# How to calculate visual acuity?

Having mastered the concept of the angular size of an object, you can now understand how to calculate visual acuity, and even perform such a measurement.

Draw on a sheet of paper twenty equal black lines with a length of a match (5 cm) and a millimeter of thickness, so that they fill the square. Having attached this drawing to a well-lit wall, move away from it until you notice that the lines no longer differ separately, but merge into a solid gray background. Measure this distance and calculate - you already know how - the angle of view, under which you cease to distinguish strips of 1 mm thickness. If this angle is equal to one minute, then your visual acuity is normal, if it is three minutes, then acuity is one third of normal vision, and so on.

Let's solve the following problem. Look at the drawing. The lines merge for your eye at a distance of 2 meters. Do you have normal visual acuity?

We know that from a distance of 57 mm a strip of 1 mm width is visible at an angle of 1 degree, that is, in 60 minutes. Consequently, from a distance of 2000 mm, it is visible at an angle x, which is determined from the proportion:

x: 60 = 57: 2000

x = 1,7 minutes

In this case, the visual acuity is below normal and is: