It really depends on your step 1 score. If you did well on step 1, I would highly recommend putting it off so as not to have the possibility of performing worse on step 2. But if Step 1 was not as strong as you would wish for Ophthalmology (>225) you might want to consider taking it early. I wouldn't just take it early to just get it over with because if you do poorly, it may ruin your application.