The human eyeball, or globe, grows substantially after birth, increasing in size by nearly 50% from infancy to adulthood. Although an infant’s eyes appear disproportionately large relative to the rest of their face, their physical size is still immature. This growth process is highly regulated and must be precise to ensure a lifetime of clear vision.
Eye Size: Birth vs. Adulthood
Eye growth is tracked using the axial length, the distance from the front surface of the cornea to the light-sensitive retina at the back of the eye. A full-term newborn’s eye has an average axial length of approximately 16.5 to 17 millimeters, which is significantly shorter than that of a mature adult eye.
The typical adult eye reaches an axial length of about 24 millimeters, representing a growth of roughly seven to eight millimeters. The increase in size is not uniform across all dimensions, but the lengthening of the axis is the most functionally relevant change for vision.
The Critical Phases of Eye Growth
The growth of the eye occurs in distinct, rapid phases rather than steadily. The most significant growth spurt takes place during the first year of life, particularly in the first six months. During this period, the eye rapidly elongates as the visual system adapts to the world outside the womb.
Following the initial rapid phase, the growth rate slows down but continues through early childhood. The eye typically achieves about 90% of its final adult size by the age of three to four years. A second, more gradual growth phase often coincides with puberty, lasting until around age 13 to 16, when the eye generally reaches its final adult dimensions.
Growth and Visual Acuity
The precise growth of the eyeball is directly linked to visual clarity. This relationship is managed by emmetropization, the biological process where the eye attempts to perfectly match its length to its optical power. The goal is emmetropia, a state where light rays focus exactly on the retina without the need for corrective lenses.
Most newborns are born with a slight hyperopia, or farsightedness, because their axial length is too short for their optical components. The eye’s post-birth growth attempts to correct this initial mismatch. If the axial length becomes too long during childhood, the focal point lands in front of the retina, resulting in myopia or nearsightedness.
Conversely, if the eye stops growing too soon, the focal point lands behind the retina, and the person remains hyperopic. The entire process is visually guided, meaning the quality of the image received by the retina signals the eye to either continue or slow its growth. This active feedback mechanism underscores the importance of proper eye development throughout childhood.