. Oxygen poisoning There are many conditions where 02 inhalation is required for treatment purposes. However, heroic 02 inhalation and the resultant o

. However, heroic 02 inhalation and the resultant over correction of 02 deficiency are associated with many dangers (chap 6, sec IV). One such special danger, in the new born, is, spasm of the central artery of the retina leading to degeneration of the retina and blindness. Recall, excess 02 causes spasm of the blood vessels PHOTO CHEMISTRY OF VISION In this portion, we will discuss, the chemical changes that occur when the light (photos) strikes a rod or a cone. The changes therefore are called photochemical changes. [At their initial phase, these photochemical changes cause development of impulse in the rods or cones. The impulses are then conveyed by the bipolar cells, then to the ganglion cells and eventually by the optic nerve to the appropriate part of the brain]. Rods and scotopic ('dim light') vision Rods are required for, as stated already, dimlight or night (scotopic) vision. Rods contain, in their discs of outer segment (fig. 10B2. 2. 3), a pigment called rhodopsin (also called 'visual purple'). Rhodopsin molecule is produced by combination of opsin (a protein) and retinal. Retinal is aldehyde of retmol, the retmol (which contains an alcoholic group, fig 7.14.1) being vit A Retinal is also known as retinene.