Correlation between Fourier-Domain Optical Coherence Tomography Parameters and HbA1c Level and Diabetes Duration in Early Stage Diabetic Retinopathy

Research Article

Austin J Clin Ophthalmol. 2014;1(4): 1020.

Correlation between Fourier-Domain Optical Coherence Tomography Parameters and HbA1c Level and Diabetes Duration in Early Stage Diabetic Retinopathy

Toshiyuki Oshitari*, Sakiko Nonomura, Miyuki Arai, Takayuki Baba and Shuichi Yamamoto

Department of Ophthalmology and Visual Science, Chiba University Graduate School of Medicine, Japan

*Corresponding author: Toshiyuki Oshitari, Department of Ophthalmology and Visual Science, Chiba University Graduate School of Medicine, Inohana 1-8-1, Chuo-ku, Chiba 260-8670, Chiba

Received: April 15, 2014; Accepted: May 10, 2014; Published: May 13, 2014

Abstract

We examined a significant correlation between Fourier–domain optical coherence tomography (FD–OCT) parameters and the glycosylated hemoglobin A1c (HbA1c) level and duration of diabetes mellitus (DM) in patients at the early stage of diabetic retinopathy (DR). Thirty eyes of 30 patients with early stage DR that were examined at the Chiba University Hospital were studied. The macular map 5 (MM5), the retinal nerve fiber layer thickness, and the ganglion cell complex thickness were obtained by FD–OCT. The coefficients of correlation between these parameters and the HbA1c level and the DM duration were determined by Spearman rank correlation. The thickness of the inferior sector of the outer ring of the MM5 was significantly correlated with the HbA1c level. The superior sector and the temporal sector of the outer ring were significantly correlated with the DM duration. Our findings suggest that the significant positive correlation between the retinal thickness of the sectors in the outer ring and the HbA1c level and DM duration may be due to a subclinical increase of the vascular permeability. A swelling of Müller cells may have also contributed to the correlation because their density is known to be higher in the perifoveal area than the central area.

Keywords: Fourier–Domain; HbA1c; Diabetes; Retinopathy

Introduction

Growing evidence indicate that neuronal abnormalities, including both the death of retinal ganglion cells (RGCs) and vascular abnormalities, are associated with the pathogenesis of early stage diabetic retinopathy (DR) [1,2]. Because the neuronal damages are irreversible, therapies for neuroprotection should be developed to protect the retina before the neuronal and vascular abnormalities develop in patients with DR [3]. The therapies should be sensitive, easy to implement, and be able to be monitored so that the abnormalities can be detected and followed at the early stage of DR [4].

Both vascular abnormalities, e.g., pericyte loss [5,6] and basement membrane thickening [7,8], and neuronal abnormalities, e.g., death of RGCs [9,10] are known to be induced by chronic high glucose exposure in vitro. To monitor the retinal changes in the early stage of DR, it would be better to correlate the retinal changes with systemic measures of the degree of diabetes, e.g., hyperglycemia by the glycosylated hemoglobin A1c (HbA1c) level. However, this would mean drawing blood each time a determination is made. Thus, a noninvasive method to monitor the degree of DR would be better.

Optical coherence tomography (OCT) is a useful non–invasive method of detecting and monitoring early retinal changes in eyeswith DR [11–15]. Because the RGCs are known to be the first neurons to be altered at the early stage of DR [14], it would be important to know what parameters of the RGCs could be used to detect the early changes of the DR. It has been established that a reduction of the thickness of the retinal nerve fiber layer (RNFL) is an early sign of DR [16]. Thus, measurements of the thickness of the RNFL as well as that of other retinal layers may be useful in detecting eyes at the early stage of DR.

Fourier–domain OCT (FD–OCT, RTVue–100) can obtain higher resolution images of the retina than time–domain OCT. The RTVue–100 has a 5 µm axial resolution and a scan rate of 26,000 axial scans⁄sec. In addition, the RTVue–100 has software embedded that can provide 5 macular maps (MM5), the thickness of the RNFL, andthe thickness of the ganglion cell complex (GCC) [17–19]. Thus, theRTVue–100 can be useful for determining whether eyes at the earlystage of DR have distinct pathognomonic features of early stage DR.

The purpose of this study was to measure three parameters embedded in the RTVue–100; MM5, RNFL thickness, and GCCthickness in patients with early stage DR. We calculated the coefficients of correlation between these parameters and the HbA1c level and theduration of the diabetes mellitus (DM). We then discuss the possible pathological mechanisms that led to the early retinal changes.

Materials and Methods

Thirty eyes of 30 patients with early stage DR, also referred to as non–DR (NDR) or mild non–proliferative (NPDR) that wereexamined at the Chiba University Hospital from December 2011 to March 2013 were studied. A written informed consent was signed by all patients, and all of the procedures conformed to the tenets of the World Medical Association Declaration of Helsinki. An approval for this study was obtained from the Institutional Review Board of Chiba University Hospital.

All of the participants had a routine ophthalmological examination. Both eyes were examined by FD–OCT (RTVue–100; Optovue Inc, Fremont, CA, USA) after pupillary dilation, and three parameters were determined. The first was the MM5 which consisted of an outer 5×5 mm grid of 11 horizontal and 11 vertical lines obtained by 668 A–scans each and an inner 3×3 mm grid of 6 horizontal and 6 vertical lines obtained by 400 A–scans each (Figure 1). The second parameter was the RNFL thickness map which was calculated from the images of 6 circular and 12 linear scans along a 3.45–mm diameter circle around the optic disc (Figure 2), and the third parameter was thickness of the GCC which was calculated from a 7×7 mm grid of the macula 1–mm temporal to the fovea (Figure 3).