Retinal detachment - Pathogenesis

Pathogenesis of rhegmatogenous retinal detachment

Rhegmatogenous retinal detachment occurs annually in approximately 1 case per 10,000 population, in 10% of cases it is bilateral. Retinal breaks, which are the cause of retinal detachment, can appear due to the interaction of: dynamic bitreoretinal traction, predisposing dystrophy in the periphery of the retina. Myopia also plays a significant role.

Dynamic vitreoretinal traction

Pathogenesis

Synchysis is a liquefaction of the vitreous. In the presence of synchysis, holes sometimes appear in the thinned cortical portion of the vitreous, which is located above the fovea. The liquefied substance from the center of the vitreous cavity passes through this defect into the newly formed retrohyaloid space. In this case, hydrodissection of the posterior hyaloid surface from the internal limiting membrane of the sensory retina up to the posterior border of the vitreous base occurs. The remaining dense vitreous body descends lower and the retrohyaloid space remains completely occupied by the liquefied substance. This process is called acute rhegmatogenous posterior vitreous detachment with ptosis. The likelihood of acute posterior vitreous detachment increases with age and in the presence of myopia.

Complications associated with acute posterior vitreous detachment

They depend on the strength and size of the present vitreoretinal adhesions.

• The absence of complications is typical for most cases of weak vitreoretinal adhesions.
• Retinal breaks occur in approximately 10% of cases as a result of traction of powerful vitreoretinal adhesions. Breaks in combination with acute posterior vitreous detachment are usually U-shaped, localized in the upper half of the fundus, and are often accompanied by vitreous hemorrhages as a result of breakage of peripheral blood vessels. From the formed break, liquefied retrohyaloid fluid can freely penetrate into the subretinal space, so prophylactic laser coagulation or cryotherapy of the break reduces the risk of retinal detachment.
• Rupture of peripheral blood vessels resulting in intraretinal hemorrhage without formation of retinal tears.

Signs of peripheral retinal dystrophies

Approximately 60% of breaks occur in the periphery of the retina and cause specific changes. These changes may be due to spontaneous breakage of the pathologically thinned retina with subsequent formation of holes or may be the cause of the retinal break in eyes with acute posterior vitreous detachment. Retinal holes are usually smaller than breaks and less often lead to retinal detachment.

"Lattice" dystrophy

It occurs in 8% of the world's population and in 40% of cases of retinal detachment. It is the main cause of retinal detachment in myopia in the young. Lattice-type changes are often found in patients with Marfan, Stickler, and Ehlers-Danlos syndromes, which are associated with a high risk of developing retinal detachment.

Signs

• typical "lattice" consists of strictly defined, peripheral, spindle-shaped areas of retinal thinning, most of which are located between the equator and the posterior border of the vitreous base. "Lattice" is characterized by a violation of the integrity of the internal limiting membrane and varying atrophy of the underlying sensory retina. Changes are usually bilateral, most often localized in the temporal half of the retina, mainly above, less often - in the nasal, below. A characteristic feature is a branched network of thin white stripes in the islets formed as a result of RPE disorders. Some "lattice" dystrophies may resemble "snowflakes" (remnants of degenerative changes in Müller cells). The vitreous body above the "lattice" is liquefied, and along the edges of the dystrophy it forms dense adhesions;
• Atypical "lattice" is characterized by radially oriented changes that extend to the peripheral vessels and may continue posteriorly to the equator. This type of dystrophy usually occurs in Stickler syndrome.

Complications

The absence of complications is observed in the majority of patients, even in the presence of small “hole-like” tears, which are often found in the islands of “lattice” dystrophy.

Retinal detachment associated with atrophic "hole" breaks occurs primarily in myopic young patients. They may not have the warning symptoms of acute posterior vitreous detachment (photopsia or floaters), and subretinal fluid leakage is usually slower.

Retinal detachments due to traction breaks can be seen in eyes with acute posterior vitreous detachment. Traction breaks usually develop along the posterior edge of the lattice degeneration as a result of dynamic traction in the area of strong vitreoretinal adhesions. Sometimes a small lattice area can be identified on the retinal break flap.

Snail track dystrophy

Signs: clearly defined circumferential bands of dystrophy in the form of tightly packed "snowflakes" that give the periphery of the retina the appearance of a white icy pattern. Usually exceed the islands of "lattice" dystrophy in extent. Although the "snail track" dystrophy is associated with liquefaction of the vitreous body covering it, significant vitreous traction in the area of its posterior border is rarely observed, therefore traction U-shaped breaks are almost never encountered.

Complications include the formation of "punch-hole" tears, which can lead to retinal detachment.

Degenerative retinoschisis

Retinoschisis is a division of the sensory retina into two layers: the outer (choroidal) and the inner (vitreal). There are 2 main types: degenerative, congenital. Degenerative retinoschisis occurs in approximately 5% of the world's population over 20 years old, mainly with hyperopia (70% of patients are hyperopic) and is almost always asymptomatic.

Classification

• typical, cleavage occurs in the outer plexiform layer;
• reticular, less common, splitting occurs at the level of the nerve fiber layer.

Signs

• Early changes usually involve the extreme inferotemporal periphery in both eyes, appearing as large areas of cystic degeneration with some retinal elevation.
• Progression may appear circumferentially, up to complete involvement of the periphery of the retina. Typical retioschisis is usually anterior to the equator, while reticular may extend posterior to it.
• On the surface of the inner layer, changes in the form of “snowflakes” can be detected, characteristic changes in the vessels such as the “silver wire” or “case” symptom, and a torn grayish-white flap can pass through the cleft cavity (“schisis”).
• The outer layer has a "broken metal" appearance and exhibits the "white with pressure" phenomenon.

Unlike retinal detachment, retinoschisis is characterized by stability.

Complications

• The absence of complications is typical for most cases with a favorable course.
• Tears may appear in the reticular form. Tears of the inner layer are small and rounded, while the rarer tears of the outer layer are large, with rolled edges and located behind the equator.
• Retinal detachment is very rare, but can occur when there are tears in both layers. Retinal detachment usually does not occur when there are tears in the outer layer, since the fluid inside the schisis is viscous and cannot quickly leak into the subretinal space. However, sometimes the fluid can liquefy and leak through the tear into the subretinal space, lifting a limited area of outer retinal detachment, which is usually within the retinoschisis.
• Vitreous hemorrhages are uncommon.

"White without pressure"

Signs

A) "white with pressure" - a translucent grayish change in the retina caused by sclerocompression. Each area has a specific configuration that does not change when the sclerocompressor moves to the adjacent area. This phenomenon is often observed in the norm, as well as along the posterior border of the islands of "lattice" dystrophy, "snail track" dystrophy and the outer layer of acquired retinoschisis;

B) "white without pressure" has a similar picture, but appears without sclerocompression. During a general examination, a normal area of the retina surrounded by "white without pressure" can be mistaken for a flat "hole" retinal tear.

Complications: Giant tears sometimes develop along the posterior border of the "no-pressure white" area.

Meaning of myopia

Although myopia affects about 10% of the world's population, more than 40% of all retinal detachments occur in myopic eyes. The higher the refraction, the higher the risk of retinal detachment. The following interrelated factors predispose to retinal detachment in myopic eyes:

• Lattice dystrophy is more common in moderate myopia and can lead to normal and perforated tears.
• Snail track dystrophy occurs in myopic eyes and may be accompanied by "hole-like" breaks.
• Diffuse chorioretinal atrophy can lead to small "hole-like" breaks in high myopia.
• Macular hole can cause retinal detachment in high myopia.
• Vitreous dystrophy and posterior vitreous detachment are common.
• Vitreous loss during cataract surgery, especially if errors were made during the operation, is associated with subsequent retinal detachment in about 15% of cases of myopia greater than 6 D; the risk is much higher with myopia greater than 10 D.
• Posterior capsulotomy is associated with a high risk of retinal detachment in myopic eyes.

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