Glasses, also known as eyeglasses or spectacles, are frames bearing lenses worn in front of the eyes for vision correction.
The first eyeglasses are thought to have been made in Italy around 1286, although it has been said that Marco Polo reported seeing pairs of glasses in China as early as 1275.
These early glasses had convex lenses that could correct hyperopia (farsightedness). It was not until 1604 that Johannes Kepler published the first correct explanation as to why convex and concave lenses could correct presbyopia (long-sightedness) and myopia (short-sightedness).
This image shows a typical eye chart. An eye chart is a chart used to measure visual acuity (clarity of vision). Eye charts are often used by health care professionals to screen persons for vision impairment.
The chart is placed at a standardised distance away from the person whose vision is being tested.
The person then attempts to identify the symbols on the chart, starting with the larger symbols and continuing with progressively smaller symbols until the person cannot identify the symbols.
The smallest symbols that can be reliably identified is considered the person’s visual acuity.