OCT Illuminates Vision Loss After Glaucoma Surgery

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With the help of optical coherence tomography (OCT), doctors at the Stein Eye Institute in Los Ange­les gained new insight into an infrequent postsurgical complication of glaucoma filtering surgery known as “snuff-out phenomenon.” The clinicians reported two patients who experienced significant, unexplained, and permanent vision loss following placement of a drain­age device; in both cases, OCT showed progressive macular thinning after the procedure.¹

It took OCT to demonstrate what had only previously been hypothesized. “This explains one of the mecha­nisms of vision loss after glaucoma surgery”—that is, ongoing loss of the retinal ganglion cells (RGCs), said Kouros Nouri-Mahdavi, MD, MS, at the Stein Eye Insti­tute. He added that the “fairly rapid RGC loss suggests the possible presence of sick cells that continue to die despite glaucoma surgery.”

Patient profiles. An 89-year-old woman with primary open-angle glaucoma underwent trabeculectomy in her right eye to lower her intraocular pressure (IOP), which was 20 mm Hg on maximal treatment prior to surgery. Pressure remained inadequate after surgery despite escalation of therapy. The patient’s best-corrected visual acuity (BCVA) was 20/50 before surgery. It then fluctuated, in the 20/70 to 20/150 range, and it never recovered to preoperative levels.

At 12 months, the patient received a 250-mm² Baer­veldt Glaucoma Implant (Johnson & Johnson). Macular OCT images taken after device implantation still showed significant thinning of the full retinal thickness, espe­cially in the superior macula.

The second patient, an 85-year-old man, had ad­vanced pseudoexfoliation glaucoma in his right eye. He had previously undergone uncomplicated trabe­culectomy and was referred for surgery because of his uncontrolled IOP. Before surgery, his IOP ranged from 28 mm Hg to 32 mm Hg on maximal treatment, and his BCVA was 20/20. He received an Ahmed Glaucoma Valve (New World Medical). One week later, his VA was hand motions, and his IOP was 5 mm Hg.

At nine months, the patient’s BCVA was 20/400. Macular OCT imaging revealed progressive macular thinning deemed to be consistent with progressive and complete central visual field loss.

Can this scenario be avoided? The findings suggest that eyes at high risk of visual loss after surgery are mainly those with advanced glaucoma or extension of the damage to the central field preoperatively, Dr. Nouri-Mahdavi said. But, he added, we need much more data before making clinical recommendations. “One could imagine, though, that a very thin macula observed preoperatively could predict possible wors­ening of vision after surgery.” For now, he said, doctors might consider preoperative imaging of the macula in eyes at high risk of visual loss after surgery, followed by continued postoperative monitoring.

—Miriam Karmel

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1 Mohammadzadeh V et al. J Glaucoma. Published online Jan. 28, 2019.

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Relevant financial disclosures—Dr. Nouri-Mahdavi: Heidelberg Engineering: L,S.

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