Miguel experienced a sudden, inexplicable blindness. tests have shown no physical basis for his symptoms. the most likely diagnosis is

The blindness is considered sudden if the loss of vision develops within a few minutes to a couple of days. It may affect one or both eyes and all or part of a field of vision. Sudden loss of vision can occur for a number of reasons.
The most common causes of sudden loss of vision are physical: damaged retina, Blockage of a major artery of the retina,Eye injury... 
But, tests have shown no physical basis for his symptoms. So, the diagnosis can some serious medical conditions such as a stroke or brain tumour.

It settles nerves, reduces the tension.

The freezing point of the ice is lowered because of the rock salt which then allows the ice to observe heat from the ice cream mixture without it melting.