Do all myopics have standard measurement of thinner retina with each degree of higher myopia? couldn't it be due to defects in anterior layers of eye?

Different issue: Myopes have a combination of greater length of the eye from front to back and a lense that is higher power. All retinas except some pathologic retinas are the same thickness. A myopic eye focuses the light inside the eye in front of the retina as the focusing is too strong. A myopic corrective lens disperses the waves moving the focus backwards onto the retina.