Improved post-operative vision using advanced optical measurement techniques

白内障（眼睛的透镜混浊）主要是一个老化问题; 65岁以上的人中有一半以上患有某种程度的白内障，白内障手术是英国最常见的手术之一，每年帮助超过25万患者。对于绝大多数患者，在摘除白内障透镜后，必须植入人工透镜以获得良好的视力。选择该晶状体以使视网膜处的模糊最小化的该晶状体的屈光力是根据眼睛的屈光元件的术前测量来计算的，所述屈光元件包括角膜、房水、透镜和玻璃体液的尺寸以及元件之间的界面处的曲率。一个多世纪以来，“示意性眼睛”或数学模型已经用于评估人眼的总体光学屈光，使用每个元件的假定折射率值。随着关于各种所需参数的更好信息的出现，这些模型多年来不断完善，至今仍在使用。21世纪世纪已经看到了用于眼睛测量的新方法的发展，特别是光学相干断层扫描（OCT），一种低功率、非激光、非侵入性成像技术，在体内测量光程长度的应用。然而，该技术的精确性对用于从示意性眼睛计算IOL屈光度的标准RI值提出了质疑。手术后人工晶状体的远视力质量一般都很好，但通常可以通过使用眼镜得到进一步的改善，特别是对于远视和近视患者，这表明假设的折射率值有时是wanted.The目的提出的研究是允许测量的折射率，在体内，为眼睛内的每个单独的元素。这将使得能够更精确地计算要为个体白内障患者做出的正确的人工透镜屈光度，从而减少或甚至完全避免手术后对用于远视力的眼镜的需要。鉴于白内障在全球的发病率，就节省成本和方便白内障患者进行手术而言，其益处将是极其广泛的。光学相干断层扫描是一种非常高分辨率的技术，可提供眼睛内部结构的详细图像，下至视网膜内的单个锥体，直径仅为几微米。然而，图像中的深度总是以物理距离和群折射率的乘积出现;这是一个与折射率相关但不相同的量。这两个参数不能分开。为了获得群折射率，从而获得折射率，需要对物理距离进行独立测量，在所提出的工作中，通过另一种称为共焦成像的光学技术提供，其中针孔被定位成使得仅来自样品内一定深度的光可以通过针孔到达检测器。在开发这种技术时要克服的困难包括：（a）产生具有足够小的聚焦光斑直径和景深的光束，以将图像内的组织边界的位置限定为约1微米，（B）消除在信号采集期间由眼睛相对于仪器的运动引起的图像伪影，以及（c）校正导致聚焦光斑模糊并因此降低测量分辨率的像差，（d）调整测量仪器以保持居中，并垂直于，已经考虑了解决所有这些问题的方法，并且预计最终版本的所得仪器将能够准确且精确地测量折射率，精确度在小数点后第三位，这是对目前缺乏体内测量这一重要参数的技术的一个重大进步。

Cataract (clouding of the lens of the eye) is primarily a problem of aging; more than half of the over 65s have some degree of cataract, and cataract surgery is one of the most frequently performed operations in the UK, helping over a quarter of a million patients per year. For the vast majority, after removal of the cataractous lens, an artificial lens must be implanted to achieve good vision. The refractive power of this lens, chosen to minimize blurring at the retina, is calculated from preoperative measurements of the refractive elements of the eye, including the dimensions of the cornea, aqueous humour, lens and vitreous humour, and the curvatures at the interfaces between element.For well over a century, 'schematic eyes', or mathematical models, have been used to assess the overall optical refraction of the human eye, using assumed refractive index values for each element. The models have been refined over the years, as better information on the various required parameters has become available, and are still used today. The 21st century has seen the development of new methods for ocular measurements, in particular the application of optical coherence tomography (OCT), a low-power, non-laser, non-invasive imaging technique, to in vivo measurement of optical path length. However the very precision of the technique calls into question the standard RI values used in calculating IOL powers from schematic eyes. The quality of distance vision resulting from artificial lenses, post-surgery, is generally good, but further improvement can often be obtained by the use of spectacles, particularly for long-sighted and short-sighted patients, suggesting that assumed refractive index values are sometimes wanting.The aim of the proposed research is to allow measurement of the refractive index, in vivo, for each separate element within the eye. This will enable a more accurate calculation of the correct artificial lens power to be made for an individual cataract patient, reducing, or even avoiding altogether, the post-surgery necessity of spectacles for distance vision. Given the incidence of cataract worldwide, the benefits, in terms of cost-savings and convenience to cataract patients following surgery, would be extremely widespread.OCT is a very high resolution technique, providing detailed images of structures inside the eye, down to individual cones, only a few micrometres across, within the retina. Depth within the image always appears, however, as the product of physical distance and group index; a quantity related to, but not identical to, refractive index. The two parameters cannot be separated. To obtain the group index, and hence the refractive index, an independent measurement of physical distance is required, provided, in the proposed work, by another optical technique known as confocal imaging, in which a pinhole is positioned such that only light from a certain depth within the sample can pass through the pinhole to reach the detector.Difficulties to be overcome in developing this technique include: (a) the generation of beams with a sufficiently small focused spot diameter and depth of field to define the location of a tissue boundary within an image to about 1 micrometre, (b) elimination of image artefacts caused by motion of the eye, relative to the instrument, during signal acquisition, and (c) the correction of image aberrations resulting in blurring of the focused light spot and hence reducing measurement resolution, (d) adjustment of the measuring instrument to remain centred on, and perpendicular to, the apex of the cornea during acquisition of a dataset.Methods have been considered to address all these problems, and it is anticipated that the final version of the resulting instrument will be able to measure refractive index with accuracy and precision in the third decimal place, a major advance over the current lack of techniques for in vivo measurement of this important parameter.