Retinal neuronal, axonal layers thinner in diabetic eyes without retinopathy

Even among patients with diabetes mellitus (DM) but no diabetic retinopathy (NDR), thinning of the retinal neuronal and axonal layers is apparent, a recent meta-analysis has found. In turn, this suggests that DR neuropathy (DRN) may be an early marker of clinically detectable DR.

Drawing from the databases of PubMed and Embase, the researchers identified 36 studies and one additional cohort eligible for synthesis. Cumulatively, 6,220 participants contributed data for the meta-analysis. Ophthalmological measurements were conducted using spectral domain optical coherence tomography (SD-OCT).

Eye layers examined included: macular ganglion cell-inner plexiform layer (m-GCIPL), macular retinal nerve fibre layer (m-RNFL), macular ganglion cell complex (m-GCC), and peripapillary RNFL (p-RNFL).

Pooled analysis revealed that even among NDR eyes, thinning of the mean m-GCIPL (standardized mean difference [SMD], –0.26, 95 percent confidence interval [CI], –0.42 to –0.11; p=0.003) and m-RNFL (SMD, –0.26, 95 percent CI, –0.51 to –0.01; p=0.046) was significantly greater than in control eyes.

The same was true for m-GCC (SMD, –0.28, 95 percent CI, –0.48 to –0.09; p=0.009) but not for p-RNFL.

When comparing NDR eyes against those with nonproliferative DR (NPDR), only the difference in p-RNFL was found to be statistically significant, reflecting greater thinning in NPDR eyes (SMD, –0.27, 95 percent CI, –0.51 to –0.03; p=0.03). All three macular layers assessed had comparable thicknesses between NDR and NPDR eyes.

“In the future, neuroretinal alterations as measured by SD-OCT may be used as surrogates of DRN to stratify DM patients at high risk for DR, and may be used as a therapeutic target or surrogate if neuroprotection treatment for earlier stages of DR is available,” the researchers said.