Useful Optic Formulas for OSE
Focal length
f  = 1/D
f  =  focal length in metre
D = lens power in dioptres, - for concave lens 
       and + for convex lens
Vergence formula
U + D = V
U = object vergence (dioptres)
D = lens power (dioptres)
V = image vergence (dioptres)
Prentice's rule
PD = h.D
PD =  deviation (prism dioptres)
  h  = distance from the optical centre (cm)
  D = lens power (dioptres)
Spherical equivalent
Se = sphere + 1/2 cylind
Se = spherical equivalent (dioptres)
sphere = sphere (dioptres)
cylind = cylinder (dioptres)
Refracting power 
of a spherical surface

DS = (n' - n) / r
DS    = refracting power of surface
(n'- n) = difference in refractive index
       r =  radius of curvature of surface
Reflecting power 
of a spherical mirror

D = 1/f =2/r
D =  surface reflecting power
f  =  focal length
r  =  radius of curvature
Power of a thin lens 
in fluid

Dair / Dfluid = (nlens - nair) / (nlens - nair)
Dair   = power of lens in air
Dfluid = power of lens in fluid
nlens  = refractive index of lens
nfluid  = refractive index of fluid
nair    = 1.000 
IOL power calculation
D = A - 2.5L - 0.9K
D = power in dioptres for emmetropia
A = a constant for each type of lens
L = axial length (mm)
K = average keratometer reading (dioptres)
Effective lens power
Dn = D/(1- dD)
Dn = lens power in the new position (dioptres)
D   = lens power in the old position
d    = difference in lens power in metre; + if moved forward 
         and - if moved backward
Simple magnifier
M = D / 4
M = magnification
D = lens power (in dioptres)
Linear or 
lateral magnification

M = image height / object height 
     = image distance/object distance 
     = U/V

M = linear or lateral magnification
U = object vergence (dioptres)
V = image vergence (dioptres)

Magnification of

M = D eyepiece / D objective

D = power of the objective and eyepiece in dioptres

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