Correspondence (letter to the editor): Impaired Visual Function

As an ophthalmologist specializing in neuro-ophthalmology, I welcome the wonderfully systematic article about gait disturbances, and especially the mention of bilateral vestibulopathy which is often overlooked. Such patients often present first to their ophthalmologist because they interpret the accompanying oscillopsia as an eye disorder. Examining the different directions of gaze is important in this setting, so as not to overlook nystagmus, which is often hardly noticeable when looking straight ahead.

The authors in their Table 3 list common gait disorders and their causes; under “Sensory deficits,” however, they mention only “loss of visual acuity”. Visual acuity is defined as spatial resolution capacity of the central retina. In elderly people, visual acuity is most often impaired as a result of age related macular degeneration. If – typically – the visual field is intact, then loss of visual acuity is only rarely the decisive criterion for gait disturbances. Additionally, partial visual rehabilitation by prescribing magnifying visual aids (example under “Therapeutic options”) is of value primarily for near distances because of the massive reduction in the width of the visual field and the change in the perceived distance to the viewed object; it cannot improve spatial orientation and consequently not gait disturbances either.

The term “impaired visual function” would have been more appropriate in table 3 to describe the situations that typically lead to difficulties in orientation in elderly people: primarily, bilateral visual field defects (which cannot always be properly evaluated by a neurologist’ perimetry) owing to chronic glaucoma, bilateral ischemic neuropathy of the optic nerve, and ischemic retinal diseases; further, localization impairments because of eye muscle paresis in the dominant eye; eventually double vision and loss of stereoscopic vision for various reasons—for example, in pathologies also with intact oculomotor function, such as decompensated phorias, suppression loss in congenital strabismus, and involutive divergence paresis. All these are most likely to be diagnosed and treated by ophthalmologists, possibly in collaboration with an orthoptist.