The formula for iseikonic lenses (without cylinder) is:

  
    
      
        
          
            Magnification
          
        
        =
        
          
            1
            
              (
              1
              −
              (
              
                
                  t
                  n
                
              
              )
              P
              )
            
          
        
        ⋅
        
          
            1
            
              (
              1
              −
              h
              F
              )
            
          
        
      
    
    {\displaystyle {\textrm {Magnification}}={\frac {1}{(1-({\frac {t}{n}})P)}}\cdot {\frac {1}{(1-hF)}}}
  where:  t = center thickness (in metres);n = refractive index;P = front base curve (in 1/metres);h = vertex distance (in metres);F = back vertex power (in 1/metres), (essentially, the prescription for the lens, quoted in diopters).
Suppose that for both eyes the other parameters are identical, namely t = 1 mm = 0.001 m, n = 1.6, P = 5 m−1, and h = 15 mm = 0.015 m.  
Then for the first eye 
  
    
      
        
          
            Magnification
          
        
        =
        
          
            1
            
              (
              1
              −
              (
              0.001
              
                /
              
              1.6
              )
              ×
              5
              )
            
          
        
        ⋅
        
          
            1
            
              (
              1
              −
              0.015
              ×
              −
              1
              )
            
          
        
        =
        1.0031
        ×
        0.9852
        =
        0.9883
        =
        98.83
        
        %
      
    
    {\displaystyle {\textrm {Magnification}}={\frac {1}{(1-(0.001/1.6)\times 5)}}\cdot {\frac {1}{(1-0.015\times -1)}}=1.0031\times 0.9852=0.9883=98.83\,\%}
  , 
while for the second eye 
  
    
      
        
          
            Magnification
          
        
        =
        
          
            1
            
              (
              1
              −
              (
              0.001
              
                /
              
              1.6
              )
              ×
              5
              )
            
          
        
        ⋅
        
          
            1
            
              (
              1
              −
              0.015
              ×
              −
              4
              )
            
          
        
        =
        1.0031
        ×
        0.9434
        =
        0.9464
        =
        94.64
        
        %
      
    
    {\displaystyle {\textrm {Magnification}}={\frac {1}{(1-(0.001/1.6)\times 5)}}\cdot {\frac {1}{(1-0.015\times -4)}}=1.0031\times 0.9434=0.9464=94.64\,\%}
  .