Components

Reading eye movements are saccadic eye movements. When reading we make a series of fixation-saccade-fixation sequences. Generally, each word is fixated, slightly to the left of the center of the word. Larger words will have multiple fixations within them. The average duration of each fixation is about 250 msec in the mature reader. As expected, it is much larger in beginning readers (>500 msec).

When people talk about reading eye movements, they usually break them down into four components:

* the saccades, the eye movement itself

* the fixation duration or the intersaccadic interval

* the regressions (i.e. right-to-left eye movements)

* the return sweeps (going from the end of one line to the beginning of another.

Electrooculogram of eye movements during reading. Note the 3 series of staircaselike traces, one representing each line of text. Upward deflections are rightward eye movements. Downward deflections are regressions. There is one regression in the middle of the first two lines. The two large deflections are return sweeps. The horizontal lines indicate fixations; their length gives you some indication of fixation duration.   The arrows indicate regressions (there are more than the number of arrows). The trace doesn't have that nice staircase- like traces. Note also the increased number of fixations per line.

The disabled readers eye movements are generally characterized by:

* more frequent saccades, i.e. shorter length

* longer fixation duration

* more frequent regressions

* great difficulty with return sweeps

1. loss of place when reading, a vry common symptoms if not the most common

This will lead to:

2. re-reading words or lines of text

3. word omissions, additions or word transpositions, i.e. skipping entire lines or reading words in the improper order

So the natural compensation for this is:

4. the need for finger or marker to keep place

There can also be:

5. return sweep confusion, i.e. a particular loss of place in finding the beginning of the next line; the ocular motor system cannot find the proper location of this line; the eyes may land in the middle or toward the end of the next, making regressions necessary

There can also be:

6. illusory text movement, i.e. the words or letter appear to be moving; this may be related to ineffective saccadic suppression processes that lead to a stable visual world when we make rapid eye movements.

All of this causes:

7. reduced reading rate and comprehension

8. asthenopia

9. generalized fatigue

1. Chairside test of saccadic eye movements

2. More quantitative assessments of sacceades:

a. SCCO system

b. NSUCO system

3. Visual-vrbal saccade tests

a. Developmental Eye Movement Test (DEM)