Complex sentence: Night blindness may be a feature of severe zinc deficiency, however most reports of night blindness and abnormal dark adaptation in humans with zinc deficiency have occurred in combination with other nutritional deficiencies (e.g. vitamin A).
Split into simpler sentences: Night blindness may be a feature of severe zinc deficiency. However, most reports of night blindness and abnormal dark adaptation in humans with zinc deficiency have occurred in combination with other nutritional deficiencies (e.g. vitamin A).