Nigel Philip Davies | PubMed Health

PubMed2003

Spatial visual filtering in diabetes mellitus.

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.

Case-Control Studies↗

PubMed2002

Color matching in diabetes: optical density of the crystalline lens and macular pigments.

PURPOSE: To measure the optical density of the crystalline lens and macular pigments in a group of patients with diabetes mellitus and compare the results with those in a group of control subjects. METHODS: Color matches were performed using a Wright tristimulus colorimeter. The reference wavelength used was 490 nm, desaturated with 650 nm. Lens optical density was measured by mixing spectral primaries of wavelengths 420, 515, and 650 nm to match the reference. Wavelengths 420 and 515 nm were chosen, because they are absorbed equally by the macular pigment. To measure macular pigment density, two color matches were performed, one foveal and one 5 degrees extrafoveal. The reference stimulus was matched by mixing spectral primaries of 460, 530, and 650 nm. The ratio of the foveal to extrafoveal color match gives the optical density of the macular pigment. Thirty-four diabetic patients and 34 control subjects performed the lens density color match, and of these, 26 diabetic patients and 30 control subjects performed the macular pigment density color matches. RESULTS: There is a significant increase in the optical density of the lens in diabetes with age in comparison to the control subjects (P < 0.001), with a duration dependence of 0.02 log units/year. The mean macular pigment density in the diabetic patients was 0.13 +/- 0.20 log units and in the control subjects 0.32 +/- 0.24 log units (P = 0.0015). Patients with grade 2 maculopathy had significantly lower pigment density than those with no maculopathy (P = 0.016). CONCLUSIONS: The ocular media of diabetic persons are abnormal, with increased lens and reduced macular pigment optical density. The relationship between reduced macular pigment levels with increasing severity of maculopathy may implicate oxidative stress as a causative factor.

Adult↗