The ability to read requires a series of learned visual and processing skills to be used in tandem. A reader must first and foremost have an understanding of the language of the text (think of how difficult it is to understand what a foreign textbook is trying to convey!). The visual system is then engaged.
A reader must have good visual acuity, which means a clear image falls on the retina of the eyes. First, visual information is passed through the visual pathway to the occipital lobe, where visual processing begins. Both eyes are activated, and the fovea (area of central, clear vision) is directed at the words on a page. The accommodative system of the eye makes an adjustment to help clear the images, and the eyes rotate inward (converge) to point at the same location in space. The images from the right and left eye must be fused together (as double vision when reading would be very debilitating!).
The eyes then begin a series of calculated, short movement across the page–these small jumps are called saccades, and they help the eyes team together to move from one word or group of words across a page and back to the start the next line of text.
The inability to process the words on a page, or if part of the reader's vision is missing, can have a serious impact on his or her ability to comfortably find the next word or process the meaning of the words.
The complex nature of reading means deficits in any of these areas can impact reading ability. It is estimated that upwards of 16% of the population struggle with reading in some form, and 5% of children have significant problems with reading.
Saccades are the very quick eye movements your eye make when you are reading. They happen over an incredibly short time at very high speeds. Your eyes dart from word to word, quickly stopping (fixating) and then continuing onward.
Saccades and fixations are types of eye movement. The spatial-temporal sampling of the ability of the human eye, demonstrates the way in which we take in the information we are receiving about the world through our vision. This includes it’s limits. As such, it is useful to study not only the properties of the eye, but it’s movements, and that is where these terminologies are derived from.
Fixations are periods where the eye or eyes are more or less still, and saccades are periods of rapid eye movement between fixation points.
In order to read, it is necessary for the eyes to maintain proper convergence. When they don't, a person with convergence insufficiency may be able to read without initial problems, but quickly become tired, get double vision, get blurry vision, or have headaches.
If you or your child is having difficulty reading, there are many ways to improve reading skills. First, get a full vision exam. That may reveal problems caused by underlying vision issues. Once you confirm it is or is not a vision issue, you should make sure you have good lighting, have proper glasses, and practice reading regularly.