When assessing patients with prediabetes, stay alert for early loss of RNFL (seen here in a glaucoma patient).

When assessing patients with prediabetes, stay alert for early loss of RNFL (seen here in a glaucoma patient). Photo: Ryan Schott, OD. Click image to enlarge.


A recent study examined the retinas of patients with elevated blood sugar and observed that many showed thinning of the retinal nerve fiber layer (RNFL) despite the absence of obvious vascular damage. While sometimes overlooked, diabetic retinopathy (DR) is not exclusive to patients with diabetes; rather, DR can cause early neuroretinal changes in prediabetes patients before developing into overt retinopathy.

Fifty patients with diagnosed prediabetes (average age: 51.6) and 50 healthy controls (average age: 50.6) were included in the study. The researchers measured RNFL using spectral-domain OCT. Not only did prediabetic patients have thinning in the temporal quadrant, but most showed loss in all four. The difference between the RNFL thicknesses of both groups was demonstrated to be statistically significant. The average RNFL thicknesses measured in each group are shown in Table 1.

“The prevalence of prediabetes varies between 19.8% and 34.6% and is more common than diabetes,” the authors of the study wrote. “In about two out of three prediabetic cases, the metabolic disorder progresses to obvious diabetes in later life. However, microvascular and macrovascular complications due to diabetes may occur in prediabetics even before diabetes develops,” they noted.

As an optometrist, you have the opportunity to recognize these early signs of disease in your patients before progression or adverse outcomes occur. Be vigilant when performing retinal exams and RNFL thickness measurements on all your patients, not only those with diabetes.

Table 1. Average RNFL Thicknesses in Prediabetics vs. Controls

Mean RNFL Thickness

Inferior Quadrant

Superior Quadrant

Nasal Quadrant

Temporal Quadrant

Prediabetes Group






Control Group






Bilen A, Ates O, Ondas O, et al. Retinal nerve fiber layer thickness in prediabetic patients. Eurasian J Med. 2022;54(1):8-11.