What is aberration, what does it mean in medicine? How many types of optical defects and aberrations are there?


Aberration is a property of optical systems, such as lenses, that causes light to scatter across a region of space instead of focusing on a point.

What is aberration?

In an ideal lens, light from any point on an object will pass through the lens and converge at a single point on the image plane. Unlike ideal lenses, real lenses do not focus light on a single point. These deviations from ideal lens performance are known as lens aberration.

What does aberration mean in medicine?

The aberration is medically known as optical aberration. Optical aberration, on the other hand, unlike ideal lenses, real lenses do not focus light on a single point. These deviations from ideal lens performance are known as lens aberration.

How many types of optical defects and aberrations?


When considering a single wavelength of light, there are five monochromatic aberrations to consider. These;

spherical deviation,



field curvature,

Distortion (Chromatic Aberration).

When the light is not monochromatic (not of a single wavelength), the lenses have a sixth aberration. But it is not found in mirrors and it is called chromatic aberration.

spherical deviation

In spherical aberration, the light rays coming from a point on the optical axis of a spherical lens do not all meet at the same point of view. Rays that pass closer to the center are focused farther than rays that pass through a circular region near the circle. A circular cross section is formed when a plane held perpendicular to the optical axis is constructed to intersect a cone. The cross-sectional area changes with distance along the optical axis. The smaller size is known as the circle of least confusion. The most spherical aberration-free image is found at this distance.


The name “coma” is derived from the fact that when rays from an off-axis point object are seen by different regions of the lens, the image of a point is blurred in the shape of a comet. In spherical aberration, images of a point object falling on a plane perpendicular to the optical axis are circular of varying sizes and superimposed around a common center. In a coma, the images of an off-axis object point are circular, varying in size, but displaced relative to each other.



Astigmatism is the result of the inability of a single lens region to focus the image from an off-axis point onto a single point. The planes are called meridian plane and sagittal plane, the meridian plane is the plane containing the off-axis object point. Oblique rays, rays that are not in the meridian plane, are focused further than those in the plane. In both cases, the rays meet as lines perpendicular to each other, not at a focal point. Between these two positions, the images are elliptical.

Field curvature and distortion

Field curvature and distortion refer to the position of image points relative to each other. The three aberrations mentioned so far can be corrected by making corrections to the lens design, but these two aberrations may remain. In field curvature, the image of a plane object perpendicular to the optical axis will lie on a paraboloidal surface known as the Petzval surface. Distortion, on the other hand, refers to the distortion of an image. There are two types of distortion namely barrel distortion and pincushion distortion.


Chromatic aberration

The inability of a lens to focus all colors into the same plane is known as chromatic aberration. Chromatic aberration affects magnification along the optical axis and the axis perpendicular to it. The first is known as longitudinal chromatic aberration and the second is known as lateral chromatic aberration. The refractive index of red is therefore the focal length of a lens in air that will be greater for red and green than it will be for blue and violet.

The refractive index is also called refractive index or index of refraction. The speed of light in a medium depends on the properties of the medium. The speed of electromagnetic waves depends on the optical density of the medium. Optical density is the tendency of atoms in a material to recover absorbed electromagnetic energy. The more optically dense the material, the slower the speed of light. One such indicator of a medium’s optical density is its refractive index.

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