Snellen eye test chart. View of a Snellen eye test chart used for measuring visual acuity. A patient stands a set distance (usually six metres) from the chart, and covers one eye before reading as far down the chart as they can. The letters decrease in size lower down the chart. If they are unable to read a sufficient amount of the chart, lenses of different strengths are used until their vision is sharp enough to allow recognition of the smallest letters. In conjunction with other visual tests, this test allows the diagnosis of eye disorders such as long- and shortsightedness (hypermetropia and myopia). These disorders can be corrected with spectacles or contact lenses.