Diabetic Eye Screening: Why Blurred Vision Comes and Goes
Vision that fluctuates with your glucose, why new glasses are the wrong first move, and the screening that catches what you can't feel.
Two different things happen to eyes with blood sugar, and confusing them costs people money and, occasionally, sight.
The one you can feel
Fluctuating blurred vision happens because the lens of the eye absorbs fluid and changes shape as glucose levels shift. Your prescription effectively changes with your blood sugar.
This is why vision can be worse some days than others, and why it often improves within weeks of glucose stabilizing.
Don't buy new glasses during a period of changing glucose. Optometrists will usually tell you this if they know — wait until levels have been stable for a few weeks, or you'll be fitted for a prescription that no longer applies.
The one you can't feel
Diabetic retinopathy is damage to the small blood vessels at the back of the eye. In its early and most treatable stages it produces no symptoms at all.
That's the entire reason screening exists. By the time vision is affected, more damage has occurred than needed to.
Screening is a photograph of the retina, takes minutes, and is offered routinely to people with diabetes in most health systems. Attendance is imperfect, and the reason is usually that nothing hurts.
What to actually do
Go to screening when invited. Every time, including the years when everything feels fine.
If you have prediabetes, ask whether eye checks are recommended for you. Retinopathy can begin before a diabetes diagnosis.
Report sudden changes immediately — a shower of floaters, a curtain across your vision, sudden loss, or flashes. Those are urgent, not routine.
Mention your diabetes at every optician visit.
On rapid glucose improvement
Worth knowing because it surprises people: rapidly lowering long-standing high glucose can temporarily worsen retinopathy before it improves. This is well recognized and is not a reason to avoid improving control — it's a reason for your team to know what you're doing and to check your eyes.
If you're making substantial changes and have existing retinopathy, tell whoever manages it.
Try this week: if you're overdue for eye screening, book it. It's the appointment most often skipped because nothing hurts.
Education, not medical advice. Sudden vision changes require urgent assessment.