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Third-nerve palsy

Position

Should be central; if dislocated, the cause can be iris or vitreous prolapse (see Chap. 2.4), or iridodialysis

Shape

Should be round; if not, the most likely cause is posterior synechia or iridodialysis

Color

Should be black;1 a pupillary membrane causes color change, as does a cataract

Reaction to accommodation

The pupil should constrict

Reaction to direct light

The pupil should constrict - if lacking a reaction, it must be determined whether this is due to a problem with afferentation (no perception of light), efferentation (injury to the parasympathical system), or there is a local cause (injury to the sphincter muscle or the presence of posterior synechia)

Reaction to indirect light

Consensual (Fig. 1.9.1)

1 Except, of course, if the illumination is coaxial (red reflex)

1 Except, of course, if the illumination is coaxial (red reflex)

If a radial laceration causes the dysfunction of the sphincter muscle, a single transcameral suture [10] is usually sufficient to restore anatomy and function (Fig. 2.6.1).

Fig. 2.6.1 Transcameral suture for damaged iris sphincter muscle.1 The initial step is to assure that there is no synechia; if there is, this must be broken before suture introduction (see Chap. 2.5). a The iris lesion may involve the pupillary margin or may be more peripheral. b A long, straight or curved needle is used to enter the AC through the cornea at a convenient location but outside the visual axis. The needle enters the torn iris on both sides of the lesion, and exits the cornea on the opposite side (thickarrow). Do not enter/exit the AC in the limbus; it is easier to catch the suture later during the procedure if the suture is in an area with greater AC depth. Once the suture has been pulled through, the needle is cut off. c A paracentesis is made somewhere in the middle plane between the two needle entry/exit points, over the iris lesion (arrow). As described in Chap. 2.5, the angle of the paracentesis must allow easy maneuvering as well as watertightness without suture. The paracentesis should not be far away from where the knot will be (see below). d A hook fashioned at the tip of a hypodermic needle or a vitrectomy forceps is used to engage the two sutures above the iris and pull them out from the AC through the paracentesis. e The sutures are tightened. The iris must be sufficiently loose because it will be tented as the suture is tightened. This is the reason why the paracentesis must be strategically placed, and placed after, and not before, the sutures are introduced into the iris. If the iris is rigid or the lesion is wide, intraocular suture tightening may have to be performed or the lesion is treated only partially.2 Internal tightening of the knot requires a paracentesis on both sides. The suture enters the AC via one paracentesis, picks up the iris as described above, and exits the AC through the other paracentesis. The suture is then partially withdrawn3 and tied using the loop: the knot is formed inside the AC, without tenting the iris. The needle is then pulled back through both paracenteses and the entire procedure is repeated. An alternative is not to bring the iris edges in apposition but leaving a small gap between them. f The iris is left to slide back in place; the suture remains visible, but the gap in the iris should disappear or become very small. If need be, additional sutures may be introduced in the same way. The procedure can also be performed in a phakic eye, after first carefully injecting cohesive viscoelastics under the iris

1 Viscoelastics are typically not necessary, although the surgeon should apply them if the AC gets shallow.

2 A description of these two techniques are given here, but neither is shown.

3 The needle remains outside the eye.

Transcameral needles are not easy to use (Fig. 2.6.2). The needle's path through the cornea acts as a fulcrum; the more forward the needle's position in the AC is, the smaller a movement with the needle holder is needed to cause in a large movement of the needle's tip. To make needle use easier, the surgeon should either bring the needle's entry point as close to its in-tracameral target as possible, or use another instrument (e.g., a vitrectomy forceps) to guide the needle inside the AC.

O Cave

Any suture placed into the iris must provide a permanent lock: there is no iris healing. The suture material must be nonabsorbable [10/0 or 9/0 polypropylene on a straight (STC-6) or curved (CIF-4) needle]5 and the knot must be made very secure. The suture must not exert undue tension on the iris to avoid "cheesewiring."

If the sphincter muscle is completely nonfunctional, an iris cerclage (purse string) suture should be used (Fig. 2.6.3).

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