Acute angle-closure glaucoma is one of the signs of glaucoma attack when the eye pressure suddenly rises. Therefore, glaucoma patients with red eyes accompanied by eye swelling and pain, headache, rainbow vision (rainbow-like circles when looking at lights), and vision loss should immediately go to the ophthalmology department and have their intraocular pressure measured. Red eyes can also be seen in diseases such as conjunctivitis, iritis, and keratitis. ”The redness disappears after the inflammation subsides, and there is usually no loss of vision and the IOP is normal. Iritis is an endogenous inflammation, and some patients have rheumatic disease associated with it. There is photophobia, tearing, eye pain, eye redness, and decreased vision. It has a rapid onset and is prone to recurrence. Complications include cataracts and glaucoma, which are a major threat to vision. Keratitis is mostly caused by bacterial, fungal, and viral infections. Patients may experience pain, photophobia, tearing, vision loss, eye redness, and clouding or ulceration of the cornea (black eye).