Vision “going in and out” is medically termed transient vision fluctuation or transient vision loss. This describes a temporary change in visual clarity or the visual field, lasting seconds, minutes, or occasionally longer, and affecting one or both eyes. While alarming, the underlying causes range widely from benign, easily corrected issues to serious conditions requiring immediate medical evaluation.
Common, Temporary Triggers
The most frequent reasons for temporary vision changes relate to lifestyle and environmental factors. Prolonged near-work, such as staring at digital screens, can lead to eye fatigue (asthenopia). This strain reduces the blink rate and overworks the small muscles responsible for focusing, resulting in intermittent blurring that resolves with rest.
Environmental conditions, such as low humidity or wind exposure, often exacerbate dry eyes, causing the tear film to evaporate too quickly. When the tear layer breaks up, it leads to momentary blurring of vision until a full blink restores the film. This fluctuation is often relieved by conscious blinking or using lubricating eye drops.
Sudden changes in posture can trigger brief visual dimming due to a temporary drop in blood pressure, known as orthostatic hypotension. Standing up quickly momentarily reduces blood flow to the brain and eyes, causing a fleeting “grey-out” or tunnel vision effect. This reduction in cerebral perfusion lasts only a few seconds before the body’s regulatory systems compensate.
Ocular Surface and Refractive Causes
Issues with the tear film’s stability or the eye’s structure can cause fluctuating vision beyond simple environmental dryness. The tear film is complex, and abnormalities in its mucus or oil components can lead to transient visual blurring. Patients often notice that vision improves immediately after a blink but quickly blurs again as the unstable tear layer deteriorates.
A change in the eye’s refractive error, which is the need for a new glasses or contact lens prescription, can manifest as intermittent blurring. Over time, the cornea or lens shape may change subtly, causing light to focus imperfectly on the retina. The eye’s internal focusing muscles attempt to compensate, leading to periods of clarity followed by fatigue-induced blurriness.
Fluctuating blood sugar levels, particularly in individuals with diabetes, can directly affect the lens of the eye. High glucose concentrations change the osmotic balance within the lens, causing it to swell temporarily and altering its ability to focus light. This results in vision that changes significantly throughout the day, signaling a need for systemic medical attention and metabolic control.
Systemic and Neurological Causes
When vision changes involve the loss of a part of the visual field or a complete blackout, the cause may lie in the vascular or neurological systems. Migraine with aura is a common neurological cause, characterized by visual disturbances that precede the onset of a headache. The aura often appears as a shimmering, zigzag pattern or a temporary blind spot that expands across the visual field.
This visual phenomenon is thought to be caused by cortical spreading depression, a slow wave of electrical activity that moves across the visual cortex in the back of the brain. Unlike other causes, migraine aura usually affects both eyes simultaneously and resolves completely, often followed by a throbbing headache. The visual symptoms are a temporary disruption of the brain’s processing, not an issue with the eye itself.
Transient vascular events that temporarily interrupt blood flow to the eye or the brain are more concerning. Amaurosis Fugax is temporary vision loss in one eye, often described as a curtain or shade descending over the vision. This is usually caused by a small blockage (embolus) originating from the carotid artery or the heart, which briefly lodges in the retinal artery.
A Transient Ischemic Attack (TIA) is a similar event where blood flow to a part of the brain is briefly blocked. If the blockage affects the occipital lobe, the region responsible for vision, it can cause a temporary loss of sight, typically affecting both eyes. Both Amaurosis Fugax and TIA are significant warning signs of potential future stroke risk, indicating underlying cardiovascular issues.
When Immediate Medical Attention Is Required
Any sudden, significant loss of vision should be treated as a medical emergency to prevent permanent damage or to address a life-threatening condition. Immediate evaluation is necessary if the vision loss is complete or near-complete and occurs abruptly. This urgency is particularly heightened if the vision loss is accompanied by other neurological symptoms.
Seek emergency care immediately if the vision change is coupled with symptoms like sudden weakness or numbness on one side of the body, difficulty speaking, or facial drooping. These combinations of symptoms suggest a TIA or a stroke. Rapid intervention is crucial for a positive outcome.
Sudden vision loss accompanied by a severe, new headache, jaw pain while chewing, or scalp tenderness is another red flag, especially in individuals over 50 years old. These symptoms can indicate Giant Cell Arteritis, an inflammatory condition requiring immediate high-dose steroid treatment to prevent permanent blindness. Timely assessment is the most important factor in managing these serious causes of transient vision loss.