Vision loss affects more than 7 million Americans and impacts quality of life, independence, social functioning, and overall health. Common and dangerous conditions causing sudden vision loss include acute angle-closure glaucoma, retinal detachment, retinal artery occlusion, giant cell arteritis, and optic neuritis. Acute angle-closure glaucoma features ocular pain, headache, and nausea; treatment includes pilocarpine eye drops, oral or intravenous acetazolamide, and intravenous mannitol. Retinal detachment presents with a curtain-like visual field defect and usually requires surgical intervention. Retinal artery occlusion causes painless vision loss in patients with vascular risk factors, and interventions aim to prevent vision loss in the other eye. Giant cell arteritis should be suspected in patients older than 50 years with scalp tenderness, jaw claudication, proximal muscle and joint pain, constitutional symptoms, and elevated C-reactive protein level, erythrocyte sedimentation rate, and platelet count. This condition requires immediate initiation of empiric steroids to prevent vision loss in the unaffected eye, as well as referral for a temporal artery biopsy. Optic neuritis is a demyelinating condition that features color desaturation, relative afferent pupillary defect, and pain with extraocular muscle movements. Treatment requires high-dose steroids, and patients should be evaluated for multiple sclerosis.