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Chapter 17: Complications in strabismus surgery :
Anterior segment ischemia
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Reduced blood supply to the anterior segment, anterior segment ischemia, occurs in most cases of strabismus surgery if looked for carefully, especially after vertical rectus muscle surgery or surgery on adjacent muscles. Olver and Lee grade anterior segment ischemia as follows: I decreased iris perfusion, II + pupil signs, III + uveitis, and IV + keratopathy. Most patients recover iris circulation to the preoperative level two weeks after surgery, although a few take up to 12 weeks. Re-perfusion takes place through deep collateral circulation and never by recanalization of the anterior ciliary vessels from the detached muscle. Although minor pupil changes may persist, the first three grades of anterior segment ischemia are not important clinically. Grade IV anterior segment ischemia is characterized by corneal edema, often with deep folds, heavy flare, and cells sometimes with hypopyon, pupillary irregularity, and sometimes cataract. All of this occurs with hypotony. Grade IV anterior segment ischemia can cause permanent damage to the eye with reduction of vision from cataract, corneal scarring, and retinal (macular) changes.
Prevention
The surgeon should avoid detaching four rectus muscles even if the procedures are performed many years apart. Instead, when possible, at least one rectus muscle should be left attached with its competent anterior ciliary circulation. I have performed a strengthening procedure when necessary on the fourth rectus muscle with tuck, preserving the anterior ciliary arteries. In other cases, which were considered ‘desperate,’ I have detached the remaining rectus muscle more than 10 years after the initial eye muscle surgery without adverse results. However, no matter how long the time interval, serious anterior segment ischemia can occur if all anterior ciliary arteries are severed. Rectus muscle recession with sparing of the anterior ciliary arteries can be performed to preserve anterior segment circulation, thereby allowing surgery on a rectus muscle while retaining the integrity of the anterior ciliary vessels. When performing a muscle splitting muscle transfer procedure care should be taken to ensure that both of the anterior ciliary vessels are not inadvertently included in the transferred slip of muscle. As a practical guide the following applies to anterior segment ischemia:
(1) vertical recti have more anterior ciliary vessels, but are not backed up by posterior ciliary arteries; (2) older or vascular compromised patients are more susceptible; (3) mild anterior segment ischemia is common and is clinically insignificant; (4) it is possible to ‘get away’ with detachment of four rectus muscles, but the time interval between surgeries does not necessarily make this a safe procedure; (5) it is not practical or perhaps possible to predict accurately which patients will have clinically significant anterior segment ischemia; and (6) if surgery is limited to two rectus muscles per procedure per eye and if no more than three rectus muscles per eye are detached in a lifetime, the chance of a patient developing clinically significant anterior segment ischemia is remote.
Exceptions do occur. I did full tendon transfer on two patients on the same day leaving the lateral rectus attached but severing the other six ciliary arteries. Both patients had sixth nerve palsy, were in their 40’s and were otherwise healthy. Both developed grade IV anterior segment ischemia. After treatment, each had residual iris atrophy and mild cataract with loss of two lines of vision (Figure 12).
Treatment
Topical and systemic steroids with dilation of the pupil is the treatment of choice for anterior segment ischemia. The topical steroid can be given as 1% prednisolone up to three or four times a day combined with prednisone orally every other day, 50 to 100 mg, with careful monitoring of the response and tapering of the drug as soon as possible. The pupil may be dilated with daily installation of homatropine 5%.
Figure 12
A Right sixth nerve palsy, preoperatively
B Corneal edema
C Eyes aligned with anterior segment ischemia, right eye
D Good alignment postoperatively with dilated pupil, segmental iris atrophy, and slight cataract; visual acuity reduced to 20/40
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