In advanced stages of glaucoma, patients may present with an annular scotoma, also known as ring scotoma, where the retinal sensitivity is concentrically reduced. However, not every patient with a ring scotoma has glaucoma. Retinal diseases such as retinitis pigmentosa or foveal spearing central retinal artery occlusions can lead to an annular scotoma too [1]. Clinical assessment allows differentiating these causes from each other. It becomes more difficult if no morphological cause for a ring scotoma can be found. Then a functional or refractive cause must be considered. The most common type of functional visual field loss is a concentric constriction of the peripheral vision forming a “tunnel vision” [2]. For the latter, moderate to severe hyperopic, as well as aphakic patients may show a refractive ring scotoma. It is an artefact caused by the high-powered and therefore thick glasses which are needed to perform visual field testing if contact lenses are not available. [3]. In addition, aphakic patients have an increased risk of developing glaucoma [4]. For this reason, the ring scotoma can be a pitfall in this group of patients and may lead to a misdiagnosis of glaucoma if clinical examination is not performed carefully.
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Contributor: Nathanael Haener, MD, Bern Switzerland
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