Typical sliver-like appearance of central posterior cornea

Introduction Corneal changes: Fuchs endothelial dystrophy has a typical silvery appearance in the posterior portion of the cornea, commonly referred to as "cornea guttata." Fuchs endothelial dystrophy, also known as cornea guttata, is a common phenomenon that increases significantly with age. In many patients with keratoconus, other aspects of the cornea are normal and do not affect vision. A small number of patients with corneal stroma and epithelial edema can cause significant loss of vision.

Cause

(1) Causes of the disease

The disease has a certain hereditary nature, the genetic pattern is not very clear, and some cases have been confirmed as autosomal dominant inheritance. The cause is unknown, and it may be multifaceted. Some unrecognized factors interfere with the structure and function of corneal endothelial cells, which ultimately leads to decompensation of endothelial pump function.

In addition to the disease, the disease is an autosomal dominant genetic disease. In 2001, Biswas et al. performed a genomic analysis on a family and found that the Q455K missense mutation occurred in the type VIII collagen Alpha2 (COL8A2) gene located in the short arm 1p34.3-p32 of chromosome 1. This may interfere with the terminal differentiation of corneal endothelial cells by type VIII collagen, disturbing the structure and function of corneal endothelial cells, resulting in abnormal basement membrane and fibrillar collagen product, drip. DDT is further damaged by corneal endothelial cells, which finally causes degeneration of corneal pump function and anti-apoptotic function, resulting in loss of useful vision.

Primary dystrophic corneal endothelial cells may cause collagen deposition behind the posterior elastic membrane. The simple drop corneal histology is the appearance of a sputum or sputum biological appearance, and in other cases it may be localized collagen deposition, an extra-covered basement membrane or a uniformly thickened posterior collagen layer. However, viral particles were found on a case of Fuchs endothelial dystrophy corneal specimens, suggesting the possibility of acquiring a causal cause.

(two) pathogenesis

Although the underlying abnormalities of the endothelium in Fuchs endothelial dystrophy are still unclear, the pathogenesis seen in clinical practice has the following aspects.

1. Collagen tissue production increases more behind the posterior elastic layer and under the epithelium. As with many other corneal diseases, Fuchs malnourished abnormal endothelial cells produce excess collagen, including abnormalities with sparse collagen, basement membranes, and layers of looser fibrillar collagen. Subepithelial connective tissue comes from fibroblasts that migrate from the limbus or stroma, but some of them may also come from the epithelium.

2. Endothelium barrier function and pump function reduction can occur at the same time as endothelial degeneration changes and is destroyed. The connection of the apical space of the cell is disrupted, allowing aqueous humor to pass through the endothelial barrier into the stroma and epithelium. Since the diseased endothelium is unable to pump these fluids, the epithelial barrier prevents it from escaping from the front of the cornea, causing edema of the cornea. In the late stage of the disease, the formation of scar under the epithelium prevents the liquid from entering the epithelium. The scar formation of the matrix causes the cornea to no longer thicken. The posterior collagen tissue increases the toughness of the posterior cornea and is difficult to swell. Therefore, the corneal structure is tighter than before, and the patient feels more comfortable. . The density of Na+-K+ pump (Na+-K+ATPase) in corneal endothelial cells increased significantly in the early stage of the disease. As the disease progressed, the density of Na+-K+ pump gradually decreased, and the final pump function was completely lost.

3. Glaucoma pathogenesis

(1) Effects of intraocular pressure on corneal endothelium: There are controversies about the association between glaucoma and dysmenorrhea and Fuchs endothelial dystrophy. One of the reasons is that elevated intraocular pressure often leads to secondary changes in corneal endothelium. Endothelial cell density reduction can be seen in: open angle glaucoma, angle-closure glaucoma and some secondary glaucoma, but the degree of corneal endothelium changes is not always consistent with the degree of intraocular pressure elevation, suggesting other factors (such as age or before) Uveitis) affects the relationship between glaucoma and changes in corneal endothelium. Therefore, in the evaluation of the relationship between glaucoma and the drip cornea and Fuchs endothelium nutrition, the above factors must be considered.

(2) Droplet cornea and aqueous humor outflow: patients with drip cornea have a higher incidence of abnormal aqueous humor fluence, but subsequent studies have confirmed that the mean value of aqueous humor flow coefficient in the drip corneal group is not statistically different from the normal group. There was also no association between the extent of keratopathy and the fluency coefficient of aqueous humor. A comparison of the drip corneal group with the drop-free corneal matching group revealed that the former had a lower mean intraocular pressure.

(3) Fuchs endothelial dystrophy and glaucoma: The relationship between open-angle glaucoma and Fuchs endothelial dystrophy remains unclear. It has been estimated that 10% to 15% of patients with Fuchs endothelial dystrophy have open-angle glaucoma. However, in the Fuchs Endothelial Dystrophy study, there was no genetic overlap between Fuchs endothelial dystrophy and primary open angle glaucoma.

Patients with shallow anterior chamber and Fuchs endothelial dystrophy are prone to angle-closure glaucoma. Obviously, this is the result of the gradual thickening of the cornea and eventually the closure of the corner. In the past, some authors proposed closed-angle glaucoma, especially acute angle-closure glaucoma with iris atrophy, and the incidence of drip cornea was higher. It has also been suggested that the anterior chamber of the patients with smear cornea or Fuchs endothelial dystrophy has a shallower anterior axis, but another study suggests that these two unrelated abnormalities exist simultaneously and may affect each other.

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Related inspection

Corneal examination epidermal growth factor

According to the clinical manifestations, combined with the characteristic changes of the cornea, the possibility of the disease should be considered, but attention should be paid to the identification.

Clinical change

(1) Corneal changes: Fuchs endothelial dystrophy has a typical silvery appearance in the posterior portion of the cornea, commonly referred to as "cornea guttata." The clinical course is usually 10 to 20 years and can be divided into 3 stages. In the first phase, the patient was asymptomatic, and there were irregular spots of mites and dusty pigment spots in the central part of the posterior cornea. Thereafter, the rear elastic layer can be grayed and thickened. In the second phase, the corneal stroma and epithelium were edematous, and the patient's vision was unclear and glaring. Matrix edema initially appears in front of the posterior elastic layer and immediately adjacent to the front elastic layer, after which all the matrix gradually becomes frosted glass, and liquid-containing cracks appear in the swelling, causing the rear elastic layer to form wrinkles. Epithelial edema initially causes the surface of the cornea to be pigskin-like or like a small droplet of water, and then gradually forms a large oval or curved epithelial vesicle, causing paroxysmal pain when ruptured.

As the matrix becomes mixed and irregular astigmatism, vision decreases sharply. Vision is particularly poor when waking up, because the tear evaporation during sleep reduces the permeability, resulting in increased corneal edema. In the third stage, connective tissue appeared under the epithelium, and the epithelial edema decreased. Although the visual acuity was reduced to only manual, it was consciously comfortable. Some complications may occur during this period, such as epithelial shedding, microbial ulcers, peripheral neovascularization, and elevated intraocular pressure.

Examination of the corneal lesions under the slit lamp begins at the central portion and gradually expands toward the periphery. The following changes can occur from the posterior to the anterior cornea: corneal punctate degeneration, thickening and wrinkling of the posterior elastic layer; endothelial pigmentation; matrix edema, epithelial connective tissue and peripheral neovascularization; epithelial edema and large vesicles. The prominent change is the appearance of the beaten silver in the center of the posterior cornea, which is similar to that seen in the ICE syndrome but is rough. The most prominent histopathological changes are located behind the posterior elastic layer, and endothelial cells produce new collagenous tissue, which is clinically characterized by thickening of the posterior elastic layer. The posterior elastic layer and the nascent collagen tissue form a multi-layer structure, which is stained with PAS and presents a layer of dark and dark, and produces a gray spiral pattern that is clinically seen.

(2) combined with glaucoma: Fuchs endothelial epithelial dystrophy can be accompanied by two types of glaucoma: open-angle glaucoma and angle-closure glaucoma, the estimated incidence of 10% to 15%. The mechanism of glaucoma in the open angle may be related to the involvement of the trabecular meshwork. In the shallow anterior chamber and Fuchs malnutrition, the corneal parenchyma gradually thickens, causing the iris corneal angle to completely close, and the acute angle-closure glaucoma occurs. In many cases, angle closure occurs before corneal edema occurs. The mechanism of glaucoma in these cases is related to hyperopia and shallow anterior chamber, and may have some association with Fuchs malnutrition. In the mechanism of glaucoma, Fuchs malnutrition is different from ICE syndrome.

Reports on corneal spots and Fuchs endothelial dystrophy with glaucoma are ambiguous. In fact, patients with elevated intraocular pressure can often undergo changes in the corneal endothelium. In patients with concurrent glaucoma, corneal endothelial cell density and morphology can also be altered. The extent of endothelial dystrophy is not always related to the degree of intraocular pressure. Other factors can also affect changes in glaucoma and corneal endothelium. For example, anterior uveitis, glaucoma-ciliary inflammatory syndrome, etc., also affect changes in corneal endothelial morphology. Similarly, normal human corneal endothelium also changes with age. Any damaging factors between glaucoma and corneal endothelium changes must be considered.

2. Clinical stage The course of the disease is divided into 3 stages, up to 20 years or longer.

(1) Phase 1 [Cornea guttata period]: This period of patients has no symptoms. When the slit lamp direct illumination method is used, it can be seen that the posterior surface of the central part of the cornea has a plurality of small, posteriorly protruding guttata, which is slightly bronzed; when used in the posterior illumination method, it is displayed on the endothelium surface. There are scattered, round, refraction gold pits; when using the wide strip illumination method tangent to the cornea, it can be seen that the Descemet film is thickened in gold foil with some irregular gray turbid spots on it. When using endoscopy, it can be seen that some black areas appear in the normal mosaic morphology of endothelial cells. The appearance of corneal drip is not meant to have a diagnostic sign of the disease, because in most cases it does not develop Fuchs corneal dystrophy, but only the product of age-related corneal endothelial cell degeneration. Corneal sputum can also be an early manifestation of the disease. As the disease progresses, the number of drips can gradually increase, blending with each other and expanding to the periphery, invading the back of the whole cornea. Once the function of the endothelial cell biopump is lost, it enters the second phase of the disease.

(2) Phase 2 (substantial and epithelial edema, ie, primary corneal decompensation): In this period, the patient's vision decreased, pain appeared and progressively worsened. When the density of corneal endothelial cells decreased and the corneal endothelial biopump function was abnormal, corneal edema was seen under the slit lamp from the parenchyma layer of the Descemet membrane. The Descemet membrane showed wrinkles, the corneal thickness increased, and the parenchyma layer was slightly turbid. Then the corneal epithelium is microcystic edema and the corneal surface is uneven. The patient often has poor vision in the early morning, and the water in the anterior surface of the cornea is evaporated during the day, the epithelial edema is improved, and the visual acuity is improved. When the intraocular pressure increases, the epithelial edema worsens. Corneal epithelium and subepithelial edema can be fused into blisters and large bubbles, and the eyes are severely damaged after the big bubbles are broken.

(3) Stage 3 (scarring stage): Long-term edema of the cornea can cause corneal angiogenesis, and a connective tissue layer is formed diffusely under the epithelium. Repeated episodes of large bubble rupture, more likely to form scars. After the formation of corneal scars, the perception subsides, the epithelial edema is relieved, the pain is relieved, but the visual acuity is more declining.

Differential diagnosis

1. ICE syndrome is that Fuchs endothelial dystrophy is a bilateral onset, completely without the angle of the ICE syndrome and iris changes.

2. PPMD lies in Fuchs endothelial dystrophy. Rarely there are bridge-like iris corneal adhesions, iris changes and PPMD-specific irregular corneal posterior changes.

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