Macular Thickness in Subjective Memory Complaints and Mild Cognitive Impairment: A Non-Invasive Biomarker

Abstract

Alzheimer's disease (AD) is the main cause of dementia worldwide, which implies an important socioeconomic problem in developed countries. Efforts to find biomarkers to diagnose AD have been intensified, especially, to detect cognitive impairment in its early stages, also known as mild cognitive impairment (MCI). Besides, there are individuals referring memory loss that is unnoticeable in the family environment and presenting normal neuropsychological tests. The former patients are included in a clinical picture that has been recently called subjective memory complaints (SMC). To achieve an early diagnosis, optical coherence tomography (OCT) has been used to measure macular thickness in patients diagnosed with MCI (supported by neuropsychological tests) and SMC (not based on neuropsychological battery). Statistically significant differences have been found in the macular thickness of the control group (274.96 ± 17.61 µm) and for both MCI (259.48 ± 22.39 µm) and SMC (261.45 ± 24.26 µm) patients. In the near future, OCT could become a reliable biomarker and a useful tool for AD screening as well as for the monitoring of the cognitive impairment associated with AD. ARTICLE HISTORY

Correlation between cognitive impairment and retinal neural loss assessed by swept‐source optical coherence tomography in patients with mild cognitive impairment

“…In the present study, full‐thickness macular measurements were reduced in all ETDRS sectors of patients with MCI, although only the superior and inferior inner sectors were significantly thinner. Using spectral‐domain‐OCT, other authors have found reductions in full macular thickness in patients with MCI [30,46], but we believe the segmented inner retinal layers provide more reliable measurements. Both clinical and histopathologic studies have documented a preference for GCL impairment in AD [26,32,47,48].…”

Optical Coherence Tomography in Mild Cognitive Impairment: A Systematic Review and Meta-Analysis

“…Seven of the 15 studies evaluated macular volumes (subjects MCI:controls, 172:213) (25,30,32,34,37,38,40). In four of the seven studies, a statistically significant reduced macular volume was noted for MCI compared with controls (subjects MCI:controls, 106:91) (30,34,38), while three studies did not find differences (subjects MCI:controls, 66:122) (25,32,37). Thus, 61.6% of all MCI patients that had their macular volume measured had a statistically significant reduction in volume compared with controls.…”

“…Communication with the authors was attempted, but no clarification was possible ( 42 , 43 ). Finally, a total of 15 studies meeting inclusion criteria were evaluated and summarized ( 21 , 23 , 25 , 26 , 28 – 32 , 34 , 36 – 40 ) (see Figure 1 ). The general description and main findings of the included studies are described in Table 1 .…”

“…The countries with the highest number of publications were from the USA (4/15) and China (3/15) ( 25 , 29 , 30 , 32 , 37 – 39 ). Other studies belonged to countries in Asia, Europe, and South America ( 21 , 23 , 26 , 28 , 31 , 34 , 36 , 40 ). Overall, there were seven different diagnostic criteria used to define MCI and one study did not report the diagnostic criteria.…”

“…The most common report was both circumpapillary and macular scanning (approximately 46.6%), followed by circumpapillary scan alone (33.3%), and macular scan alone (20%). Macular thickness was reported by five studies (25,26,34,37,40). Macular volume was reported in five studies with some studies reporting both volume and thickness (25,26,30,32,37).…”