'Great vision' is translated into Italian in more than one way depending on what type of 'vision' is in question.
Grande visione is the most straight-forward Italian translation, but this would be used to refer to an apparition, rather than anything else. However, if you mean 'vision' as in 'eyesight', then the more common phrase would be buona visione which actually means 'good vision' rather than 'great'. To complicate things even further, there is another option too, if, by 'vision', you mean 'insight' rather than 'eyesight'. If this were the case, you would use the phrase grande intuizione.
The adjective grande also works as something of a 'super-word' that can reflect a whole range of meanings including 'great', 'large', 'big', and 'grand' amongst others. Some examples of the various uses for grande include: un grand'albero (a tall tree), un grande fumatore (a heavy smoker), grande calore (intense heat), or the phrase 'a gran voce' (which means 'loudly').
As shown by the last example, grande, can often be shortened to gran in spoken Italian. This is conventionally done by native speakers to make a sentence flow, but is grammatically optional. However, one rule to watch out for when using gran is that it is never used before vowels (grand' being the preferred shortened version in this case), or plural nouns.
