Vision can become worse in both eyes for several reasons, including a change in glasses prescription, dry eyes, cataracts, or changes in blood sugar. Sometimes, problems affecting the retina, optic nerves, or brain can also alter vision. The speed of the change matters: gradual blurring is often related to common eye conditions, but sudden or major vision loss needs emergency care. An eye examination can help identify the cause.
When vision becomes less clear in both eyes, everyday activities such as reading, driving, working on a computer, or recognizing faces may become more difficult. The change may develop gradually or appear unexpectedly. Although many causes are treatable, worsening vision should not automatically be attributed to aging, tiredness, or screen use. Understanding when the change started, how it affects your sight, and whether other symptoms are present helps determine what kind of medical assessment is needed.
What can cause vision to get worse in both eyes?
Both eyes can experience similar vision changes when an issue affects their ability to focus light, the clarity of their surfaces or lenses, or the structures responsible for transmitting visual information. Common explanations include changes in eyesight that require a different prescription, dry eyes, and cataracts. Medical conditions affecting the retina or other parts of the visual system may also contribute.
1. A change in your glasses prescription
One common reason for gradually worsening vision is a refractive error. This occurs when the shape of the eye prevents light from focusing correctly on the retina, the light-sensitive tissue at the back of the eye. Nearsightedness can make distant objects blurry, while farsightedness and age-related difficulty focusing up close can affect near vision. Astigmatism may cause blurred or distorted vision at different distances.
Changes in a prescription can occur during childhood and adulthood. Presbyopia, which makes it harder to focus on nearby objects, commonly begins around middle age. If vision is no longer clear with existing glasses or contact lenses, an eye examination can determine whether the prescription needs adjustment. According to MedlinePlus, refractive errors can also cause eye strain, headaches, glare, and difficulty focusing while reading or using a computer.
2. Dry eyes and an unstable tear film
The surface of each eye needs a healthy layer of tears to remain comfortable and support clear vision. When tears are insufficient or evaporate too quickly, the surface may become irritated and vision may appear blurry. Dry eyes can affect both eyes and may cause burning, a gritty sensation, watering, or sensitivity to light. Some people notice that their vision becomes temporarily clearer and then blurry again.
Dryness may be associated with prolonged screen use, environmental conditions, contact lens wear, or certain health conditions and medications. These factors do not establish the cause in an individual person. Cleveland Clinic identifies dry eye, refractive errors, cataracts, and medication side effects among the possible causes of blurred vision. Persistent or worsening blurring deserves an eye examination rather than repeated assumptions that dryness is responsible.
3. Cataracts
A cataract develops when the normally clear lens inside the eye becomes cloudy. This makes it harder for light to pass through the lens clearly. Cataracts usually develop gradually and become more common with age, although they may also occur in younger people in certain circumstances.
Vision affected by cataracts may seem cloudy, hazy, or dim. Bright lights may cause glare or halos, colors may appear less vivid, and seeing in low light may become more difficult. Cataracts can affect both eyes, although one eye may be affected more than the other. According to MedlinePlus, cataracts commonly progress slowly and can cause difficulties with vision at different distances. An eye examination can establish whether a cataract is present and whether it is affecting daily activities enough to consider treatment.
4. Changes in blood sugar and diabetes-related eye problems
Blood sugar changes can affect vision in more than one way. Higher-than-usual blood sugar or rapid changes in blood sugar may cause temporary blurring by changing the amount of sugar and water in the eye's lens. This type of blurring is different from diabetic retinopathy, which involves damage to the small blood vessels in the retina.
Diabetes-related eye disease may develop without obvious early symptoms. As it progresses, vision may become blurry or gradually worsen, and some people may notice floaters or missing areas in their vision. According to MedlinePlus, people with diabetes need regular eye examinations because retinal damage can occur before noticeable vision changes develop. New or worsening vision problems should be discussed with an eye care professional even when blood sugar changes seem like a possible explanation.
5. Glaucoma and other conditions affecting the retina or optic nerves
Glaucoma refers to a group of eye conditions that can damage the optic nerve, which carries visual information from the eye to the brain. Some forms progress gradually and may affect peripheral vision before a person notices a clear change. Glaucoma can affect one or both eyes, and vision damage may be permanent if it progresses without appropriate treatment.
Other conditions involving the retina, the macula responsible for detailed central vision, or the optic nerves can also affect how clearly a person sees. These conditions do not all produce the same pattern of vision loss, and early symptoms may be limited or absent. The National Eye Institute explains that glaucoma can be detected through a comprehensive eye examination, which may include pupil dilation and visual field testing. Sudden eye pain with a red eye, nausea, and blurred vision can indicate an eye emergency requiring immediate assessment.
6. Medication effects, migraine, or a problem involving the brain
Some medicines can cause blurred vision as a side effect. If the change began after starting a medicine or changing its dose, tell the prescribing healthcare professional. Do not stop a prescribed medicine or change its dose without appropriate guidance.
Migraine can cause temporary visual disturbances, including flashing lights, zigzag patterns, or areas of altered vision. Problems involving the brain or its blood supply, including a stroke or transient ischemic attack, can also cause sudden changes in sight. These possibilities cannot be distinguished reliably from an eye problem based on blurring alone. A sudden change affecting both eyes, particularly when accompanied by other new neurological symptoms, needs emergency medical assessment.
Does it matter if vision gets worse suddenly or gradually?
Yes. The timing is an important part of understanding a change in vision, although it cannot identify the cause by itself.
- Gradual blurring: Changes in a glasses prescription, cataracts, dry eyes, and certain progressive eye conditions may cause vision to worsen over time.
- Intermittent blurring: Vision that comes and goes may be associated with dry eyes, changes in blood sugar, or other conditions that require assessment in context.
- Sudden blurring or vision loss: An abrupt change can be associated with a serious eye problem, a blood vessel problem, or a neurological emergency. It should not be assumed to be temporary.
- Unequal changes between the eyes: One eye may become worse than the other even when both eyes have some vision changes. This pattern needs evaluation rather than an assumption that the same condition affects both eyes equally.
The NHS guidance on vision loss recommends emergency assessment if someone suddenly loses vision in one or both eyes or develops sudden severe eye pain. Sudden visual changes should be assessed urgently even when there is no pain.
When should worsening vision in both eyes be treated as an emergency?
Seek emergency medical care immediately if vision suddenly becomes much worse or is suddenly lost in either or both eyes. Do not wait to see whether it improves on its own. Avoid driving yourself to obtain emergency care.
Other warning signs that require urgent assessment include:
- A sudden increase in floaters, flashes of light, or a dark curtain or shadow across the vision.
- Sudden blurred vision accompanied by intense eye pain, a red eye, or nausea.
- Vision changes occurring with difficulty speaking, facial drooping, weakness, confusion, or a sudden severe headache.
- New double vision or a marked change in vision that appears unexpectedly.
These symptoms can occur with conditions that threaten vision or may indicate a neurological emergency. Contact local emergency services when stroke symptoms or sudden major vision loss occur. Even without these warning signs, arrange a prompt eye examination for persistent, progressive, or otherwise unexplained changes in vision.
How do healthcare professionals find the cause?
An eye care professional will generally ask when the change began, whether it appeared suddenly or gradually, whether it affects near or distant vision, and whether it is constant or intermittent. They may ask about eye pain, headaches, other symptoms, previous eye conditions, medical history, current medicines, contact lens use, and existing glasses prescriptions.
The examination may include several assessments depending on the symptoms and findings:
- Visual acuity testing: Checks how clearly you can see at different distances.
- Refraction testing: Helps determine whether glasses or contact lenses could improve focus.
- Examination of the front of the eye: Allows the clinician to look for problems involving the eye's surface, cornea, and lens.
- Dilated retinal examination: Helps assess the retina, optic nerve, and other structures at the back of the eye.
- Eye pressure testing: May help assess for glaucoma and related problems.
- Additional medical tests: Blood sugar testing or neurological assessment may be appropriate when the history and examination suggest a need for them.
Not everyone needs every test. The appropriate assessment depends on the timing and nature of the vision change, medical history, examination findings, and other relevant information.
What can help improve vision in both eyes?
Treatment depends on the underlying cause. A refractive error may improve with an updated glasses or contact lens prescription. Dry eyes may respond to suitable lubricating eye drops and changes recommended by an eye care professional. Cataracts that significantly interfere with everyday activities may be treated with surgery. Diabetes-related eye disease and glaucoma require condition-specific monitoring and treatment to help protect remaining vision.
When a medicine may be contributing to blurred vision, a healthcare professional can review the treatment and decide whether an adjustment is appropriate. Conditions involving the retina, optic nerves, or brain may require urgent specialist care and a different treatment approach.
Until the cause is clear, avoid driving or operating machinery if your vision is not sufficiently clear to do so safely. Follow any recommended follow-up examinations, particularly if you have diabetes or a known eye condition. Do not rely solely on new glasses or lubricating drops to address vision that is suddenly or progressively worsening.
What should you do if both eyes are getting worse?
If the change is sudden or substantial, seek emergency care. For persistent or gradually worsening vision, arrange an eye examination rather than assuming that the problem is a normal part of aging. Make a note of when the symptoms started, how they affect everyday activities, and any associated symptoms. Bring your current glasses prescription and a list of medicines to your appointment if available.
Worsening vision in both eyes can have relatively straightforward explanations, but it can also be an early sign of an eye disease or another medical problem. An appropriate examination helps determine what is happening and which treatment or follow-up is needed.