Truffles cure eye diseases

I heard the Prophet ﷺ saying, "Truffles are like Manna (i.e. they grow naturally without any care) and their water heals eye diseases."  

سَمِعْتُ النَّبِيَّ ﷺ يَقُولُ: «الْكَمْأَةُ مِنَ الْمَنِّ وَمَاؤُهَا شِفَاءٌ لِلْعَيْنِ:»