Which of the following is NOT a reason why visual acuity is poor until age 3–5 years?

• A. Foveal cone photoreceptor length and density reach adult levels around age 4
• B. Myelination of the visual pathway is incomplete
• C. The visual cortex is not fully developed in infants
• D. An infant's cornea is often cloudy until age 5

Answer: (D)

Visual acuity improves as the eye and brain mature in tandem—the fovea, the optic pathways, and the visual cortex all undergo changes that slow early vision but gradually enhance it.

The foveal cones reach their mature length and density around age four, which means the retinal sampling of detail becomes fine enough to support sharper vision. If the fovea isn’t yet fully developed, acuity will be limited because the retina isn’t sampling the scene at adult-like resolution.

Myelination of the visual pathway continues after birth, so the transmission of visual signals from the retina through the optic nerve and into the brain is slower and less reliable in infancy. This reduced speed and fidelity dampen the clarity of the visual signal until myelination progresses toward adult patterns.

The visual cortex also matures after birth, with ongoing refinement of cortical maps, receptive fields, and binocular integration. As cortical processing becomes more efficient and precise, acuity improves.

By contrast, saying that an infant’s cornea is often cloudy until age five isn’t a typical developmental constraint for normal vision. Healthy corneas are clear in infancy, and cloudiness would cause broad visual impairment rather than explain the normal gradual improvement in acuity seen through early childhood.