Erythema multiforme (EM) is a medical term for skin eruptions. Doctors/medical experts like to use this term if the skin problem is localized, i.e. limited to small patches on the body.

Stevens-Johnson syndrome (SJS) and "toxic epidermal necrolysis"  (TEN, Lyell´s syndrome) are two variants of the same condition- a skin exfoliating adverse drug reaction that causes blisters on both the outside, and inside of the body.  Two doctors, Dr Stevens and Dr Johnson, identified this adverse drug reaction in the 1920's, and the words "toxic epidermal necrolysis" loosely translated mean "poisonous killing of skin".

Stevens Johnson Syndrome and Toxic Epidermal Necrolysis are insidious, potentially deadly variants of the same disease in which the human body fools itself into thinking the skin, mucous membranes, and visceral organs are foreign invaders; so the body literally attempts to rid itself of the skin and internal organs.

Ocular involvement is common in patients with SJS and TEN. 
Late complications are more frequent in patients with severe initial eye involvement but may also develop in patients without patent initial ocular
symptoms.

There's a growing body of evidence that if SJS is correctly diagnosed in the early stages and medically treated correctly, it will not get to the blistering and life-threatening stage.

SJS/TEN is essentially drug-induced. A few cases are related to infectious agents as mycoplasma pneumoniae, or other viruses and bacteria. Some cases remain unexplained.

SJS/TEN after-effects can include:
painful eyes, dry eye syndrome, photophobia, ingrowing eyelashes, 
corneal ulcers, lid/corneal scarring, symblepharon, blindness, liver damage, lung damage, asthma/allergy, runny nose, joint pain, loss of nails or hair, 
sun sensitivity, depression, chronic fatigue syndrome....