Mørkesyn

Mørkesyn is a term used in Danish and Norwegian to describe reduced vision in dim light, typically when entering a dark room or during nighttime. In medical contexts it overlaps with nyctalopia, defined as impaired night vision due to dysfunction of rod photoreceptors or retinal conditions, rather than a complete loss of sight.

Causes of mørkesyn include nutritional deficiencies such as vitamin A deficiency, which impairs the eye’s ability to adapt to darkness. It can also arise from inherited retinal diseases such as retinitis pigmentosa or cone-rod dystrophy, as well as from ocular media changes like cataracts that reduce overall brightness and contrast in low light. Other contributing factors may include glaucoma, diabetic retinopathy, and certain medications or systemic conditions that affect dark adaptation. In some cases mørkesyn is a symptom of broader degenerative or syndromic conditions, such as Usher syndrome.

Diagnosis is typically made by an ophthalmologist through patient history and a complete eye examination. Tests may include visual acuity assessment, pupil and fundus examinations, measurements of dark adaptation, electroretinography to evaluate rod function, and, when appropriate, genetic testing to identify hereditary causes.

Treatment targets the underlying cause. Vitamin A deficiency is addressed with dietary changes or supplementation. Cataracts or other treatable eye diseases may be managed surgically or medically. For functional improvement in daily life, lighting enhancements, high-contrast materials, and assistive devices can be beneficial. The prognosis varies with etiology: nutritional deficiencies may be reversible with treatment, while hereditary retinal diseases are often progressive with more limited options.

Mørkesyn is primarily used in Danish and Norwegian medical and colloquial language; in English, terms such as night blindness or nyctalopia are more common.