PURPOSE: To investigate spatial visual filtering in a group of diabetic patients and compare the results with those of a group of controls. METHODS: The luminance threshold of a moving 2 degrees achromatic target, viewed against a 17 degrees achromatic background grating, was measured as a function of grating periodicity from 0.21 to 31.4 cpd in 22 diabetic patients and 12 controls, giving a response characteristic of the spatial function of a sustained-response type of visual channel. A previously published model of spatiotemporal filtering, integrating photoreceptor kinetics with difference-of-Gaussian circularly symmetric receptive fields, was used to analyse the data. METHODS: The model gave a good fit to the data in the control group, with a mean central space constant of 0.046 degrees and centre:surround ratio of 1:5.2 and mean R(2)=0.78 (SD 0.12). The mean central space constant in the diabetic group was 0.051 degrees and the centre:surround ratio 1:4.2, although best fit was significantly worse, at R(2)=0.54 (SD 0.19), P=0.001. The best fit for diabetic subjects with grade 2 maculopathy was significantly worse than for those with no maculopathy ( P=0.03). CONCLUSION: The study demonstrates a disruption of circularly symmetric centre-surround receptive field structure of the sustained-response channel in the diabetic retina to a degree that is consistent with the retinal level of anatomical change in diabetic maculopathy.
PURPOSE: To investigate spatial visual filtering in a group of diabeticpatients and compare the results with those of a group of controls. METHODS: The luminance threshold of a moving 2 degrees achromatic target, viewed against a 17 degrees achromatic background grating, was measured as a function of grating periodicity from 0.21 to 31.4 cpd in 22 diabeticpatients and 12 controls, giving a response characteristic of the spatial function of a sustained-response type of visual channel. A previously published model of spatiotemporal filtering, integrating photoreceptor kinetics with difference-of-Gaussian circularly symmetric receptive fields, was used to analyse the data. METHODS: The model gave a good fit to the data in the control group, with a mean central space constant of 0.046 degrees and centre:surround ratio of 1:5.2 and mean R(2)=0.78 (SD 0.12). The mean central space constant in the diabetic group was 0.051 degrees and the centre:surround ratio 1:4.2, although best fit was significantly worse, at R(2)=0.54 (SD 0.19), P=0.001. The best fit for diabetic subjects with grade 2 maculopathy was significantly worse than for those with no maculopathy ( P=0.03). CONCLUSION: The study demonstrates a disruption of circularly symmetric centre-surround receptive field structure of the sustained-response channel in the diabetic retina to a degree that is consistent with the retinal level of anatomical change in diabetic maculopathy.