Which index of the lenses should I choose?
                    In simplicity, 1.56 Index is the most thick, and 1.74 Index is the thinnest.
                    
                    
                        
                            
                                | (±) 0.00 ~ 2.75 | 3.00 ~ 5.75 | 6.00 ~ 7.75 | 8.00 ~ | 
                            
                                | 1.56 Index | 1.61 Index | 1.67 Index | 1.74 Index | 
                        
                    
                    
                    Please note: the above is just the recommendation, it's not compulsory.
                    For example, if SPH is -2.00, you still can choose 1.67 index; if SPH is -8.00, you can choose 1.56 index, but it will be very thick