reciprocal value of the focal length of a lens measured in metres: a power of +5 dpt therefore has a reciprocal length of 1/5 metres or 20 centimetres. What is long-sightedness? In the case of long-sightedness [...] read we require a functioning retinal surface of around 2.5 degrees to the left and right of the fixation point, i.e. a visual angle of around 5 degrees in total. A reading angle is necessary as our eyes [...] required for reading travel timetables. Other minimum values include: 0.4 for watching television, 0.5 for reading the newspaper and 0.7 for reading a telephone directory. Is the ability of the eye to read
