Worn by chemists indulging in their passion for working in hot smelly rooms full of poisonous and/or explosive chemicals, lab specs come in three varieties:
The completely clear ones - square with transparent sides.
The coloured ones - slightly rounded, with blue or black edging. Cool.
The presciption ones - hardcore.
Most people however are unaware of the real purpose of lab specs. Since the wearers come into almost daily contact with highly carcinogenic or mutagenic material, great lengths are taken to prevent them from inadvertantly adding to the gene pool. Officially approved lab specs are required to make the wearer sufficiently unattractive that he or she is in no danger of attracting a member of the opposite sex.
This they achieve with great success.