More Pieces to the Crowding Puzzle

Previously we introduced the idea of crowding, and what a vital concept it is in vision therapy.  The basis for crowding resides in the idea of contour interaction, first introduced by one of my early mentors, Dr. Mert Flom.   There is an excellent overview of crowding as a developmental phenomenon, and how it specifically relates to reading and dyslexia that you can read about here.

Dennis Levi, currently Dean at the College of Optometry at UC Berkeley, is a very active researcher in the field of amblyopia.  He has pointed out the parallels between visual function in amblyopia and challenges in the visual elements of reading, and it is worth taking a look at his paper on the subject.  I’ve made the case earlier that contour interaction and crowding cuts across many lines of vision therapy, and applies to patients of all ages.

Beyond mastery of the Hart Chart Saccadic procedure, one of the more useful procedures to deal with contour interaction and crowding is letter tracking.  In our practice we refer to this as “Michigan Letter Tracking” or MLT, deriving its name from the source, Ann Arbor Publishers in Michigan.  Here’s the key:  the beginning phase has large print and liberal spacing, reducing the crowding effect.  As the patient works through the paragraph, circling each letter in alphabetic sequence, all 26 letters of the alphabet  are present.  So if the patient comes to the end of the paragraph, and the last letter circled is the “s” in the example above, then she knows that she must have skipped a letter.  her job is to back track and find which letter she skipped.  The concept of self-inspection, recognition of errors, and self-correction is crucial to making progress.

Ultimately, when a paragraph can be completed accurately, with all 26 letters circled in correct sequential order, the patient will proceed to progressively smaller print, where the crowding effects of tight spacing become more of a factor in visual search.  Even though there is a space at the bottom of each section for time in minutes and seconds, we’re not concerned with time at the outset as much as we are with accuracy.  However, as the patient improves in visual search accuracy, we look toward improved speed without trading off accuracy.  This then becomes another index of visual efficiency.

Once the patient has mastered letters, you can convert this into a modified “word search” by giving the patient a word verbally, and ask her to circle the letters in correct sequential order; then proceed to a phrase.  Ultimately there are sentence tracking booklets where the sentence is pre-printed and the patient has to find the words in correct sequential order among nonsense words.   If the patient is nonverbal or pre-language, symbol tracking books can be used to progressively improve serial visual search as crowding becomes more complex.

You can order these workbooks directly from Ann Arbor Publishers, or obtain them through OEPF or Bernell.


– Leonard J. Press, O.D., FCOVD, FAAO

5 thoughts on “More Pieces to the Crowding Puzzle

  1. Thanks for sharing this important information about crowding. Another aspect to consider is the push toward single letter sound correspondences by those who are strongly in the ‘phonetic decoding’ camp of how to read. You often hear a parent or teacher say, “just sound it out”. The difficulty is that almost half of the first words learned up to second grade are phonetically incorrect. Take a look at the vowels “o” and “e”, they each have 9 different sounds….how is one to remember which to use for each word? The simple answer is to learn to “see” the word first. By knowing the word first, sounding out seems relatively easy. This comes back to another reason why the MLT often helps kids do better in reading. By looking for bigger chunks(words vs. letters) and increasing visual processing to the right of print, one has less crowding. And often this results in the child trying to see words vs. simply isolated letters. The faster scores on the MLT are often made by those that reduce the crowding effect by chunking more peripheral information vs. simply seeing isolated single letters that appear to run into each other.

  2. We use this procedure with a patch for amblyopes, and without a patch for tracking with other patients. It is also a good procedure to send home. Sharon Weems

    • Totally agree, Sharon. Great procedure in and out of office. Relative to the “better” eye, the amblyopic eye is learning disabled, since researchers now agree that amblyopia is a developmental disorder of spatial vision. No wonder, then, the procedures are so valuable for reducing the common origins of disability.

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