Department of Physics, Florida International University, 11200 SW 8th Street, Miami, 33199 FL USA.
Eye Vis (Lond). 2016 Sep 12;3(1):24. doi: 10.1186/s40662-016-0054-6. eCollection 2016.
Cataract, a leading cause of vision impairment, is due to the lens becoming excessively optically dense. Change in the lens optical density (LOD) could be a useful indicator of incipient nuclear cataract and would necessitate the development of accurate measurement techniques. Mapcat sf™ is a heterochromatic flicker photometer for measuring macular pigment optical density (MPOD) under photopic conditions. In the process, it also measures LOD that is needed in the calculation of MPOD. LOD is then converted by the instrument to "lens equivalent age" (LEA). However, varying cone photoreceptor ratios among individuals could affect the LEA measurement. Scotopic vision is mediated by rod photoreceptors; therefore, LEA measurement under scotopic conditions potentially provides a reliable standard for assessing other methods. The study was conducted to test the level of agreement between the LEA data obtained under photopic and scotopic conditions for a sample population. We also comment on factors that might contribute to any disagreement.
LEAs were obtained by Mapcat sf for 25 subjects and compared with those obtained under absolute scotopic threshold conditions.
The mean scotopic LEA for the subjects was 2.7 years higher than the mean photopic LEA, but this difference was not statistically significant. Measurements by the two methods were reasonably correlated (r(2) = 0.59, p < 0.0001). Significant individual differences in LEA by the two methods were found for six of the 25 subjects. Although our calculations included a standard long- to medium-wavelength-sensitive cone ratio, we found that different ratios could be found that rendered the differences in LEA insignificant for two of these six subjects. Variability in pupil diameter during scotopic measurements was considered another potential source of discrepancy between LEAs by the two methods.
The absolute threshold technique, with long adaptation times, is probably impractical for routine lens density measurement, whereas Mapcat sf provided a rapid, straightforward test that may find its application in optometric/ophthalmic practice.
白内障是导致视力损害的主要原因，其原因是晶状体变得过于光学致密。晶状体光学密度 (LOD) 的变化可能是核性白内障初期的一个有用指标，因此需要开发准确的测量技术。Mapcat sf™ 是一种用于测量明视条件下黄斑色素光学密度 (MPOD) 的异色调闪烁光度计。在此过程中，它还测量了计算 MPOD 所需的 LOD。然后，仪器将 LOD 转换为“晶状体等效年龄”(LEA)。然而，个体之间的锥形光感受器比例的变化可能会影响 LEA 的测量。暗视觉由视杆光感受器介导；因此，暗视条件下的 LEA 测量为评估其他方法提供了可靠的标准。本研究旨在测试在样本人群中，明视和暗视条件下获得的 LEA 数据之间的一致性水平。我们还对可能导致任何差异的因素进行了评论。
Mapcat sf 为 25 名受试者获得了 LEA，并与绝对暗视阈值条件下获得的 LEA 进行了比较。
受试者的平均暗视 LEA 比平均明视 LEA 高 2.7 岁，但差异无统计学意义。两种方法的测量值具有相当的相关性(r²=0.59，p<0.0001)。在 25 名受试者中，有 6 名受试者的两种方法的 LEA 存在显著的个体差异。尽管我们的计算包括了一个标准的长-中波敏感锥细胞比例，但我们发现，对于其中的 6 名受试者中的 2 名，不同的比例可以使 LEA 的差异变得不显著。暗视测量期间瞳孔直径的变化被认为是两种方法的 LEA 之间差异的另一个潜在来源。
绝对阈值技术具有较长的适应时间，可能不适用于常规晶状体密度测量，而 Mapcat sf 提供了一种快速、直接的测试方法，可能会在视光/眼科实践中得到应用。
