Tighter Blood Sugar Range May Protect Vision in Type 1 Diabetes

What Was Studied and Why It Matters

Diabetic retinopathy — damage to the tiny blood vessels in the eye — is one of the most serious complications of type 1 diabetes and a leading cause of vision loss. Doctors have long used a measure called Time in Range (TIR), which tracks how often blood sugar stays between 70 and 180 mg/dL, to gauge diabetes control. But a newer, stricter measure called Time in Tight Range (TITR) focuses on an even narrower window: 70 to 140 mg/dL.

Researchers in Spain wanted to know: does TITR do a better job than TIR at predicting who will develop or worsen diabetic eye disease? They followed 309 adults with type 1 diabetes who used multiple daily insulin injections and wore a flash continuous glucose monitor (CGM) over 12 months.

What the Study Found

At the start of the study, about 64% of participants had no retinopathy, 23% had a mild form, and 13% had a more advanced form. Over the following year:

• About 5% of those with healthy eyes developed retinopathy.
• About 23% of those who already had retinopathy saw it worsen.

The key findings were:

• TITR was a stronger predictor of new retinopathy than TIR. For every 1% increase in time spent in the tighter range, the risk of developing eye disease dropped meaningfully.
• TIR alone did not significantly predict new retinopathy in this group.
• TITR was especially powerful for people whose HbA1c was already close to target (below 7.1%) — a group where traditional measures often struggle to detect differences in risk.
• For people who already had retinopathy, both TITR and TIR performed similarly in predicting worsening.
• Other important risk factors included how long someone had diabetes, high blood pressure, smoking, and HbA1c — all of which still mattered alongside CGM data.

What This Means for Real Patients

If you use a CGM — whether a traditional continuous monitor or a flash scanner like the FreeStyle Libre — your device is already collecting the data needed to calculate TITR. This study suggests it may be worth asking your diabetes care team to look beyond just your TIR percentage and HbA1c when assessing your eye health risk.

For people whose HbA1c looks good on paper, TITR may reveal hidden blood sugar swings that still put the eyes at risk. Reducing time spent above 140 mg/dL — even if you rarely go above 180 mg/dL — could offer an extra layer of protection.

Managing supplies consistently is part of staying on top of CGM-based metrics. MDS Diabetes makes it easy to keep your CGM sensors and diabetes supplies stocked so there are no gaps in your monitoring data.

Bottom Line

Spending more time in the tighter blood sugar range of 70–140 mg/dL appears to better predict the development of diabetic eye disease than the standard 70–180 mg/dL range — particularly for people who already have near-normal HbA1c. Ask your care team whether your CGM data includes TITR, and don't overlook controlling blood pressure and avoiding smoking as equally important protective steps.