Vergence facility: developmental trends in a school age population.

We examined 310 schoolchildren to determine what normal values might be expected for successive convergence and divergence ocular movements. Vergence facility may affect the efficiency of visual information processing. The population consisted of children in grades 1 through 8. The subjects wore anaglyph glasses and viewed a nonvariable square-X-circle anaglyph target alternately through a 16 delta base-out and 4 delta base-in prism flipper. The subjects were directed to keep the target "clear and single." The total number of vergence cycles was recorded for 1 min. Students in higher grade levels were able to complete more vergence changes than students in beginning grades. The average number of changes accomplished per minute at each age level is presented for this population.