Best target refraction varies with age in children with congenital cataracts

Preschool-age children should be targeted for hyperopia, and school-age children should be closer to emmetropia, study suggests.

In children undergoing bilateral surgery for congenital cataract, postoperative refraction should be targeted based on the age of the child at the time of surgery, a study suggests. There was a trend toward myopic shift and axial elongation after bilateral cataract extraction and IOL implantation in young children, the study found.

Lixin Xie, MD, and Yusen Huang, MD, of the Shandong Eye Institute in Qingdao, China, assessed changes in refractive error, corneal curvature and axial length after primary IOL implantation in 49 children (32 boys and 17 girls) with bilateral congenital cataracts. The children ranged from 2 to 12 years old at the time of surgery, with a mean age of 6 years. They were followed for a mean period of 5 years, ranging from 4.5 to 5.5 years.

Lixin Xie

Drs. Xie and Huang observed a “mild trend” toward myopic shift and axial elongation in the follow-up period after performing cataract surgery with anterior vitrectomy and IOL implantation. Corneal curvature appeared stable, they said.

“How to make the best selection of IOL power for growing eyes of children with cataracts remains difficult,” Dr. Xie, the study’s corresponding author, said in an e-mail to Ocular Surgery News. “Data based on refraction, corneal curvature and axial length in children undergoing cataract surgery with IOL implantation should help to determine IOL power for pediatric patients. The homogeneity of patient data is important.”

PMMA, acrylic IOLs

The patients were assigned to one of four groups based on their age at surgery: 2 to 3 years (group A), 4 to 5 years (group B), 6 to 7 years (group C) and 8 to 12 years (group D).

Nine children had total cataracts, 25 had nuclear cataracts, seven had lamellar cataracts, five had anterior polar cataracts and three had posterior lenticonus cataracts.

Patients with persistent hyperplastic primary vitreous, retinopathy of prematurity, congenital glaucoma, microphthalmos, severe posterior capsular opacity, primary or secondary glaucoma, or strabismus of more than 10 D were excluded from the study.

Dr. Xie performed all of the surgeries, operating on both eyes within 1 week. He used a 3.5-mm or 6-mm scleral incision through clear cornea and into the anterior chamber, and performed a manual anterior continuous curvilinear capsulorrhexis. He used irrigation and aspiration or phacoemulsification to aspirate all of the lenses’ contents and filled the capsular bag with viscoelastic material. He also created a manual posterior continuous curvilinear capsulorrhexis and performed primary anterior vitrectomy.

After implanting the lens in the capsular bag, Dr. Xie removed the viscoelastic material and closed the incision with 10-0 nylon sutures.

Dr. Xie used one of two types of IOL: the 6-mm-optic PMMA EZE60 (Bausch & Lomb) or the foldable acrylic MA60BM lens (Alcon).

The immediate postop refraction was targeted for 0 D to +3 D in children 2 to 7 years old and 0 D to –1 D in children older than 8, the authors said.

Follow-up visits were scheduled at 1, 3 and 7 days, 2 weeks, and then monthly. Full spectacle correction with bifocals was prescribed for all patients 1 month after surgery. Once the eye condition was stable, follow-up was done every 6 to 12 months, depending on amblyopic status, the authors said.

Targeting postop refraction

“The authors recommended targeting the immediate postoperative refraction for mild hyperopia in preschool children and emmetropia or mild myopia in patients older than 6 years,” Dr. Xie told OSN. “This can avoid a marked myopic shift or high-level hypermetropia in the early years after the operation. Meanwhile, patients can enjoy relatively good uncorrected near vision and satisfactory distance vision when the refraction is stable.”

Complete data were available on 38 patients (76 eyes).

Each group had a “mild” myopic shift by 5 years postop, the authors reported. The mean rate and range of refractive change decreased with patient age. The differences in the rate of refractive change between groups A and C (P = .003), groups A and D (P = .001), groups B and C (P = .001), and groups B and D (P = .003) were statistically significant.

A total of 67 eyes showed increasing myopia (–0.125 D to –5 D), eight eyes showed a hyperopic shift (+0.125 D to +1.50 D), and one eye was unchanged.

Mean axial lengths were 22.67 ±1.93 mm before surgery and 23.52±1.77 mm at 5 years after surgery. Differences in the rate of axial elongation between groups A and C (P = .001) and groups B and D (P = .006) were statistically significant, the authors said.

Patients older than 2 years had only minor changes in corneal curvature (43.21±1.68 D before surgery to 43.24±1.66 D at 5 years postop). Differences in corneal curvature between any two groups were not statistically significant before surgery and at final follow-up, the data showed.

At last follow-up, with data on 84 eyes (42 patients), 53 eyes had best corrected visual acuity better than 20/40, seven eyes had BCVA of 20/50 to 20/70, 22 eyes had BCVA of 20/80 to 20/200 and two eyes had BCVA of 20/400 or worse.

There was no statistically significant relationship between BCVA and refractive change or between BCVA and axial elongation, the authors noted.

Changes with age

Corneal curvature decreases dramatically in the first year of life and changes little after that, the authors said. Axial growth is rapid in the first 2 to 3 years and then slows until the end of the first decade. Lens growth occurs throughout childhood.

Drs. Xie and Huang noted that, if IOL power is selected to be appropriate for the child at the time of surgery, a myopic shift may occur in later years. However, using powers appropriate for adults in these patients would produce high hyperopia in the early years of life. Partial undercorrection tends to minimize the degree of anisometropia immediately after surgery and later in life.

The authors recommended aiming for a refraction of 1 D to 2 D of myopia when refraction stabilizes, so that patients experience good uncorrected near vision and acceptable distance vision.

Spectacle correction is required at certain points to maximize VA and reduce anisometropia and amblyopia, the authors said.

“Because all the patients in this study were older than 2 years and most of the refractive change in human eyes occurs during the first 18 months of life, this series does not show a full picture of the changes in refraction and axial length in pediatric pseudophakia,” the authors concluded. “More patients, with wider age ranges and longer follow-up, should be studied.”

The study is slated to be published in Ophthalmology in 2007. It is available online now at www.ophsource.com.

For more information:

• Lixin Xie, MD, can be reached at Shandong Eye Institute, 5 Yanerdao Road, Qingdao 266071, China; e-mail: lixinxie@public.qd.sd.cn.

Reference:

• Xie L, Huang Y. Long-term follow-up of eye growth after bilateral intraocular lens implantation in children with congenital cataracts. Ophthalmology. Accessed online before print publication at www.ophsource.com, Nov. 2006.

• Matt Hasson is an OSN Staff Writer who covers all aspects of ophthalmology, and focuses on regulatory, legislative and practice management topics.