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 [...] Objects in our near vision appear blurred. This process usually becomes apparent between the ages of 40 and 65. You will then need a pair of glasses to be able to read at a normal distance of approximately
