University of Houston, College of Optometry, Houston, Texas 77204, USA.
Invest Ophthalmol Vis Sci. 2012 Aug 24;53(9):5788-98. doi: 10.1167/iovs.12-9937.
Retinal nerve fiber layer (RNFL) thickness measures with spectral domain-optical coherence tomography (SD-OCT) provide important information on the health of the optic nerve. As with most retinal imaging technologies, ocular magnification characteristics of the eye must be considered for accurate analysis. While effects of axial length have been reported, the effects of anterior segment optical power on RNFL thickness measures have not been described fully to our knowledge. The purpose of our study was to determine the influence of the optical power change at the anterior corneal surface, using contact lenses, on the location of the scan path and measurements of RNFL thickness in normal healthy eyes.
We recruited 15 normal subjects with less than 6 diopters (D) of ametropia and no ocular pathology. One eye of each subject was selected randomly for scanning. Baseline SD-OCT scans included raster cubes centered on the optic nerve and macula, and a standard 12-degree diameter RNFL scan. Standard 12-degree RNFL scans were repeated with 10 separate contact lenses, (Proclear daily, Omafilcon A/60%) ranging from +8 to -12 D in 2-D steps. The extent of the retinal scan, and RNFL thickness and area measures were quantified using custom MATLAB programs that included ocular biometry measures (IOL Master).
RNFL thickness decreased (0.52 μm/D, r = -0.33, P < 0.01) and the retinal region scanned increased (0.52%/D, r = 0.97, P < 0.01) with increase in contact lens power (-12 to +8). The normalized/percentage rates of change of RNFL thickness (-0.11/mm, r = -0.67, P < 0.01) and image size (0.11/mm, r = 0.96, P < 0.01) were related to axial length. Changes in the retinal region scanned were in agreement with transverse scaling, computed with a three surface schematic eye (R(2) = 0.97, P < 0.01). RNFL area measures, that incorporated the computed transverse scaling, were not related significantly to contact lens power (863 μm(2)/D, r = 0.06, P = 0.47).
Measurements of RNFL thickness by SD-OCT are dependent on the optics of the eye, including anterior segment power and axial length. The relationships between RNFL thickness measures and optical power are a direct reflection of scan path location with respect to the optic nerve head rim, caused by relative magnification. An incorporation of transverse scaling to RNFL area measures, based on individualized ocular biometry, eliminated the magnification effect.
利用谱域光学相干断层扫描（SD-OCT）测量视网膜神经纤维层（RNFL）厚度可以提供视神经健康状况的重要信息。与大多数视网膜成像技术一样，必须考虑眼球的眼轴放大特性，以进行准确分析。虽然已经报道了眼轴长度的影响，但我们所知的是，前节光学力对 RNFL 厚度测量的影响尚未完全描述。我们研究的目的是确定使用接触镜改变角膜前表面的光学力对正常健康眼扫描路径位置和 RNFL 厚度测量的影响。
我们招募了 15 名屈光度小于 6 屈光度（D）且无眼部病理学的正常受试者。每个受试者的一只眼睛被随机选择进行扫描。SD-OCT 基线扫描包括以视神经和黄斑为中心的光栅立方体，以及标准的 12 度直径 RNFL 扫描。使用包括眼生物测量（IOL Master）的定制 MATLAB 程序，对 10 个单独的接触镜（Proclear 日抛，Omafilcon A/60%）重复进行标准的 12 度 RNFL 扫描，范围从+8 到-12 D 的 2-D 步长。使用定制的 MATLAB 程序（包括眼生物测量），量化视网膜扫描的范围以及 RNFL 厚度和面积测量值。
随着接触镜功率的增加（从-12 到+8），RNFL 厚度减少（0.52μm/D，r=-0.33，P<0.01），扫描的视网膜区域增加（0.52%/D，r=0.97，P<0.01）。RNFL 厚度（-0.11/mm，r=-0.67，P<0.01）和图像大小（0.11/mm，r=0.96，P<0.01）的归一化/百分比变化率与眼轴长度有关。扫描区域的变化与使用三个表面示意图眼（R2=0.97，P<0.01）计算的横向缩放一致。考虑到计算出的横向缩放，RNFL 面积测量值与接触镜功率没有显著关系（863μm2/D，r=0.06，P=0.47）。
SD-OCT 测量的 RNFL 厚度取决于眼球的光学特性，包括前段光学力和眼轴长度。RNFL 厚度测量值与光学力之间的关系直接反映了相对于视盘边缘的扫描路径位置，这是由相对放大引起的。根据个体眼生物测量学，对 RNFL 面积测量值进行横向缩放的整合消除了放大效果。
