IRIS

Injuries of the iris compromise its function as an optical aperture and a mechanical barrier between the AC and the posterior chamber/vitreous. The iris

base, along with the ciliary body and angle, is especially sensitive to the shear stress caused by contusion. In open globe injuries, even total aniridia due to actual iris extrusion or subsequent iris retraction may occur.1,2 Discussed separately below are the five major consequences of trauma to the iris:

1.mydriasis;

2.iatrogenic iris laceration;

3.prolapse;

4.iridiodialysis; and

5.aniridia.

MYDRIASIS

Pathophysiology

Mydriasis (see Tables 18–1 and 18–2) may be an immediate or late complication of contusion or laceration; it can also occur as a result of head trauma. Mydriasis may present early or late and may be unior bilateral. There are various causes of pupil dilatation.

•Sphincter rupture/laceration has been reported from rare sources (water jets, water balloons19,20) and accompanies cataract surgery in 1.321 to 2.3%22 of eyes. It is irreversible, and secondary scarring further restricts pupil motility.

•Third cranial nerve injury may result from uncal herniation causing mechanical compression of the third nerve and subsequent brain stem compromise. A decrease in the brain stem blood flow is another frequent cause.23

•Aberrant cranial nerve regeneration can follow severe head trauma, even if the eye is uninjured. The pupil does not react to light or near but correlates with horizontal gaze. Constriction of the pupil reflects misdirected regeneration of abducens nerve neurons into the parasympathetic pathway of the oculomotor nerve.

•Anterior PVR involves fibrovascular membranes connecting the peripheral retina, ciliary body, and the peripheral iris. Membrane contraction and collagen deposition lead to iris retraction (see Chapter 19 and the Appendix).

PEARL... It is difficult to free the iris from scar tissue during secondary reconstruction. A thorough primary anterior vitrectomy is much more effective in avoiding iris retraction and anterior PVR in combined ante-

rior/posterior segment injury.

Therapy

If glare and visual deterioration persist, surgical reconstruction should be considered.

•A single suture (Fig. 18–1) constricts the pupil by apposing the sphincter muscle and pupillary margin to each other.24

•A running suture (Fig. 18–2) distributes the forces to the pupillary margin more evenly,25 acting as an “encircling band.” Surgical steps include:

limbal paracentesis in each quadrant;

loosening of posterior synechiae and mobilizing all iris remnants;

weaving of a transchamber needle through the iris margin in each quadrant;

continuing until the suture is passed through the pupillary margin in all quadrants;

exiting through the first paracentesis and preparing a knot; and

tightening the knot inside the AC.

IATROGENIC IRIS LACERATION

This may occur during phacoemulsification, usually while sculpting anteriorly if the critical distance between the phaco tip and the iris is not maintained. Additional risk factors include atonia/atrophy of the iris, miosis, and high flow. The pigment epithelium or even the stroma may be injured. The consequences include:

•cosmetic problems;

•visual symptoms and peripheral synechia development due to deep sphincterectomy that tend to enlarge with time;

•iridodialysis26; or even

•complete aniridia.a

Therapyb

The need for and type of intervention depend on the lesion. A simple laceration may easily be sutured (McCannel method, see later in this Chapter) using a straight transchamber needle introduced at the limbus through the two iris flaps and out through the limbus on the other side. The needle is cut, and the suture is retrieved through a paracentesis, tightened, and released back into the AC.

PROLAPSE (SEE ALSO CHAPTER 16)

The consequences of prolapse include:

•adhesion to the corneal wound;

•intraocular infection;

•ischemia/necrosis/atrophy;

•goniosynechia and secondary glaucoma (with prolapses at or near the limbus);

•surface epithelization (this starts immediately following the injury,27–29 although epithelial downgrowth into the AC, which can be modulated,30 is rare); and

•monocular diplopia (likely to occur when an area of extensive iris resection with an intact pupillary margin is exposed to the palpebral fissure; usually requires suturing).

Therapy

Reposition early to prevent intraocular infection31; in addition to spatula sweeping from the AC, use viscoelastics (see Chapter 16).32 A peripheral iridectomy is

a W. Konen, personal communication, 2000.

CHAPTER 18 IRIS • 149

advised whenever it is impossible to reposition the iris and to free the angle.

PEARL... Necrosis and surface epithelization are indications for iris resection.

This causes less complications than preserving poorly repositioned and nonviable iris tissue. The resulting defect can usually be sutured.24,33

IRIDODIALYSIS

Pathophysiology

Iridodialysis represents a rupture of the iris at its root: the peripheral portion is torn off the ciliary spur. It is typically a consequence of contusion, stretching the iris at and from its insertion. The complaints (glare, monocular double vision) depend on the size of the defect and its position relative to the lid fissure.

Treatment

The most widely used technique is based on the principles of the McCannel34,35 suture. A scleral incision is prepared as a fixation site. Using a double-armed straight transchamber polypropylene suture, the torn iris is brought out through the incision so that one loop is in front of the iris and the other underneath it (Fig. 18–3). The knot is either internalized or buried by a scleral flap. For a large iridodialysis, two or more sutures may be required. Complications of the procedure include:

•epithelial downgrowth with secondary glaucoma36; and

•late suture erosion in eyes with less resistant sclera (e.g., children or high myopia)—this can be prevented by use of a scleral tunnel incision.37

ANIRIDIA

Pathophysiology

See Table 18–3 for differential diagnosis.

Complete loss of the iris may occur in ruptured eyes with wounds near the limbus.1,2 Structural weakness in this region (e.g., Elliot’s trepanation,39 ICCE and ECCE incisions, or, to a lesser extent, corneoscleral tunnel incisions40) is a risk factor (see Chapter 27).

Treatment

b The treatment is the same if the laceration is caused by noniatrogenic trauma.

Aniridia results in serious subjective and objective consequences and should be addressed.

PEARL... Several options are available for patients with aniridia to fight the cosmetic and optical consequences. Implants41,42 have the advantage of maintaining two ocular

compartments.

Iris print contact lenses (e.g., Hema contact lens) give the appearance of iris tissue. They are also helpful for albinism, iris coloboma, essential iris atrophy, and leukoma corneae.43 These lenses (Fig. 18–4) diminish glare but may also reduce visual acuity and contrast sensitivity44 and are therefore most useful in blind eyes.

Corneal tattooing is cost-effective and involves localized staining of the corneal stroma, corresponding to the iris defects. Originally described for leukoma, it has recently been proposed for iris defects.45–47 Different techniques are available.

•Lamellar corneal preparation is created at 50% depth of the stroma, from

limbal incisions45 or from a

central half-depth 4-mm trephination46 (this is especially suitable for complete aniridia, when complete staining is required).

•For smaller iris defects (Fig. 18–5), the pigment is applied in a punctuated fashion.47

The pigment used for skin tattooing seems to be sufficiently inert for intracorneal application. It is usually possible to achieve the desired color because the

pigment is available in different shades. Side effects such as inflammation, epithelial irregularities, or stromal vascularization have not yet been noted.

P I T F A L L

Long-term results for pigment stability and tolerance by the corneal stroma are unavailable. Currently, corneal tattooing is best recommended for cosmesis in blind eyes.

FIGURE 18–5 Corneal tattoo of about three clock hours. The dye is based on candle soot. Its black color contrasts with the light blue iris color. Soot particles are appropriate for dark irises.

Stained intraocular optical diaphragms (see Table 18–4) are implanted during or after cataract extraction.51 If attached to a capsular tension ring, an intact capsular bag is required. In eyes without (firm) capsular bags, transscleral fixation of a stained IOL is recommended. Because of the size and the stiffness of such PMMA devices, 180° corneoscleral incisions are required. Chronic low-grade inflammation may ensue.

PEARL... In phakic eyes with aniridia, the surgeon may perform lens removal with an atypically large capsulorrhexis, followed by

IOL implantation. If the rim of the lens capsule attaches to the IOL’s equator, subsequent capsular fibrosis will opacify the peripheral capsular bag and will at least cosmetically imitate light iris tissue.

Clear intraocular mechanical (Heimann) diaphragms

(see Tables 18–5 and 18–6) were designed because severely injured eyes commonly need permanent sili-

TABLE 18–5 SPECIFICATIONS OF THE HEIMANN

DIAPHRAGMS*

cone oil tamponade (see the Appendix) to fight aqueous production insufficiency and eventual phthisis.41,42,53 These eyes are usually aphakic and have a compromised iris; the artificial iris diaphragm prevents corneal touch by the silicone oil and thus band keratopathy. Two types of diaphragm are available:

1.The open (stiff) diaphragm is designed for eyes with normal IOP. Success (i.e., silicone oil retained behind the diaphragm) has been reported in 40% of eyes during a mean follow-up of 579 days.41,42 Causes of failure include:

•closure of the Ando iridectomy (35%);

•tractional retinal redetachment (5%); and

•permanent ocular hypotony (25%).

TABLE 18–6 TECHNIQUE OF IMPLANTATION OF THE

CLOSED TYPE OF HEIMANN DIAPHRAGM

Vitrectomy with membrane peeling if necessary

PFCL to reattach the retina and stabilize the eye

Sclerotomies 4 mm from the limbus to keep the instruments clear from the position of the later diaphragm near the ciliary sulcus

Four scleral flaps 2 mm posterior to the limbus to cover the fixation sutures subsequently

A clear corneal incision or a corneoscleral tunnel in the superior circumference

Four sutures attached to the diaphragm at the same distance from each other (looped 9-0 Prolene with 15-mm- long needles*)

The two inferior sutures, then the diaphragm itself, then the two superior sutures placed into the eye. The diaphragm can be folded to narrow the size of the tunnel

AC stabilized by viscoelastic

PFCL–silicone oil exchange and IOP normalization (Fig. 18–8)

2.The closed (flexible) diaphragm is designed for eyes with low IOP, whether from primary damage to the ciliary body or from secondary fibrous overgrowth (PVR, uveitis, endophthalmitis,

advanced proliferative diabetic retinopathy).42,54 It may be used, however, in eyes with normal IOP because the aqueous does tend to penetrate the barrier.

FIGURE 18–8 Implantation of a flexible closed iris diaphragm through a clear corneal incision with four fixation sutures.

PEARL... Today we implant only the closed diaphragm; the success rate is 50%.

In addition, although the IOP is below 10 mm Hg in 75% of eyes, the silicone oil prevented or delayed phthisis in two thirds of cases.

PEARL... Diaphragm implantation in trauma-related aniridia must be performed at the time of secondary reconstruction to pre-

vent fibrous overgrowth of the implant.

Failure to retain the silicone oil behind the closed diaphragm is independent of the IOP. The reason for failure is commonly (46%) unknown; a valve mechanism may develop from unavoidable gaps between

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Wrapping or stretching must be avoided by accurate intraoperative fitting. The four scleral fixations must closely correspond to the holes of the implant. When silicone oil moves anteriorly despite more than two revisions, further revisions do not appear to be effective.

P I T F A L L

Because silicone oil and the silicone diaphragm have the same refractive index, it is sometimes difficult to determine whether there is oil in the AC. An abnormal glistening reflex from the anterior surface of the iris and a lack of fluorescein penetration into the AC indicate the presence of silicone oil in the AC.

SUMMARY

Damage to the iris is a common manifestation of severe open and closed globe injuries. In most cases, the damage to the iris is without major consequences other than that its presence should alarm the clinician to the possibility of damage to other ocular structures. In some cases, however, partial or total loss of the iris can cause visually disabling symptoms, and has the potential of causing secondary complications if silicone oil use is required. For such eyes various surgical treatments are available typically requiring referral to a specialist.

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