Pannus

PANNUS (Lat. pannus—sheet, flap), or keratitis pannosa, represents an inflammation of the cornea characterized by the development of infiltration in its superficial parts with the new formation of connective tissue and the development of blood vessels in the affected area [see separate plates (vol. XII, pp. 583–584), figs. 2 and 3]. The cause of pannus in the overwhelming majority of cases is trachoma, and trachomatous pannus (p. trachomatosus) is particularly typical in its clinical picture. The second frequent cause of pannus is scrofula, in which various lesions of the cornea are observed, and one of the severe forms is scrofulous pannus [see separate plates (vol. XII, pp. 583–584), fig. 5] (syn. lymphatic, eczematous—p. scrofulosus, lymphaticus, eczematosus). Furthermore, degenerative changes of the cornea in blind eyes, especially in absolute glaucoma and severe iridocyclitis, also serve as a cause for the development of vessels and corneal opacities in the superficial parts of the cornea, resembling pannus (p. degenerativus). Finally, the cause of pannus can be corneal ulcers in the period of their healing—the so-called p. reparativus. The pathogenesis of pannus appears different in relation to individual forms. Regarding trachomatous pannus, the prevailing opinion was that pannus arises almost exclusively as a result of mechanical impact on the cornea from either the conjunctiva with its growths or scars, with the deformation of the cartilage, etc., or from improperly growing eyelashes or entropion. At the present time, this view is not recognized as correct, and the origin of pannus in trachoma is attributed to the influence of a number of factors. Besides purely mechanical moments, pannus also arises as a result of the spread of a specific trachomatous process to the cornea. In this case, trachoma spreads from the site of its usual localization—the transitional folds of the upper eyelid—first to the scleral conjunctiva and then to the cornea, producing the picture of pannous inflammation. This has been confirmed by histological studies of both the scleral conjunctiva and the cornea in trachomatous pannus. It is also considered quite admissible for trachomatous pannus to arise through contact, when, with the scleral conjunctiva not yet altered, the cornea, which constantly comes into contact in its upper segment with the trachoma-affected conjunctiva of the upper eyelid, is involved in the process due to toxic influences or due to the inoculation of the trachoma virus into the cornea. It goes without saying that in some cases mixed causes play a role in the origin of pannus—both mechanical moments and the specific effects of trachoma infection. Scrofulous pannus in its origin is identical to other forms of scrofulous keratitis (see Keratitis). Degenerative and reparative pannus are processes that are not independent in their origin: either they are preceded by degenerative changes of the cornea, or the pannus is merely a stage of healing of a corneal ulcer. The pathological anatomy of pannus has been most studied in relation to trachomatous pannus, although complete uniformity in the interpretation of the anatomical picture of such pannus still does not exist. The process is characterized by the development beneath the epithelium, between it and Bowman's membrane, of a layer of infiltration with a diverse cellular composition and a mass of blood vessels. In many cases, the inflammatory infiltration also passes beneath Bowman's membrane, destroying it in various places, and the stronger the pannous inflammation, the greater the extent to which Bowman's membrane is destroyed and the deeper the infiltration and newly formed vessels spread. In very severe cases, with the clinical picture of the so-called fleshy pannus, a significant part of the cornea, sometimes a full third or half, is seized by inflammatory changes. The cellular elements of the infiltration in trachomatous pannus consist predominantly of lymphocytes and plasma cells, and in the marginal parts of the cornea they are arranged particularly densely; there are rare cases when cellular accumulations are observed among diffuse infiltrates, giving the picture of a follicle identical to the follicles of the trachoma conjunctiva. In the area of the lesion, an early development of young connective tissue and a mass of newly formed blood vessels are noted. In severe cases, a significant part of the cornea is replaced by connective tissue rich in cellular elements and vessels, with the subsequent formation of dense scar tissue. Scrofulous pannus in its anatomical relations has many common features with trachomatous pannus in its mild, superficial forms, but here, besides the development of a connective tissue layer with a mass of vessels, one also observes the presence of isolated infiltrates—nodules of round-cell elements, which are usually located in the periphery of the cornea, clinically forming the so-called corneal phlyctenules. Scrofulous pannus is also located partly subepithelially and partly beneath Bowman's membrane. Degenerative pannus is characterized predominantly by the new formation of a connective tissue layer beneath the epithelium, and sometimes also beneath Bowman's membrane, with newly formed vessels being the primary element. These changes in the cornea are usually combined with other preceding processes observed in a blind eye. Reparative pannus also represents an anatomically non-independent process, being a stage of the healing of ulcerative keratitis. Symptomatology and course of pannus. Trachomatous pannus has a typical clinical picture by which in the majority of cases it is distinguished from other types of pannus. At the beginning of its development, it is localized almost as a rule in the upper segment of the cornea, and the primary element of the process—the formation of vessels in the cornea—is preceded by the appearance above, near the very edge, of localized superficial infiltrates and punctate opacities, which subsequently rapidly break down into superficial ulcers, toward which newly formed vessels are directed from the marginal network. Beginning from the periphery, the opacity of the cornea, permeated by superficial and tree-like branching vessels, can spread more and more within the cornea and seize the entire upper segment, half of the cornea, and even the entire cornea. The surface of the pannously altered cornea is uneven, rough. The borders of pannus, when it has not yet seized the entire cornea, often appear sharp, but with the progression of pannus, infiltrates and ulcers arise at the borders, trailing vessels behind them. According to the degree of its development and the different character of the process, three forms can be clinically distinguished: p. tenuis—thin, p. vasculosus—vascular, and p. crassus or carnosus—fleshy. Thin pannus is spoken of when the opacity caused by pannus, with insignificant development of infiltration and vascularization, appears weakly saturated and grayish in color. Vascular pannus means that form where vessels running among little-opacified corneal tissue are particularly abundantly developed. In fleshy pannus, the process assumes a more serious character, seizing a significant part of the cornea both in thickness and on the surface. Here the opacity is sharply expressed: due to deep infiltration by a mass of vessels and newly formed connective tissue, the cornea takes on the appearance of fleshy growths resembling granulation tissue; in severe forms, the entire cornea presents papillomatous growths. This kind of pannus leads to extremely severe visual disorders, in a number of cases leading to complete blindness, but with any pannus, the patients' vision suffers to one degree or another. Apart from visual disorders, pannus is accompanied by a whole range of other painful phenomena—photophobia, lacrimation, blepharospasm. As outcomes of pannus, only in very mild cases do noticeable traces fail to remain; usually, persistent opacities are observed due to superficial cicatricial changes of the cornea; severe forms of pannus, especially fleshy pannus, leave behind deep corneal scars—leukomas. In the course of pannus, a great tendency of this process to relapse is noted. Pannus arises at various stages of trachoma, in rare cases even in the first months after the disease with trachoma, but most often in regressive stages in the presence of pronounced changes in the conjunctival cartilage and especially in trichiasis and entropion. The clinical picture of scrofulous pannus is also characterized by opacity of the cornea in the superficial parts and the formation of vessels, with the new formation of vessels and corneal opacity arising here in any place of the cornea where corneal phlyctenules appear and frequently relapse, toward which vessels stretch from the periphery; characteristic of the process is the presence of other eye lesions of a scrofulous character—conjunctival phlyctenules, blepharitis, eyelid eczema, etc. Degenerative pannus has no definite clinical picture; it arises as a secondary phenomenon among other degenerative phenomena of a blind eye that has undergone a severe disease of the internal membranes, such as glaucoma or iridocyclitis; it is preceded by the formation of superficial defects in the cornea, after which vessels and corneal opacity develop in one part of the cornea or another. The picture of reparative pannus is obtained during the healing of an ulcer, when, during the replacement of the ulcer defect from the periphery, vessels advance toward the ulcer, creating a semblance of the development of pannus.

Treatment of trachomatous pannus is first and foremost the treatment of trachoma (see). Locally, in relation to the pannus itself, remedies commonly used in the treatment of keratitis are employed—disintoxicating and disinfecting ointments (xeroform, airol, yellow mercurial ointment, etc.); furthermore, if the iris is involved in the process, which occurs not infrequently in pannus, atropine is prescribed, whereas usually the administration of pilocarpine is beneficial. Stubborn cases of pannus require surgical intervention. Among the operations used are peritomy or periectomy, i.e., either the division near the limbus of the conjunctiva with the vessels passing onto the pannosed cornea, or the excision of a strip of conjunctiva near the cornea corresponding to the location of the pannus by two parallel incisions, one of which runs directly near the limbus and the other, retreating 3-4 mm, through the conjunctiva concentrically to the first. The purpose of the operation is the division of the vessels running into the pannus, their obliteration, and the subsequent clearing of the cornea. In recent years, Denig's operation has entered the practice of pannus treatment; Denig proposed as early as 1911 to combine the periectomy operation with the transplantation of mucous membrane from the lip onto the wound surface after the removal of the scleral conjunctiva. The beneficial effect of this operation is explained by the fact that upon replacing the affected conjunctival tissue with healthy lip mucosa, a barrier is created that prevents the penetration of the trachomatous process onto the cornea. As an adjunctive measure in stubborn forms of pannus, protein therapy is successfully employed, particularly in the form of autohemotherapy. There are also successful attempts at treating pannus with X-rays. In the treatment of scrofulous pannus, those remedies are appropriate which are used in the treatment of scrofulous keratitis in general (see Keratitis). The same must be said regarding reparative pannus as a stage in the course of ulcerative keratitis. The therapy of degenerative pannus is futile.