Table 2

The summary of current findings on retinal neuronal changes, retinal capillary changes, retinal arteriolar and venular changes, and choroidal vasculature changes

Preclinical AD or MCIAD dementia
Retinal neuronal changes
Peripapillary RNFL thickness
  • Some studies showed reduced peripapillary RNFL, macular GC-IPL and GCC thicknesses, compared with controls

  • But a few studies showed no differences in the measures, compared with controls and AD dementia

  • A few studies also showed thickened peripapillary RNFL and macular GC-IPL thicknesses in MCI, compared with controls

  • Majority of studies and meta-analysis showed reduced peripapillary RNFL, macular GC-IPL and macular thicknesses, compared with controls

  • But a few studies showed no differences in the measures, compare with controls

  • A few studies also showed thickened peripapillary RNFL and macular GC-IPL thicknesses, compared with controls

  • In a population-based study, reduced peripapillary RNFL associated with incident AD dementia

Retinal capillary changes
Vessel density and foveal avascular zone
  • Majority of studies showed decreased vessel density and enlarged foveal avascular zone area, compared with controls

  • But a few studies showed no differences in the measures, and one study showed increased vessel density in preclinical AD, compared with controls.

  • Majority of studies showed decreased vessel density and enlarged foveal avascular zone area, compared with controls

  • But a few studies showed no differences in the measures.

Retinal arteriolar and venular changes
Vessel calibre (CRAE and CRVE)
  • No data

  • Majority of studies showed narrower CRVE, compared with controls

Fractal dimension
  • No data

  • Majority of studies showed decreased arteriolar and venular fractal dimensions, compared with controls

Tortuosity
  • No data

  • The association is equivocal. Both increased and decreased retinal vascular tortuosity were observed

Choroidal vasculature changes
Choroidal thickness
  • No data

  • Reduced choroidal thicknesses, compared with controls

  • A larger reduction in choroidal thicknesses over a 12-month follow-up, compared with controls

  • AD, Alzheimer's disease; CRAE, central retinal artery equivalent; CRVE, central retinal vein equivalent; GCC, ganglion cell complex; GC-IPL, ganglion cell-inner plexiform layer; MCI, mild cognitive impairment; RNFL, retinal nerve fibre layer.