February 2010

 

OPHTHALMOLOGY NEWS

 

Light-induced maculopathy


by Matt Young EyeWorld Contributing Editor

   
Microscope light-induced retinal phototoxic maculopathy may not be as common as macular degeneration, pictured here, but surgeons still should minimize patient’s light exposure during surgery

Source: Eyeland Design Network

Combined pars plana vitrectomy and transscleral sutured posterior chamber IOL (TSS PC-IOL) implantation should be completed quickly; otherwise, patients could suffer from operating microscope light-induced retinal phototoxic maculopathy. “Operating microscope light-induced retinal phototoxic maculopathy can occur more frequently after TSS PC-IOL implantation than after casual cataract surgery, especially when TSS PC-IOL is combined with vitrectomy surgery,” according to a report by Nam Chun Cho, M.D., department of ophthalmology, Chonbuk National University Medical School, Jeonju, South Korea, and colleagues. The study was published online in July 2009 in the journal Retina. “We recommend that combined pars plana vitrectomy and TSS PC- IOL implantation be completed as quickly as possible and that as many precautions as possible be taken to prevent operating microscope light-induced retinal phototoxic maculopathy,” Dr. Cho noted.

A tale of toxicity

Dr. Cho analyzed 118 patients who underwent TSS PC-IOL implantation. Fourteen such patients also had combined three-port pars plana vitrectomy and TSS PC-IOL insertion. The rest did not have the combined procedure but were implanted with the TSS PC-IOL alone. Overall, 10 patients (8.47%) experienced phototoxic maculopathy, as determined by ophthalmoscopic and fluorescein angiography findings. Characteristics of the disorder include mild yellow-white retinal discoloration, depigmentation of retinal pigment epithelium, and retinal edema. The occurrence was much more frequent in the combined group (42.86%) than in the nonvitrectomy group (3.39%). “The association between combined surgery and phototoxicity might be caused by longer operation time, precise focus of the operating microscopic light causing minimal distortion, and endoillumination-induced photic injury during vitrectomy,” Dr. Cho reported.

Phototoxic injury: less frequent but still serious

The phototoxicity reports after cataract surgery have been declining. That said, “this entity is still usually seen after complicated surgery,” Dr. Cho reported. In this study, beyond the frequent surfacing of phototoxicity after combined surgery, Dr. Cho also reported that the condition led to extreme lesions and severely diminished vision. “The lesions are enormous in size,” Dr. Cho reported. “Five of the phototoxic maculopathy patients (50%) had best-corrected visual acuity (BCVA) of 20/200 or worse at last follow-up.”

Recovery from such phototoxicity has been reported. “Such recovery may continue for as long as two years,” Dr. Cho noted.

Prevention over treatment

Prevention, of course, is preferred to treatment. In that regard, here are a few points Dr. Cho recommended to keep in mind while performing these combined procedures: • Total energy applied to the retina should be as minimal as possible. Use a lower light intensity for the shortest term possible.

• Don’t prolong surgery if you don’t have to.

• Employ a filter to prevent excessive light from reaching the pupil.

• Don’t focus light on a fixed retinal area (instead, use eye rotation, change the patient’s head position, or tilt the microscope).

• Fill the anterior chamber with air bubbles (to defocus the light).

• Place shields over the central cornea.

Combined procedure patients may still have to risk phototoxicity to achieve the benefits of surgery. “The fiberoptic endoillumination tip has virtually no radiation barrier compared with the microscope light, and it is very near the retina during vitrectomy,” Dr. Cho reported. “A significant proportion of the shorter wavelengths are reflected or absorbed by anterior ocular structures. Thus, macular photochemical damage may be inevitable during vitrectomy, even when precautions are taken.”

John D. Sheppard, M.D., professor of ophthalmology, microbiology, and immunology, Eastern Virginia Medical School, Norfolk, Va., said that unfortunately, it’s often hard to know if phototoxicity has occurred. “The sad thing is we don’t know,” Dr. Sheppard said. “Unless you obtain detailed pre- and post-op measurements, it’s hard to determine what the damage to the photoreceptors of the macula actually is.” Even if analysis is undertaken, opacities could prevent procurement of precise data on the macular receptors, Dr. Sheppard said. “Many times we have to rely on animal models to quantify the cumulative lumen dose it takes for damage to occur.” Nonetheless, Dr. Sheppard said, all surgeons have encountered patients with less than optimal visual acuity following surgery—something that could be due to phototoxicity. Surgery is getting faster, though, and that helps to keep such problems at bay. “We’re able to perform cataract surgery fairly quickly,” Dr. Sheppard said. “Retina doctors can perform vitrectomy under 45 minutes as well.”

That said, it’s important to keep light intensity at the lowest levels possible, Dr. Sheppard said. “Clearly, the longer the case, the greater the risk of light exposure.” In cataract surgery, more light is required for the capsulorhexis and to insert the IOL, he said. A hypermature cataract also requires more light to perform the capsulorhexis. “Then again, with darker, more light-absorbing lenses, there’s less risk of phototoxicity to the retina anyway,” Dr. Sheppard said.

Editors’ note: Dr. Cho has no financial interests related to this study. Dr. Sheppard has no financial interests related to his comments.

Contact information

Cho: cnauo@chonbuk.ac.kr
Sheppard: 757-622-2200, docshep@hotmail.com

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