The biggest feature of human eyes is the ability to recognize details, which is often expressed by the resolution of viewing angle, called vision.
The standard of expressing vision is the opening angle of the smallest character that human eyes can recognize. The visual acuity of normal eyes is above 1.0. Usually, vision refers to the minimum separable vision of the eyes, not the minimum visible vision.
Therefore, the eye chart reflects the minimum separation visual angle between the two points of the subject's gaze, that is, the minimum separation visual acuity, or the visual angle of 1', which can represent the subject's best visual function.
Extended data:
Abnormal vision
shortsighted
The professional definition is that "distant objects are refracted by the eyeball and focused in front of the retina, rather than forming a clear image on the retina".
Myopia is the most common eye disease among children in China, and the high myopia rate in Chinese mainland is much higher than that in other countries and regions. Many eye diseases caused by high myopia are threatening the eyesight and eye health of many children.
long sight
Nearby objects are refracted by the eyeball and focused on the back of the retina, forming a blurred image on the retina.
So hyperopia patients can't see clearly. Myopia in infants is rare. More than 90% of preschool children are hyperopia, most of which are physiological, reflecting the normal development of eyes.
20% ~ 25% hyperopia is pathological, which is the main reason for children's poor eyesight and eye dysplasia.
amblyopia
Amblyopia is a disease that seriously affects visual function. It refers to those who have no obvious organic lesions in the eyeball, and their near and far vision is less than 0.8, so they can't drive straight. According to statistics, the number of amblyopia patients has exceeded150,000, which has become a social problem that needs urgent attention.
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