What is Strain?
Strain can be defined as unnecessary and inappropriate effort applied to the task at hand. If you strain to see, the eye muscles become tense, the eye does not move freely and the retina becomes desensitised.
In the early stages of a visual problem, it may be quite easy to let go of the strain: if it has become established it can be difficult to let go. That is why so many optometrists believe that the eye is fixed and vision does not change.
As Bates wrote:The eye with normal sight never tries to see. If for any reason, such as the dimness of the light, or the distance of the object, it cannot see a particular point, it shifts to another. It never tries to bring out the point by staring at it, as the eye with imperfect sight is constantly doing.