How the eye focuses: Basic mechanisms & opportunities for advanced displays

当眼睛失焦时，眼睛内部的晶状体会改变形状，使图像回到清晰的焦点中。科学家们不知道眼睛是如何知道哪个方向--向内或向外--聚焦的，也不知道眼睛如何知道何时实现了最佳聚焦。这项研究的第一个目的是使用一种创新的自适应光学设备来操纵三种可能的线索，这些线索用于在聚焦时引导眼睛，并测量对眼睛聚焦反应的相应影响。根据研究结果，研究人员可以构建一个人类眼睛聚焦的一般模型。这项研究的第二个目标是开发一种新的图形渲染技术，该技术考虑了观察者的光学特性，并在视网膜上创建更逼真、更自然的图像，用于虚拟和增强现实(VR和AR)显示。更好地了解眼睛的聚焦反应和开发适当的图形技术可能会有显著的实际和临床好处。例如，迅速进入市场的VR和AR设备已知会导致视觉不适、性能下降和深度感知扭曲。更好地了解眼睛如何聚焦并确定观看场景的三维程度，将有助于科学家和工程师确定如何最好地设计和评估这种下一代显示器。这项研究还可能有助于临床程序的设计，如LASIK眼科手术和调节性人工晶状体(AOL)。这些程序会影响正在研究的聚焦线索，所以更好地了解这些线索是如何使用的可能会导致这些程序的改进。研究调查了视觉系统如何决定调节反应的方向和大小，以确保视网膜上有一个清晰的聚焦图像。眼睛可以使用三种线索：1)色差。有些颜色，如蓝色，通常集中在视网膜前面，而另一些颜色，如红色，通常集中在视网膜后面。这可以帮助判断焦距是太近还是太远；2)高阶像差。当焦距太近时，视网膜图像的某些特性与当焦距太远时不同；以及3)微小波动。眼睛的焦点状态以每秒1到2次的速度波动，这可以提供焦点是否太近、太远或恰到好处的信息。以前的研究已经令人信服地表明，使用了色差。一些研究表明使用了高阶像差，但证据并不令人信服。还没有研究测试是否使用了微波动。本研究综合考虑了这三种线索，构建了一个线索-组合调节模型。

When the eye is out of focus, the lens inside the eye changes shape to bring the image back into sharp focus. Scientists do not know how the eye knows which direction--in or out--to focus, or how the eye knows when the best possible focus has been achieved. The first aim of this research is to use an innovative adaptive-optics apparatus to manipulate three possible cues that are used to guide the eyes when focusing and to measure the corresponding effects on the eye's focusing response. From the results, the researchers can construct a general model of focusing in human eyes. The second aim of this research is to develop a novel graphics-rendering technique that takes into account the optics of the viewer and creates more realistic, natural images on the retina for virtual and augmented reality (VR and AR) displays. A better understanding of the eye's focusing response and the development of appropriate graphics techniques could have significant practical and clinical benefit. For instance, VR and AR devices, which are rapidly entering the marketplace, are known to cause visual discomfort, decreased performance, and distorted depth percepts. A better understanding of how the eye focuses and determines the three-dimensionality of the viewed scene will help scientists and engineers determine how best to design and evaluate this next generation of displays. The research may also aid the design of clinical procedures such as LASIK eye surgery and accommodating intra-ocular lenses (AOLs). These procedures affect the focusing cues under investigation, so a better understanding of how the cues are used may lead to improvements in these procedures.The research investigates how the visual system determines the direction and magnitude of accommodative responses needed to assure a sharply focused image on the retina. There are three cues that the eye could use: 1) Chromatic aberration. Some colors, such as blue, are generally focused in front of the retina while other colors, such as red, are usually focused behind the retina. This can help tell whether focus is too near or too far; 2) Higher-order aberrations. When focus is too near, some properties of the retinal image are different compared to when focus is too far; and 3) Micro-fluctuations. The eye's focus state fluctuates at a rate of about 1 to 2 times per second and this could provide information about whether focus is too near, too far, or just right. Previous research has shown convincingly that chromatic aberration is used. Some research suggests that higher-order aberrations are used, but the evidence is not convincing. No research has tested whether micro-fluctuations are used. The present research considers all three cues to construct a cue-combination model of accommodation.