Neurovascular Coupling in Subjects With Amblyopia

• Retinal (arterial and venous) oxygen saturation [ Time Frame: once on the study day ]
• Retinal blood velocity in response to flickering light [ Time Frame: once on the study day ]
• High resolution functional and anatomical imaging of the visual pathway [ Time Frame: once on the study day ]
• Inner Retinal Function [ Time Frame: once on the study day ]

Amblyopia is a developmental condition that is characterized by reduced vision of the eye due to the presence of a sensory impediment during visual development, such as strabismus (ocular misalignment) or anisometropia (unequal refractive error), occurring early in life. Recent studies in humans and animals point towards a cortical locus for the processing deficit in amblyopia, revealing sensory deficits at the signal cell level. If changes in retinal neuronal function are also present, is unknown.

Like in the brain, blood flow in the retina is coupled to neuronal activity. This phenomenon has been measured by different study groups with non invasive techniques in the brain and retina. It has been shown in previous studies that stimulating the retina with diffuse luminant flickering light increases retinal vessel diameter and blood flow. However, it is unknown whether this is also the case in the retina of amblyopic eyes. Additionally, the introduction of blood oxygen level dependent (BOLD) fMRI also makes it possible to directly access the vascular response in the brain to visual stimuli.

Therefore, the aim of the present study is to investigate the effect of luminant flickering light on retinal vessel diameter and retinal blood flow in subjects with amblyopia. Also, oxygen saturation in retinal vessels will be assessed as well as pattern ERG for assessment of retinal function. Additionally, a high resolution image of the visual pathway will be taken with 7 Tesla MRI to investigate whether anatomical or functional alterations are present.

• Amblyopia ex Strabismus
• Amblyopia ex Anisometropia

• Device: Dynamic Vessel Analyzer
  retinal vessel diameter, retinal oxygen saturation
• Other: Laser Doppler Velocimetry
  retinal blood flow velocity, retinal blood flow
• Device: 7-Tesla MRI
  High resolution functional and anatomical imaging of the visual pathway
• Other: Pattern electroretinography
  inner retinal function
• Other: Fourier domain optical coherence tomography
  Blood flow in retina.

• Experimental: amblyopia ex anisometropia
  20 male and female volunteers with amblyopia ex anisometropia
  Interventions:

  • Device: Dynamic Vessel Analyzer
  • Other: Laser Doppler Velocimetry
  • Device: 7-Tesla MRI
  • Other: Pattern electroretinography
  • Other: Fourier domain optical coherence tomography
• Experimental: amblyopia ex strabismus
  20 male and female volunteers with amblyopia ex strabismus
  Interventions:

  • Device: Dynamic Vessel Analyzer
  • Other: Laser Doppler Velocimetry
  • Device: 7-Tesla MRI
  • Other: Pattern electroretinography
  • Other: Fourier domain optical coherence tomography
• Experimental: control subjects
  20 healthy male and female control subjects
  Interventions:

  • Device: Dynamic Vessel Analyzer
  • Other: Laser Doppler Velocimetry
  • Device: 7-Tesla MRI
  • Other: Pattern electroretinography
  • Other: Fourier domain optical coherence tomography

Inclusion Criteria:

• Men and women aged between 18 and 55 years
• Non-smokers (for at least 6 months)
• Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant
• Normal ophthalmic findings except amblyopia on one eye resulting from anisometropia or strabismus with a visual acuity of Snellen ≤ 0.3 with best correction on the amblyopic eye and Snellen 0.9 or better in the contralateral eye (for subjects with amblyopia)
• Normal ophthalmic findings with visual acuity of Snellen ≥ 1.0 in both eyes (for control subjects)

Exclusion Criteria:

• Symptoms of a clinically relevant illness in the 3 weeks before the first study day
• Presence or history of a severe medical condition as judged by the clinical investigator
• Regular use of medication, abuse of alcoholic beverages, participation in a clinical trial in the 3 weeks preceding the study (except oral contraceptives)
• Blood donation during the previous three weeks
• Pregnancy, planned pregnancy or lactating
• Any metallic, electric, electronic or magnetic device or object not removable except dental fillings
• Claustrophobia
• Epilepsia, history or family history of seizures