26 Prosthetic Iris Device Implantation
26.1 Introduction
The normal iris serves several functions: it regulates light entrance into the eye, reduces the spheric and chromatic aberration induced by the peripheral lens, and increases the depth of focus through accommodative miosis. The physiological pupil can vary dynamically from 1.5 to 8 mm. As we reflect on iris anatomy, the stroma provides structural framework. The posterior stromal layer contains the iris sphincter muscle, which receives parasympathetic innervation subserving constriction and the dilator muscles, with sympathetic innervation. Both muscles lie just anterior to the posterior pigment epithelial layer, the cells of which contain abundant pigment granules. These cells limit ingress of ambient light. The color of the iris, as it appears to the observer, is primarily dictated by pigment on or within the stromal fibers. This pigment has less impact on physiological light absorption and primarily impacts appearance.
26.2 Making the Case for Iris Prostheses: Why Bother?
Deficiency of any component of the iris may have significant clinical symptoms, depending on the extent of structures involved, any comorbid ocular pathology, density of choroidal pigment, and the coping mechanisms of the individual. Typically, the greater degree of iris absence or damage, the greater the degree of symptoms. Patients with lighter irides and less choroidal pigment might be expected to have less absorption of incoming light, thus perhaps more symptoms. Also, concomitant corneal, lens, optic nerve, and retinal disease may either exacerbate or mitigate photic symptoms, depending on the specific pathology and the stage of the disease process.
Light sensitivity can affect some people profoundly. Many patients will be compelled to avoid outdoor activities, such as sporting events and spending time at the beach. Such events may either be uncomfortable, even with dark sunglasses. One posttrauma patient who was an avid roller-coaster enthusiast had to suspend her favorite hobby until her situation was remediated. Another patient welcomed her advancing posttraumatic cataract because it provided relief from pronounced light photophobia, despite sacrificing binocular vision. Some of our patients even choose to wear a black patch over the eye, strictly to tolerate daily activities. Lest one should presume that this is the outdoors alone, severe photophobia can occur at well-lit public places, such as stores and banks, or even in normal, dim light for the most-affected individuals.
Not surprisingly, other patients’ problems may be greatest at night when oncoming headlights strike their eyes. The dark adaptation of the photoreceptors at night can truly exacerbate glare in the patient with iris defects.
Patients with iris defects that create pseudopolycoria or expose an aphakic space or an IOL edge may report monocular multiplopic images—the classic example of when more is not better. In fact, pseudophakic patients are much more vulnerable to exposed aphakic space phenomena and lens edge artifact than their phakic or cataractous peers because the crystalline lens occupies the majority of the limbus-to-limbus aperture, whereas all commercially available intraocular lenses (IOLs) have a much smaller diameter and thus a greater likelihood of some of the ambient light being unfocused by the lens. The ensuing contrast sensitivity reduction is akin to the effect noticed when one is watching a movie in a dark cinema and the lights are turned on, or when another theatergoer opens a door to a brightly lit corridor or to the outside on a sunny day. The same amount of light hits the screen, and that light is still well focused, but when the unfocused ambient light is introduced, the screen appears washed out.
While our attention is often focused on the optical effects of an altered iris, the abnormal appearance reduces cosmesis and affects personal body image. Though not well studied, the impact of an abnormal iris on psychosocial well-being can be quite real and is likely substantially underestimated, especially in individuals with light-colored irides.
26.3 Other Fixes
While some iris defects can be surgically repaired without augmentation by an artificial iris device, in many cases this is just not possible due to the inadequate amount or quality of residual iris tissue.
Reports of intrastromal corneal tattooing, with pigment placed into lamellar corneal pockets created either manually or with a microkeratome or a femtosecond laser, 1 , 2 , 3 showed a range of cosmetic results and variable success in relieving light-related symptoms. Currently, there are no pigments marketed for this purpose worldwide, and no tattoo pigments that are Food and Drug Administration (FDA) approved for ocular use. Pigment granules could migrate through corneal lamellae from their initial location of placement, and their safety has not been well established with prospective studies. 4
“Aniridic” contact lenses with opaque outer diaphragms are commercially available (Fig. 26.1), though they tend to be both expensive and less comfortable and, therefore, less tolerable than their non-opaque peers. They are particularly challenging in patients with comorbid corneal pathology, common in cohorts with iris anomalies. Alleviation of photic symptoms with these contact lenses can be variable; also, in cases of multiple or shadow images from pseudopolycoria, these extra images may persist because the pseudo pupil aperture in the more anterior corneal plane may still permit nonaxial light to fall within polycoric spaces. Furthermore, due to their position at the corneal plane, anterior to the nodal point, they can cause symptoms of tunnel vision from the reduced peripheral light.
Although we have now established an obvious need for prosthetic irides, their entry into the marketplace has been slow.
26.4 From Concept to Execution: Who, When, and What?
The first prosthetic iris was first designed by Peter Choyce in the United Kingdom as a polymethyl methacrylate (PMMA) anterior chamber implant with three-point sutureless angle fixation. It was available with plate haptics in blue, brown, or gray-green (produced by Rayner and Keeler Ltd.) and was first implanted by Choyce in 1964.s. Literatur , 6 These implants were also available with nylon loops for external fixation where there was insufficient iris support. In 1991, Sundmacher and colleagues reported a black PMMA diaphragm device manufactured by Morcher GMBH. 7 , 8 This device came with an incorporated clear PMMA optic. Due to its rigid nature and large outer diameter, wound sizes for implantation were very big. To reduce the corneal–scleral wound size during surgical implantation, Volker Rasch developed with Morcher a multipiece black PMMA endocapsular tension ring-based prosthesis, first implanted by Kenneth Rosenthal (K. Rosenthal, MD, “Original Technique and Case Report: Combined ‘True Sutureless’ Phaco Trabeculectomy with Insertion of Opaque Capsular Tension Ring in a Patient with Essential Iris Atrophy (Axenfeld-Rieger), Secondary Glaucoma and Cataract,” presented at the Baylor–Welsh Cataract Congress, Houston, Texas, USA) and, shortly thereafter by Robert Osher, both in 1996. Subsequent iterations with differing “fin” sizes and apertures are named eponymically with Rasch, Rosenthal, Masket, and Miller monikers (Fig. 26.2).
Ophtec has also introduced larger single-piece (model 311) and smaller incision multipiece rigid iris prosthetic devices, which come in light blue, light green, and medium brown (Fig. 26.3). The 311 comes with or without an incorporated optic. Unlike the Morcher 67 series in which the optic has a square edge that is fused to the internal square edge of the black PMMA iris device carrier, the optic for this device is inset into a gentle bevel in its Perspex carrier. The smaller-incision, multipiece IPS device designed by Heino Hermeking is placed within the capsular bag, along with an IOL and a capsular tension ring (CTR). The unit consists of two orthogonal elements and a third locking ring to prevent the other elements from moving or migrating within the bag. Placing this locking piece requires extraordinary surgical dexterity (Fig. 26.4).
In the early 2000s Hans Reinhard Koch and Humanoptics GMBH developed a custom-matched iris device. This flexible, customized device can be placed either in the sulcus or in the capsular bag and has become a versatile option for cases of widely differing anatomy and pathophysiology.
Morcher introduced the Irismatch series of combined IOL/iris prosthesis devices on a colorless PMMA backbone with an anterior opaque white diaphragm colored by dots of red, blue, yellow, and black to create 45 different shades (Fig. 26.5). There are anecdotal reports of a blistery, vacuolated appearance occurring over the device, including the optical component, and others who have patients with sustained good optical visual function and symptom control over many years with the device, though it is no longer available in the marketplace.
Pozdeyeva et al 9 reported the use of an elastomer prosthesis that works by angle fixation. We do not believe this device is currently marketed.
26.5 Iris Prostheses: Who Needs These?
One way to think about the pathologies that might lead to the need for an iris prosthesis is to think about the anatomical iris structures that are either absent, deficient, or nonfunctional in a given condition.
26.5.1 Pigment Epithelial Deficiency
In patients with ocular albinism, for example, the stromal layer, pupil, sphincter, and dilator are unaffected. In fact, the pigment epithelial layer is anatomically and physiologically normal, except, of course, for the absence of melanin pigment within the pigment epithelial cells. The resultant photophobia, glare, and other photic symptoms can be profound. These patients can often be even worse off in the pseudophakic state because light will pass directly through the iris stroma to strike the IOL edge (Fig. 26.6). Admittedly, the stroma may provide some modest diffusion of the light striking an IOL margin, but photic symptoms are nearly omnipresent. Some patients may be lacking iris pigment from inherited conditions, such as Hermansky–Pudlak’s syndrome, Chédiak–Higashi’s syndrome, and Waardenburg’s syndrome type 2. Others may have secondary pigment loss due to inflammation, herpetic eye disease, medication reactions, and the like. 10 In some of these pathologies, the sphincter and dilator muscles may also be affected. Surgical misadventure can lead to pigment loss as well, with or without stromal or sphincter damage, especially in intraoperative floppy iris syndrome (IFIS). 11 Many of these cases would be well suited for the surgeon to consider an iris prosthesis. 12
26.5.2 Sphincter Deficiency
Some patients can have a chronically dilated pupil from traumatic injury, inflammation, or even Adie’s pupils. This may be so even when the stroma and pigment epithelium are satisfactory, though it is often very difficult to discern preoperatively whether these structures are of acceptable quality. Hence attempted repairs cannot always achieve the desired outcome. Accordingly, careful scrutiny during the preoperative exam can provide a more informed prognosis, and a candid discussion with the patient should include the alternative of placing an iris device in lieu of or in addition to structural repair.
26.5.3 Partial Stromal Deficiency
In some cases, the iris can be partially or sectorally affected by the underlying pathophysiology. In congenital coloboma, for example, an inferonasal section of iris is absent. Surgical injury from IFIS, for example, is commonly temporal, whereas iris tumor excision or trauma may affect any area and can be highly variable in extent. Some irides may be very stretchy and can be sutured, with or without the use of an underlying iris device, whereas in other cases the native iris material may not be able to stretch at all to cover a defect or deficiency. In case of iridocorneal endothelial (ICE) syndrome, the iris will rarely stretch at all, even when large amounts of tissue appear to be present. This is likely due to the multilaminar, basement membrane–producing “ICE membrane,” which grows over the native iris surface in these cases. 13
Some cases of trauma, iridodialysis, iatrogenesis, or ICE syndrome, especially the essential iris atrophy variant, may present with corectopias or (one or more) pseudopupils, which can sometimes result in monocular diplopia, mutiplopia, or shadow images in addition to other photic complaints.
26.5.4 Subtotal or Total Stromal Deficiency
Congenital aniridia syndrome is an uncommon genetic disorder inherited in an autosomal dominant pattern with variable expressivity 14 affecting roughly 1 in 60,000 individuals. These patients may have no iris tissue, a rudimentary iris stub, or surprisingly large amounts of iris stroma. 15 Very rarely, some patients with this condition, even with the familiar PAX 6 deletion, may have a normal or nearly normal appearing iris in the so-called aniridia with iris variant. 16 Obviously, this peculiar latter group is unlikely to need a prosthetic iris element and is thus beyond the scope of this chapter.
Management of congenital aniridic eyes also requires extreme attentiveness to the thinner capsules and known zonular fragility, 17 which frequently necessitate specialized techniques for both cataract removal and stabilization of the potentially decentered capsular bag, discussed elsewhere in this textbook. Similarly, comanagement of any underlying glaucoma issues or corneal limbal stem cell deficiencies must be coordinated with subspecialists with appropriate skill sets and experience.
For surgeons who intend to tackle congenital aniridic cases, it is crucial to be fully aware of aniridia fibrosis syndrome (AFS), 18 a vexing condition noted for an unrelenting and potentially sight- and eye-threatening process, affecting roughly 5% of cases, even following pristine surgical technique. The incidence of AFS appears to be irrespective of whether an iris device is used or not. Despite this similar incidence, it is the authors’ opinion that in-the-bag placement of an iris device (when possible) in these vulnerable eyes seems wiser than sulcus placement in which device–uveal contact can occur. Because it is very difficult to reopen an aniridic capsular bag secondarily, iris device placement at the same time as cataract surgery in these cases, when regulatory burdens and logistics permit, is prudent. Off-label use of indocyanine green (ICG) dye is superior to trypan blue for staining these fragile, thinner capsules.
26.5.5 Posttraumatic Injury
Following ocular trauma, defects of the iris can take on a wide variety of patterns and can affect a wide variety of structures. In some trauma cases the iris can be lost from the eye entirely, whereas in other cases, like large mydriasis and iridodialyses, the tissue may be present and of reasonable quality, but the sphincter will be nonfunctional due to denervation and ischemia. The greater the extent of injury, the more likely the need for a prosthesis.
26.6 Device Properties and Device-Specific Tips and Tricks
Device selection may be dictated by factors including the size of the defect that needs to be remediated, the importance of cosmetic appearance, the size of the wound required for the surgery, and the availability of devices in the surgeon’s environment.
The availability may be limited by regulatory factors, such as in the United States, where implants are accessible at this time only through an FDA investigational device exemption (IDE) study for the Humanoptics CustomFlex device at study sites. In some settings cost may limit the options.
For many patients, appearance of the eye and body image are very important. A careful discussion should occur to determine how these things are important to each person because the answers may not be readily obvious. The overwhelming majority of patients prefer a restoration of a physiologically sized pupil of a color and reflectivity similar to unaffected peers or, perhaps, their fellow eye. Tellingly, we treated one blue-eyed patient who had bilateral iris atrophy and mydriasis and had previously received a black opaque iris device for one eye. Both eyes, obviously, had enlarged pupils, and this patient strongly preferred to have a black device implanted in this second eye to maintain a symmetric appearance.
Devices vary in terms of the materials they are made of, their rigidity or flexibility, the incorporation of or the lack of an optical component, the color in which they are available, and the relative contour and reflectivity of the surface of the device.
26.6.1 Rigid Lens–Iris Diaphragm Prosthetic Iris Device with Incorporated Optic
Currently, two companies offer these lenses: Ophtec BV and Morcher. These designs are intended to be implanted in the posterior chamber, either within the capsular bag or in the sulcus (with or without sutured scleral fixation). In-the-bag placement of these large rigid devices can be very challenging and risks tearing of the capsulorhexis or stressing remaining zonules. The Ophtec 311 is available in light blue, light green, or medium brown. It has an outer-diaphragm diameter of 9 mm and a 4 mm pseudopupil. Although rigid in its diaphragm, the haptics have ample flex and do not easily fracture. The surfaces of this device are smooth and can reflect ambient light. This property and the limited color availability can result in what some have described as an unnatural aesthetic appearance. The incorporated optic is inset in a bevel in the opaque carrier. A wide power range is available from 1 to 30 diopters (D) in 0.5 D increments. A plano optic can also be ordered.
The Morcher implants are available only in black. Their outer diameters and pseudopupillary apertures vary depending on model. The size of the optic ranges from 3 mm (Morcher 67B) to 6.5 mm. Haptic-to-haptic distance ranges from 12.5 to 13.75 mm (Table 26.1). Some units are made with asymmetric anatomy for cases in which some iris tissue remains, so as to minimize wound size. The optics, available from 10 to 30 D, have a square edge that is fused to the internal square edge of the pseudopupil carrier. The black PMMA material is rendered opaque by a process that also renders the PMMA more brittle than regular PMMA. Accordingly, the haptics are more prone to fracture when stressed.
Both Morcher and Ophtec can deliver these devices without an optic as well. Rigid diaphragm implants have the longest history, and several reports document their use and some pitfalls. 19 , 20
Ophtec also custom-makes an Artisan iris-clipped iris device for anterior chamber implantation, though it is the uncommon patient in which enough healthy iris tissue is available for enclavation, but a suture repair is not possible. 21
Combined iris diaphragm–IOL implants address both aphakia and aniridia with just one device, with reasonable outcomes. However, dysphotopsia with smaller optics can occur. Due to the very low number of devices implanted compared to commonly used IOLs, this phenomenon is difficult to study in cohorts who receive these units. The color of these diaphragms is not customizable, and the surface is smooth and reflective and thus may appear to some observers as unnatural or unmatched when compared to the remnant iris or the contralateral eye. Because PMMA material is rigid, these implants require wound sizes upward of 9 to 10 mm for implantation, due to the device’s size.
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