Normative data for modified Thorington phorias and prism bar vergences from the Benton-IU study

The use of a phoropter for measuring phorias and vergences in children is common in the optometric profession. For young children, the use of the phoropter can be confusing, making it difficult to obtain accurate measurements. Free space testing allows for direct observation of the eyes in a natural environment and is easier for children to understand the directions. The normal values for phorias and vergences used with children are derived from testing with a phoropter or free space measurements with mostly adult patients.

The Benton-IU Project was a large multidisciplinary study of factors affecting school performance conducted by the Indiana University School of Optometry and the Indiana University Department of Speech and Hearing with the cooperation of the Benton Community School Corporation (Benton County, Indiana). This project allowed the authors to obtain data on modified Thorington phorias and prism bar vergences from a nonselected group of first and fourth graders as part of an eye/vision examination.

In this report, central tendency and variability statistics for modified Thorington and prism bar vergences are reported based on the data from the Benton-IU Study.

The data presented in this report can be used by optometrists when deciding if the patient's phorias and vergences are within normal limits for children in the first through fourth grades.