Division of Pharmacy and Optometry, School of Health Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK.
Ophthalmic Physiol Opt. 2022 Jul;42(4):717-729. doi: 10.1111/opo.12983. Epub 2022 Apr 7.
To explore the factors affecting the linear magnification of the intermediate fundus image during indirect ophthalmoscopy with a slit-lamp biomicroscope.
A simple paraxial model, based on a 'reduced' eye and a 'thin' ophthalmoscopy lens, is used to develop equations showing the effects of the power and ametropia of the eye, and the equivalent power and position of the ophthalmoscopy lens on fundus magnification. Predicted magnifications are compared with practical results found in earlier published experimental studies, which used Volk ophthalmoscopy lenses in conjunction with physical model eyes with adjustable levels of axial ametropia.
The model's magnification predictions, as a function of the eye's ametropia, are in good agreement with previous experimental measurements, provided that the equivalent powers of the Volk lenses are used rather than their labelled nominal powers. Magnification values typically change by approximately ±10% over the practical range of each parameter if other parameters are held constant. In particular, normal variations in the equivalent power of the adult emmetropic eye result in magnifications which range from about 90-120% of the nominal value given for an eye power of +60.00 D. It is demonstrated that the recommended working distances for different powers of Volk ophthalmoscopy lenses approximate optimal matching between the various pupils of the eye-Volk lens-slit-lamp biomicroscope system.
All the parameters considered have marked effects on magnification. The magnification values quoted by manufacturers can be regarded as only approximations of those which may be found in practice. Better estimates of magnification can be obtained by inserting the appropriate parameter values into the equations derived in this paper, using, where appropriate, the equivalent power of the indirect ophthalmoscopy lens, rather than the lens' labelled, 'nominal' power.
探讨间接检眼镜用裂隙灯显微镜检查时中间眼底图像线性放大率的影响因素。
采用基于“简化”眼和“薄”检眼镜透镜的简单傍轴模型，建立了显示眼的屈光力和像差、检眼镜透镜的等效屈光力和位置对眼底放大率影响的方程。预测放大率与先前发表的实验研究中使用 Volk 检眼镜透镜结合可调节轴向像差的物理模型眼的实际结果进行了比较。
该模型的放大率预测值与以前的实验测量值吻合良好，前提是使用 Volk 透镜的等效功率而不是其标称额定功率。如果其他参数保持不变，每个参数的实际范围内，放大率值通常会变化约±10%。特别是，成年人正视眼的等效功率的正常变化导致放大率在给定眼功率+60.00 D 的标称值的 90-120%范围内变化。证明不同 Volk 检眼镜透镜功率的推荐工作距离接近眼球-Volk 透镜-裂隙灯显微镜系统各个瞳孔之间的最佳匹配。
所有考虑的参数对放大率都有显著影响。制造商给出的放大率值可以被认为只是实际中可能发现的放大率的近似值。通过将适当的参数值插入本文中推导的方程中，并在适当的情况下使用间接检眼镜透镜的等效屈光力而不是透镜的标称“额定”功率，可以获得更好的放大率估计值。
