Wavefront Analysis

Lower and higher order aberrations

A glasses prescription describes the eye's lower order aberrations: defocus and astigmatism, which account for most of the blur in most eyes. Real eyes also have higher order aberrations, small irregularities in how light is focused that vary across the pupil and matter most when the pupil is large, at night. Spherical aberration blurs the edges of lights into halos; coma smears points into comet tails; trefoil produces starbursts. Two patients with the same prescription can have very different night vision because of them.

How the measurement is taken

A low-energy beam is focused on the retina and the light reflected back out of the eye passes through an array of tiny lenses onto a sensor. A perfect eye would produce a regular grid of spots; aberrations displace the spots, and the displacement at each point maps the wavefront's deviation. The result is a map of the eye's aberrations across the pupil and a set of numbers describing each type. It takes seconds and needs no contact, though a dilated pupil captures more of the map.

Uses

• Designing custom wavefront-guided LASIK, in which the excimer laser treats the higher order aberrations along with the prescription
• Explaining night vision complaints, halos and glare in patients whose glasses prescription is correct
• Assessing optical quality before and after refractive or cataract surgery, and diagnosing the cause of dissatisfaction after it
• Detecting irregular corneas and early keratoconus alongside tomography, since they produce characteristic aberrations
• Designing wavefront-guided scleral lenses for irregular corneas whose vision is limited by residual aberrations

Wavefront and the consultation

Wavefront analysis may be part of your LASIK consultation where appropriate, both to design the treatment and to screen the eye's optics. Patients with a large amount of higher order aberration, or large pupils, are the ones who gain most from a custom treatment, and the measurement identifies them.