The retina is located on the back of the inner wall of the eye and is instrumental in creating image information for the brain. Age, disease, and congenital disorders can impede the function of the retina, which has a complex structure, in many ways. A large number of successful therapeutic procedures exist.
What is the retina?
Schematic illustration showing the anatomy and structure of the eye with retinal detachment. Click to enlarge. The retina is a light-sensitive layer of tissue on the inner wall of the eye. Light entering the eye through the pupil and striking the retina images the external environment on it; thus, the retina functions much like the film in a still camera. The incidence of light stimulates chemicals and nerves. These nerve impulses then reach the brain as information via the optic nerve. In embryonic growth, the retina forms out of the brain along with the optic nerve, so it is seen as part of the central nervous system and is brain tissue. The retina is the only part of the central nervous system that can be considered non-inversive. The retina consists of a tissue of several layers, with many layers of neurons, connected by synapses. The only neurons directly exposed to light are called photoreceptors and consist of the rods and cones to be designated.
Anatomy and structure
The retina is composed of 10 distinct layers. These are (listed from the vitreous body of the eye to the optic nerve):
Inner limiting membrane, nerve fiber layer, ganglion cell layer, inner plexiform layer, inner granular layer, outer plexiform layer, outer limiting membrane, inner segment, outer segment, retinal pigment epithelium. These layers can be broken down into four basic stages: Photoreception, transmission to bipolar cells, transmission to ganglion cells (which also have photoreceptors), the photosensitive ganglion cells, and transmission to the optic nerve. At each synaptic level, there are also connections between horizontal and amacrine cells. The optic nerve is a central nerve cord of many ganglion cell axons, primarily connecting the corpus geniculatum laterale to the forebrain.
Function and Tasks
An image is produced by stimulation of the cones and rods within the retina. The cones respond to bright daylight and transmit high-resolution color during the day. The rods respond to even less light and are responsible for monochrome outlines. In most light situations, an interaction of cones and rods is required. The reaction of the cones to different light waves is called their spectral sensitivity. It is divided into subgroups. If one of these subgroups does not react correctly, it leads to numerous eye problems, such as color blindness. Light particles (photons) strike the outer layer of the retina and activate a cone or rod. Within cones and rods is an arrayed stack of visual membranes, which in turn contain the visual pigment rhodopsin. Rhodopsin stimulates transducin, a protein, which in turn stimulates an enzyme that breaks down to cyclic guanosine monophosphate. This GMP is passed to the next membrane. When light falls on the rods, this process effectively aligns red and green wave information, by stimulating the activated rods, and passes the ratio to the optic nerve. What exactly happens to this information after it is passed on is still obscure.
Diseases and disorders
There are a variety of congenital disorders or developing diseases that can affect the retina. These include:
Retinopathy pigmentosa: A group of congenital vision defects that cause night blindness. Macular degeneration: Refers to a group of disorders that result in a piecemeal deterioration of the central field of vision. Cone-rod dystrophy: A disorder during which the cones begin to lose their function and then slowly spread to the rods. Retinal detachment: This can have many causes and must be treated quickly before the damage to vision becomes irreparable. Hypertensive or diabetic retinopathy: Both hypertension and diabetes can cause disruption of the blood supply to the retina. This reduces function and leads to generally poorer vision.Retinoblastoma: This is a malignant tumor on the retina that, if left untreated, leads not only to vision loss but also to death. The chances of recovery with treatment, however, are very good.
