Investigations of Human Cone Directionality

描述（申请人提供）：人的中央凹是高度专业化的，具有出色的视觉敏锐度和对比敏感度。为了提供这种能力，中央凹中心的锥体比中央凹旁的锥体直径小。为了补偿相对于远离中心的锥体的横截面积的减少，中央凹锥体具有更长的外段，因此其锥体光色素的光学密度更高。视锥细胞也起着天线的作用：内部的部分优先收集来自瞳孔的光线，并将光线引导到外部的部分。这些锥状体的波导特性在中央凹中也有所不同，中央凹中心的锥状体比几百微米外的锥状体接受来自瞳孔更宽区域的光。这种增加的来自瞳孔的光收集既提高了它们的灵敏度，也允许它们使用更宽的瞳孔区域，从而具有更高的光学分辨率。因此，中央凹代表了紧密耦合的因素的平衡，以提供良好的视力。随着眼睛年龄的增长，这种平衡可能会改变。中央凹曲率改变（中央凹变宽），视锥光色素对称分布不规则。此外，中央凹锥体的高光密度降低，离中央凹中心几度的锥体变得更相似。这种光密度的变化可能是由于外段长度的减少、光色素的减少或锥的波导特性的变化而发生的。在早期ARM中，中央凹和旁中央凹锥体的光密度下降得更多。

DESCRIPTION (provided by applicant): The human fovea is highly specialized for excellent visual acuity and contrast sensitivity. To provide this capability the cones in the center of the fovea are smaller in diameter than parafoveal cones. To compensate for the decreases in cross sectional area relative to cones further from the center, the foveal cones have longer outer segments, and therefore a higher optical density of their cone photopigments. The cones also act as antennae: the inner segments collect light preferentially from the pupil and guide the light along the outer segments. These waveguide properties of the cones also vary across the fovea, with the cones in the foveal center accepting light from a wider region of the pupil than cones just a few hundred microns away. This increased collection of light from the pupil both increases their sensitivity and also allows them to use a wider region of the pupil, and thereby have higher optical resolution. Thus, the fovea represents a balance of factors which are tightly coupled to provide excellent vision. As the eye ages this balance may change. The curvature of the fovea changes (the foveal pit widens) and irregularities in the symmetric distribution of the cone photopigment appear. In addition, the high optical density of the foveal cones decreases, becoming more similar to cones a few degrees away from the center of the fovea. This change in optical density may occur due to either a decrease in the outer segment length, decreases in the amount of photopigment, or changes in the waveguide properties of the cones. With early ARM the optical density of both the foveal and parafoveal cones decrease even more. Modern optical technology now allows us to directly measure the optical factors controlling the capture of light by the foveal cones. We will use state of the art instrumentation and analysis techniques to study the fovea in normals and patients with early age-related macular degeneration (ARM). We will use adaptive optics imaging with an SLO to directly image the cones and related structures. We will use photoreceptor alignment reflectometry and retinal densitometry to measure the optical properties of the cones. We will relate changes to the cones in aging and early ARM to RPE health, determined by measuring near infrared light scattering and lipofuscin fluorescence. We will test whether changes in RPE health are related to changes in the optical efficiency of the overlying cones. These studies will provide a unique quantitative framework for evaluating the fovea of the human eye as an imaging system, and provide information on how the functional capacities of the fovea change with both age and early ARM. Such measurements will be critical for both understanding the development of ARM, and to better explain visual complications that occur prior to the permanent loss of vision.