Combine cream cheese and milk in the bowl of a small slow cooker. Cover, and cook on high 45 minutes, giving it a good stir. The cheese should be melted and creamy. Add the Parmesan, crab meat, dried onion, Old Bay, garlic powder, black pepper, and Worcestershire, and stir to combine. Cover and cook 30 minutes. Give it a good stir again, and add the lemon juice, if using. Remove from the slow cooker to a serving bowl, and garnish with fresh chives.