My son had an eye check up the doc said eyes r completely fine but in class he looks at white board he gets both his eyesball close to his nose what ?

Strabismus?: if you mean that he appears to become crosseyed, with one eye turning in, then he has an intermittent strabismus. A child may lose sight in one eye if he depends on vision from 1 eye only because the other eye is not focused with the dominant eye. A parent can check by shining a light at the eyes--the reflection of the light in both pupils should be in exactly the same spot