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Iris Reconstruction 8 Steven P Chapter 8 Iris Reconstruction 8 Steven P. Dunn and Lori Stec Key Points scope and microsurgical instrumentation, were not readily available. Drops, sutures, various lasers, tattoo Surgical Indications pigments, and tinted intraocular lenses are some of the • Decreased visual acuity approaches available today. Th is chapter discusses the • Incapacitating glare surgical anatomy and healing response of the iris as • Photophobia well as a variety of approaches for use when recon- • Diplopia struction is necessary. • Cosmesis Instrumentation • Contact lens 8.2 • Argon laser Iris Anatomy and Wound Healing • Polymethyl methacrylate (PMMA) pupil ring • Intraocular iris prosthesis Th e unique characteristics of the iris, its structure, and • Polypropylene suture response to disease and injury make an appreciation of Surgical Technique iris anatomy and wound healing of particular impor- • Laser iridoplasty tance when contemplating iris repair. • Suture iridopexy Th e structure of the normal human iris consists of • Pupil shaping with PMMA dilating ring two parts, the anterior stroma and the posterior dou- • Insertion of single-piece prosthetic iris with ble-layered pigmented epithelium. Between these lay- intraocular lens (IOL) ers are sandwiched the iris dilator and sphincter mus- • Insertion of multipiece prosthetic iris cles (Fig. 8.1). Th e stroma, in contrast to other ocular Complications structures, has a very loose, discontinuous architec- • Glaucoma ture. Th e anterior surface is made up of stromal cells, • Iritis fi brocytes, and melanocytes. Th ese cells have no de- • Subluxation of IOL fi ned linkage to one another and are separated by very • Decreased vision large intercellular spaces. Th e intercellular space con- • Intraocular hemorrhage tains a few collagen fi brils, ground substance, and aqueous humor. Within the stroma is a loosely orga- nized mix of melanocytes and iris blood vessels. Th e only continuous cell layer is found at the posterior sur- 8.1 face of the iris, and it is formed by the sphincter muscle Introduction ring, the dilator myofi brils, and the pigment epitheli- um. Th e muscle cells of the iris sphincter form a dense Th e function of the iris as a light-limiting diaphragm mass adjacent to the pupil. Th e dilator muscle origi- has been recognized for several thousand years. Initial nates and is thickest near the iris root and thins as it attempts to modify the iris and pupil were pharmaco- extends toward the pupillary edge (Table 8.1). logic in character. Th e concept of surgically modifying Clinical and pathologic studies indicate that trau- or repairing the iris did not receive much attention un- matic and surgical iris wounds do not heal spontane- til 1917, when Key fi rst wrote about his eff orts at re- ously. When a gap occurs in the iris (i. e., iridotomy), pairing an iridodialysis by suturing the iris edge to the and no bridging scaff old exists for stromal cells, pig- sclera. Iris-to-iris repair was fi rst described by Emm- ment cells, or fi broblasts to migrate across, scarring erich in 1957. Neither of these contributions attracted between the margins of the defect does not occur. signifi cant attention when initially published. In large Clinical observations have raised the question of part this was because suitable equipment to facilitate whether true wound healing occurs or whether a me- surgical reconstruction, namely the operating micro- chanical apposition of the wound margins is all that 72 Steven P. Dunn and Lori Stec Table 8.1 Standard measurements of the iris takes place. Research in primates and human patho- Diameter 12 mm logic specimens indicates that iris wounds do not show Circumference 37.5 mm any healing tendency or formation of scar tissue ex- cept in the area immediately surrounding an iris su- Th ickness: region 0.2 mm ture. At the site of the iris suture, there is a faint scar of the iris root with activated fi broblasts, a few plasma cells and mac- Th ickness: region 1.0 mm rophages, but very little collagen deposition. Long- of the collarette term apposition of an iris wound thus appears to be Pupillary diameter 1.2–9.0 mm wholly dependent on the presence of sutures. If a sig- nifi cant fi brinoid reaction occurs, a cyclitic membrane Width of the 0.6–0.9 mm may form, leading to “closure” of an iris defect. Th is, sphincter muscle however, does not lead to the reestablishment of nor- Th ickness of the pigment 12 µm mal iris architecture or to the formation of a collage- epithelium: miosis nous scar, and can result in further pathology. Th ickness of the pigment 50–60 µm epithelium: mydriasis 8.3 Nonsurgical Approaches Th is chapter is devoted to the surgical management of iris defects; however, it is worth emphasizing that many iris problems require no treatment or can be managed nonsurgically. Nonsurgical approaches to iris repair include the use of miotics and contact lens- es. Miotics such as pilocarpine have minimal eff ect on the pripheral iris. Pupillary margin defects and trau- matic paralytic mydriasis also respond poorly or not at all to strong miotics. For the sphincter muscle to con- strict the pupillary opening, it must be able to pull against another structure. Under normal circumstanc- es, it pulls against itself; however, when it is transected or a portion is missing, there is nothing against which the muscle can work. Alpha-2 agonists such as brimo- nidine have been used to temporarily induce miosis (without signifi cant myopia or brow ache) in post–re- fractive surgery patients suff ering from halos associ- ated with enlarged pupils. Long before contact lenses became a consumer commodity, custom labs were manufacturing them in various materials for therapeutic purposes. Th ey were initially designed with a black pupillary zone and tint- ed periphery to hide corneal scars. Subsequent designs with a clear pupillary zone and opaque periphery be- came available for use in patients with aniridia and partial iris loss. Design parameters for these custom lenses are infi nite. In many cases, the pupil diameter can be custom-designed to produce a near-pinhole ef- fect if glare is signifi cant. Th e need for the peripheral opaque portion of the lens to extend to the limbus of- ten necessitates the use of soft and rigid gas-permeable contact lenses with large diameters. Th e greater gas permeability of today’s lens materials has had a major aff ect on the success of these lenses. Whereas most lenses have a paint/tint schema that is concentric in Fig. 8.1 Histologic cross section of pupillary and peripheral nature, focal painting/tinting can be done using trun- portions of the iris. cated lenses. Chapter 8 Iris Reconstruction 73 8.4 the fi rst of which is a detailed history of the condition Surgical Indications causing the iris defect and the various treatments, medical and surgical, that have produced the present Many iris abnormalities, both congenital ( albinism, picture. aniridia, and coloboma) and acquired ( traumatic my- Factors that should be determined preoperatively driasis, aniridia, and iridodialysis) benefi t from surgi- include the amount of iris that is missing, the amount cal intervention aft er nonsurgical options have been of iris that remains, and the specifi c portion of iris that exhausted. remains (i. e., collarette versus midperipheral). Th e Modifi cation or repair of the iris is indicated in character of the iris tissue is important to assess. Are three clinical settings. Th e fi rst of these, and by far the multiple transillumination defects present? Is there most common, is associated with functional diffi cul- schisis or delamination of the iris? Is there fraying of ties such as glare, photophobia, and/or diplopia. Th ese the surface or iris edge? Is rubeosis or abnormal vascu- optical symptoms are caused by an enlarged pupillary larization present? Th e presence or absence of periph- opening secondary to trauma, surgery or a congenital eral anterior synechia ( PAS), lens capsule, iridocapsu- defect. An intact and functioning iris diaphragm de- lar adhesions, or iris or vitreous incarceration in old creases aberrations arising from the periphery of the surgical or traumatic wounds must to be determined lens. Traumatic or congenital aniridia is the ultimate preoperatively. example of pupil enlargement. A symptomatic para- Evaluation of the lens should determine if a cataract central or peripheral iridotomy or iridectomy would is present. If aphakic, it is important to look for a capsu- constitute the opposite extreme. Th e functional diffi - lar ring with maximal dilation. If an intraocular lens is culties that these anatomic distortions present can of- present, the type, placement, and stability of the intra- ten be confi rmed by occlusion with the lid, the strate- ocular lens should be assessed. When the results of slit- gic obstruction of an iridotomy or sector iridectomy lamp examination are inconclusive, the angle, iris thick- with a cotton applicator or the use of an opaque con- ness, and posterior chamber can be evaluated by high tact lens with a small, clear pupillary zone. frequency ultrasound biomicroscopy (UBM) or ante- Th e second indication for repair is restoration of the rior chamber optical coherence tomography (OCT). iris diaphragm as part of a multifaceted surgical recon- Th e overall integrity of the corneal surface, includ- struction. A large iris defect might require closure to ing surface staining, corneal sensation, and Schirmer support an anterior chamber intraocular lens. If a pos- testing, should be determined. Th e clarity of the cor- terior chamber lens is implanted, the edges of an iris nea, the presence or absence of corneal edema or gut- defect might be drawn together in an eff ort to reduce tata, and an endothelial cell count are important fac- postoperative glare or diplopia (either because of the tors to measure when planning a surgical approach.
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