Optimal Print Size

Best Close Reading Distance, Optimal Print Size
 
When calculating print size, know that you will have the opportunity to take a class with an Optometrist (you get a broader understanding of vision conditions, correction and optics) and a Low Vision class where you will have the opportunity to administer portions of tests and observe low vision exams being performed.  So no need to think you need to know it all in this class. 
 
When determining print size a few things are necessary. The standard for this is M Units.  When looking at printed material, you test for this.   Some basic informtion 8 pt Times New Roman is equal to 1 M, 16 pt TMR = 2 M and 32 pt TNR =4 M. 
 
Best Close Reading Distance is where print material should be placed for the child to most effectively read.  To do this you have a child read a reading chart at a comfortable distance, measure the distance at which they are holding the card.  Then you will multiply that distance by 1.5 to get the Best Close Viewing Distance.  So if you measure 10 cm multiply that by 1.5 and 15 cm become the best close viewing distance for that student. Any student needing to hold the card closer than 15 cm or 6 inches should be one that you consider teaching braille. 
 
Next you want to find the Optimal Print Size.  To do this you have the student complete a reading test where print begins large and gets smaller (commercial test).  The student holds the reading card at their Best Close Viewing Distance and begin reading down the card until their reading speed decreases quickly.  At that point you move up 1 line on the card and that is the Optimal Print Size or Critical Angular Size. 
 
If you have a Best Close Reading Distance of 10 inches and 4 M is the Optimal Print Size then you can convert that number to get the Optimal Print Size at various distances.  At 5 inches use 2 M and at 20 inches use 8 M. Each of these equates to a visual acuity of 20/400 on a Snellen chart. 
 
 
 
 
 
 

1. Why doesn't the mm double as point size and inch increments double- that is because the conversion from mm to inches is 0.39.  So inches = mm x 0.39. 
    
2. Best Close Viewing Distance is measured by handing the child something to read and having them read to the smallest print they can.  Measure the distance in cm.  Usually I do this by holding a ruler along side the child head, beginning at the side of the eye and extending to the side of the paper they are holding.  I try not to interfere with their reading.  Then you multiply that distance by 1.5 and you get the BCVD. 

 

1. When you have calculated the BCVD and the Optimal Print Size it is possible to convert that to Snellen equivalents.