CLINICAL APPLICATIONS & DISEASE - Cataracts

Clinical Applications & Disease > Cataracts 1 | 2 | 3 | 4 |

Cataracts affect six out of ten people by age 60. Cataracts create lens opacities of different shapes and sizes, causing light to scatter. Such a condition results in a loss of image contrast or causes everything to look "milky" or "washed out." This is not the same as blurry vision, which is a function of visual acuity. A cataract patient may still have good visual acuity, while simultaneously experiencing clouded vision.

Sine-wave Gratings vs. Pelli-Robson in Cataract Studies In this study, Pelli-Robson contrast sensitivity scores were similar for all tested lenses at the three lower frequencies. Lenses with an opacity of any type showed contrast sensitivity loss at the two higher frequencies. As can be seen in Chart 1 below, the Pelli-Robson test shows cortical and nuclear cataracts having a higher sensitivity than a clear crystalline lens, which is not reasonable or accurate. The sine-wave grating test results, illustrated in Chart 2 below, show the loss of contrast due to cataract. (Results have been adjusted for patient age and visual acuity; PSC means posterior subcapsular and cpd is cycles per degree). (In references, see: Adamsons I, et al. The effect of early cataracts on glare and contrast sensitivity.)

Chart 1- Pelli-Robson scores:

Chart 2 - Sine-wave grating scores:

The contrast and spatial frequency range tested by the sine-wave gratings and the Pelli-Robson charts can be directly compared when the published data are plotted on the same chart (see Chart 3 below). This comparison shows that the Pelli-Robson chart is less sensitive to contrast for the same range of spatial frequencies tested. Further, it shows that the Pelli-Robson chart is testing a very narrow range of low spatial frequencies, much lower than the largest losses shown from the gratings. The lack of reasonable sensitivity of the Pelli-Robson chart is evident from the higher sensitivity to the cortical and nuclear cataract than the clear lenses. (In references, see: Adamsons I, et al. The effect of early cataracts on glare and contrast sensitivity.)

Chart 3 - Pelli-Robson and Sine-wave grating scores comparison:

Clinical Applications & Disease > Cataracts 1 | 2 | 3 | 4 |

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