sizes are more susceptible, especially when their pupils open wider in low light conditions. However, large pupil size is not the only factor that causes higher-order aberrations. Corneal scarring, cataracts and irregular tear film, crystalline lens can also cause higher-order aberrations. People with smaller pupils are also found to suffer from poor vision caused by the disease.

Adaptive optics for correcting higher-order aberrations

Various forms of adaptive optics have been developed to correct higher-order aberrations. All of those treatments aim at modifying the corneal surface, such as new kinds of spectacles, contact lenses, intraocular lenses and refractive surgeries. Adaptive optics can achieve a flatter wavefront shape by reducing the eye’s distortion.