Appearing much the same as any other magical lenses, eyes of minute seeing enable the wearer to see 100 times better at distances of 1-ft or less. 

Thus, tiny seams, minute marks, even the impression left from writing can be seen, thus secret compartments and hidden joints can be noted and the information acted upon. 

The effect of wearing but one of these crystals is the same as given for eyes of the eagle.

Note: Mixing eye types is certain to cause immediate insanity for 2-8 (2d4) turns.