Yii Fabian, Strang Niall, Moulson Colin, Dhillon Baljean, Bernabeu Miguel O, MacGillivray Tom
Robert O Curle Ophthalmology Suite, Institute for Regeneration and Repair, The University of Edinburgh, Edinburgh, UK.
Centre for Clinical Brain Sciences, The University of Edinburgh, Edinburgh, UK.
Ophthalmol Sci. 2024 Oct 10;5(1):100631. doi: 10.1016/j.xops.2024.100631. eCollection 2025 Jan-Feb.
Dimensional measures of retinal features are subject to the optical influence of ocular magnification. We examined the impact of ocular magnification on the association between axial length (AL) and measurements of retinal vessel caliber in fundus photographs.
Cross-sectional study.
Eighty-two normal right eyes from healthy participants aged 16 to 31 years.
Central retinal arteriolar and venular equivalents (CRAE and CRVE) were derived from color fundus photographs using semiautomated software. Ordinary least squares linear regression was used to assess the influence of AL (independent variable) on CRAE and CRVE, controlling for age, sex, and ethnicity, both before and after magnification correction using different formulae. These formulae estimate magnification based on different ocular parameters: AL only (Bennnett's formula), refractive error only (Bengtsson's formula), and refractive error combined with keratometry (Littmann's formula). Previous research has primarily relied on Bengtsson's formula, which is less accurate than Bennett's formula. We also examined the impact of treating the nontelecentric fundus camera used in this study as telecentric when applying these magnification correction formulae.
Central retinal arteriolar and venular equivalents (in pixels).
Before magnification correction, increasing AL was associated with decreasing CRAE (β: -0.49, 95% confidence intervals: -0.89 to -0.09, = 0.02) and CRVE (β: -0.91, 95% confidence intervals: -1.62 to -0.20, = 0.01). After magnification correction, this observation was no longer evident, regardless of the correction formula applied. When inappropriately assuming the fundus camera to be telecentric, we observed a bias toward increasing magnification-corrected CRAE and CRVE with increasing AL (β coefficients were positive or became more positive), reaching statistical significance ( < 0.05) for CRAE corrected using Bennett's or Littmann's formula, and for CRVE corrected using Bennett's formula.
Failing to correct for ocular magnification results in apparent narrowing of vessels in longer eyes, while inappropriate assumptions about telecentricity during magnification correction introduce an optical artifact that causes apparent widening of vessels. These findings suggest that myopic changes in retinal vessel caliber are optical (not biological) in nature. Proper correction of this effect to accurately derive dimensional measures is a crucial-yet often overlooked-methodological consideration in "oculomics" research investigating retinal biomarkers of systemic conditions.
Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.
视网膜特征的尺寸测量受眼放大率的光学影响。我们研究了眼放大率对眼轴长度（AL）与眼底照片中视网膜血管管径测量值之间关联的影响。
横断面研究。
82名年龄在16至31岁之间的健康参与者的正常右眼。
使用半自动软件从彩色眼底照片中得出视网膜中央动脉和静脉等效直径（CRAE和CRVE）。采用普通最小二乘法线性回归评估AL（自变量）对CRAE和CRVE的影响，在使用不同公式进行放大率校正前后，均对年龄、性别和种族进行控制。这些公式基于不同的眼部参数估计放大率：仅AL（贝内特公式）、仅屈光不正（本特松公式）以及屈光不正与角膜曲率计测量值相结合（利特曼公式）。以往研究主要依赖本特松公式，其准确性低于贝内特公式。我们还研究了在应用这些放大率校正公式时，将本研究中使用的非远心眼底相机当作远心相机会产生的影响。
视网膜中央动脉和静脉等效直径（以像素为单位）。
在放大率校正前，AL增加与CRAE减小相关（β：-0.49，95%置信区间：-0.89至-0.09，P = 0.02），与CRVE减小相关（β：-0.91，95%置信区间：-1.62至-0.20，P = 0.01）。放大率校正后，无论应用何种校正公式，这一观察结果均不再明显。当不适当地假定眼底相机为远心相机时，我们观察到随着AL增加，放大率校正后的CRAE和CRVE有增大的偏差（β系数为正值或变得更正），对于使用贝内特公式或利特曼公式校正的CRAE以及使用贝内特公式校正的CRVE，达到统计学显著性（P < 0.05）。
未校正眼放大率会导致眼轴较长的眼睛中血管明显变窄，而在放大率校正过程中对远心性的不恰当假定会引入一种光学伪像，导致血管明显变宽。这些发现表明视网膜血管管径的近视性变化本质上是光学性的（而非生理性的）。在研究全身疾病视网膜生物标志物的“眼组学”研究中，正确校正这种效应以准确得出尺寸测量值是一个关键但常被忽视的方法学考量。
在本文末尾的脚注和披露中可找到专有或商业披露信息。
