While the overall size of the eyeball itself stabilizes relatively early in life, the internal structures of the eye undergo continuous transformations throughout a person’s lifespan. These changes can significantly influence vision and contribute to various age-related eye conditions.
Eye Size Over a Lifetime
The human eyeball experiences its most significant growth during infancy and childhood. At birth, a baby’s eyes are approximately 16.5 millimeters in length, about 70% of their adult size. The eye reaches its adult dimensions, around 24 millimeters, by approximately age 7 or 8.
After this period of early development, the overall size and length of the eyeball remain largely stable. While the external dimensions of the eye become fixed, the components within the eye continue to change and evolve, influencing visual function.
Internal Transformations of the Eye
Even as the eyeball’s size becomes constant, the structures inside it undergo continuous physical and structural changes with age. The crystalline lens, located behind the pupil, gradually thickens and hardens over time. This process reduces its flexibility, impacting its ability to change shape and focus light effectively. The pupil, which controls the amount of light entering the eye, tends to become smaller with age and responds less efficiently to changes in light levels due to weakening muscles.
The vitreous humor, a gel-like substance filling the middle of the eye, also undergoes age-related alterations. It can begin to liquefy and shrink, a process known as syneresis, which may lead to the formation of small, visible protein clumps called floaters. The retina, the light-sensitive tissue at the back of the eye, experiences changes in its light-sensing cells and blood vessels. Accumulations of debris, known as drusen, can also form beneath the retina, particularly in the macular area.
Vision Changes and Conditions as We Age
The internal transformations within the eye have direct consequences for vision and can lead to several common age-related conditions. Presbyopia, often noticeable in the early to mid-40s, results from the lens losing its flexibility, making it difficult to focus on close-up objects. Individuals with presbyopia often find themselves holding reading material farther away to see clearly.
Cataracts involve a clouding of the eye’s natural lens, which can cause vision to become blurry, hazy, or dim. This clouding occurs as proteins within the lens break down and clump together, leading to reduced light transmission to the retina. Glaucoma encompasses a group of conditions that damage the optic nerve, often linked to increased pressure inside the eye. Untreated glaucoma can lead to gradual loss of peripheral vision and, eventually, central vision.
Age-related macular degeneration (AMD) affects the macula, the central part of the retina responsible for sharp, detailed vision. AMD can cause blurred central vision, distorted lines, or blank spots, making activities like reading or recognizing faces challenging. While AMD rarely causes total blindness, it significantly impacts the quality of central vision.