Abstract
Objective: The high energy demand of the auditory and visual pathways render these sensory systems prone to diseases that impair mitochondrial function. Primary open-angle glaucoma, a neurodegenerative disease of the optic nerve, has recently been associated with a spectrum of mitochondrial abnormalities. This study sought to investigate auditory processing in individuals with open-angle glaucoma. Design/Study sample: Twenty-seven subjects with open-angle glaucoma underwent electrophysiologic (auditory brainstem response), auditory temporal processing (amplitude modulation detection), and speech perception (monosyllabic words in quiet and background noise) assessment in each ear. A cohort of age, gender and hearing level matched control subjects was also tested. Results: While the majority of glaucoma subjects in this study demonstrated normal auditory function, there were a significant number (6/27 subjects, 22%) who showed abnormal auditory brainstem responses and impaired auditory perception in one or both ears. Conclusions: The finding that a significant proportion of subjects with open-angle glaucoma presented with auditory dysfunction provides evidence of systemic neuronal susceptibility. Affected individuals may suffer significant communication difficulties in everyday listening situations.
Highlights
The auditory and optic nerves are involved in several genetic disorders of mitochondrial function including autosomal dominant optic atrophy, Mohr-Tranebjaerg syndrome, and Lebers hereditary optic neuropathy (Weiller & Ferbert, 1990; Tranebjaerg et al, 1995; Ceranic & Luxon, 2004; Amati-Bonneau et al, 2008; Huang et al, 2009)
Preliminary analyses comparing the findings for high tension (N ϭ 17) and normal tension (N ϭ 10) glaucoma subjects revealed no group difference on any of the experimental measures in this study
Despite enjoying essentially normal sound detection, a significant proportion of the glaucoma subjects in this study showed abnormal auditory nerve function and auditory processing deficits consistent with impaired representation of timing cues in the central auditory pathways
Summary
The auditory and optic nerves are involved in several genetic disorders of mitochondrial function including autosomal dominant optic atrophy, Mohr-Tranebjaerg syndrome, and Lebers hereditary optic neuropathy (Weiller & Ferbert, 1990; Tranebjaerg et al, 1995; Ceranic & Luxon, 2004; Amati-Bonneau et al, 2008; Huang et al, 2009). Glaucoma is a neurodegenerative disease of the optic nerve characterized by the degeneration of retinal ganglion cells and their axons, resulting in permanent vision loss if left untreated. The incidence and prevalence of the disease increases with increasing age and affects up to 10% of individuals over 80 years (Wensor et al, 1998). Primary open-angle glaucoma is the most common form of disease and is diagnosed following clinical evaluation of the anterior segment of the eye with specific confirmation that the angle or area where aqueous fluid drains out from the eye is unobstructed (Weinreb & Khaw, 2004).There is accumulating evidence that primary open-angle glaucoma may result from increased neuronal susceptibility to oxidative stress which may be consequent to mitochondrial dysfunction (Jarrett et al, 2008; Kong et al, 2009). Abu-Amero and colleagues examined the entire mitochondrial coding sequence in a cohort of primary open angle glaucoma patients and reported high levels of mitochondrial DNA changes compared to controls (Abu-Amero et al, 2006)
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