The lines show up as the skin gets thicker. IV seems to respond well to the acid creams - salicylic, lactic, glycolic or urea/uric. The other choice is to literally file it off. Some people do well with a pumice stone. Others do better with heavy-duty nail files from a beauty supply store (we use the 100 grit ones).
I don't know if IV gets bad enough to crack and bleed, but the type we have does, and the files minimize the problem, as does having the person with ichthyosis rub themselves with one thick spot onto another.
Ichthyosis-en-Confetti Type 2
Husband, Nathan - 10, Elliot - 7, Oliver - 4, all affected.
I also have an unaffected daughter, age 8.
email: jennifer at confettiskin dot com
facebook - find me on "ichthyosis mommy spot" or "friends of ichthyosis"