Curcio C A, Millican C L, Allen K A, Kalina R E
Department of Ophthalmology, University of Alabama at Birmingham 35294-0009.
Invest Ophthalmol Vis Sci. 1993 Nov;34(12):3278-96.
Because previous studies suggested degeneration and loss of photoreceptors in aged human retina, the spatial density of cones and rods subserving the central 43 degrees of vision as a function of age was determined.
Cones and rods were counted in 27 whole mounted retinas from donors aged 27 to 90 years with macroscopically normal fundi. Photoreceptor topography was analyzed with new graphic and statistical techniques.
Changes in cone density throughout this age span showed no consistent relationship to age or retinal location, and the total number of foveal cones was remarkably stable. In contrast, rod density decreased by 30%, beginning inferior to the fovea in midlife and culminating in an annulus of deepest loss at 0.5 to 3 mm eccentricity by the ninth decade. Space vacated by dying rods was filled in by larger rod inner segments, resulting in a similar rod coverage at all ages. At the temporal equator, cone density declined by 23%, but rods were stable throughout adulthood.
The stability of both rod coverage and rhodopsin content despite decreasing cell number suggests plasticity of the adult rod system and that age-related declines in scotopic sensitivity may be due to postreceptoral factors. There is no evidence for the massive loss of foveal cones required to explain even modest decrements in acuity, consistent with evidence that visual deficits at high photopic levels may be largely due to optical factors. Why the rods of central retina, which share a common support system and light exposure with the neighboring cones, are preferentially vulnerable to aging remains to be determined.
由于先前的研究表明老年人类视网膜中光感受器会发生退化和丧失，因此确定了作为年龄函数的、服务于中央43度视野的视锥细胞和视杆细胞的空间密度。
对27例来自27至90岁供体的全视网膜标本进行视锥细胞和视杆细胞计数，这些供体的眼底在宏观上是正常的。采用新的图形和统计技术对视光感受器地形图进行分析。
在整个这个年龄范围内，视锥细胞密度的变化与年龄或视网膜位置没有一致的关系，并且中央凹视锥细胞的总数非常稳定。相比之下，视杆细胞密度下降了30%，从中年开始在中央凹下方出现下降，并在九十岁时在偏心度为0.5至3毫米处形成最深损失的环带。死亡视杆细胞腾出的空间被更大的视杆细胞内节填充，导致在所有年龄段视杆细胞的覆盖范围相似。在颞侧赤道处，视锥细胞密度下降了23%，但视杆细胞在整个成年期都保持稳定。
尽管细胞数量减少，但视杆细胞覆盖范围和视紫红质含量的稳定性表明成年视杆细胞系统具有可塑性，并且暗视敏感性的年龄相关下降可能是由于感受器后因素。没有证据表明需要大量丧失中央凹视锥细胞来解释即使是轻微的视力下降，这与强光下视觉缺陷可能主要归因于光学因素的证据一致。为什么与相邻视锥细胞共享共同支持系统和光暴露的中央视网膜视杆细胞更容易受到衰老影响仍有待确定。
