• Comprehensive Ophthalmology, Neuro-Ophthalmology/Orbit, Retina/Vitreous

    This study highlights how spectral-domain OCT (SD-OCT) measurements can be used as a biomarker for Alzheimer disease (AD).

    Study design

    Investigators performed a systemic review and identified 30 eligible studies comprising 1,257 AD patients, 305 patients with mild cognitive impairment and 1,460 healthy controls. They performed a meta-analysis to assess differences in SD-OCT measurements, including the ganglion cell-inner plexiform layer (GC-IPL), ganglion cell complex (GCC), macular volume, choroidal thickness, retinal nerve fiber layer (RNFL) and macular thickness.

    Outcomes

    Patients with AD had significantly reduced GC-IPL thickness, GCC thickness, macular volume and macular thickness of all inner and outer sectors, peripapillary RNFL thickness and choroidal thickness compared with controls (all P<0.001). Macular GC-IPL and peripapillary RNFL were both thinner than controls in cases of mild cognitive impairment, but the difference was not statistically significant.

    Limitations

    As with all meta-analyses, the study may have been skewed by the variable methodologies and the inclusion and exclusion criteria used in the studies. However, all of the studies used SD-OCT and not time-domain OCT. The heterogeneity of disease severities in different studies may have impacted the estimation of the true effect size. The authors explain that the effect sizes with respect to changes in SD-OCT measurements were less vigorous when compared with biomarkers from magnetic resonance imaging (MRI) and amyloid positron emission tomography.

    Clinical significance

    Increasingly, patients are asking whether their ophthalmic and retinal exams can reveal their risk for developing Alzheimer disease. Unlike current methods of diagnosing early AD that are expensive and logistically cumbersome, retinal measurements by SD-OCT are fast, noninvasive, technically simple to acquire and inexpensive.

    This study provides a nice analysis of published literature and confirms the associations between several SD-OCT measurements and AD. These measurements have some potential to be biomarkers of AD either independently (if sensitivity and specificity can be improved) or as part of a multi-modal assessment. It is possible that the true diagnostic and prognostic value of SD-OCT measurements may lie in their integration with other clinical and imaging biomarkers, such as retinal vessel morphologic features and brain MRI biomarkers.