The squiggly lines you are seeing are the result of leafminer damage. The citrus leafminer is a moth larva that feeds on the tissue between the upper and lower leaf surfaces and produces serpentine mines as it feeds. This results in curling leaves that often have a silvery film over them. The problem frequently seems worse on young trees because of the numerous flushes of new growth which are most susceptible to this pest. As the tree ages, the damage appears less severe. To control this pest, apply a fine, horticultural oil spray to upper and lower leaf surfaces whenever a new flush appears.

Additional Resource
http://trec.ifas.ufl.edu/mannion/pdfs/CitrusLeafminer.pdf