When light enters a healthy eye, it passes through clear structures to focus precisely on the retina. Cloudy or hazy vision occurs when this path is interrupted, causing light to scatter before it reaches the light-sensitive tissues at the back of the eye. This scattering reduces contrast and sharpness. The underlying causes are varied, ranging from slow, age-related changes to sudden medical events. Because vision changes can indicate a range of conditions, any onset of cloudiness should be evaluated promptly by an eye care professional.
Gradual Causes: Changes in the Lens
The most common cause of gradually cloudy vision is the development of a cataract, involving the eye’s natural lens. The lens sits behind the iris and is normally clear, relying on a specific arrangement of proteins to remain transparent and focus light. Over time, particularly with age, these proteins break down and clump together, a process known as opacification. This clumping forms the cloudy area characteristic of a cataract, which interferes with light transmission and causes visual blurring.
This process is typically slow, often taking years or decades to significantly affect vision. In the early stages, cloudiness may only cause a slight reduction in vision or increased sensitivity to glare from lights at night. Risk factors that accelerate cataract formation include prolonged exposure to ultraviolet (UV) light, smoking, and diabetes.
The specific location of the opacification affects the type of visual complaint. For example, a nuclear cataract forms in the center of the lens and may initially cause temporary near-vision improvement before distance vision blurs. As the lens hardens and becomes denser, the cloudiness makes it increasingly difficult to perform daily tasks like reading or driving.
Surface Issues: Problems with the Cornea and Tear Film
Cloudy vision can also originate from the outermost structures of the eye, specifically the cornea and the tear film. The cornea is the clear front surface of the eye, and its clarity is maintained by an inner layer of endothelial cells. If these cells are damaged, they fail to pump fluid out efficiently, leading to corneal edema.
This fluid buildup causes the cornea to swell and lose transparency, resulting in a hazy or foggy view. A person with corneal edema may notice their vision is particularly cloudy upon waking, as closed eyelids reduce fluid removal overnight. Superficial issues, such as severe dry eye syndrome, can also cause fluctuating cloudiness.
When the tear film is unstable or inadequate, the eye’s surface becomes irregular, scattering light and leading to temporary blurring that improves with blinking. More serious surface inflammation, known as keratitis, results from infection or injury to the cornea. Keratitis causes the corneal tissue to become inflamed, which can lead to rapid vision decline accompanied by pain and redness.
Acute Onset and Systemic Health Links
A sudden onset of severe cloudy vision accompanied by pain is considered an ocular emergency, often indicating acute angle-closure glaucoma. This condition involves a rapid increase in internal eye pressure because the fluid drainage angle becomes physically blocked. The high pressure quickly causes the cornea to swell, resulting in noticeable cloudiness, severe eye pain, headache, and the perception of colored halos around lights.
Vision changes may also be linked to systemic health conditions, most notably diabetes. Chronically high blood sugar levels can damage blood vessels in the retina, leading to diabetic retinopathy. If these damaged vessels leak fluid into the macula, it causes swelling known as diabetic macular edema.
This fluid accumulation distorts and blurs central vision, making activities like reading difficult, and may cause vision to fluctuate throughout the day. Conditions like acute glaucoma can lead to permanent vision loss within hours. Therefore, symptoms such as sudden clouding, intense pain, nausea, or a rapid loss of vision require immediate emergency medical attention.