联合小视野扩散张量成像和光学相干断层成像技术研究原发性视网膜色素变性视网膜神经节细胞轴突

Reduced field-of-view diffusion tensor imaging together with optical coherence tomography in detecting alterations of retinal ganglion cell axons in patients with retinitis pigmentosa

目的通过定量分析原发性视网膜色素变性（RP）视神经小视野扩散张量成像（rfov-DTI），与视网膜神经纤维层（retinal nerve fiber layer，RNFL）厚度的变化及两者之间的相关性，以全面地评价RP视网膜神经节细胞轴突的变化。方法收集2014年8月至2017年3月34例经眼科确诊的RP患者（68眼，病变组）和33名无眼科相关疾病的健康正常人（66眼，对照组）进行前瞻性研究。所有被试均行3.0 T MR视神经rfov-DTI和视网膜光学相干断层成像（OCT）。比较两组间部分各向异性（FA）、平均扩散率（MD）值、平行扩散率（λ//）、垂直扩散率（λ⊥）的差异运用两独立样本t检验（数据正态分布）；视盘周围RNFL颞侧厚度、鼻侧厚度（数据不符合正态分布）之间的比较均采用Mann-Whitney U检验；视盘周围RNFL平均厚度及下象限厚度、上象限厚度（数据正态分布）之间的比较均采用两独立样本t检验；RP视神经DTI参数与视盘周围RNFL厚度之间的关系采用Spearman相关分析。结果病变组视神经DTI的FA、MD、λ//、λ⊥值以及RNFL平均、颞侧、鼻侧、下方、上方象限厚度分别为0.445±0.078，（1.330±0.236）、（5.502±0.263）、（4.494±0.238）×10-3mm2/s以及（104.7±25.4）、（104.0±31.0）、（65.0±25.0）、（122.0±33.3）、（117.4±37.7）μm；对照组相应的各项参数值分别为0.581±0.043，（1.079±0.146）、（5.349±0.214）、（4.195±0.126）×10-3mm2/s，（101.2±10.6）、（70.0±10.8）、（81.3±13.4）、（127.3±12.5）、（126.3±11.5）μm。与对照组相比，病变组视神经平均FA值降低，平均MD值、λ//、λ⊥值升高，RNFL颞侧厚度增厚、鼻侧厚度变薄，差异均有统计学意义（DTI各参数的t值分别为-12.388、7.394、3.695、9.062，RNFL颞侧厚度、鼻侧厚度的Z值分别为-8.384、-4.518，P值均〈0.01），而RNFL上、下方象限、平均厚度差异无统计学意义（t值分别为-1.217、-1.843、1.049，P值分别为0.227、0.069、0.297）。RP患者视神经FA值与颞侧RNFL厚度呈弱相关（r=0.268，P=0.029），与鼻侧RNFL厚度不具有相关性（r=0.164，P=0.186）。结论rfov-DTI和OCT联合应用可以较为全面地反映RP视网膜神经节细胞轴突的在体病理变化，但视网膜神经节细胞轴突的组成部分中视网膜神经纤维层与视神经的病理改变之间相关性较弱，两者表现存在不一致性。

Objective To investigate the damage of retinal ganglion cell （RGC） axons in retinitis pigmentosa （RP） quantitatively by using reduced-filed-of-view DTI （rfov-DTI） together with optical coherence tomography （OCT）.MethodsThirty four patients（68 eyes,Patient group）and 33 healthy controls（66 eyes, Control group） were enrolled in this study. Measures of rfov-DTI and OCT of both eyes in all subjects were performed by 3.0 MRI. The difference of fractional anisotropy （FA）, mean diffusivity （MD）, axial diffusivity （λ//） and radial diffusivity （λ⊥） were compared by two independent sample t test. The peripapillary retinal nerve fiber layer （RNFL） thickness in temporal and lateral nose, which data don＇t conform to normal distribution, were calculated by average and four quadrants and compared by Mann-Whitney U test, the average RNFL thickness and RNFL thickness in low quadrant and upper quadrant were compared by two independent sample t test.Spearman rank were performed to determine the correlation between DTI parameters of optic nerves （ONs） and RNFL thickness.Results The value of FA, MD, λ//, λ⊥, average, temporalside, nasal side, low quadrant and upper quadrant RNFL thickness in patient group were 0.445±0.078, （1.330±0.236）×10^-3mm^2/s, （5.502±0.263）×10^-3mm^2/s, （4.494±0.238）×10^-3mm^2/s, （104.7±25.4）μm, （104.0±31.0）μm, （65.0±25.0）μm, （122.0±33.3）μm, and （117.4±37.7）μm respectively and the data in control group were 0.581±0.043, （1.079±0.146）×10^-3mm^2/s, （5.349±0.214）×10^-3mm^2/s, （4.195±0.126）×10^-3mm^2/s, （101.2±10.6）μm, （70.0±10.8）μm, （81.3±13.4）μm, （127.3±12.5）μm, （126.3±11.5）μm respectively. Compared with the control group, the value of MD, λ//, λ⊥ were significantly higher but FA was significantly lower （t=-12.388, 7.394, 3.695, 9.062;all P〈0.01）. The temporal RNFL was significantly thicker while the nasal RNFL was much thinner than that in control group respectively（Z=-8.384, -4.518;all P〈0.01）;the average, low quadrant and upper quadrant RNFL thickness showed no significant differences compared with the control group（t=-1.217, -1.843, 1.049;P=0.227, 0.069, 0.297）.Especially, there was a weak correlation between the temporal RNFL thickness and FA （r=0.268,P=0.029）, however, no correlation of nasal RNFL thickness with mean FA was found （r=0.164,P=0.186）.ConclusionsrFOV-DTI together with OCT can provide information about the pathology of RGC axon disease in patients with RP. there is a weak correlation between the retinal nerve fiber layer and the pathological changes of optic nerve in the retinal ganglion cells,but the performance were not coincident.