Retina abiotrophy – diverse group of the hereditary diseases of dystrophic character caused by gradual destruction of a retina with decrease in visual acuity, and at some forms - a total blindness. Symptoms are variable: decrease in visual acuity, a gemeralopiya, violations of color perception can be observed. Diagnostics is performed by ophthalmologic and genetic methods (an oftalmoskopiya, an elektroretinografiya, a fluorescent angiography, studying of the family anamnesis and identification of defective genes). At the majority of forms of an abiotrophy of a retina specific treatment is absent, the symptomatic and supporting therapy is capable to weaken some symptoms and to slow down progressing of a disease.
Retina abiotrophy (retina degeneration, retina dystrophy) – pathology of an organ of vision at which dystrophy of a mesh cover of an eye develops. Can be a part of simptomokompleks of some hereditary diseases, act as independent pathology, the secondary degeneration after injuries and other influences is in certain cases possible. Independent hereditary forms of an abiotrophy of a retina have different prevalence, on average it fluctuates within 1-10:10000. The mechanism of inheritance of various forms can be autosomno-prepotent, autosomno-recessive and linked to a floor. For this reason strong distinctions and in sexual distribution of a disease – from an equal porazhayemost of persons of both floors to almost full prevalence of men among the diseased (are observed at the H-linked inheritance). Genetically caused retina abiotrophy - the most common cause of loss of sight of hereditary character.
Retina abiotrophy reasons
The etiology of an abiotrophy of a retina differs depending on concrete type of a disease. The general mechanism – a mutation of a certain gene or genes which are coded by the specific squirrels participating in activity of a mesh cover of an eye. At the same time the pathogenesis of the majority of forms is studied insufficiently.
The reason of the most common form of an abiotrophy of a retina – pigmentary dystrophy – more than 150 options of mutations in several tens genes, the majority of which are inherited on autosomno-prepotent type, can be. Nearly a quarter of all cases of a pigmentary abiotrophy of a retina is caused by various mutations in a gene of protein of an opsin. In a gene of protein of photoreceptors of CRB1 the mutation has the recessive nature of inheritance, and in genes of RP2 and RPGR – linked to the H-chromosome. There is the most rare form of a pigmentary abiotrophy of a retina with a mutation in mitochondrial DNA and, therefore, inheritance from mother to posterity. Despite a huge number of various options of primary violation at a pigmentary retinit, the pathogenesis of a disease in general is identical – there is a violation of utilization of the fulfilled sticks therefore they become a source of toxins in a retina. Because concentration of sticks grows towards the periphery of a mesh cover, pathological changes begin exactly there, formation of new photosensitive cages is slowed down, as leads to decrease in a photosensitivity.
The Belotochechny abiotrophy of a retina is associated with mutations of one of four genes - RHO, PRPH2, RDH5 or RLBP1, at the same time the form caused by changes of a gene of PRPH2 coding protein is most widespread. The disease is inherited on autosomno-recessive type. It is supposed what participates in stabilization of membranes of photoreceptors, mainly sticks therefore violations in its structure do them less steady and leads to their destruction. The Belotochechny abiotrophy of a retina has the progressing current, at the same time the first violations (which are noticeable at survey of an eye bottom in the form of white points) are formed on the periphery of a retina.
The Zheltopyatnisty abiotrophy of a retina (Shtargardt's disease) is also caused by mutations of several genes. The most common form of a zheltopyatnisty degeneration of a mesh cover is connected with violation of structure of protein ABCA4 which performs transport and power functions in membranes of photoreceptors. This form of a disease is inherited on autosomno-recessive type. Change of structure of transmembrane protein ABCA4 leads to accumulation in a retina of toxic metabolites (in particular, a lipofustsina), as causes dystrophy of a photosensitive layer. Other option of a disease of Shtargardt with autosomno-prepotent inheritance is caused by change of structure of protein ELOVL4 which controls formation of dlinnotsepochny fatty acids in eye tissues. In this case the degeneration of photoreceptors is connected with violation of synthesis of some components of their membranes. One more type of a zheltopyatnisty abiotrophy of a retina is associated with PROM1 gene mutation. The pathogenesis of violations in this case is thoroughly not studied.
The abiotrophy of a retina of Best is caused by mutations of a gene of BEST1 which product of a transcription is protein , belonging to the class of anion channels. Inheritance is autosomno-prepotent, the pathogenesis of dystrophy is unknown.
The congenital stationary night blindness is a generalized abiotrophy of a retina with primary defeat of sticks, it is also followed by other violations of an organ of vision – squint, a cataract. Allocate full and incomplete forms of a congenital stationary night blindness, both are inherited on the H-linked mechanism. The full type is caused by a mutation of a gene of NYX coding the protein providing transfer of excitement from sticks to bipolar cages. As a result of it information transfer from photoreceptors is broken, there is a gemeralopiya with almost total absence of sight in the dark, at the same time sharpness and color perception usually do not suffer. The incomplete form is caused by a mutation of a gene of CACNA1F which product is similar protein, but it is available both for sticks, and for flasks. At the same time, however, transfer of an impulse is not blocked completely therefore twilight sight is only weakened, but also sharpness and color perception suffers.
Classification of an abiotrophy of a retina
In ophthalmology all hereditary forms of dystrophy of a mesh cover of an eye divide into three groups:
1. Peripheral at which violations arise mainly at the edges of an eye bottom, but at some forms of an abiotrophy they can progress and occupy the central regions, up to a yellow spot. Besides, at them peripheral sight most strongly suffers, adaptation of an eye to darkness is broken, often there is a gemeralopiya. Carry a pigmentary and belotochechny abiotrophy of a retina to them.
2. Central which are characterized by primary defeat of a yellow spot and the central regions of an eye bottom. At the same time color perception is broken, visual acuity strongly falls. Such manifestations accompany Shtargardt's disease and Best's disease.
3. At some mutations or their combination the abiotrophy of a retina can mention all mesh cover of an eye therefore some researchers allocate also the third group of dystrophies – generalized. The congenital stationary night blindness belongs to such type. Generalized violations of a retina accompany other hereditary diseases – for example, Lebera.
At the same time because of a large number of various mutations the above described division is a little conditional. So, some forms of pigmentary dystrophy can gain generalized character, and at PROM1 gene mutation (the fourth type of a disease of Shtargardt) the abiotrophy from the central regions of a retina can extend to the periphery.
Retina abiotrophy symptoms
Symptoms of an abiotrophy of a retina are quite variable because of a large number of various mutations which lead to development of this pathology. But in too time, between various options of dystrophy within one group (peripheral, central or generalized an abiotrophy) there is a number of similar manifestations.
Peripheral retinas of an abiotrophy (pigmentary dystrophy, belotochechny abiotrophy) begin with primary defeat of sticks therefore the gemeralopiya will be one of the first symptoms of a disease. With progressing of pathology, at further destruction of sticks, decrease in night sight can develop into its total loss – a niktalopiya. Peripheral sight is broken, there is concentric scotoma after which the field of vision is narrowed so that becomes "tubular". At a belotochechny abiotrophy of a retina heavier violations most often do not develop, day sight and color perception remains without changes. In some cases pigmentary dystrophy flasks also are involved in pathological process that leads to falling of day sight, decrease in its sharpness and sometimes a total blindness. The course of a disease can take decades though also rapid, and also juvenile forms meet.
The central retinas of an abiotrophy are characterized by primary defeat of flasks which concentration the highest in the field of a yellow spot – therefore they are also called makulodistrofiya. Into the forefront sharp decrease in visual acuity acts, perception of flowers is broken, at final fracture of photoreceptors in the center of an eye bottom the central scotoma develops. If pathological process does not extend to peripheral areas of a retina, then peripheral and twilight sight is affected poorly. At the forms of an abiotrophy which are characterized by focal damage of photoreceptors blind spots under review develop. At especially severe forms there can be an atrophy of fibers of an optic nerve and a total blindness.
The full form of a congenital stationary night blindness is characterized by the expressed niktalopiya with preservation of day sight and color perception. At the same time progressing of a disease does not happen. Symptoms of the VSNS incomplete form is the moderate gemeralopiya, the lowered visual acuity, anomalies of color sight, complexity of adaptation to the lowered illumination.
Diagnostics of an abiotrophy of a retina
Patients with an abiotrophy of a retina have to be consulted by the geneticist and the ophthalmologist. Definition of dystrophic processes in a mesh cover of an eye is made on the basis of data of survey of an eye bottom, elektroretinografiya, a research of visual acuity and color perception. An important role is played by studying of the hereditary anamnesis, and also genetic researches regarding identification of mutations in the genes associated with this or that type of an abiotrophy of a retina.
At pigmentary dystrophy on the periphery of an eye bottom the centers of adjournment of a pigment come to light, they can be observed also on the central sites at the corresponding form of a disease. Narrowing retinas is noted, and at late stages there is an atrophy of capillaries of a vascular cover of an eye. In some cases the wax-like atrophy of a disk of an optic nerve comes to light. Elektroretinografiya shows considerable decrease in amplitude of all waves that demonstrates sharp reduction of number of photoreceptors in a retina. Sekvenirovany DNA for the purpose of identification of mutations are most often produced concerning genes of RP1, RHO, RDS, RLBP1, PRPF8 and some others.
The Belotochechny abiotrophy of a retina at survey of an eye bottom is characterized by existence white, sometimes with a metal shade, the centers located on the periphery of a retina. Arteriola of a mesh cover are narrowed, pigmentary deposits are presented in single quantity, the pobledneniye of a disk of an optic nerve comes to light. Changes on an elektroretinografiya are expressed poorly and are not reliable diagnostic criterion. Genetic diagnostics is presented by PRPH2 gene sekvenirovaniye.
At Shtargardt and Best's diseases at an oftalmoskopiya the atrophic centers of a light shade which are quite often surrounded with deposits of a pigment come to light. The sizes and quantity of the centers can differ considerably and reflects weight of defeat of a mesh cover of an eye. Generally they settle down in the central areas, but can extend also to the periphery. On an elektroretinografiya sharp decrease in amplitude of a wave comes to light And that demonstrates primary destruction of flasks. Genetic diagnostics comes down to identification of mutations in genes of ABCA4 and CNGB3 and to studying of the hereditary anamnesis.
Treatment and the forecast at a retina abiotrophy
Specific etiotropny treatment of any form of an abiotrophy of a retina does not exist for today. As the supporting treatment detaining progressing of a disease medicines of vitamins A, E, Riboflavinum are used. Vasodilating means allow to improve blood supply of a retina that also slow down dystrophic processes. In recent years there were data on successful application of the bionic implants of a retina (Argus, Argus 2) which allowed to return partially sight to the patients who completely lost it because of an abiotrophy. Some practices in the field of use of stem cells, gene therapy also pursue the aim to find a method of treatment of an abiotrophy of a retina.
Because of a large number of mutations which are the reason of an abiotrophy, and various clinical course of dystrophic processes in a retina the forecast practically always uncertain. Some types of pigmentary dystrophy can be limited to a gemeralopiya and violation of peripheral sight whereas other forms of this pathology lead to a total blindness. By vitamin A administration of drugs in some cases it is possible to slow down progressing of an abiotrophy of a retina, according to some information use of sunglasses also allows to achieve similar result.