A blurry spot in one eye, medically known as a scotoma, is an area of diminished or lost vision surrounded by preserved sight. This visual field defect can manifest as a dark, fuzzy, or flickering patch, often only noticeable when the unaffected eye is closed. Since vision relies on a clear pathway from the front of the eye to the light-sensing cells at the back, any obstruction or damage along this route can produce reduced clarity. While some scotomas are temporary, others indicate conditions requiring immediate professional attention.
Temporary and Surface-Level Causes
Blurry spots often originate from temporary and less severe issues on the exposed front surface of the eye. Eye strain, frequently linked to prolonged screen use (computer vision syndrome), can temporarily impair the eye’s focusing ability, causing blurriness. This fatigue reduces the efficiency of the ciliary muscle responsible for accommodation, leading to transient visual discomfort. Dry eye syndrome is another superficial cause, where an unstable tear film creates irregularities on the corneal surface. Since the cornea provides the majority of the eye’s refractive power, this uneven surface scatters light incorrectly, resulting in a temporary blurry spot until the tear film is restored.
Minor corneal abrasions, or superficial scratches, can also cause localized blurriness alongside pain and light sensitivity. These small injuries disrupt the smooth optical surface, interfering with light transmission to the retina. A scintillating scotoma is a distinct temporary spot, appearing as a shimmering, zigzag pattern that expands over several minutes. This phenomenon is a visual aura associated with a migraine, caused by a wave of altered electrical activity in the visual cortex. The visual disturbance usually resolves spontaneously within about 30 minutes, sometimes preceding a headache.
Structural Changes in the Lens and Vitreous
Moving deeper into the eye, physical changes to internal, transparent structures can create persistent areas of reduced clarity by blocking the light pathway. Cataracts involve the clouding of the eye’s natural lens, which sits behind the iris. As lens proteins clump together, they scatter incoming light, causing a hazy or blurry spot that develops gradually over time. This opacity reduces the amount of light reaching the retina, making vision less sharp and colors less vibrant.
Floaters are another common cause of spots and shadows, appearing as small specks or strands that drift across the visual field. These are debris or condensed collagen fibers within the vitreous humor, the clear, gel-like substance filling the eye’s main cavity. As the eye ages, the vitreous gel liquefies and shrinks, a process known as Posterior Vitreous Detachment (PVD). This separation pulls the vitreous away from the retina, causing clumps of material to cast shadows onto the light-sensing tissue, perceived as moving blurry spots. A sudden increase in the number or size of floaters can signal a retinal tear, which requires urgent evaluation.
Urgent Conditions Affecting the Retina and Blood Vessels
Conditions impacting the retina or its blood supply are often sight-threatening and require immediate medical care. Retinal detachment occurs when the retina separates from the underlying supportive tissue, interrupting its blood and nutrient supply. This separation presents as a sudden increase in floaters and flashes of light, followed by a dark shadow or a “curtain” across the field of vision. The resulting blurry spot or vision loss is a consequence of photoreceptor cells being deprived of oxygen.
Wet Age-Related Macular Degeneration (AMD) causes a rapid onset of central blurry vision due to the growth of abnormal, fragile blood vessels beneath the macula. When these vessels leak fluid or blood, they damage the macula, the area responsible for sharp central sight. This leakage results in a quickly developing central scotoma, often causing straight lines to appear wavy or distorted.
A retinal vascular occlusion is an “eye stroke” where a blockage occurs in the arteries or veins supplying the retina. Central Retinal Artery Occlusion (CRAO) involves a blocked artery, leading to sudden, profound, and painless vision loss in one eye because the retina is instantly starved of oxygen. Central Retinal Vein Occlusion (CRVO) involves a blockage in the main draining vein, causing blood and fluid to back up and hemorrhage into the retina. This congestion and swelling, known as macular edema, results in rapid, severe blurring and can cause large floaters or a shadow.
Diabetic Retinopathy, caused by chronically high blood sugar, damages the tiny vessels in the retina, causing them to leak fluid or bleed. If the central macula swells from this leakage, it causes diabetic macular edema, creating a blurry spot in the center of vision. In advanced cases, abnormal vessels can bleed into the vitreous gel, causing a sudden, large shadow or cloudiness that severely limits sight.
The Diagnostic Process and Immediate Actions
A sudden onset of a blurry spot or any rapid change in vision necessitates immediate professional evaluation. Certain symptoms serve as red flags, including the sudden appearance of a dark curtain or shadow, a shower of new floaters, or flashes of light. If the blurry spot is accompanied by severe eye pain, headache, nausea, or sudden loss of peripheral vision, this could signal an ocular emergency like angle-closure glaucoma or a vascular event. Prompt action is crucial because conditions like retinal detachment or vascular occlusions can lead to permanent vision loss within hours if not treated.
During a comprehensive eye examination, the specialist uses a slit lamp, a specialized microscope, to examine the cornea, lens, and anterior chamber for structural issues. The pupil is often dilated to allow for a detailed view of the retina and the optic nerve. They may use Optical Coherence Tomography (OCT), a non-invasive imaging technique, to create cross-sectional scans of the retina to detect fluid, swelling, or macular damage. Visual field testing is also performed to map the exact size and location of the scotoma, helping differentiate between conditions affecting the central macula versus the peripheral retina or optic nerve.