Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in which their body consists of a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 micrometres (0.00033 in) to 33.6 metres (110 ft). They have complex interactions with each other and their environments, forming intricate food webs. The scientific study of animals is known as zoology. Most living animal species are in Bilateria, a clade whose members have a bilaterally symmetric body plan. The Bilateria include the protostomes, containing animals such as nematodes, arthropods, flatworms, annelids and molluscs, and the deuterostomes, containing the echinoderms and the chordates, the latter including the vertebrates. Life forms interpreted as early animals were present in the Ediacaran biota of the late Precambrian. Many modern animal phyla became clearly established in the fossil record as marine species during the Cambrian explosion, which began around 539 million years ago. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago. Historically, Aristotle divided animals into those with blood and those without.
Although it might be described by some as a "degeneration", the term macular degeneration should be reserved for the specific disease "age-related macular degeneration". Very few affected individuals go completely blind from retinoschisis, but some sufferers have very limited reading vision and are "legally blind". Visual acuity can be reduced to less than 20/200 in both eyes. Individuals affected by XLRS are at an increased risk for retinal detachment and eye hemorrhage, among other potential complications. Retinoschisis causes acuity loss in the center of the visual field through the formation of tiny cysts in the retina, often forming a "spoke-wheel" pattern that can be very subtle. The cysts are usually only detectable by a trained clinician. In some cases vision cannot be improved by glasses, as the nerve tissue itself is damaged by these cysts. The National Eye Institute (NEI) of the National Institutes of Health (NIH) is conducting clinical and genetic studies of X-Linked Juvenile Retinoschisis. This study began in 2003 and as of 2018 is continuing to recruit patients. A better understanding of why and how XLRS develops might lead to improved treatments. Males diagnosed with X-linked juvenile retinoschisis and females who are suspected carriers may be eligible to participate. In addition to giving a medical history and submitting medical records, participants submit a blood sample and the NEI will perform a genetic analysis. There is no cost to participate in this study. Tractional retinoschisis
This may be present in conditions causing traction on the retina especially at the macula.