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Elevated blood glucose poses a threat to the eyes even prior to a diabetes diagnosis, according to a Dutch population study.

In cross-sectional data of participants, a more adverse glucose metabolism status was linked with a lower z score of corneal nerve fiber measures compared with a normal status (-0.14, 95% CI -0.25 to -0.04, P for trend=0.001), reported Sara Mokhtar, a PhD student at Maastricht University Medical Center in the Netherlands, and colleagues.

This corneal nerve damage was seen even in those with prediabetes (-0.08, 95% CI -0.17 to 0.03), they noted at the European Association for the Study of Diabetes (EASD) meeting.

"That implies that the corneal nerve damage is a process that starts before the onset of type 2 diabetes," Mokhtar said during her presentation.

"Having prediabetes is equal to 10 additional years for the corneal nerves," she explained. "Having type 2 diabetes is equal to 17 additional years for the corneal nerves."

Mokhtar pointed out that even continuous measures of glycemia, such as higher fasting plasma glucose, were associated with greater cornea nerve fiber damage (-0.09 per SD, 95% CI -0.13 to -0.05).

Additionally, several other continuous factors related to diabetes were found to be associated with worse corneal nerve fiber measures:

• 2-hour post-load glucose: -0.07 per SD (95% CI -0.11 to -0.03)
• HbA1c: -0.08 (95% CI -0.11 to -0.04)
• Skin autofluorescence: -0.05 (95% CI -0.08 to -0.01)

Duration of diabetes also trended toward an association with greater corneal nerve damage (-0.09, 95% CI -0.17 to 0.0).

For this observational study, Mokhtar and team used data from the Maastricht Study on 3,471 adults ages 40 to 75 living in this area of the Netherlands.

Participants were divided into three groups -- those with normal glucose metabolism, prediabetes, or type 2 diabetes -- based on fasting plasma glucose and 2-hour post-load glucose according to WHO criteria. Of this cohort, 21% had type 2 diabetes, and 14.7% had prediabetes. Nearly half were men, and mean age was 59.4.

The researchers adjusted for several factors including age, sex, education level, cardiovascular profile, smoking status, and alcohol use.

Nerve damage was measured with corneal confocal microscopy, which works by scanning corneal nerves located in the subbasal plexus, assessing the structure of nerves like corneal nerve branch density, fiber density, fiber length, and fractal dimension.

The associations reported were also seen with all individual measures of corneal nerve damage.

This tool is "less complicated, precise, less expensive, and noninvasive" compared with other ways to measure diabetes-related nerve damage throughout the body, like MRI, said Mokhtar.

Future research should be directed at investigating whether early correction of hyperglycemia can potentially prevent or reverse this progressive corneal nerve damage, the researchers suggested.

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