I assume you mean by optic axis the axial length of the eye, and not the axis of your astigmatism. An axial length of 29 is very long, and does put you at risk of retinal complications from high myopia. You should have a dilated exam with a retina specialist periodically, and immediately if you have sudden light flashes and new floaters. Another reason for progressive myopia may be that the corneal curvature is changing; a keratometry reading and corneal topography will help determine if this is the case.
Yes, Dr. Fazio, it is axis length. I carry out regular check very 6 month, including retina and corneal. For the time being, I have no idea what contributes to the development of my myopia. Is it the elongation of axis or the corneal curvature. Currently my axis length is 29.2 and myopia is -15D. But according to one of my medical report15 years ago, my axis length was 29 and myopia is -10D, is it possible?