Interactions between abiotic and biotic factors

the visual field is only a few inches. 

Research shows that reading slows and retention rates fall as line length begins to exceed the ideal width.*

This may be caused by having 

columns that are too wide. If lines of text are too long, your readers get lost when their eyes return to the left side. The long length makes it difficult to determine when the text starts and ends.

Do not use the full length of your 

slide; break your pages into columns.

On the flip side, if lines of text are too short, the eye has to travel back and forth too often. This is tiring on the eye and frustrating to readers who 

are unable to read a complete 

thought.