Vomiting is a common and unpleasant experience. The physical strain it causes often leads to a noticeable, though usually harmless, side effect in the eyes. While the dramatic appearance of a red eye after a severe episode can cause alarm, significant, long-term damage to vision is extremely rare. Understanding the underlying physical mechanisms and distinguishing between common cosmetic effects and rare severe symptoms can provide reassurance.
The Mechanism: Pressure Changes During Vomiting
The act of vomiting is a powerful, coordinated reflex that involves a rapid and forceful contraction of the body’s musculature. Before the stomach contents are expelled, a deep breath is taken, and the glottis closes to prevent aspiration. Simultaneously, the abdominal wall muscles and the diaphragm contract vigorously against a closed airway, which is known as a Valsalva maneuver.
This sudden and forceful contraction causes a spike in both intra-abdominal and intra-thoracic pressure. Because the blood vessels in the head and neck are connected to the circulatory system, this pressure surge impedes the normal venous return of blood from the head back to the heart. This blockage causes a rapid increase in pressure within the venous system of the head, including the capillaries supplying the eyes.
This increase in pressure is the direct mechanical cause of most eye-related symptoms following severe retching or vomiting. The sudden pressure overload can momentarily affect the fine blood vessels in the eye and surrounding tissues. This pressure spike affects the small blood vessels nearest the surface, causing them to rupture and bleed in a confined space.
Common Eye Effects: Subconjunctival Hemorrhage
The most frequent and visible result of a severe vomiting episode is a subconjunctival hemorrhage, often appearing as a bright red patch on the white of the eye. This effect occurs when one of the tiny capillaries beneath the conjunctiva—the thin, transparent membrane covering the sclera—breaks due to the increased venous pressure. The blood then becomes trapped between the sclera and the conjunctiva, creating a red spot.
Despite its dramatic appearance, a subconjunctival hemorrhage is essentially a bruise on the surface of the eye and is painless. It does not affect vision, as the bleeding is superficial and does not involve the cornea, iris, or pupil. Patients may report a mild scratchy or foreign body sensation on the eye’s surface, but this is a minor irritation.
The condition is benign and self-limiting, resolving on its own. Like a bruise, the bright red patch will gradually change color over time as the body reabsorbs the blood, transitioning to shades of brown, purple, or yellow. Resolution typically takes between one and three weeks, depending on the size of the hemorrhage. Reassurance is often the only management needed, as the appearance of the hemorrhage can cause anxiety due to its visibility.
When to Worry: Recognizing Severe Visual Changes
While subconjunctival hemorrhages are common and harmless, the intense pressure from forceful vomiting can theoretically lead to rare, more serious complications. These are generally only associated with chronic, severe retching or in individuals with pre-existing risk factors, such as extreme nearsightedness. One complication is a retinal hemorrhage, where bleeding occurs in the light-sensitive tissue at the back of the eye.
More concerning, though exceptionally rare, is the potential for a retinal tear or detachment. The retina captures light and sends visual signals to the brain; its detachment is a medical emergency that can lead to permanent vision loss. While straining, coughing, or vomiting are not known to directly cause a retinal tear or detachment in a healthy eye, the pressure spike could aggravate an already weakened retina, such as one with pre-existing lattice degeneration.
Recognizing specific symptoms is important and warrants immediate medical attention. Red flags include a sudden onset of new, persistent floaters—dark spots or squiggly lines drifting across the vision—or flashes of light (photopsia). A dark shadow or a “curtain” descending over the field of vision is a symptom of a possible detached retina and requires an emergency evaluation by an eye care professional. Following any severe vomiting episode, focusing on rest and hydration supports recovery.