Effects of hypoxia on color vision with emphasis on the mesopic range

10.1586/EOP.11.32 Oxygen is fundamental to animal life. It is a prerequisite for the production of biological energy through cytoplasmic glycolysis and mitochondrial oxidative phosphorylation, typically as adenosine triphosphate (ATP), to fuel metabolic reactions. ATP is generated on demand, requiring a continuous supply of oxygen, so hypoxia may be simply defined as a state of oxygenation that fails to meet metabolic needs. Hypoxia can be classified according to where in the pathway from ambient air to subcellular reaction, the supply of oxygen is interrupted. Hypoxic hypoxia indicates reduced oxygenation of arterial blood, termed hypoxemia (e.g., decreased inspiratory oxygen concentration; impaired pulmonary ventilation); anemic hypoxia describes reduced blood oxygen-carrying capacity (e.g., blood dyscrasia; carbon monoxide poisoning); ischemic hypoxia results from impaired tissue perfusion (e.g., cardiac failure; microvascular disease); and histotoxic hypoxia is due to compromised subcellular oxygen utilization (e.g., cyanide poisoning). Hypoxia may therefore be local or systemic and pathological processes are often associated with multiple mechanisms. The nervous system comprises approximately 2% of body mass but accounts for some 20% of the oxygen consumed at rest. It is extremely sensitive to hypoxia, such that interruption of cerebral blood supply causes loss of consciousness in seconds, yet the retina consumes even more oxygen per unit mass than the brain. Thus, retinal oxygenation holds particular interest when considering the effects of hypoxia on visual function and especially on color vision. Retinal oxygenation remains topical in the context of tissue vitality in disease states such as retinal detachment [1], retinitis pigmentosa [2] and retinal vascular occlusion [3]. By contrast, the extent to which visual discrimination abilities, such as visual acuity or color sensitivity, are influenced by changes in oxygenation state, particularly at mesopic luminance, is less well documented but is starting to emerge as increasingly relevant John L Barbur†1 and Desmond M Connolly2