Atropine appears to limit axial growth in short term

New York-The muscarinic inhibitor, atropine, has been shown to slow the growth of axial length in the short term in children treated once daily, according to Mitsugu Shimmyo, MD.

In a prospective trial of children aged 5 to 16 years (mean of 10 years) with -0.5 to -3.5 D of myopia and minimal cylinder (<1 D), 300 were assigned to atropine 1% once at night in both eyes and 192 received placebo. The initial axial length ranged from 22 to 26 mm and was measured using a DBR 300 A-Scan biometer with water bath, noted Dr. Shimmyo, clinical instructor, New York Medical College, New York.

"Both groups were similar in terms of age and gender, except the treated group had slightly larger initial myopia and slightly larger axial length," Dr. Shimmyo said.

Patients were treated for 2 years with follow-up at 6 months, 12 months, and 24 months. In the control group, refractive errors progressively increased over the 2-year period. In the treated group, Dr. Shimmyo noted a reduction in myopia at 6 to 12 months and then the progression of myopia at 2 years.

As far as axial length was concerned, the control group eyes had a steady progression from 6 months to 2 years. Yet in the treated group, there was little elongation at 6 months and half the growth compared with the control group at 1 year. However, at 2 years, there was no difference between the groups, Dr. Shimmyo said.

"At 6 months, one-third of the eyes treated with atropine showed shortening of the axial length up to 0.3 mm. This accounted for a 1-D reduction in myopia, especially in eyes in the younger group between 6 and 9 years of age," he continued.

One-third had no change in this time frame and one-third showed elongation, he said. Dr. Shimmyo attributes the retardation of myopic progression by atropine partly to cycloplegia-the muscarinic-2effect, and partly to retardation of axial growth-the muscarinic-1 effect.

"Treatment of high-risk children with early onset axial myopia may be possible with better agents," Dr. Shimmyo said. "We need to be open-minded about new ideas and possibilities."

In earlier studies published in the lit-erature, atropine has been considered asa possible agent for myopic progression,according to Douglas R. Fredrick, MD, who discussed the paper during the annual meeting of the American Academy of Ophthal- mology.

"The mechanism of action (of atropine) has been mechanical through its anti-accommodative effect or biochemical through its effect on drug modulation at the level of the retina, sclera, or choroid," said Dr. Fredrick, a pediatric ophthalmologist with the University of California, San Francisco Medical Center.

"We know from previous studies of atropine that the rate of myopic progression is slowed during the study with the use of atropine, typically 0.1 to 0.25 D as in the current study," he continued.

Because the study's two treatment groups differed in terms of amount of myopia, with the treated group having more myopia than the control group, the statistical effect of regression to the mean could have taken place. "This means you can expect to see less progression in the treatment group even if there is no effect with the treatment that you are providing. So in this study, one would expect less progression of myopia," Dr. Fredrick said.

In addition, compliance was not mentioned in the study and there appeared to be a high dropout rate by 2 years because of the side effects of the atropine, he said. Less than half of those enrolled in the study completed it.

Future studies should enroll similar study groups, he said.

"Atropine may tend to slow axial growth in the short term, but long-term efficacy is unknown," Dr. Fredrick said.