Constructing knowledge systems is viewed as a modeling activity for developing structured knowledge and reasoning models. To ensure well-formed models, the use of some knowledge engineering methodology is crucial. Additionally, reusing models can significantly reduce the time and costs of building a new application. Reusing knowledge components across different applications and domains can help acquire expert knowledge and accurately describe the reasoning process. In fact, current knowledge engineering research has taken major initiatives in the development of knowledge systems by reusing generic components, such as ontologies or problem-solving methods. The article shows how we developed a diagnosis-aid system by reusing and adapting genetic knowledge components for diagnosing eye emergencies.