Pannus

PANNUS (Latin pannus—patch, flap), or keratitis pannosa, is an inflammation of the cornea characterized by the development of infiltration in its superficial parts with the formation of connective tissue and the growth of vessels in the affected area [see separate table (vol. XII, pp. 583–584), figs. 2 and 3]. The cause of P. is, in the vast majority of cases, trachoma, and trachomatous P. (p. traehomatosus) is particularly typical in its clinical picture. The second frequent cause of P. is scrofulosis, in which various corneal lesions are observed, and one of the severe forms is scrofulous P. [see separate table (vol. XII, pp. 583–584), fig. 5] (syn. lymphaticus, eczemato-sus—p. scrofulosus, lymphaticus, eczemato-sus). 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 P. (p. dege-nerativus). Finally, corneal ulcers during their healing period can also be a cause of P.—the so-called p. reparativus. The pathogenesis of P. appears to be different with respect to the individual forms. With regard to trachomatous P., the prevailing opinion was that P. arises almost exclusively as a result of mechanical action on the cornea from the conjunctiva with its overgrowths or scars, with curvature of the cartilage, etc., or from the improperly growing eyelashes or entropion. At present this view is not considered correct, and the origin of P. in trachoma is attributed to the influence of a number of factors. In addition to purely mechanical moments, P. also arises as a result of the spread of the specific trachomatous process onto the cornea. In this case, trachoma spreads from its usual place of localization—the transitional folds of the upper eyelid—first to the scleral conjunctiva, and then to the cornea, giving the picture of pan-nous inflammation. This is confirmed by histological studies of both the scleral conjunctiva and the cornea in trachomatous P. It can be considered quite admissible that trachomatous P. also occurs by contact, when, with the scleral conjunctiva still unchanged, the cornea, constantly coming into contact in its upper segment with the affected trachomatous conjunctiva of the upper eyelid, becomes involved in the process due to toxic influences or due to the inoculation of the trachomatous virus into the cornea. Naturally, in some cases, mixed causes play a role in the origin of P.—both mechanical moments and specific influences of trachomatous infection. Scrofulous P. is identical in origin to other forms of scrofulous keratitis (see Keratitis). Degenerative and reparative P. are not independent processes in origin: either they are preceded by degenerative changes of the cornea, or P. is only a stage in the healing of a corneal ulcer. The pathologic anatomy of P. is most studied in relation to trachomatous P., although a complete uniformity in the interpretation of the pathologic-anatomic picture of such P. still does not exist. The process is characterized by the development, under the epithelium, between it and the Bowman's membrane, of a layer of infiltration with a different cellular composition and a mass of vessels. In many cases, the inflammatory infiltration also passes under the Bowman's membrane, destroying it in certain places, and the stronger the pan-nous inflammation, the greater the extent to which the Bowman's membrane dies, and the deeper the infiltration and newly formed vessels spread. In very severe cases, in the clinical picture of the so-called fleshy P., a significant part of the cornea, sometimes a whole third, a half, is captured by inflammatory changes. The cellular elements of the infiltration in trachomatous P. consist mainly of lymphocytes and plasma cells, and they are located especially densely in the peripheral parts of the cornea; there are rare cases when, among diffuse infiltrates, cellular accumulations are observed giving the picture of a follicle identical to those of trachomatous conjunctiva. In the affected area, early development of young connective tissue and a mass of newly formed 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 P. has many common features in pathologic-anatomic relation with trachomatous P. in its mild, superficial forms, but here, in addition to the development of a layer of connective tissue with a mass of vessels, the presence of individual infiltrates—nodules of round-cell elements—is also observed, which are usually located in the periphery of the cornea, forming clinically the so-called corneal pustules. Scrofulous P. is also located partly subepithelially and partly under the Bowman's membrane. Degenerative P. is characterized mainly by the formation of a connective-tissue layer under the epithelium, and sometimes also under the Bowman's membrane, the main element being the newly formed vessels. These changes in the cornea are usually combined with other preceding processes observed in the blind eye. Reparative P. is, in anatomic relation, also a non-independent process, being a stage in the healing of ulcerative keratitis.

Treatment of Pannus is first and foremost the treatment of trachoma (see). Locally, with respect to the pannus itself, agents usually employed in the treatment of keratitis are used—disinfecting ointments (xeroform, aural, yellow mercurial ointment, etc.), and in case the iris is involved in the process, which is often the case with pannus, atropine is prescribed; usually, however, pilocarpine is beneficial. Intractable cases of pannus require surgical intervention. Operations include peritomy or periectomy, i.e., either cutting the connective tissue near the limbus with vessels extending into the pannusous cornea, or excising a strip of connective tissue around the cornea according to the location of the pannus with two parallel incisions, one of which runs directly near the limbus and the other, stepping back 3–4 mm, through the conjunctiva concentrically to the first. The aim of the operation is to cut the vessels entering the pannus, their obliteration, and the subsequent clearing of the cornea. In recent years, Denig's operation has entered the practice of treating pannus; he proposed this operation in 1911, combining periectomy with the transplantation of lip mucosa onto the wound surface after removal of the scleral conjunctiva. The beneficial effect of this operation is explained by the fact that the replacement of the diseased conjunctival tissue with healthy lip mucosa creates a barrier preventing the penetration of the trachomatous process onto the cornea. As an auxiliary measure in intractant forms of pannus, protein therapy is successfully applied, especially in the form of autogenous hemotherapy. There have been successful attempts to treat pannus with X-rays. In the treatment of scrofulous pannus, the means used in the treatment of scrofulous keratitis in general are appropriate (see Keratitis). The same should be said regarding reparative pannus as a stage of the course of ulcerative keratitis. Therapy of degenerative pannus is futile.