A am not very clear by the term "angle of deviation". I believe it is another term used for angle of refraction.
In the phenomenon of refraction of light the angle that a ray of light falling on surface separating two mediums, makes with the normal to the surface is called angle of incidence. As the light enters the second medium it bends or refracts. The angle this bent light makes with the normal is called the angle of refraction.
The extent to which the light bends or the relationship between the angels of incidence and angle of refraction depends on the refractive index between the two medium.
The refractive index (n) is constant for a pair of mediums and is defined by the relationship:
n = (sin i)/(sin r)
Where i is angle of incidence and r is angle of refraction.
Light propagates in a straight line in a medium of uniform density. However when light travels from one medium to another medium of higher density, it bends towards normal in the higher density medium and vice versa. The principle of light bending in denser medium when light passes from lighter medium and bending away when the light enters from a denser to a lighter medium is called refraction. The ratio of the sine of the angle of refraction and the sine of the angle is called the refractive index of the denser medium with respect to lighter medium. So the Angle of incidence - angle of refraction is the deviation of the refracted ray from the angle of incidence.
The angle formed by a ray incident on a surface and a perpendicular to the surface at the point of incidence is called the angle of incidence and the angle between the direction of the refracted ray and the direction of the incident ray when a ray of light passes from one medium to another is called the angle of deviation.