If the refractive indices are same in both medias then there will be no refraction and light will pass without any refraction.And when the incident ray is striking perpendicular to one media to another the light will pass without any refraction.

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The condition for refraction  from medium1 to medium 2, when medium 1 is optically more dense than medium 2 : 

  we have snell's law:      Sin i  / Sin r  =  μ₂ / μ₁        ---- (1)

1)   Condition for  total internal reflection is :  when  r = 90 deg.
     i = i_C =  Sin ⁻¹ (μ₂ / μ₁)

  If the angle of incidence is more than i_C  then  the light rays are reflected back into the medium 1 and do not refract.

2)  When the light is travelling from medium 1 to medium 2 , the refractive indices can be related in any manner.

   if    angle of incidence = i = 0 , then angle of refraction r = 0    from formula (1)
         So,  there is no refraction.

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