FIGURE 29.2 Horner syndrome left eye Note the smaller pupil (miosis) and smaller lid opening (ptosis) on the left When trying to establish whether the anisocoria is of relatively recent or acute onset, as opposed to long-standing anisocoria, it is helpful to view old photographs Sometimes, chronic physiologic anisocoria will not have been noticed previously The direct ophthalmoscope can be used to provide magnification and illumination of the photograph so the pupils can be viewed Set the focusing dial on progressively higher black (or green) numbers until adequate magnification has been achieved while viewing through the direct ophthalmoscope It is also important to note any other symptoms that accompanied the onset of anisocoria (headaches, pain, double vision, or blurred vision) The causes of anisocoria are summarized in Tables 29.1 to 29.3 FIGURE 29.3 Patient with right mydriasis Relative difference between the pupil sizes is greater in bright illumination (A) than in dim illumination (B)