The eye functions as a convergent optical system with a total power of approximately .

: Provides about 70% of the eye's refractive power (approx. 43 diopters). It has a fixed curvature.

: Provides about 20 diopters . Unlike the cornea, it is flexible and changes shape to focus on near objects, a process known as accommodation .

The (ocular refraction) is the process by which the eye's optical system—primarily the cornea and crystalline lens —bends light to focus it precisely on the retina . When this process works perfectly, it is called emmetropia , and the image of distant objects is sharp. If the light does not focus correctly, it results in an ametropia or refractive error. Anatomy of Ocular Refraction