Preschool age(3-6 years old)is a critical period for visual development, and it is crucial to detect and treat visual problems in preschool children as early as possible. Visual acuity charts are important tools for screening visual issues in children. In China, the commonly used charts are the standard logarithmic visual acuity chart and the pediatric optotype chart, while overseas, the Lea, HOTV, and ETDRS visual acuity charts are frequently employed. Numerous studies have reported the measurability, repeatability, and sensitivity of these three charts in diagnosing visual-related problems in children. However, the application of these three charts is relatively limited in China. This article provides a comprehensive review of the design principles, clinical applications, and characteristics of these three visual acuity charts, so as to better understand their applicability and limitations in preschool children, and provide reference for the selection and improvement of vision examination methods in the future.

The elderly are prone to develop severe disease or die after infection with SARS-CoV-2, and inoculation of COVID-19 vaccine is of great significance to reduce the serious case and death. Several COVID-19 vaccines have been administered and demonstrated their safety and effectiveness in the real world. This review summarizes the safety and effectiveness of COVID-19 vaccines in the real-world studies, especially the rare adverse reactions associated with vaccine and protection against severe disease, hospitalization and death in different epidemiological contexts.