Acrylic IOLs may not prevent PCO in pediatric eyes

Even with biocompatible materials, the child’s biology may be the determining factor of PCO.

---Kenneth P. Cheng, MD

SAN DIEGO — Acrylic lenses may not be as effective in preventing posterior capsule opacification (PCO) in pediatric eyes as they are in adult populations.

While some surgeons have reported a reduction of PCO using acrylic lenses, this may not be true for the pediatric patient due to the biology of the pediatric eye.

According to Kenneth P. Cheng, MD, PCO in children is a product of lens epithelial cell migration, proliferation and deposition of extracellular matrix material. This process is influenced by the number of residual cells “left behind” at the time of cataract surgery, the biologic activity of the cells, and by mechanical factors related to the surface properties and mechanical features of the IOL. He and other surgeons addressed the issue at the American Association for Pediatric Ophthalmology and Strabismus meeting in April.

Strongest factor

According to Maria Gabriela Salvador, MD, and Kenneth W. Wright, MD, “PCO remains to be the most common late complication after pediatric cataract surgery. The majority of the pediatric literature reports an incidence close to 100%.”

She and senior author Dr. Cheng conducted a retrospective study to compare the incidence of PCO between PMMA and acrylic IOLs.

Inclusion criteria were patients aged 19 years old or younger with an intact posterior capsule postoperatively, non-inflammatory etiology, minimum 6 months follow-up, or previous YAG or surgical capsulotomy.

She enrolled 20 patients with 25 eyes. PMMA IOLs were implanted in 16 cases and acrylic IOLs were implanted in nine cases. The surgical technique used bimanual vitrectomy instrumentation. Two incisions were made at the limbus, one for the infusion and one for the vitrectomy probe. An anterior capsulectomy was performed using a high cut rate and low suction. The lens nucleus and cortical fibers were aspirated, leaving the posterior capsule intact. Then, the IOL was placed in the bag.

The mean age of surgery for the PMMA group was 5 years 8 months, and for the acrylic group was 8 years 5 months.

The mean follow-up was 11 months for PMMA with a maximum of 5 years, and 7.33 months for acrylic with a maximum of 2 years. PCO occurred in 11 eyes (68.7%) in the PMMA group and six eyes (66.6%) for the acrylic group.

Of the 11 eyes with PMMA, four developed PCO before 7 months and seven eyes developed PCO after 7 months. In the acrylic group, three eyes developed PCO before 7 months and three eyes developed PCO after 7 months.

PCO is age related, and the scientific literature has reported lower PCO rates when acrylic foldable IOLs were used compared with PMMA. However, Dr. Salvador said her study suggests that PCO occurs at the high rate despite the new materials.

“We believe that even with biocompatible materials, children’s biology remains to be the strongest factor for producing PCO,” she said. “The mitogenic potential of cells is age related, with children’s tissues being much more reactive.”

YAG ineffective in young children

Another study conducted by David R. Stager Jr., MD, showed that acrylic lenses may not be effective in preventing PCO in children under 4 years old. He did find that there was a significantly lower incidence of PCO in children over 4 years old when compared to PMMA lenses.

PCO is a well known problem in pediatric cataract surgery, so some surgeons advocate a primary capsulectomy and anterior vitrectomy. These methods are technically difficult and incur complications.

The acrylic lens’ usefulness in preventing PCO is based on three theories, he said.

First, the square edge of the acrylic lens’ optic can act as a barrier in preventing lens epithelial cellular migration. Second, the greater biocompatibility of the material may lead to less inflammation. Third, the capsular adherence of the optic to the bag may prevent the lens epithelial cellular migration.

“However, this data is largely confined to the adult population,” he said. “We therefore asked ourselves if this were true in children, and if this effect was durable and long lasting, would this obviate the need for primary capsulectomy and anterior vitrectomy?”

To answer the question, Dr. Stager prospectively examined 26 consecutive eyes in 18 children. He implanted the acrylic lenses through a small incision in all of these patients, leaving intact the posterior capsule.

The parameters studied included the age at surgery, retinal and vitreous complications, the incidence of PCO, and recurrence of opacification of the visual axis. YAG laser posterior capsulotomy was applied to all but one capsule that developed opacification.

Age at surgery ranged from 21 months to 14 years. The average was 8.3 years. Minimum follow-up was 2 years. However, most patients were followed substantially longer with a mean of 2 years 9 months.

To study the outcomes, Dr. Stager grouped the eyes in patients less than 4 years old (five eyes) and more than 4 years old (21 eyes).

Of the eyes less than 4 years old, all developed PCO at a mean of 8 months follow-up. All of those underwent YAG laser capsulotomy. Two of those eyes have maintained a clear visual axis with a mean of 32 months of follow-up. However, three eyes developed recurrent opacification. Two of those are clear at a minimum of 11 months with a pars plana procedure. One of those is clear after 28 months following repeated lasering.

Of the eyes more than 4 years old, eight developed PCO at a mean of 14 months follow-up. Of those eight, one traumatic cataract underwent a pars plana procedure and has remained clear for 15 months. Seven eyes underwent YAG laser, with six remaining clear at a mean of 13 months. One eye with traumatic cataract required repeated laserings and has remained clear for 4 months.

“None of these cataracts were congenital in origin,” Dr. Stager said. “There were no microphthalmic eyes. These were basically acquired cataracts. Eighteen were developmental, five traumatic, two systemic steroid related and one due to radiation.”

The protective effect of the acrylic lens is limited in children less than 4 years old, Dr. Stager concluded. YAG laser may be ineffective in providing lasting clarity in this age group, with a 60% recurrence in young children. The protective effect of the acrylic lens also may be limited in patients with traumatic cataracts.

More investigation is needed to define the best surgical approach to young children with cataracts, he said.

Care needed

Dr. Cheng added that the number of residual cells left behind at the time of surgery is important to the development of PCO. “When we’re performing cataract surgery in children, we need to be especially meticulous and careful to perform our procedures as cleanly as possible,” he said.

The AcrySof lens (Alcon; Fort Worth, U.S.A.) has surface properties and a truncated edge design that provide a mechanical barrier to the migration of lens epithelial cells in adult patients.

“Whether these factors are completely effective in children remains to be seen, and certainly the greater incidences reported suggest that they are not,” he said.

However, one aspect of the AcrySof design may help prevent PCO, Dr. Cheng added. Implanting the entire optic of the IOL within the capsular bag while using a slightly smaller anterior capsule opening seems to retard lens epithelial cell migration, and the AcrySof lens is easier to place entirely within the capsular bag.

Dr. Cheng added that what is of particular clinical significance is that YAG procedures are more difficult in young children and the timing involved is important. “We must consider the onset of PCO and the time that we have between the conclusion of cataract surgery and the development of visually significant opacification. This interval will help us determine if the young child will have enough time to mature and be cooperative enough to sit at a YAG laser for capsulotomy without further general anesthetic sessions or whether a primary capsulotomy and anterior vitrectomy should be performed at the time of cataract surgery.”

For Your Information:

Kenneth P. Cheng, MD, can be reached at Stonewood East, Ste. 310, 1000 Stonewood Drive, Wexford, PA 15090 U.S.A.; +(1) 724-934-3333; fax: +(1) 724-934-3371. Dr. Cheng has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Maria Gabriela Salvador, MD, can be reached at the University of California at Irvine, 118 Med Surg 1, Irvine, CA 92697-4375 U.S.A.; +(1) 949-824-3760; fax: +(1) 949-824-4015. Dr. Salvador declined to disclose whether or not she has a direct financial interest in any of the products mentioned in this article or if she is a paid consultant for any companies mentioned.

David R. Stager Jr., MD, can be reached at Ste. 140A, LB 23, 8201 Preston Road, Dallas, TX 75225 U.S.A.; +(1) 214-369-6434; fax: +(1) 214-696-6273. Dr. Stager has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.