Many reading comprehension problems occur because of poor visual skills. In other words, the eyes are not seeing the text properly. The reader cannot see all the words clearly, in the right order, and at the right speed in order to make sense of the content. Obviously, if the words are not clear, the reader will mistake words, read much slower, and get the wrong meaning. Less obvious, is that words that are read out of order, severely hampers comprehension. Words read in the wrong order causes confusion, slower processing (thinking) and poorer understanding. Also keep in mind that the added effort expended by reader to keep their eyes tracking properly competes with the effort needed to concentrate on the meaning.
Sometimes, parents can recognize tracking errors in their children, if they have them read aloud. If the child omits, adds, substitutes, or transposes words, and/or has labored reading, the child should be suspected of having eye tracking problems causing there comprehension problem. This is especially true, if the reader has good comprehension while having material read to them but does not when reading the material for them selves. Frequently, readers with tracking errors are completely unaware that their eyes do not track properly even when they read aloud. This occurs because eyes take in information faster than they process the information, and they have time to rescan if necessary. Of course, less rescanning is preferred, and makes for a better reader and better comprehension.
Tracking problems as they relate to reading ability can be assessed and treated by some eye doctors that specialize in this area. Special computerized instruments can measure eye tracking movements used while reading and also be used to improve tracking ability along with reading comprehension.