Prediabetes, a condition characterized by elevated blood sugar levels below the diagnosable threshold for diabetes, can lead to significant thinning of the macula, researchers posited. A study published in the British Journal of Ophthalmology shows these early, subtle changes to the posterior segment structure caused by prediabetes. The researchers add that the finding supports the neurodegenerative theory of diabetes-induced changes in the retina. 

Researchers used optical coherence tomography (OCT) to measure the total macular volume, average macular thickness, and average thicknesses of the 9 macular subfields of 2005 qualifying study participants. They also measured the subjects’ ganglion cell layer (GCL) thicknesses. The participants were divided into 3 groups. The first group had normal glucose metabolism (1638 participants), the second had prediabetes (310 participants), and the third had diabetes without retinopathy (57 participants). Digital fundus images were also used to measure the retinal arteriolar and venular calibers. 

An evaluation of the data shows that the macular thicknesses of the patients with prediabetes were significantly reduced as compared with the NGM group in all 9 subfields of the macular thickness map. In particular, the macular cube average thickness for the patients with prediabetes had decreased by approximately 2.69 μm (P <.05) and average cube volume by approximately 0.10 mm3 (P <.05). Changes in the GCL of the prediabetes group were not significant. The macular thickness was also significantly reduced in the diabetic group compared with the NGM group.  


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The diameters of retinal arteries were decreased by impaired glucose metabolism, the study shows. In fact, the thinning of the macula, as observed on OCT, may reflect early neurodegenerative changes already in patients with prediabetes. The research points to prior studies showing that vascular changes may appear before neural changes in the diabetic retina

“Recently, the neurodegenerative theory behind diabetic changes in the retina has gained more support. According to this theory, the first changes in prediabetic or hyperglycaemic retina are neurally based, and vascular changes are consequences of the neural damage,” study authors reported. 

These changes may trigger apoptosis in ganglion cells and a loss of  neural cells that could explain aspects of subtle functional vision loss seen in early diabetes. These subtle changes include a loss of contrast sensitivity and impaired color vision, according to the study.

The researchers note that the study’s cross-sectional nature of eye measurements can be considered a limitation. In addition, the prevalence of prediabetes in the research was relatively low.

Reference

Huru J, Leiviskä I, Saarela V, Liinamaa J. Prediabetes influences the structure of the macula: thinning of the macula in the Northern Finland birth cohort. Br J Ophthalmol. Published online October 7, 2020. doi: 10.1136/bjophthalmol-2020-317414