Higher-order aberration diagnosis

It is less known that nearsightedness, farsightedness and astigmatism all belong to lower-order aberrations. And there are also higher-order aberrations such as coma, spherical aberration and trefoil. 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.

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

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

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.

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 surgery. Adaptive optics can achieve a flatter wavefront shape by reducing the eye’s distortion.

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