Unfortunately, contrast sensitivity, the third suspect, is not. There are a lot of eye doctors who talk about it, but few who do anything about it or measure it. Contrast sensitivity is basically the ability to see different size objects or different size contrasts. It is very important in many activities of daily living, such as driving, reading, and walking around. Even patients with good vision, apparently can have changes in their contrast sensitivity.
Contrast sensitivity is measured in the laboratory using a sine-wave generator.
The sine-wave generators have different frequencies, phases, orientations, and amplitudes and by putting the different sinusoidal gradings up on a screen for a patient to look at, you develop a contrast sensitivity curve. The interesting thing about using this method is that you can build almost any scene if you have the right number of sinusoidal curves. The process is called Fourier analysis. Just about any visual scene, if you have an appropriate computer to break it down into a sinusoidal component, can be generated as an image by using different types of sine waves. When it comes to contrast sensitivity, we see things at about four to five cycles per degree on the sine wave, much better than we see things at about thirty cycles per degree.