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Dear All,
The modern free form PAL's offer wide variety of progression corridor lenghts - 10, 11, 12, 13, 14, 15, 16mm., and so on.
In the past the rule was to fallow the frame shape deep as a guide - top the deep frames - long coridor and short to short frames, having in mind that, the long coridor offer wide near vision, and short offer narrow.
At present I suppose this is not the right way, because the proper corridor has to correspond to the patient pupils hight at reading position.
I began to observe the client's pupil positions durring the reading, and note that, almost everybody lowers his eyes at maximim 12mm down?!, so he will not be so happy to adapt to progression lengt highet than this level. I did that test with mirror method. So, the conclusion should be more and more short PAL, Am I right?
How do you shoose the proper corridor lenght?
The modern free form PAL's offer wide variety of progression corridor lenghts - 10, 11, 12, 13, 14, 15, 16mm., and so on.
In the past the rule was to fallow the frame shape deep as a guide - top the deep frames - long coridor and short to short frames, having in mind that, the long coridor offer wide near vision, and short offer narrow.
At present I suppose this is not the right way, because the proper corridor has to correspond to the patient pupils hight at reading position.
I began to observe the client's pupil positions durring the reading, and note that, almost everybody lowers his eyes at maximim 12mm down?!, so he will not be so happy to adapt to progression lengt highet than this level. I did that test with mirror method. So, the conclusion should be more and more short PAL, Am I right?
How do you shoose the proper corridor lenght?
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