and 30.2 ) The total spectrum of diseases that cause visual impairment can be understood best if the visual pathway is divided into its parts, and each part is considered sequentially ( Table 30.1 ) Vision may be limited by periorbital diseases such as periorbital cellulitis, tumor, infection, or allergic swelling of the eyelids Orbital cellulitis should be considered if decreased visual acuity, proptosis, ophthalmoplegia, or pain with eye movements is present Blunt trauma to the eye may cause a blowout fracture of the orbit The weakest portion of the orbit, the floor, most commonly breaks, and this may entrap the extraocular muscles Visual impairment may be limited to double vision when looking in a certain direction, particularly upward Testing the extraocular movements reveal the limitation Careful inspection of the globe is also necessary Diseases of the cornea that cause visual impairment are predominantly infectious or traumatic Infections of the cornea and conjunctiva can be caused by bacteria, viruses, and fungi (see Chapters 27 Eye: Red Eye and 123 Ophthalmic Emergencies ) All these diseases may present as a unilateral or bilateral process, usually affecting only the conjunctiva and cornea Onset is variable but usually occurs over or days, and vision is not greatly impaired In the newborn period, gonococcal, chlamydial, and herpetic infections must be considered Staphylococcus species are the leading cause of bacterial keratitis Pseudomonas species is the most commonly isolated bacteria in patients who wear contact lenses In the United States, the most common corneal infection that causes permanent visual impairment is herpes simplex keratoconjunctivitis, whereas trachoma infection is the most common cause worldwide A careful ophthalmoscopic or slit lamp examination will reveal the characteristic dendritic ulcers of herpes simplex infection after the eye has been stained with fluorescein Unless this disease is excluded, steroid-containing medications should not be used With a recent eye injury or foreign-body intrusion, fungal infections are possible There are various types of traumatic injuries to the cornea Injury secondary to alkali burns constitute one of the true ophthalmologic emergencies Alkali burns in general carry a worse prognosis than acid burns Immediate copious irrigation of the eye with normal saline is imperative to prevent permanent visual impairment and to preserve visual acuity Both ultraviolet and infrared light can cause damage to the cornea, resulting in severe pain and photophobia within 24 hours of exposure Lacerations with perforation of the cornea usually affect other parts of the eye as well and can lead to significant visual impairment Careful inspection of the globe with associated lid trauma is mandatory The anterior chamber of the eye consists of the aqueous humor, the iris, and the lens Acute iritis is rare in children, and the cause is often uncertain There is a sudden onset of pain, redness, and photophobia that usually affects one eye only The degree of visual impairment varies with the severity of inflammation Certain diseases, such as juvenile idiopathic arthritis, have associated iritis Blunt trauma can also cause iritis, but vision is only slightly impaired unless other structures are involved Traumatic iritis often presents 24 to 72 hours after the trauma TABLE 30.1 CAUSES OF ACUTE VISUAL DISTURBANCES Traumatic Nontraumatic Periorbital Eyelid hematoma, edema from trauma Cornea and conjunctiva Cortex Chemical burns, thermal burns, ultraviolet or infrared burns, laceration of cornea Traumatic iritis, hyphema, posttraumatic cataract, dislocation of lens, glaucoma Vitreous hemorrhage Severed retinal artery, retinal tears or detachment, commotio retinae Head trauma Orbital or periorbital cellulitis, tumor, allergic edema Conjunctivitis (bacterial, viral, fungal) Other Carotid artery trauma Anterior chamber Posterior chamber Retina Acute iritis, glaucoma, uveitis Endophthalmitis Retinal vein or artery obstruction, spontaneous Optic neuritis, toxins, hysteria, hypoglycemia, leukemia, cerebrovascular accidents, migraine, multiple sclerosis, acute disseminated encephalomyelitis, meningitis, encephalitis, seizure, cerebral venous sinus thrombosis, idiopathic intracranial hypertension, posterior reversible encephalopathy syndrome Poisoning Shunt malfunction Vitamin A deficiencies Measles Neoplasm