PAL designs have an hourglass shape with a wide distance field and a very narrow intermediate with a slightly wider near portion.  The most common side effect of PAL lenses is blurry or fuzzy peripheral vision. The blurriness is usually most noticeable

through the lower portion of the lens and to the left and right of near and intermediate zones. 

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After extensive studies of eye-lens ergonomics, frame shapes, lens designs, and fitting height NAL® technology was developed based on the natural eye's movement from far distance to close near. 

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NAL® designs have a funnel shape that that begins rim to rim in the distance and gradually decreases to the bottom of the frame.   Since the intermediate and near zones are wider than a PAL the eye moves effortlessly through these zones eliminating the distorted peripheral that plagues PAL designs