Final answer:
The squinting eyes in the 3-year-old child is most likely due to hyperopia, a condition where the eyes cannot properly focus on nearby objects, which can be corrected with the use of glasses.
Step-by-step explanation:
The cause of squinting eyes in a 3-year-old child can vary, but one common reason is hyperopia (farsightedness), where the child's eyes may struggle to focus on nearby objects, leading to squinting. Hyperopia occurs when the eyes are unable to converge light rays from close objects onto the retina, producing a blurry image. This can be due to insufficient power in the lens of the eye or the eye being too short. Children with hyperopia may wear glasses that contain convex lenses to correct this condition, allowing them to see close objects more clearly without squinting.
Hyperopia contrasts with myopia (nearsightedness), where distant objects are blurred, and with astigmatism, where the eye's irregular shape causes blurred vision at any distance. While the hyperopic eye struggles to focus on close objects, the myopic eye does so with distant ones.