Several studies have demonstrated that respondents react to the size and design of the answer field offered with open-ended questions in Web surveys. Larger answer boxes seem to pose an additional burden and yield fewer answers and higher rates of item nonresponse as compared to smaller answer boxes. At the same time larger answer boxes work as a stimulus that increases the length of the response provided by those respondents who actually answer the question. Similar findings have been demonstrated for list-style open-ended questions were respondents are supposed to type short responses (e.g. name of countries, cities, or brand names). In this paper we evaluate a method optimizing the extent of the answer to list-style open-ended questions without increasing item nonresponse. We use a dynamic screen design were respondents initially were exposed to one fixed answer box. If respondents entered a response into an initially visible answer box, a second answer box appeared. If they again entered a response a third box appeared (and so on). In a randomized field-experimental study embedded in a large scale survey (n=6,100) we tested several question versions combining various numbers of fixed and dynamic answer boxes in a between-subjects design. Results indicated that the optimal design consisted of three initially visible (fixed) answer boxes and dynamically providing further answer boxes if the respondents wanted to answer more extent. Findings are discussed in light of the impact of the dynamic visual design on the question answer process.