Allopurinol Hypersensitivity Syndrome: This condition is a well-documented adverse reaction to allopurinol, characterized by a rash, which can progress to blistering, and is often accompanied by systemic symptoms such as fever and can involve the eyes. The timing of the symptoms in relation to the initiation of allopurinol strongly supports this diagnosis.

Stevens-Johnson Syndrome (SJS): While SJS can be a part of allopurinol hypersensitivity syndrome, it's worth considering separately due to its severity. SJS is characterized by blistering of the skin and mucous membranes, including the eyes, and can be triggered by medications like allopurinol.
Toxic Epidermal Necrolysis (TEN): Similar to SJS, TEN is a severe skin condition usually triggered by medications. It involves widespread skin necrosis and detachment, and the eyes can be severely affected. The recent introduction of allopurinol makes this a plausible, though less common, diagnosis.

Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS): Although less common than allopurinol hypersensitivity syndrome, DRESS is a potentially life-threatening condition that can be triggered by allopurinol. It presents with a rash, fever, lymphadenopathy, and internal organ involvement, which could include the eyes.
Severe Cutaneous Adverse Reaction (SCAR): This is a broad category that includes conditions like SJS, TEN, and DRESS. Recognizing SCAR is crucial due to its potential severity and the need for immediate withdrawal of the offending drug.

Erythema Multiforme: A skin condition characterized by target lesions, which can be triggered by medications or infections. While it can involve the eyes, it's less likely to be directly related to allopurinol compared to other diagnoses listed.
Pemphigus Vulgaris: An autoimmune disease causing blistering of the skin and mucous membranes. It's rare and not typically associated with medication use, making it a less likely diagnosis in this context.