The human eye undergoes a unique growth process. While eyes grow significantly from birth, this growth is precisely regulated and affects specific components, influencing vision. Understanding how eyes grow provides insight into common vision conditions that arise throughout life.
The Growth Trajectory
The most substantial period of eye growth occurs from infancy through early childhood. At birth, a baby’s eyes are approximately 16 to 17 millimeters in length, about 70-75% of adult size. Growth continues rapidly, with the eyeball reaching 22.5 to 23 millimeters by three years of age.
After this initial rapid expansion, eye growth decelerates but continues at a slower rate. The eye reaches its full adult size, 24 millimeters in length, by the late teens or early twenties. Although eye dimensions stabilize in early adulthood, minor changes can still occur.
Specific Components of Eye Growth
Eye growth involves an increase in axial length, the measurement from the front (cornea) to the back (retina) of the eyeball. At birth, the axial length averages 16.5 millimeters, expanding to 24 millimeters in adulthood. This elongation influences how light focuses on the retina.
Other parts of the eye, such as the cornea and the lens, do not significantly increase in size or cell number after early development. While the cornea reaches its full size by three months of age, its curvature can change. The lens, though not growing in size, continues to add layers and increase in weight throughout life.
How Eye Growth Influences Vision
Precise eye growth is important for clear vision. The eye’s length must coordinate with the refractive power of the lens and cornea to ensure light focuses directly on the retina. This coordinated development is part of a natural process called emmetropization, where the eye adjusts growth to minimize refractive errors.
Deviations in growth can lead to common refractive errors. If the eyeball grows too long, light focuses in front of the retina, causing myopia (nearsightedness), making distant objects blurry. Conversely, if the eyeball is too short, light focuses behind the retina, causing hyperopia (farsightedness), making nearby objects blurry. Children are born with a mild degree of hyperopia, which corrects itself as the eye grows to length.
Mature Eye Changes
Once the eye completes primary growth phase in early adulthood, it continues to undergo structural and functional changes throughout life, distinct from growth. One common age-related change is presbyopia, beginning at age 40. This condition occurs when the natural lens becomes less flexible and hardens, losing ability to change shape and focus on close-up objects.
Another change is the formation of cataracts, cloudy areas on the lens. This clouding occurs as proteins within the lens break down and clump, reducing light to the retina. These age-related alterations affect vision but are not a result of continued eye growth.