Table 1.
Ocular symptoms associated with Alzheimer’s disease (AD).
| Tissue | Symptoms | Contradictory Findings |
|---|---|---|
| Clinical Manifestations | ||
| Visual Dysfunction | Impaired contrast sensitivity [16,17,18,19,20], color vision [16,17,19,20], visual acuity [17,19], and visual integration [17]. Macular thinning [16,17], visuospatial deficits [18,19,20], visuomotor impairment [21,22,23,24], visual field loss [25] | |
| Cornea | Increased corneal sensitivity [26], corneal thinning [27,28] | |
| Retina | Reduced retinal nerve fiber layer thickness in superior and inferior quadrants [13,16,29,30], retinal astrogliosis [31], reduction of retinal ganglion cells [13,32] most notably in fovea [32] | |
| Pupil | Increased pupil diameter during cognitive effort [33], slowed pupillary responses to light and target detection task [34], exaggerated pupil response with dilute tropicamide [35,36], smaller baseline pupil size [37] | |
| Lens | Equatorial supranuclear cataracts [38,39] | Opacity not related to Alzheimer’s disease [40,41] |
| Optic Nerve | Axonal degeneration [42,43], thinner lamina cribrosa [28] | No axonal damage [44] |
| Intraocular pressure | Increased intraocular pressure in Alzheimer’s disease patients [45,46] | |
| Pathological Changes | ||
| Cornea | Fibroblasts, epithelium express amyloid precursor protein and amyloid β [47], A disintegrin and metalloproteinase domain-containing protein ADAM-10 and beta-site amyloid precursor protein cleaving enzyme 1 increased in fibroblasts [47], decreased microvilli and altered morphology in corneal epithelia [27], several-fold increase in amyloid precursor protein expression, amyloid β deposition, and increased apoptosis in corneal epithelia [27] | |
| Retina | Reduced oxygen metabolism [48,49], amyloid β plaques [50,51], accumulation of phospho-tau [52,53], amyloid β deposition in retinal microvasculature and pericytes [54], compromised blood-retinal barrier [54], retinal vasculature abnormalities [55,56], increased retinal vascular amyloid β40 and amyloid β42, decreased vascular platelet-derived growth factor receptor β, and decreased vascular low-density lipoprotein -1 [54] | |
| Lens | Increased amyloid β aggregation in lens [38,57], presenilin expression in lens [58] | No aggregation of amyloid β [40,41] |
| Aqueous Humor | Increased levels of amyloid β [59,60] | |
| Vitreous Humor | Presence of Alzheimer’s disease -associated proteins [59,61] | |
| Choroid | Thinning of choroid [62,63] | |
| Optic Nerve | Tau deposition [20] | |