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Consultation section

refractive surgical problem

Esquenazi, Salomon MD

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Journal of Cataract & Refractive Surgery: March 2004 - Volume 30 - Issue 3 - p 536-538
doi: 10.1016/j.jcrs.2004.02.006
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▪ In this challenging case, induced astigmatism after trabeculectomy is present. This complication occurred in the early postoperative period with an overall mean with-the-rule (WTR) change up to 3 months postoperatively. This was followed by an against-the-rule (ATR) shift, which has been demonstrated to be continuous in some cases.

Some authors suggest that the astigmatism is influenced by the rate of filtration during the short postoperative time and by the extraction of the releasable sutures. Others suggest the use of small-flap trabeculectomy (microtrabeculectomy), which produces fewer changes in corneal curvature that resolve sooner that those induced by large-flap techniques.

The astigmatism induced by filtration surgery with MMC is long lasting. This may be related to impaired healing of the trabeculectomy wound and lower IOP that is common in this group of patients.

This patient has a high astigmatic defect induced by the second trabeculectomy performed in the superotemporal quadrant with steepening of this axis and flattening of the axis 90 degrees apart. It is likely the patient initially had regional changes in corneal curvature that were not readily detected from alterations in refraction or keratometry until 1 year later, when they were sufficiently great to have a significant effect on visual function.

I would first try a trial of RGP toric contact lens wear; the lens would be 46.00/51.00 D with a diameter of approximately 8.5 mm. If the patient is intolerant of the new contact lens, surgical options can be considered.

The first surgical option is revision of the second superotemporal trabeculectomy, which shows an impaired healing process with severe scarring that is producing steepening at 65 degrees. The sclera should be examined; if an altered healing process is evident, the patient will need a scleral graft to increase the arc length in the superotemporal meridian with topography-guided suture of the scleral flap. The sclera of the patient has an altered healing process in which the use of MMC could have played an important role, as evidenced by the continuous steepening between the 2 topographies done 5 months apart. The use of a scleral graft will produce better and more stable results.

The second option is an excimer laser procedure using a bitoric ablation to partially correct the corneal astigmatic defect. I would initially recommend photorefractive keratectomy (PRK) rather than laser in situ keratomileusis (LASIK) because the thinnest corneal pachymetry is 466 μm. If a 160 μm flap is created, the surgeon has only 56 μm to work with to leave a safe bed of 250 μm, which is insufficient to safely correct this high astigmatism. In addition, using the suction ring in LASIK can damage the filtering bleb. Part of the residual defect can be further corrected with glasses to help the patient achieve better visual acuity than that currently. The patient should be advised that the healing process in the trabeculectomy site is evolving and that further regression of the refractive results after PRK should be expected.

The last option is penetrating keratoplasty (PKP), which may correct most of the astigmatic defect without compromising the second functional trabeculectomy. If residual myopia or astigmatism is present 18 to 24 months after PKP, it can be corrected by PRK or LASIK.

I would not perform incisional corneal surgery in this glaucomatous patient because incisions in patients with ocular hypertension and glaucoma tend to be unpredictable, with frequent gapping and epithelialization of the incisions.

© 2004 by Lippincott Williams & Wilkins, Inc.