The bottom number indicates the distance at which a person with normal eyesight could read the same line you correctly read.

Thoseglasses would render a man of normal eyesight practically blind.

People with normal eyesight can use it too, and they do.

Those glasses would render a man of normal eyesight practically blind.

Round about two o'clock you will notice a small, dark oval: anyone with normal eyesight can find it quite easily.

The second number is the distance from which people with normal eyesight can read the same line on the eye chart.

It was invisible, at least to normal eyesight.

Easy enough for a toddler with normal eyesight.

The hole was well above the level of normal eyesight.

Suilin found it odd to be able to see considerable distances with his normal eyesight.