In contrast, two other studies did not find significant difference between aMCI and controls after adjusting for confounders 19, 25. 22 reported thinning in the superior quadrant. 20 found the temporal quadrant significantly thinner, whereas Liu et al. 18 found all quadrants of the “peripapillary” RNFL (except nasal) to be significantly thinner in aMCI subjects compared with cognitively healthy controls. Several studies have used OCT to examine the RNFL in subjects with a clinical diagnosis of MCI 17- 26. In particular, amnestic MCI (aMCI), where episodic memory is impaired without impairment of executive function, language, or other domains, is viewed by some as prodromal DAT 1, 16. MCI is a clinical condition which can represent a transition to dementia of the Alzheimer type and consists of cognitive impairment on standard tests but no impairment of activities of daily living. With this insight there is an interest in identifying early changes in subjects with mild cognitive impairment (MCI). However, many researchers argue that early detection should identify candidates for therapy before the onset of cognitive impairment, as the damage is likely irreversible once symptoms arise 15. To date, many researchers have reported RNFL thinning on OCT in patients with DAT, and two recent meta-analyses noted RNFL thinning affected all quadrants of the optic nerve head 13, 14.įinding RNFL thinning in DAT is a milestone toward validating the eye as a surrogate organ for disease detection and monitoring.
Advantages of OCT include that it is noninvasive, readily available in most ophthalmology and many neurology clinics, and can provide high-resolution cross-sectional imaging of the RNFL and macula 12. Over the past 25 years, optical coherence tomography (OCT) has emerged as a powerful tool aiding in the diagnosis and management of various ocular diseases and for identifying ocular involvement in systemic and neurologic diseases 6- 11. 5, which revealed at least 12 different visual or ocular potential markers of the disease. Since then, multiple studies have reported significant findings in the eyes of DAT patients, which was recently in a paper by by Javaid et al. 4 in 1986 identified histopathologic evidence of axonal degeneration of the optic nerve and reduced thickness of the retinal nerve fiber layer (RNFL) in patients with DAT, making the eye a potential surrogate organ to detect the pathologic changes of the disease. Therefore, along with continued and redoubled efforts to understand the disease and develop new therapies, numerous groups have set out to identify more sensitive (and perhaps less invasive) diagnostic approaches. Today, the definitive diagnosis of DAT is made at brain autopsy, whereas clinical diagnosis and staging involves relatively invasive and expensive techniques 2, 3. The inverse relationship between cognitive testing and RNFL thickness suggests that retinal involvement may include paradoxically increased thickness of the RNFL, which could suggest gliotic reactive changes.ĭementia of Alzheimer's disease type (DAT) was first described nearly 110 years ago by the psychiatrist Alois Alzheimer 1. The meta-analysis revealed a statistically significant decrease in RNFL thickness in MCI subjects. In aMCI subjects, we found an inverse relationship between RNFL thickness and two cognitive tests (delayed story recall and a word-list learning test and the word-list test). We found no statistically significant differences in OCT between amnestic MCI (aMCI) and controls. We also performed a meta-analysis of the world literature using a random-effects model.
We investigated the correlation between optical coherence tomography (OCT) of the retinal sublayers, including the retinal nerve fiber layer (RNFL), and cognitive function in subjects with amnestic MCI and compared the OCT findings with matched controls. Retinal structural changes in subjects with mild cognitive impairment (MCI) remain a subject of controversy.
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