Langenbucher Achim, Szentmáry Nóra, Seitz Berthold
Department of Medical Physics, University of Erlangen-Nürnberg, Erlangen, Germany.
Ophthalmic Physiol Opt. 2007 May;27(3):295-302. doi: 10.1111/j.1475-1313.2007.00479.x.
The calculation of phakic lenses (PL) was described by van der Heijde et al. [Klin. Monatsbl. Augenheilkd (1988) Vol. 193, pp. 99-102], but a formalism for estimating relative magnification compared with spectacle correction and accommodation effects are not yet published. The purpose of this study was to describe a mathematical strategy for calculating PL and relative magnification as a function of object vergence (phakic accommodation).
Parameters used for the calculations are the spectacle refraction before and after (target refraction) surgery, the vertex distance, corneal refraction, and the predicted position of the phakic intraocular lens. The lens power is determined as the difference in vergences between the spectacle-corrected eye and the uncorrected eye at the reference plane of the predicted lens position. If we simplify the crystalline lens to a single refracting surface located at the principal plane of the crystalline lens, the vergence of the eye with spectacle correction and with PL is determined as a function of object distance [object vergence 0 D (infinity) to 10 D (object at a distance of 10 cm)] to evaluate accommodation effects of the crystalline lens.
The method was applied to two clinical examples. In example 1 we calculated the power of a PL for correction of a 10-D myopia and determined the relative magnification and the vergence at the principal plane of the crystalline lens as a function of object vergence. Magnification gain increases with objects at near from 17% to 26%, whereas the vergence at the principal plane of the crystalline lens changes by 3.04 D less than in the spectacle-corrected eye. In example 2, a 20-D myopia was corrected with a PL. The gain in magnification changed from 33% to 58% with nearer objects. The change in vergence at the principal plane of the crystalline lens with objects at near was much higher with the PL compared with the spectacle correction, which implies that the refractive change necessary for focusing objects at near distance is much higher in the PL correction.
Even if the predictability of postoperative refraction with PL is comparable or better than in other methods of correcting high or excessive ametropia, the effects of lateral magnification change and accommodation have to be considered to avoid image-size disparities (aniseikonia) and to maintain binocular vision, especially with monocular PL implantation and anisometropia.
范德海伊德等人[《眼科临床月刊》（1988年）第193卷，第99 - 102页]描述了有晶状体眼人工晶状体（PL）的计算方法，但与框架眼镜矫正及调节效应相比估算相对放大率的形式体系尚未发表。本研究的目的是描述一种数学策略，用于计算PL以及作为物方聚散度（有晶状体眼调节）函数的相对放大率。
计算中使用的参数包括手术前后的框架眼镜验光度数（目标验光度数）、顶点距离、角膜屈光度数以及有晶状体眼人工晶状体的预测位置。晶状体屈光力通过在预测晶状体位置的参考平面处，框架眼镜矫正眼与未矫正眼的聚散度差值来确定。如果将晶状体简化为位于晶状体主平面的单个折射面，则框架眼镜矫正眼和有PL眼的聚散度可根据物距[物方聚散度从0 D（无穷远）到10 D（物体位于10 cm处）]来确定，以评估晶状体的调节效应。
该方法应用于两个临床实例。在实例1中，我们计算了用于矫正10 D近视的PL的屈光力，并确定了相对放大率以及晶状体主平面处的聚散度作为物方聚散度的函数。随着物体靠近，放大率增益从17%增加到26%，而晶状体主平面处的聚散度变化比框架眼镜矫正眼少3.04 D。在实例2中，用PL矫正20 D近视。随着物体更近，放大率增益从33%变化到58%。与框架眼镜矫正相比，有PL时晶状体主平面处的聚散度随近处物体的变化要大得多，这意味着在PL矫正中，聚焦近处物体所需的屈光变化要大得多。
即使PL术后屈光的可预测性与其他矫正高度或超高度屈光不正的方法相当或更好，但仍必须考虑横向放大率变化和调节的影响，以避免像大小差异（像不等）并维持双眼视觉，尤其是在单眼植入PL和屈光参差的情况下。
