Studies on students' conceptions and reasoning in geometric optics have revealed that students have scientifically incorrect knowledge or lack of understanding in basic optical phenomena. For this reason, as well as the identification of these conceptions or reasoning, the factors or sources that may cause the construction of them should be determined. In the literature, textbooks are considered as one of the main sources of students' unscientific or lacking conceptions. In introductory optics, students may not recognize the role of the observer's eye in the formation and the observation of an image. In this study, nine commonly used physics textbooks around the world and the physics textbook advised by Ministry of National Education in Turkey analyzed in terms of the use of observer's eye and critiqued as a potential source of students' unscientific or lack of conception in optics. Document analysis method is used in order to analyze the ten textbooks. It is found that the role of the observer's eye is ignored or not specifically emphasized in the image formation or observation process in the textbooks. It is suggested that textbooks should be reviewed by experts and the role of observers' eye should be considered especially at the introductory optics for students' better understanding of the optical phenomena.