In this retrospective longitudinal study, the authors examined changes in retinal layer thickness in patients taking hydroxychloroquine without evidence of retinopathy. Patients were drawn from a hydroxychloroquine screening clinic and required at least two OCT scans, at least one year apart. In total, 144 eyes of 144 patients were studied over an average of 38 months. The mean daily dose of hydroxychloroquine was 4.89mg/kg. Study patients had been on treatment for an average of four years. Changes in retinal thickness between the first and second OCT scan were determined using automated analysis. The authors found a small (2.2µm), but statistically significant, decrease in the thickness of the inner retinal layers at the fovea (in particular the ganglion cell layer). This finding concurs with some previous studies, though others have not detected a change in retinal thickness before overt toxicity occurs. However, the study is limited by a lack of a control group and its retrospective design.