Читать книгу Essentials of Veterinary Ophthalmology - Kirk N. Gelatt - Страница 134

One of the most fascinating adaptations for enhanced scotopic vision is the evolution of a reflective tapetum in the choroid. Light photons striking this layer bounce back onto the retina, thus giving them a second chance to be absorbed by the photoreceptors. This second opportunity is not significant in daytime, as cones absorb enough photons during their “first pass” through the retina. In fact, the tapetum has a detrimental effect on visual acuity in broad daylight, as the light is reflected onto a photoreceptor different from the one in the original trajectory. However, at night this detrimental effect on visual resolution is insignificant as cones are inactive. Instead, the retina benefits from the increased probability that rods will absorb the few photons entering the eye in a dim environment, thus enhancing scotopic vision.