These patches are common after RD surgery with or without a scleral buckle, with or without gas or air or oil put in the eye. Use the search feature and archives to read about them. Since there are multiple causes it's not possible to tell you how long yours will last. Most likely the gas bubble is the cause but can't say for sure. You need to ask your surgeon. Sometimes these can be permanent and occure 180 degrees away from extensive laser or cryotherapy