Evaluation of thickness of retinal nerve fiber layer, ganglion cell layer, and choroidal thickness in essential tremor: can eyes be a clue for neurodegeneration?

Abstract

The pathology of essential tremor (ET) and underlying mechanisms of the disease are still unclear, but an increasing amount of research has been conducted on the subject. Discussions are ongoing about ET's definition as a neurodegenerative disease. Optic coherence tomography (OCT) provides a window to the brain where direct visualization of central nervous system (CNS) changes may be possible, and it can help us to develop a new point of view on ET. The goal of this study was to examine OCT parameters in ET. 40 ET patients and 40 healthy controls, i.e., a total of 160 eyes were evaluated. Retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), and choroid thinning were analyzed using spectral domain OCT. The mean age was 25.77 ± 8.98 in the ET group and 27.25 ± 8.22 in the control group. We found a decreased global RNFL thickness for both eyes in ET patients. All GCL and IPL thickness parameters were lower in the patients with ET (P < 0.001, P 0.03). Choroid was significantly thicker in ET patients than the controls (P < 0.001). Our study's results suggest that the usefulness of OCT in detecting neurodegeneration in ET. RNFL, GCL, IPL measurements are highly reproduced findings of neurodegeneration. Increased choroid volume may indicate neuroinflammation. Eyes in ET may shed light on nature of the disease, and may be used as a diagnostic tool.

Essential tremor: the most common form of cerebellar degeneration?

“…A popular disease model, initially proposed in the 1970s [138], attempted to link ET to an abnormal inferior olivary nucleus; however, empiric support for that model is limited [57,139,140] and the model has recently fallen out of favor [55,56]. More recent research in the field has focused on the cerebellum, where there has been a reconceptualization of the disease as one of cerebellar degeneration, as will be discussed below [29,35,[37][38][39][40][41][42][43][44][45][46][47].…”

“…The pathophysiology is of ET unclear, and is likely heterogeneous. Recent work has recast it as one that is often due to cerebellar and cerebellar pathway dysfunction [28][29][30][31][32][33][34][35][36] as well as one that is likely degenerative [29,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51].…”

Retinal nerve fiber layer thickness in patients with essential tremor and Parkinson’s disease

“…In the literature, there are very few researches on visual functions in ET, and color vision abnormalities have not been detected [16,17]. The studies determining RNFL thickness with OCT in ET had different results [18][19][20]. However, we did not find any study comparing RNFL thickness in both PD and ET patients.…”

“…Interestingly, we also found similar decreases in RNFL thickness in the ET group. We found few studies in the literature where RNFL of ET patients was assessed by OCT [18][19][20]. One of these studies was a pilot study with a small number of patients where it was found that foveal thickness decreased in ET patients compared to the controls, but this difference was not statistically significant [18].…”

“…RNFLm values were obtained by averaging RNFLs,i,n,t quadrants. Because a small number of studies reported that asymmetry may be present in OCT measures, both eyes of the individuals were examined with OCT [18][19][20][21].…”