Seeing flashes of light, spots, or shimmering patterns—commonly called “seeing stars”—is medically termed photopsia. While temporary visual changes are common during pregnancy, the visual system is highly sensitive to changes in blood pressure and circulation. Therefore, any new or persistent visual disturbance always warrants immediate reporting to a healthcare provider for evaluation.
Temporary Causes: Dehydration and Positional Changes
A frequent and generally harmless cause of brief visual disturbance is orthostatic hypotension, a sudden, temporary drop in blood pressure. This occurs when moving quickly from lying or sitting to standing, causing blood to pool in the lower extremities. The resulting momentary reduction in blood flow to the brain and eyes can lead to dizziness, lightheadedness, or the sensation of seeing stars.
Dehydration significantly contributes to this effect because reduced fluid volume lowers the overall circulating blood volume. Maintaining steady blood sugar levels is also important. Hypoglycemia, or low blood sugar, especially between meals, can trigger lightheadedness and visual changes because the brain is not receiving adequate glucose. These transient episodes are usually resolved quickly by sitting down, rehydrating, or consuming a small snack.
Visual Symptoms Associated with Preeclampsia
Persistent, severe, or sudden vision changes can signal preeclampsia, a serious hypertensive disorder that usually develops after 20 weeks of gestation. Visual disturbances are a classic warning sign, occurring in up to 25% of individuals with severe preeclampsia. Symptoms include seeing spots, flashing lights (photopsia), blurred vision, or temporary loss of vision.
Visual changes related to preeclampsia stem from the disorder’s impact on blood vessels, causing endothelial dysfunction and vasospasm. High blood pressure can cause arteries in the retina—the light-sensitive tissue at the back of the eye—to narrow, restricting blood flow. The resulting lack of oxygen, combined with fluid leakage (edema), can lead to retinal swelling or serous retinal detachment.
In severe cases, high blood pressure can impact the occipital cortex, the area of the brain responsible for processing vision. This can cause cortical blindness, a profound loss of vision that is typically reversible once blood pressure is controlled. Other symptoms associated with preeclampsia include a severe, persistent headache, pain in the upper right side of the abdomen, and new swelling of the face and hands.
Other Systemic Factors Affecting Vision
Beyond blood pressure crises, hormonal shifts can alter pre-existing conditions or trigger new ones, such as migraines. A migraine with aura, sometimes called an ocular migraine, involves visual changes before or during the headache phase. The aura can manifest as shimmering zigzag lines, blind spots, or flashes of light that can last up to an hour.
While migraines without aura often improve during the second and third trimesters, migraines with aura may persist or develop for the first time during pregnancy. These visual effects are caused by temporary changes in electrical activity across the visual cortex. Separately, severe anemia (low red blood cell count) can contribute to visual symptoms. Anemia reduces the blood’s oxygen-carrying capacity, and the resulting systemic fatigue and reduced oxygen delivery to the brain may exacerbate lightheadedness and associated visual dimming.
Knowing When to Seek Urgent Care
A rapid medical assessment is necessary if visual disturbances are sudden, severe, or do not resolve within a few minutes. Contact a healthcare provider immediately if seeing stars or flashes is accompanied by a severe, unrelenting headache not relieved by pain medication. This combination is a significant warning sign requiring urgent evaluation to rule out severe preeclampsia or neurological complications.
Other red flags include pain beneath the ribs, which may signal liver involvement, or new, rapid swelling of the face and hands. Any visual change combined with a blood pressure reading of 160/110 mmHg or higher is an emergency. Prompt medical intervention ensures the safety of both the pregnant individual and the fetus when a serious condition is suspected.