Introduction

This cyclopean eye model explains the occurrence of double images that occur even with normal vision, a phenomenon known as PHYSIOLOGICAL DIPLOPIA. If two pencils are held upright and 1 0 0 millimetres apart along the straight ahead direction, then two types of diplopia can be distinguished. If the nearer pencil is fixated, as shown in Fig. 1.2, then the further pencil appears as a double image. In this and the subsequent figure, F denotes the point of fixation and P denotes the pencil which appears as a double image. Closing the left eye demonstrates that the image from the right eye appears on the right. Hence this type of physiological diplopia is referred to as UNCROSSED DIPLOPIA. If the further pencil is fixated, as shown in Fig. 1.3, then the nearer pencil appears as a double image. Closing the left eye demonstrates that the image from the right eye appears on the left. Hence this type of physiological diplopia is referred to as CROSSED DIPLOPIA.