<prompt> Intrastromal corneal ring segments intacs are used in all exceptPost LASIK keratectasiaKeratoconusLow myopiaIrregular astigmatism  <response>: Intacs are not used for irregular astigmatism. Intacs consists of 2 semicircular rings made of PMMA and are used to flatten the cornea. It does not disturb vision. Intacs require atleast 400 microns of corneal stromal thickness. They are used most impoantly for keratoconus. It is also used for low myopia -1 to -3 D. But it has no role in irregular astigmatism which requires contact lenses for correction. 