Aberrometry is an examination that allows us to study the optical defects of the human eye, in other words, it allows us to evaluate the quality of vision.
The eye is often compared to the optical system of a camera. The pupil has the same function as a camera's diaphragm, controlling the amount of light absorbed by the eye. The crystalline lens (the eye's natural lens) has the function of focusing the images and making them sharper, and finally the retina (the back of the eye) is responsible for capturing the images and sending them to the brain. Like all optical systems, the eye also has certain imperfections that vary from person to person and which result in aberrations that alter the quality of the image viewed.
The aberrometer identifies and quantifies optical aberrations throughout the eye by measuring and analyzing image distortion through the emission of a small-diameter infrared light beam focused on the retina.
The focus of light is affected by the optical systems of the eye and is analyzed by a set of lenses that compare them with the ideal optical system.
Shack-Hartmann systems evaluate the light reflected by the eye and numerous lenses focus on the reflected wavefront. If there are no aberrations, the pattern of dots is uniform and the spacing between the dots is perfectly visible. If there are aberrations, the image appears distorted.
We know that the various optical media are not homogeneous and as such, the light rays are deflected, causing distortions in the wavefront. It is these distortions, which we call aberrations, that we will evaluate in aberrometry.
There are three types of optical aberration: chromatic aberration, diffraction and monochromatic aberration. Chromatic aberration and diffraction depend on the wavelength of the light and have little influence on image quality, not being measured by aberrometers. Monochromatic aberrations, on the other hand, depend essentially on the shape of objects and can be: spherical aberration, coma, astigmatism, field curvature and distortion. It is these which alter visual quality and which are the subject of this examination.
The shape of the wavefront, which comprises all the optical defects, i.e. aberrations, of the human eye, can be analyzed and decomposed using a mathematical function - the Zernick polynomials. The values obtained in the Zernick polynomials are related to the size of the pupil at the time of the examination, since this alters the amount of light received by the eye. Thus, for the same person, comparisons between exams are only valid when they have the same pupil diameter.
Aberrometry is a quick test that is usually carried out on both eyes. No prior preparation is necessary, although your ophthalmologist may need to apply eye drops to dilate the pupil. Contact lens wearers should take a break from wearing them until the examination.
