Question
My child has been born and their eyes always tear up, and they always cry. What is the principle behind the standard logarithmic visual acuity chart?
Answer
The visual acuity chart is designed based on the principle of visual angle. So what is a visual angle? It is the angle formed by two points outside the eye, which converge at the eye’s node. Under normal circumstances, the human eye can distinguish the smallest distance between two points that form a visual angle, which is known as the minimum visual angle, or one minute of visual angle. The visual acuity chart is designed with one minute of visual angle as the unit.