By default, the Thomson Test Chart  displays LogMAR letters with a one-letter-width gap between each letter as is the convention.  However, research has shown that the spacing of the letters impacts on the acuity measured and this effect is particularly marked in patients with amblyopia. For this reason, it has been suggested that the gap between letters should be decreased when screening for amblyopia.


To accommodate this, the LogMAR chart can be displayed with one-letter-width gaps (uncrowded) or half-letter-width gaps (crowded).  This is achieved by selecting the C button on the toolbar or pressing C on the keyboard.




Uncrowded LogMAR chart


Crowded LogMAR chart