Contrast sensitivity mediated by inferred magno- and parvocellular pathways in type 2 diabetics with and without nonproliferative retinopathy.
OBJECTIVE
To evaluate achromatic contrast sensitivity (CS) with magnocellular- (M) and parvocellular- (P) probing stimuli in type 2 diabetics, with (DR) or without (NDR) nonproliferative retinopathy.


METHODS
Inferred M- and P-dominated responses were assessed with a modified version of the steady-/pulsed-pedestal paradigm (SP/PP) applied in 26 NDR (11 male; mean age, 55 ± 9 years; disease duration, 5 ± 4 years); 19 DR (6 male; mean age, 58 ± 7 years; disease duration = 9 ± 6 years); and 18 controls (CTRL; 12 male; mean age, 55 ± 10 years). Thresholds were measured with pedestals at 7, 12, and 19 cd/m(2), and increment durations of 17 and 133 ms. The thresholds from the two stimulus durations were used to estimate critical durations (Tc) for each data set.


RESULTS
Both DR and NDR patients had significant reduction in CS in both SP and PP paradigms in relation to CTRL (Kruskal-Wallis, P < 0.01). Patients' critical duration estimates for either paradigm were not significantly different from CTRL.


CONCLUSIONS
The significant reduction of CS in both paradigms is consistent with losses of CS in both M and P pathways. The CS losses were not accompanied by losses in temporal processing speed in either diabetic group. Significant CS loss in the group without retinopathy reinforces the notion that neural changes associated with the cellular and functional visual loss may play an important role in the etiology of diabetic visual impairment. In addition, the results show that the SP/PP paradigm provides an additional tool for detection and characterization of the early functional damage due to diabetes.
Departamento de Psicologia Experimental, Instituto de Psicologia, USP, São Paulo, Brasil. mirellag@usp.br
Mirella
M
Gualtieri
Marcio
M
Bandeira
Russell David
RD
Hamer
Francisco Max
FM
Damico
Ana Laura Araújo
AL
Moura
Dora Fix
DF
Ventura
D015350:Contrast Sensitivity / Q000502:physiology*; D003924:Diabetes Mellitus, Type 2 / Q000503:physiopathology*; D003930:Diabetic Retinopathy / Q000503:physiopathology*; D005260:Female; D005829:Geniculate Bodies / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012165:Retinal Ganglion Cells / Q000502:physiology; D014786:Vision Disorders / Q000503:physiopathology*; D014795:Visual Pathways / Q000503:physiopathology*