It has been reported in Divine narrations (Ahadith) that Allah (SWT) revealed: I have prepared things for God’s devout servants that no eye has seen and no ear has heard and has not entered the heart of any human being [1]. Of course the damned ones (residents of the hell) will also face amazing things that causes blindness of their eyes, as their sorrow and grief are increased and salty tears come out of their eyes leading to blindness. According to the Quran, as the residents of the heaven face unseen things that cause their eyes to light up; the residents of the hell will be confronted with unknown torments which will amaze them. That is why these torments have been interpreted as unknown and very difficult (Nokr) in the holy Quran; Ayah 87 of Surah Al-Kahf: “A punishment unheard of (before)”.
[1] Beharul Anwaar, Vol., Page 92 & 548; Kanz-ul-Aa’maal, Vol. 15, Page 778, Hadith 43069; Sahih Bokhari, Hadith 4779.