Chorioid dystrophy

Dystrophic processes in the choroid may be hereditary or secondary in nature, for example, a consequence of previous inflammatory processes.

According to localization, they can be generalized or focal, for example, located in the macular region of the retina. In case of choroidal dystrophy, the retina, especially the pigment epithelium, is always involved in the pathological process.

The pathogenesis of hereditary choroidal dystrophy is based on genetically determined abiotrophy (absence of vascular layers) and secondary changes in photoreceptors and pigment epithelium.

The main ophthalmoscopic sign of this disease is choroidal atrophy, accompanied by changes in the retinal pigment epithelium with accumulation of pigment granules and the presence of a metallic reflex. In the initial stage of choriocapillary layer atrophy, large and medium-sized vessels seem unchanged, but dysfunction of the retinal photoreceptors is already noted, caused by a disruption in the nutrition of its outer layers. As the process progresses, the vessels become sclerotic and acquire a yellowish-white color. In the final stage of the disease, the retina and choroid are atrophic, the vessels disappear and only a small number of large choroidal vessels are visible against the background of the sclera. All signs of the dystrophic process are clearly visible with fluorescent angiography (FA).

Choroidal atrophy is a common feature of many hereditary dystrophies of the retina and pigment epithelium.

There are various forms of generalized choroidal dystrophies.

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Choroideremia

Choroideremia is a hereditary dystrophy of the choroid. It is a rare disease in males. Already in the early stages, along with signs of atrophy in the choroid, changes in the photoreceptors are noted, mainly in the rods on the middle periphery of the retina.

The inheritance type is X-linked, gene locus is Xq21.

• All daughters of a sick father are carriers. 50% of sons of women carriers are sick. 50% of daughters of women carriers are also carriers.
• A sick father cannot pass on the gene to his sons.
• In female carriers, there are minimal changes, areas of peripheral atrophy and mottling in the RPE layer. Visual acuity, peripheral fields and electroretinogram are normal.
• It manifests itself as nyctalopia in the first decade of life.

As the process progresses, night vision decreases, concentric narrowing of the visual fields is revealed, ERG is subnormal. Central vision is preserved until the late stage of the disease.

Ophthalmoscopically, a wide range of changes are detected in male patients - from atrophy of the choriocapillaries and minor changes in the retinal pigment epithelium to the complete absence of the choroid and outer layers of the retina. In the first or second decade of life, changes are expressed in the appearance of a pathological reflex during ophthalmoscopy, the formation of coin-shaped foci of atrophy of the choroid and retinal pigment epithelium, and pigment accumulation in the form of fanules or bone bodies.

The diagnosis can be established on the basis of family history data, examination results of patients and their family members, ERG and visual field studies.

Symptoms (in order of appearance)

• On the middle periphery there are areas of choroidal atrophy and RPE atrophy.
• Diffuse atrophy of the choriocapillaris and RPE with preservation of medium and large vessels.
• Atrophy of medium and large choroidal vessels with exposure of the underlying sclera.

Compared with primary retinal dystrophies, the fovea is preserved for a long time; the optic disc and retinal vessels remain relatively normal.

• Electroretinogram. Scotopic electroretinogram is not registered, photopic is sharply subnormal.
• The electrooculogram is subnormal.
• FAG of the middle stage of choroideremia reveals filling of the retinal vessels and large choroidal vessels, but not of the choriocapillaries. Hypofluorescence corresponds to an intact fovea, the surrounding zone of hyperfluorescence - with "final" defects.

The prognosis is extremely unfavorable, but most patients retain vision until the sixth decade of life, despite its sharp decline.

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Central areolar choroidal dystrophy

The inheritance type is autosomal dominant, the gene locus is on p. 17. It manifests itself in the 3rd decade of life as a gradual bilateral decrease in central vision.

Symptoms (in order of appearance)

• Non-specific granularity in the fovea.
• Demarcated areas of RPE atrophy and choriocapillary layer atrophy in the macula.
• Slowly expanding zone of "geographic" atrophy with visualization of large choroidal vessels.

Electroretinogram is normal. Electrooculogram is normal.

The prognosis is unfavorable: poor visual functions - by the 6th-7th decades of life.

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Diffuse choroidal atrophy

The inheritance type is autosomal dominant. It manifests itself in the 4th-5th decades of life as a decrease in central vision or nyctalopia.

Symptoms (in order of appearance)

• Parapapillary and pericentral atrophy of the RPE and choriocapillaris.
• Gradual expansion of zones to involve the entire fundus.
• Atrophy of most of the large choroidal vessels and translucency of the sclera.
• The retinal vessels are of normal caliber or slightly narrowed.
• Electroretinogram is subnormal.

The prognosis is poor due to early changes in the macula.

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Helical parapapillary chorioretinal degeneration

The inheritance type is autosomal dominant. It manifests itself in childhood.

Symptoms

• Bilateral, slowly expanding, tongue-shaped, clearly defined bands of chorioretinal atrophy originating from the optic disc.
• The foci can be separate, peripheral, circular.
• Electroretinogram from normal to pathological.

The prognosis varies: in young people the course may be severe, while in older people it is more favorable.

Pigmentary paravenous retinochoroidal atrophy

Pigmentary paravenous retinochoroidal atrophy is a rare disease, usually detected by chance in young men. The type of inheritance is not reliably known, both types, linked to the X chromosome and even linked to the Y chromosome, have been described.

Symptoms

• Bilateral pigment deposition in the form of "bone bodies" along large retinal vessels.
• Adjacent, demarcated areas of chorioretinal atrophy that may be located around the optic disc.
• Electroretinogram is usually normal.

The prognosis is good because macular changes are rare.