Retina Could Serve as Biomarker for Hearing Loss

Endothelial cell dysfunction in microcirculatory networks could explain the relationship between retinal fractal dimension and auditory loss, as the cells play an important role in vascular tone modulation and blood flow dynamics. Cell malfunction can undermine the blood-labyrinth barrier in the cochlea, which is needed to preserve electrochemical equilibrium for auditory function. These images, from an unrelated study, show patients with high (top image) and low (bottom image) retinal vascular fractal dimension. Photo: Chelvin CA, et al. Nephrology Dialysis Transplantation. 2010; 25(7):2252-8. Click image to enlarge. A newer retinal metric called fractal dimension (FD), which quantifies vascular branching intricacy and density,  can be evaluated via fundus photography. Since reduced FD values may be indicative of less dense vascular networks—possibly reflecting significant microvascular changes linked with systemic illnesses—researchers wanted to test if this measurement could be used as a proxy biomarker for early hearing loss.Conducted at Shanghai Health and Medical Center, the retrospective investigation included 575 participants who were part of a health checkup and received ophthalmological and audiological assessments. After evaluation, results showed that higher retinal fractal dimension values were associated with better hearing acuity. That is, each standard deviation increase in arteriolar FD was associated with a 2.85dB decrease in the hearing threshold at 1kHz; each standard deviation increase in venular FDcorresponded with a 2.61dB decrease at 2kHz. Essentially, higher values for any of three three measures (arteriolar, venular, total) of fractal dimension were associated with better hearing acuity, as reflected in lower hearing thresholds.In their paper for Scientific Reports, the authors elaborated on many potential reasons for this relationship to exist, suggesting that it “may be due to shared microvasculature pathologies affecting retinal and cochlear circulation.” This is because both tissues are highly vascularized and sensitive to ischemic damage,  both are thus vulnerable to systemic microvascular dysfunction. In turn, reduced retinal vascular density could indicate underlying microvascular insufficiencies affecting cochlear blood flow, causing hearing loss by sensory hair cell degeneration. To illustrate this relationship, the authors mention Susac syndrome, which involves occlusive microvascular disease of the brain, retina and inner ear, showcasing that microvascular pathology can impact both structures examined here.In addition to this possibility, the researchers also propose two of their own hypotheses for potential mechanisms explaining this relationship. The first involves a deficit in neurovascular coupling, as recent brain studies have found pericytes along capillary walls which actively regulate vessel tone and local blood flow in response to neuronal activity. Pericyte loss or dysfunction may impair neurovascular coupling and reduce oxygen delivery, with a similar mechanism possibly existing in the cochlea; this is where pericytes are densely distributed, contributing to cochlear blood flow regulation. As a result, accelerated hearing loss may happen when disruption of pericyte-mediated regulation in the cochlear microvasculature occurs, causing transient ischemia.Their other hypothesis has to do with glymphatic-like clearance deficit. Similar to the brain’s glymphatic pathway, the cochlea contains a glymphatic-like system which removes waste like amyloid-beta by paravascular fluid transport. The investigators believe that “as indicated by lower retinal FD, a reduction in systemic microvascular complexity may compromise this clearance mechanism, leading to toxin accumulation and damage to auditory structures.”The authors convey that, more broadly, “this study suggests that retinal FD may serve as a noninvasive biomarker for early detection of hearing loss and could assist in the development of preventive strategies.”Click here for the journal source. Xu R, Qi X, Li Y, et al. Association between retinal vascular fractal dimension and hearing loss: a cross-sectional study. Sci Rep. 2025;15:30425. This article was developed by the editorial staff in conjunction with experts in the field. In the process, AI may have been among the editorial tools used to meet the goals of human editors, who approved all content.