How Could Visual Acuity Improve

How Could Visual Acuity Improve

Without Glasses?

               Although for many years it has been known that

contrast adaptation occurs in the visual system,

it was discovered only recently that contrast

adaptation can partially compensate for poor

focus. This mechanism can also increase visual

acuity without there being any optical changes

in the eye. A compelling demonstration was

published by Webster et al.

   . If the subject views an image that has been low pass filtered or

defocussed and has, accordingly, low contrast or

complete absence of high spatial frequency

components, the visual system increases its sensitivity

at the respective spatial frequencies.As a

result, the image appears sharper).

 

             On the other hand, if an image is viewed that

has high contrast and high spatial frequency

content, the visual system reduces its contrast

sensitivity at the respective spatial frequencies.

Since contrast adaptation has a fast and a

slow component, extended exposure to defocus

makes the image appear sharper . Contrast

adaptation has to be taken into account when an

increase of visual acuity is claimed following

eye training procedures.No biometrical and optical

changes have been found in the eye, following

vision training.

 

Chapter 1 Development of Ocular Refraction: Lessons from Animal Experiments

 

             Illustration of the effect of spatial frequency

selective contrast adaptation on the impression of

focus. First fixate the red spot in the upper picture for

about 20 s. Then rapidly move your fixation to the red

spot in the lower picture. For a short period of time,

the picture on the right appears sharper and has more

contrast, even though the left and right picture are

identical (demonstration replotted with new sample

pictures after Webster et al.

 

Visual acuity can somewhat be improved

under prolonged defocus as a result of

contrast adaptation. In contrast to occasional

claims, there are no solid data showing

a regression of myopia and a reduction

of eye growth as a result of vision training

 

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