King's College London

The paper explores the organization of the Distance Vision Test as a process through which optometrists derive an objective test score from subjective assessments of their clients’ quality of reading out lines of letters. The analysis of video-recorded optometric consultations explores how the standard letter-chart features in the interaction between optometrist and client. It examines specific fragments of test procedures to reveal how aspects of the chart are used by optometrist and client to practically organize the test and to determine the quality of clients’ distance vision. The paper argues that the objective definition of the test result requires that optometrists carefully introduce clients to the test procedure to avoid the reading quality and the test result being influenced by influences such as anxiety. Only after this introduction to the test, clients are encouraged to read a line of letters that follows a larger line they had difficulty to read out from the chart. The quality of the reading out of this line then is transformed into the visual acuity score. This process of transforming incommensurable qualities, reading out and seeing, into quantities in order to make them comparable, is called commensuration.