Comment on "Olfactory Function Assessment of Blind Subjects Using the Sniffin' Sticks Test".

When a patient loses visual ability, new synapses may develop in the brain to adapt to new situations and sustain life with other sensory organs. We appreciate the article titled “Olfactory Function Assessment of Blind Subjects Using the Sniffin’ Sticks Test,” written by Çomoğlu et al. In this study, olfactory functions were found to be better in blind patients than in normal individuals. Enhancement in olfactory functions may occur by development of new synapses. Brain-derived neurotrophic factor (BDNF) is a protein that facilitates the growth and differentiation of new neurons and synapses. It is active in the brain areas vital to memory and learning. In a recent study, the serum level of BDNF in patients with age-related macular degeneration (AMD) was found to be higher than that in normal individuals. Visual acuity is known to decrease in AMD; therefore, BDNF may be a mediator of adaptation to new conditions in situations of low vision. We suggest that BDNF plays a role in the enhancement of olfactory functions by mediating the development of new synapses. However, in a study, BDNF overexpression was found to increase olfactory bulb granule cell dendritic spine density in vivo. If authors have possibility, it would be a good research topic to measure BDNF levels in their study and control groups. Yet, because patients with AMD have low vision, their olfactory functions would be expected to be better than those of the healthy population. However, olfactory functions have been found to be worse in patients with AMD. This finding was associated with the neurodegenerative nature of AMD. Numerous studies have demonstrated the impairment of olfactory functions in neurodegenerative diseases. Although there is no information about the etiology of acquired blindness, the existence of AMD could have a negative impact on results of olfactory functions in the current study.