Patients with Alzheimer’s disease (AD) have been shown to exhibit retinal changes as well as impaired contrast sensitivity, color vision, visual attention and saccadic eye movements. However, a new study is among the first to focus specifically on cases of  mild cognitive impairment (MCI) that represent prodromal AD, which may be more difficult for doctors to diagnose, as disease symptoms are just beginning to progress. These patients too may be identifiable by ocular examination, the study finds. 

Fourteen subjects with MCI caused by AD and 16 controls without visual impairment were observed through a series of tests to determine performance variances. The average participant age was 75, and each had a best-corrected binocular visual acuity between 20/20 and 20/ 25. Participants underwent the following tests: 

• High- and low-contrast letter acuity (LCLA) testing

• Vision-specific quality of life scales, including the 25-Item National Eye Institute Visual Function Questionnaire (NEI-VFQ-25) and 10-Item Neuro-Ophthalmic Supplement

• OCT scans

Investigators also used a picture naming test common in cognitive assessment called the Mobile Universal Lexicon Evaluation System (MULES). 

Results from the study showed that both the MULES test of rapid image naming and binocular LCLA at 1.25% contrast were found to distinguish patients with MCI due to AD from participants without visual impairment. MCI patients were only able to identify one-third the number of letters seen by the controls, a difference of 10 letters in binocular LCLA. The MCI group’s test times were 1.6x longer, and they also committed three times as many errors.

“Lower (worse) binocular LCLA scores at 1.25% contrast, longer (worse) MULES test times, and greater numbers of MULES errors were significant predictors of MCI vs. control status, accounting simultaneously for ocular pathology,” the researchers said in their paper.

“Because MCI is prodromal to AD, it is important that these visual measures are showing early promise as future markers to identify disease states and to potentially follow patients in clinical trials and observational research. Notably, both MULES and LCLA were stronger predictors of the MCI disease status than was hippocampal atrophy on MRI; however, our cohort size may have limited our findings in this regard,” the researchers said in their paper.”

Rapid image naming and binocular LCLA could one day become diagnostic tools for prodromal AD. Larger and longer studies will help model the protocol’s effectiveness and that of other visual tests as biomarkers.