There is no evidence to show that contact lenses can prevent myopia from worsening. Myopia generally worsens over time, mainly during childhood and teenage years, and may slow down or stop when one is in their 20s. However, one study concluded that contact lenses (rigid gas permeable) could slow the progression of myopia or nearsightedness compared to soft contact lenses. The findings were not significant enough to warrant a prescription of RGP lenses. Besides, the effect of RGP lenses is mild and may not be permanent. Orthokeratology lenses, which are worn during sleep, may however temporarily reduce or correct myopia.