Our eyes focus different wavelengths of light differently through a process called chromatic aberration. Chromatic aberration occurs because different wavelengths of light have different refractive indices, meaning they bend or change direction to varying degrees when passing through a lens.
In the human eye, the cornea and lens work together to focus light onto the retina, which contains the light-sensitive cells (cones and rods). The cornea is primarily responsible for bending incoming light, and the lens further adjusts the focus to ensure a sharp image is formed on the retina.
However, due to the differences in refractive indices for different wavelengths of light, the focal length of the eye's lens varies. Blue light, for example, has a shorter wavelength and is refracted more than red light, which has a longer wavelength.
This difference in refraction causes the various wavelengths of light to converge at slightly different focal points on the retina. As a result, when light containing multiple wavelengths enters the eye, the image formed on the retina can have slight blurring or color fringing.
To compensate for chromatic aberration, the human eye uses a combination of optical and neural mechanisms. The optical mechanism involves the shape and structure of the lens, which helps to reduce the chromatic aberration to some extent. Additionally, the neural mechanism involves the brain's processing of the information received from the cones in the retina, enabling us to perceive a sharp and well-defined image.
While the eye's optical and neural mechanisms mitigate chromatic aberration, it is not completely eliminated. However, the effect is generally minor and does not significantly impact our everyday vision.