Triangular pterygium on corneal surface

Introduction The triangular surface of the cornea is a clinical manifestation of pterygium. The palpebral conjunctiva is hypertrophied and gradually stretches toward the surface of the cornea, forming a triangular vascular tissue with vascular tissue, resembling an insect's wings, hence the name pterygium. It occurs mostly on the nasal side, and there are fewer cases on the temporal side. When extending to the cornea, it can invade the front elastic layer and the shallow matrix. Pterygium is a common and frequently-occurring disease in ophthalmology. It is generally considered to be a chronic inflammatory lesion of local conjunctival fibrovascular tissue caused by external stimuli. It is triangular and can invade the cornea, involving single or both eyes. Because its shape resembles the wings of insects, it is called pterygium, and Chinese medicine is called "shrimp." It is one of the most common eye diseases in the clinic and the oldest eye disease. It can not only cause eye irritation and appearance defects, but also affect vision in varying degrees. Most occur in outdoor workers. May be related to long-term stimulation such as sand, smoke, sunlight, and ultraviolet light.

Cause

(1) Causes of the disease

At present, there are still many controversies about its pathogenic factors. It is generally believed that it may be the result of a combination of internal factors (genetic factors) and external factors (environmental factors). Among the external causes, ultraviolet rays in sunlight are the most important environmental factors. In addition, sand, dust, and dryness are also important environmental factors that affect the incidence.

Environmental factors

Epidemiological survey results show that the incidence of people living in hot, sunny and dusty areas is significantly higher, and outdoor workers are also susceptible to the disease. It has been found in rats that high-dose ultraviolet radiation can cause epithelial hyperplasia, anterior elastic layer degeneration and vascularization in the corneal stroma, indicating that the formation of pterygium has a significant relationship with ultraviolet light, which may be the most important environmental factor.

2. Genetic factors

Genetics have a certain effect on the occurrence of pterygium, but it does not play a decisive role. This inheritance is a dominant inheritance with low penetrance. However, it seems that the true lesion is not hereditary, and the only effect of the eye on the environmental stimuli is the tendency to develop pterygium.

3. Immunity factors

Because plasma cells, lymphocytes, and immunoglobulins are found in pterygium, they are thought to be related to immunology. Monoclonal antibody studies have shown that almost all lymphocytes are T cells that cause cell-mediated immune responses and type IV hypersensitivity reactions. Immunofluorescence studies have shown that immunoglobulins are IgG and IgE, and IgG is mainly in the corneal stroma, which is consistent with the area infiltrated by plasma cells and lymphocytes. IgE is mainly distributed in the epithelial and stromal regions. The presence of IgE indicates type I or immediate hypersensitivity reactions. Immunofluorescence studies of normal conjunctiva did not reveal IgG and IgE. If IgE persists, it will lead to chronic inflammation. Stimulation of this antigen can come from exogenous factors like pollen, dust particles or even viruses. It is worth noting that although IgE is sometimes found by chance, this immunological theory still has some appeal. The discovery of T lymphocytes, IgG and IgE in pterygium can indicate that humoral and cell-mediated hypersensitivity is closely related to the occurrence of pterygium.

4. Chronic inflammation and proliferative diseases

Chronic inflammation from any cause (such as focal conjunctivitis occurring at the edge of the limbus) can lead to inflammatory edema, repair and neovascularization, and a fibrovascular response characteristic of pterygium.

5. Other

Biedner et al believe that the occurrence of pterygium is related to the secretion of basic tears. Monselise et al. pointed out that angiogenesis can also contribute to the formation of fat. Some people think that there are many conjunctiva and corneal chronic ulcers in the formation and development of fat, which is mainly conjunctival ulcer. In recent years, it has also been suggested that the occurrence of pterygium is associated with limbal stem cell dysfunction.

(two) pathogenesis

The specific pathogenesis is still not fully explained. There are various theories about the pathogenesis of pterygium. Early studies have found a large number of lymphocytes, plasma cell infiltration and mast cell responses in pterygium tissue, suggesting that there is an immunological mechanism in the pathogenesis of pterygium. Studies have also found that IgG, IgE and a small amount of IgA and IgM in the pterygium tissue, and the basement membrane has granular immunoglobulin and C3 deposition, so the incidence of pterygium is considered to be related to type I and type III allergies. However, mast cells appear only in the subcutaneous matrix of the pterygium, especially near the denatured elastic fibers, and are not detected in the epithelial layer and the limbus. Therefore, it is currently impossible to judge that the immune response is the primary in the pathogenesis of pterygium. Sexuality is still a secondary change.

In recent years, research on the pathogenesis of pterygium has yielded many very meaningful results. Coroneo combined the results of recent years and proposed the hypothesis of two-stage development of pterygium. This hypothesis artificially divides the pathogenesis of pterygium into two stages: in the first stage, the limbal stem cells are destroyed, and the keratoconjunctival barrier function is impaired; in the second stage, the cell proliferation is active, and inflammation and vascularization occur. The connective tissue is reshaped and the cornea is "conjunctival", resulting in pterygium. This hypothesis is contrary to the concept that pterygium was previously considered to be a degenerative disease.

According to the "two-stage" theory, limbal stem cell dysfunction is the basis of the onset of pterygium. As mentioned above, when the light from the temporal side is projected to the posterior limbal limbus, the intensity of the light can be amplified by a factor of 20, where the epithelial basal cells are "struck" from behind, which can cause stem cell dysfunction and number. cut back. The intact limbus is a barrier to the growth of the conjunctiva to the cornea. Once the barrier is destroyed, the proliferating and active conjunctival fibroblasts (in other words, the transformed limbal stem cells) tend to grow in the cornea.

For Phase 2, more and more research supports that pterygium is a proliferative disease, and degeneration is a secondary or secondary change. The main evidence includes:

1 The expression of certain growth factors regulating proliferation in pterygium tissues, such as transforming growth factor- (TGF-), basic fibroblast growth factor (bFGF), etc.;

2 pterygium fibroblasts were transformed: studies have shown that cultured pterygium fibroblasts proliferate actively and can be proliferated by (TGF-);

3 pterygium epithelial cells proliferate active: their epithelial cells vary in thickness and hyperkeratosis, suggesting an increase in the expression of the proliferating epidermal growth factor receptor (EFGR) family and keratin (such as K3, K8, K16, etc.);

4 pterygium epithelial cells increased p53 protein expression, loss of heterozygosity and microsatellite instability, and these changes are generally detected in tumor cells and precancerous lesions, so some scholars recommend pterygium Known as benign neoplastic lesion;

5 pterygium epithelial and subepithelial fibroblasts inhibited the expression of bcl-2, suggesting that the occurrence of pterygium may be related to the decrease of normal apoptosis;

6 Some anti-proliferative drugs and treatment methods can reduce the recurrence rate of pterygium after surgery, such as local application of anti-metabolites and -ray radiotherapy. In addition, recent studies have also found that the activity of tissue metalloproteinases and their inhibitors in pterygium epithelium is disordered, suggesting that the occurrence of pterygium is associated with inflammation, tissue remodeling and vascularization.

an examination

Related inspection

Corneal examination

Clinical manifestations:

For example, the pterygium is artificially divided into three parts: the head, the neck and the body. The head is the part of the cornea, the neck is the part of the limbus, and the body is located on the surface of the sclera. Mature pterygium often has characteristic changes in the corneal epithelium at the anterior border of the head, manifesting as a lipidal change in the corneal epithelium and subepithelial, which usually has a transparent zone with the head. Most pterygium is located in the cleft palate. If the initial lesion originates from the cleft palate, the diagnosis of primary pterygium should be considered cautiously.

In addition, pterygium adheres to the limbus at the limbus, while pseudo-caries are adhesions of the sacral and bulbar conjunctiva, usually not adhering at the limbus, and can be distinguished by a glass rod under local anesthesia.

Although the changes in pterygium are very intuitive, misdiagnosis often occurs. The following are diagnostic criteria for pterygium:

Mature pterygium is a raised, triangular lesion on the cornea with its base at the conjunctiva next to the limbus and the tip pointing toward the center of the cornea.

Differential diagnosis

Diagnosis of pterygium sometimes needs to be differentiated from plaque, pseudo-caries, and squamous cell carcinoma.

False scorpion

Pseudo-caries usually have clear causes of disease such as inflammation, trauma, especially chemical injuries, etc., can occur anywhere in the keratoconjunctiva, irregular shape, and most of the lesions are still. Some pseudo-caries have only the head connected to the cornea, and the bottom probe near the limbus can pass. True pterygium is the result of chronic inflammation of the conjunctiva and subconjunctival tissue and progression to the cornea. Pseudopterin is generally an acute injury in the marginal zone of the cornea, where the conjunctiva and the corneal lesion are adjacent to each other to form a conjunctival bridge.

2. Squamous cell carcinoma conjunctival squamous cell carcinoma

More common in the elderly, can occur in any part of the keratoconjunctiva. The tumor is uneven or papillary, rapidly infiltrating into the surrounding tissue, the neovascular disorder is easy to bleed, and the tissue invading the cornea is mostly irregular. A pathological biopsy can be diagnosed if necessary.

3. Cracks

The palpebral fissure is located in the conjunctiva of the cleft palate near the limbus. It is a horizontally banded, triangular or elliptical, bulging gray-yellow lesion. The pterygium is characterized by invading the cornea, while the plaque is not. However, occasionally large plaques may invade the cornea and be confused with pterygium.

4. Benign tumor of the limbus

Conjunctival papilloma is a translucent, lustrous red dome-shaped lesion that can be located on the nasal or temporal side near the limbus and is confused with pterygium, but conjunctival papilloma rarely invades the cornea, histopathological examination Can distinguish between the two. The corneoscleral prosthesis often occurs under the ankle, a hemispherical bulge with a smooth white surface, which can be lightly hyperemia and visible on the surface. It should be differentiated from pterygium when it occurs on the temporal side.

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