Differential diagnosis for red eye

● Conjunctival Problems

Bacterial conjunctivitis 
Viral conjunctivitis 
Chlamydial conjunctivitis 
Allergic conjunctivitis 

● Corneal Disorders

Corneal Ulceration
Herpes Simplex Keratitis
Corneal Abrasion
Uveal and Scleral Inflammation

● Anterior Uveitis (Iritis/Iridocyclitis)

Episcleritis
Scleritis

● Glaucoma

Acute Angle-Closure Glaucoma

● Miscellaneous/Adnexal Disorders

Blepharitis
Inflamed Pterygium/  Pingueculum
Orbital Cellulitis
Dacryocystitis