眼轴长度和光学放大效应对频域OCT视网膜神经纤维层测量影响

The effects of axial length and optical magnification on retinal nerve fiber layer measurement with spectral domain OCT

目的采用频域光学相干断层扫描仪（SD—OCT）分析评估眼轴长度和光学放大效应对近视眼视盘旁视网膜神经纤维层（RNFL）测量的影响。方法一共120名健康近视眼纳入研究，所有受试者均接受详细的眼科检查，包括眼压、视力、最佳矫正视力、电脑验光，裂隙灯、散瞳眼底检查、IOLMaster眼轴测量、视野检测、SD—OCT视盘旁RNFL扫描。每名受试者随机选择1只眼纳入分析。对0CT测量的RNFL厚度进行光学放大效应矫正，对RNFL峰值间距进行测量并转换为RNFL峰值分布角度进行分析。结果光学放大效应矫正前及矫正后RNFL平均厚度分别为（98．64±8．54）μm和（103．64±8．65）μm，差异具有统计学意义。矫正前的平均RNFL厚度与眼轴长度呈负相关关系（r=-0．335，P〈0．01），与屈光度呈正相关关系（r=0．216，P=0．018）；相反地，矫正后的平均RNFL厚度与眼轴长度呈正相关关系（r=0．219，P=0．017），与屈光度呈负相关关系（r=-0．198，P=0．031）。矫正前及矫正后RNFL厚度差异与眼轴长度呈正相关关系（r=0．993，P〈0．001）。RNFL厚度峰值分布角度与眼轴长度呈正相关关系（r=0．349，P〈0．001）。结论近视眼频域OCTRNFL测量受眼轴长度及光学放大效应影响。眼轴越长，光学放大效应越明显。随着近视度数的增加（眼轴增长），RNFL厚度呈增加趋势，而RNFL峰值分布趋向于颞侧偏移。对近视眼RNFL进行频域OCT检测时，其RNFL分析报告须综合考虑光学放大效应的影响以及眼轴长度对RNFL分布的影响。

Objective To investigate the effects of axial length and optical magnification on retinal nerve fiber layer measurement with spectral domain OCT in myopic eyes. Methods A total of 120 eyes from 120 healthy myopic subjects were included. Each subject received complete ophthalmic examinations including intraocular pressure （IOP） measurement, visual acuity, refraction, slit lamp, dilated fundus examination, axial length measurement by IOL master, visual field and peripapillary retinal nerve fiber layer （RNFL） with SD OCT. One eye from each participant was randomly selected for the study. The RNFL thickness measurements were adjusted with optical magnification. The distance between peaks of RNFL profile were recorded and converted to degrees for analysis. Results The mean RNFL thickness measurements were （98.64±8.54）μm before optical magnification and （103.64±8.65）μm after adjustment. Before adjustment, the mean RNFL thickness measurement was negatively associated with axial length （r =-0.335, P 〈0.001）, and positively associated with refractive error （r =0.216, P =0.018）; Conversely, the mean RNFL thickness measurement was positive- ly associated with axial length （r =0.219, P =0.017）, and negatively associated with refractive error （r =-0.198, P =0.031） after adjustment for magnification. Axial length was positively associated with the difference between RNFL thickness measurements of before and after magnification adjustment （r =0.993, P 〈0.001）. The RNFL peak thickness angle was positively correlated with axial length （r = 0.349, P 〈0.001）. Conclusions Axial length and optical magnification have significant effect on retinal nerve fiber layer measurement with spectral domain OCT in myopic eyes. The optical magnification effect increased with axial length. When axial length increases, RNFL thickness decreases and the RNFL peak thickness angle tends to shift to the temporal region. Evaluation of RNFL measurement in myopic eyes should be interpreted in the context of axial length and the magnification effect.