Korean J Ophthalmol Vol.23, No.3, 2009 OD OS Fig. 2. Multifocal ERG; trace arrays and 3D-topography ofthe response density in the right eye shows prominent suppression of the central sig- nal compared with that of the left eye. D iscussion Of ocular masquerade syndromes, PIOL is reported to be the most common.14 PIOL typically presents as a posterior uveitis4 non-specific findings of vitreous debris, chorioretinal thicke- ning, widening of the optic nerve, elevated chorioretinal lesions, and retinal detachment can be seen in ultrasonography.15 Sub- retinal and sub-RPE infiltrations of PIOL are reported to be common, and creamy-yellow lesions on a fundal exam might be associated with PED,16 which was demonstrated in our OCT images. On fluorescein angiography, small sub-RPE in- filtrations may appear as blocked hypofluorescence, and as the tumor regresses, it can become an RPE window defect.16 In our case, vasculitis and disc leakage disappeared as the tumor 212 regressed; the granular pattern which might have been due to clumps of pigment epithelial cells, RPE atrophy and subretinal fibrosis, were persistent. Vitreous biopsy can be a useful tool to diagnose PIOL, but prior steroid therapy might suppress the number of vitreous cells, including lymphoma cells, which may result in a negative vitreous cytology.17 Electrophysiological findings obtained from eyes with PIOL were commented on in a brief report by Wang et al.18 which showed subnormal rod and cone responses. In our case, the b wave amplitude of the scotopic ERG of the left eye was mar- kedly decreased; other ERG waves might be subnormal but were relatively well preserved. The EOG Arden ratio was signifi- cantly reduced in both eyes and could represent abnormal outer retinal and RPE functions.