Heat stroke is a severe medical emergency characterized by a core body temperature rising above 104°F (40°C). This extreme elevation overwhelms the body’s ability to regulate its temperature, causing widespread cellular damage and multi-organ dysfunction. The systemic failure triggered by heat stroke can directly and indirectly affect the highly sensitive structures of the eye. Effects can range from temporary blurring to permanent vision damage.
How Heat Stroke Affects the Body’s Systems
The physiological failures initiated by heat stroke create a hostile environment for the eye, which depends on stable blood flow and hydration. A primary systemic effect is severe dehydration from fluid loss, which reduces plasma volume in the bloodstream. This fluid loss lessens tear production and increases blood viscosity, making the blood thicker and more prone to clotting.
Extreme hyperthermia causes widespread endothelial damage, injuring the lining of blood vessels throughout the body. This triggers a systemic inflammatory response syndrome (SIRS), where inflammatory molecules damage delicate tissue, including the fine vasculature supplying the eye. Cellular injury and inflammation activate the coagulation cascade, increasing the risk of microvascular blockages in small capillaries.
Circulatory collapse occurs as the body struggles to maintain blood pressure while redirecting flow for cooling. This instability can lead to low blood pressure (hypotension) or shock, reducing the pressure that drives blood flow to the brain and eyes. Reduced perfusion of the optic nerve and retina quickly leads to ischemia, a lack of oxygen that causes rapid cell death in these structures.
Ocular Manifestations of Extreme Heat Stress
The systemic stress of heat stroke results in specific conditions affecting both the surface and internal structures of the eye. The most common surface effect is severe dry eye syndrome (keratoconjunctivitis sicca), resulting from dehydration and reduced tear film quality. This dryness leaves the cornea and conjunctiva vulnerable to irritation, inflammation, and erosion, often causing a gritty sensation and redness.
Temporary visual disturbances are frequent symptoms during a heat stroke episode, including blurred or double vision. Patients may also experience photophobia, which is extreme sensitivity to light, linked to systemic neurologic distress. These temporary effects usually resolve once the core body temperature is stabilized and central nervous system dysfunction abates.
More concerning is the potentially permanent damage affecting the vascular supply of the eye. Thickened blood and circulatory stress can lead to an “eye stroke,” the lay term for anterior ischemic optic neuropathy (AION) or retinal artery occlusion. This occurs when blood flow to the optic nerve or retina is severely impaired or blocked by a clot, causing sudden vision loss. Severe circulatory fluctuations and clotting issues can also lead to retinal hemorrhages.
Mitigating Risk and Seeking Emergency Care
The most effective strategy against heat stroke and its ocular complications is prevention, focusing on maintaining hydration and avoiding prolonged heat exposure. It is important to drink plenty of fluids consistently, even before feeling thirsty, to counteract fluid loss from sweating. Avoiding strenuous activity during the hottest parts of the day (typically 10 a.m. to 4 p.m.) and seeking air-conditioned or shaded environments are also effective preventative steps.
If heat stroke is suspected, treat it as a life-threatening medical emergency and contact emergency medical services immediately. While waiting for help, move the person to a cooler area and rapidly cool them, ideally through methods like cold water immersion or misting the skin while fanning. Do not give fluids to a person experiencing confusion or unconsciousness due to the risk of aspiration.
After recovery from the acute episode, specialized ocular follow-up is necessary to check for subtle, long-term damage. Consult an ophthalmologist or optometrist for a comprehensive eye exam, including a check for latent retinal or optic nerve injury, even if vision appears normal. This is important for individuals with underlying conditions like diabetes or hypertension, which increase the risk for vascular problems.