title: Neurovisual abnormalities preceding the retinopathy in patients with long-term type 1 diabetes mellitus.
abstract: BACKGROUND
  Changes in the retina caused by diabetes may lead to visual impairment in dim light, even with good visual acuity and visual fields. To evaluate the visual abnormalities preceding the retinopathy in patients with type 1 diabetes mellitus (DM), we applied electrophysiological methods.
  
  
  METHODS
  The visual evoked responses were recorded with sinusoidally modulated vertical gratings at 10 spatial frequencies presented sequentially on a high-resolution monitor in patients with type 1 DM and in normal volunteers. Similarly, the contrast visual evoked responses of 10 contrast levels were recorded at five spatial frequencies. Both amplitudes at the second harmonic were calculated by discrete Fourier transform. The visual acuity and contrast thresholds were determined objectively.
  
  
  RESULTS
  There was dissociation between the Snellen and the estimated visual evoked response acuity measurements in patients with diabetes (r2=0.077, P=0.44). The saturation phenomena were observed at lower levels of contrast stimuli than in normal individuals at. 1.0, 2.0, 4.0 and 8.0 cycles per degree (P=0.0001). The contrast sensitivity function was deeply abnormal in all tested patients despite the metabolic control. The values of the area under the curve of the visual evoked response amplitude-contrast level function at five spatial frequencies were smaller in patients with DM than in the control group (P<0.05) at all spatial frequencies tested.
  
  
  CONCLUSIONS
  Patients with type 1 DM without retinopathy showed significant lower amplitude of the visual evoked responses at all spatial frequencies tested, with the saturation phenomena observed at lower level of contrast stimuli. In addition, there was a dissociation between the sweep visual evoked responses and the Snellen acuity measurements. A significant and nonselective neuronal visual loss involving the visual pathway precedes the ophthalmoscopically detectable retinopathy in patients with type 1 DM.
authors.affiliation: Schepens Eye Research Institute, Schepens Retina Associates, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Lopes de Faria
authors.forename: O
authors.initials: O
authors.lastname: Katsumi
authors.forename: E
authors.initials: E
authors.lastname: Cagliero
authors.forename: D
authors.initials: D
authors.lastname: Nathan
authors.forename: T
authors.initials: T
authors.lastname: Hirose
mesh_terms: D000328:Adult; D019540:Area Under Curve; D016022:Case-Control Studies; D015350:Contrast Sensitivity / Q000502:physiology; D003922:Diabetes Mellitus, Type 1 / Q000175:diagnosis* / Q000503:physiopathology; D003930:Diabetic Retinopathy / Q000175:diagnosis* / Q000503:physiopathology; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012160:Retina / Q000503:physiopathology; D014786:Vision Disorders / Q000175:diagnosis* / Q000503:physiopathology; D014792:Visual Acuity / Q000502:physiology; D014795:Visual Pathways / Q000473:pathology*