Date Published: January 23, 2017
Publisher: Public Library of Science
Author(s): Hyun Seung Yang, Jong Eun Woo, Min-ho Kim, Dong Yoon Kim, Young Hee Yoon, Patrice E Fort.
We investigated the relationship between the peripapillary retinal nerve fiber layer and peripapillary retinal thickness in patients with diabetic macular edema. Fifty eyes (group I) with non-proliferative diabetic retinopathy and diabetic macular edema receiving intravitreal anti-VEGF injection, and 90 eyes (group II) without diabetic macular edema were included in this case-control study. The peripapillary retinal nerve fiber layer thickness, peripapillary retinal thickness, and a new retinal nerve fiber layer index using a modeled relationship between the two parameters were evaluated with spectral-domain optical coherence tomography, at baseline and at the 6-month follow-up. In group I, the peripapillary retinal nerve fiber layer thickness decreased from 126.4 μm at baseline to 117.6 μm at 6 months (p < 0.001), while the peripapillary retinal thickness decreased from 376.0 μm at baseline to 359.6 μm at 6 months (p < 0.001) after intravitreal anti-VEGF injection. In group II, however, both the parameters remained stable at the 6-month follow-up (100.7 to 102.1 μm and 311.1 to 316.2 μm, respectively, and all p > 0.01). Analysis with the new index to adjust for retinal edema showed no significant change from baseline to 6 months in both groups (p = 0.593 and p = 0.101, respectively). The peripapillary retinal nerve fiber layer thickness is strongly affected by the peripapillary retinal thickness. Therefore, the measured changes in peripapillary retinal nerve fiber layer thickness may not represent the real gain or loss of the retinal nerve fiber layer. Therefore, the new retinal nerve fiber layer index, which corrects for the component of macula edema, could be a better means of assessing the changes of peripapillary retinal nerve fiber layer thickness in patients with diabetic macular edema.
Diabetic retinopathy (DR) has many elements that suggest chronic neurodegeneration as well as glaucoma and retinitis pigmentosa, including: neural apoptosis, loss of ganglion cell bodies, reduction in thickness of the inner retina, glial reactivity, neurofilament abnormality, slowing of optic nerve retrograde transport, changes in electrophysiological activity, and resultant deficits in perception . Optical coherence tomography (OCT) can be used to detect gradual retinal neural tissue loss by more precise and easier measuring of RNFL thickness in DR patients with or without treatment. Dijk et al. reported that RNFL thickness decreased with DR progression . Oshitari et al. showed that peripapillary RNFL thickness (pp-RNFLT) was also lower in early DR patients than in normal or non-DR patients . Neurodegenerative changes in DR also may be affected by the severity and progression of DR, or the various treatments such as intravitreal injection and panretinal photocoagulation (PRP) [2,4–6]. While some studies showed that peripapillary RNFL thickness increased after PRP, other studies showed variable results after intravitreal anti-VEGF injection [7–10].
Recently, it has been found that retinal function loss in diabetic patients and/or those with early DR is not only due to changes in micro-vascular pathology, but also neurodegenerative change [1,6,15,16]. The degeneration of retinal ganglion cells (RGCs) has been reported to begin early after the onset of diabetes in rats, and it is suggested that since this neurodegeneration may proceed to retinal micro-vasculopathy, it may contribute to capillary degeneration . Several studies also showed that RGC loss and/or decreased Rarebit visual field test results have a relation with the presence or duration of diabetic retinopathy with minimal vascular change [1,15].