Unlock Your Vision: Ace the NBEO Human Development Exam 2026 – Eye-Opening Success Awaits!

The main idea here is how much the eye’s length grows during development. The axial length is the distance from the front of the eye to the back along the optical axis, and it lengthens as a child grows. In newborns the eye is roughly 16 to 17 mm long, and in an adult it’s about 23.5 to 24 mm. The difference is about 7 to 8 mm, which is typically rounded to about 8 mm in exam references. So from birth to adulthood, the axial length increases by about 8 mm.

This growth in length is the major driver of changes in refractive status during development. The cornea and lens also change, but the net result is that the eye shifts from a hyperopic state in infancy toward emmetropia in adulthood. If axial length increases a bit more than the compensating changes in corneal and lenticular power, myopia can develop; if it grows less, residual hyperopia may persist.