The histochemical examination of the fibers of pterygium by elastase

The Ets-1 transcription factor is involved in pterygial angiogenesis

Pterygial pathology is characterized by abnormal corneal epithelial proliferation, stromal modulation, matrix degradation and a strong tendency for otherwise absent corneal vascularization. As the proto-oncogene Ets-1 is known to play a key role in angiogenesis and matrix degradation in other tissues, its involvement in corneal vascularization was investigated. Fifteen pterygia representing two groups were studied. Group 1 consisted of five clinically active pterygia, and group 2 consisted of 10 samples of clinically non-active pterygia. (35)S-labelled ets-1 antisense and sense riboprobes were used for in-situ hybridization of Ets-1 transcription factor in all pterygia. The cytoplasm of blood vessel endothelial cells showed strong expression of ets-1 mRNA in all group 1 pterygia. In contrast, no expression of ets-1 was found in group 2 pterygia. Proto-oncogene ets-1 expression has been shown for the first time in the metaplastic pterygium, an eye tissue of unknown pathogenesis.

Mechanism of abnormal elastin gene expression in the pinguecular part of pterygia

Elastodysplasia and elastodystrophy are two known manifestations in the conjunctival, ie, pinguecular, part of pterygia. But the mechanisms are still not understood. The purpose of this study is to investigate the mechanism of enhanced elastin gene expression in fibroblasts from the pinguecular part of pterygia, which is related to abnormal elastic fiber expression in the pinguecular part of pterygia. Elastin in surgical specimens of normal conjunctiva and the pinguecular part of pterygia from age-matched patients was detected by immunohistochemical staining. Northern hybridization and quantification of radiolabeled tropoelastin were performed in conjunctival fibroblasts cultured under different doses of ultraviolet (UV) B irradiation, and in cultured pinguecular fibroblasts from pterygia. In vitro translation was also performed to analyze the tropoelastin production in rabbit reticulocyte lysate. The level of tropoelastin in reticulolysates from UV-treated conjunctival and pinguecular fibroblasts of pterygia was higher than in normal conjunctival fibroblasts. The coding sequence and 3'- untranslated region of tropoelastin mRNAs were amplified by reverse transcription-polymerase chain reaction, and mutations were checked by DNA sequencing. Immunohistochemical staining revealed elastin in pinguecular subepithelial connective tissues of pterygia, but not in normal conjunctiva. Tropoelastin mRNA levels were not elevated in cultured pinguecular or conjunctival fibroblasts with or without ultraviolet B irradiation. However, tropoelastin synthesis was enhanced in culture medium of pinguecular and UV-irradiated conjunctival fibroblasts, but not in normal conjunctival fibroblasts. Direct DNA sequencing revealed mutations in the 3'-untranslated region but not in the coding sequence of tropoelastin mRNA, in both pinguecular and UV-irradiated conjunctival fibroblasts. The increased expression of tropoelastin in pinguecular and UV-irradiated fibroblasts is not a result of increased levels of steady-state mRNA, but is a result of posttranscriptional modification of tropoelastin.

Pingueculae and pterygia

Pingueculae and pterygia are benign peribulbar lesions composed of degenerated basophilic subepithelial tissue. Pingueculae do not affect vision, and minor irritation can usually be managed with artificial tears. Pterygia may affect the visual axis and require surgical and adjunctive treatment. The various therapeutic strategies are reviewed. A conservative approach is advocated, as surgical removal of primary pterygia may result in recurrent ptergyia that are more difficult to manage than the primary lesions.

Histology of pterygium: an electron microscopic study

An electron microscopic study of the cap areas of several pterygia shows the presence of active fibroblasts in the natural tissue planes surrounding Bowman's layer. The hypothesis is advanced that the fibroblasts originate in the limbal connective tissue. They advance in the cornea above and below Bowman's membrane, destroying the latter and a variable amount of superficial corneal stroma.

Elastodysplasia and elastodystrophy as the pathologic bases of ocular pterygia and pinguecula

Specimens of normal conjunctiva from three adult patients were examined by electron microscopy, which revealed normal elastogenesis in the substantia propria, but more prominently, in the episcleral tissues. Ultrastructural examination of eight pterygia and three pinguecula also disclosed evidence of elastogenesis, but in these lesions the morphogenetic sequence of fiber formation was distorted, and the elastic fibers were abnormal. The zone of hyalinization of the substantia propria immediately beneath the epithelium was the only site that manifested clear-cut evidence of collagen degeneration, which assumed the forms of effacement of the longitudinal periodicity of the collagen fibers, and of microfibrillar unfurling of the ends of the collagen fibers. Fibroblastic activity and elastic fiber formation were inconspicuous in this region. Beneath the hyalinized zone were collections of eosinophilic granular material. This material was shown ultrastructurally to be composed of excessive numbers of hollow-centered microfibrils (an elastic fiber precursor), with a tendency to clump centrally in the larger aggregated sheets and to acquire electron-dense inclusions. Numerous fibroblasts were found within this material. Finally, the elastotic fibers of light microscopy represented an abnormal maturational phase of elastic fiber production. These abnormal elastic fibers had microfibrils at their peripheries, but numerous electron-dense inclusions were associated with focal zones of amorphous elastin deposition. Occasionally histiocytes appeared to be engulfing these abnormal fibers. We have concluded that a large component of pinguecula and pterygia is the result of newly synthesized elastic fiber precursors and abnormal maturational forms of elastic fibers (elastodysplasia) that undergo secondary degeneration (elastodystrophy). These structures are presumed to be elaborated by actinically damaged fibroblasts of the substantia propria.

Pinguecula and actinic elastosis. An ultrastructural study

Three cases of pinguecula (conjunctival elastosis) were ultrastructurally investigated. Findings were compared with the features described in cutaneous actinic elastosis. Changes observed were not uniform. In both diseases, numerous elastotoc fibers were present with a finely granular matrix and masses of dense grains. The degenerative changes of the elastotic fibers evolved differently in conjunctival stroma and in dermis. The superficial extracellular concretions observed in pinguecula seemed to be an ultimate stage of elastotic degeneration. Like actinic elastosis and elastosis observed in chronic radiodermatitis, pinguecula is believed to result from a dystrophic increased elastogenesis induced by chronic irradiation, with secondary degenerative changes.

[Pinguecula and pterygium: histologic and electron microscopic study (author's transl)]

Two pingueculae combined with pterygia were studied by light and electron microscopy. Hyaline degeneration of the collagen, dark staining granular, von Kossa negative concretions and elastotic material were observed in both conditions together with marked changes in the fibroblasts, endothelial cells, pericytes and the basement membrane of conjunctival capillaries and small veins. The elastotic material is similar to that observed in solar elastosis, where the collagen fibers are less severely damaged. Chronic sun exposure of the pericorneal conjunctiva may damage endothelial cells primarily and disturb vascular exchanges. This would result in accelerated degeneration and regeneration of endothelial cells, in thickening of the basement membrane and, secondarily, disturbed metabolism of fibroblasts with alterations of the collagen and elastic fibers.

[Ultrastructural studies on the pterygium. II. Connective tissue, vessels and nerves of the conjunctival part (author's transl)]

The stromal part of the pterygium is remarkably rich in plasma cells. The connective intercellular substance shows two different pathological modifications: A clotting together of collagen fibres to broad, osmiophilic, elastoid bands and a widening of the spaces containing the granular nonfibrillar ground-substance . The vascular system consists mostly of fenestrated sinusoid capillaries. Their endothelial cells frequently show degenerative changes and the basement membrane of the vessels can be as thick as up to 50--100 fold the normal size. For the first time nervous formations could be found in the pterygium. Axons of the autonomic system join the basal epithelial cells, where they form terminal endings. Encapsulated myelinated and nonmyelinated corpusles probably stem from the sensory nervous system.