Embryonic lens of the human eye as an optical structure.

The spherical aberration of the excised embryonic (18 to 22 weeks) human lens was determined by photographing the refractive effects of the lens on fine parallel laser beams. All lenses showed little evidence of focal variation with laser position although a slight tendency toward positive (undercorrected) spherical aberration was noted. One lens from the eye of a newborn showed slight negative (overcorrected) aberration. It is assumed that the continued growth of the lens, with central compression of old tissue, produces a refractive index distribution which contributes to lens optical quality, even in the uterine environment. Frozen sections of embryo eyes of the same period (18 to 22 weeks) indicate that a major part of the change from a spherical to an elliptical lens shape takes place between the fourth and fifth month of development.