By L. E. Leguire Ph.D., MBA
Article: Factors Associated with Recurrence of Amblyopia on Cessation of Patching
Holmes et al, Ophthalmology, 2007; 114: p1427 – 1432
As part of the PEDIG (Pediatric Eye Disease Investigator Group) study group, Holmes and colleagues undertook a study of 69 amblyopic children under the age of 8 years who had previously been “successfully” treated for amblyopia with glasses and patching of the good eye. Some of the children may also have had eye muscle surgery to correct the strabismus (eye misalignment). The children in the study had amblyopia due to an eye misalignment (strabismus) or due to a difference in refractive error between the eyes (anisometropia). The investigators were interested in how patching was stopped; suddenly or gradually, and the effect on later visual acuity. For example, the suddenly stopped patching group of children had their patching stopped suddenly after wearing the patch for 6 – 8 hours per day. The gradually stopped group of children had their patching first reduced from 6 – 8 hours per day to 2 hours per day followed by the termination of all patching. There was also a group of children who were patched just for 2 hours per day and than also completely stopped.
The children in each group were followed for one year after the termination of patching to see how much visual acuity, if any, the children lost after patching was stopped. Those children who lost two or more lines on the visual acuity chart were considered to have lost a significant amount of vision (visual acuity); that is, they “regressed” or had a recurrence of amblyopia.
The authors found that those children who had the best visual acuity after the termination of patching had the greatest chance of losing visual acuity. This was a very surprising finding. On the other hand, those children who had the worse visual acuity after stopping patching had the least amount of regression of visual acuity. Also, the authors found that those children who had excellent depth perception (stereopsis) and had excellent eye alignment (i.e., no or minimal strabismus) were just as likely to lose visual acuity after the termination of patching as those children who had eye misalignments or poor depth perception – another unexpected finding. The authors also found that those children with a history of regression of visual acuity also had an increased chance of regression following the termination of patching – no surprise here.
Another surprising finding of the study was that the risk of regression (i.e., loss of visual acuity) was the same regardless of the age of the child at the time patching was stopped. Children about 7 years of age were just as likely to regress in visual acuity as children three years of age. Traditionally, doctors believed that the older the child at the time patching is stopped the less likely the child would regress in visual acuity.
Based on the study findings, the investigators suggested that regardless of how well a child does in terms of amblyopia therapy and regardless of the child’s visual acuity at the end of patching therapy, there is a need for “careful and prolonged follow-up” of children who are treated for amblyopia.
This article has generated a lot of discussion in the eye doctor community, primarily because of all the unexpected findings. Indeed, the authors of the study go to great lengths, in the Discussion section of the article, to point-out that their results are contrary to previous study results, unexpected and counterintuitive. In the Discussion section of the article, the authors point-out numerous possibilities as to what might have gone wrong with the study and what might have lead to the unexpected study results.
What should we take away for the study? Perhaps that there needs to be more study on this topic before the current results are taken seriously. There are so many questions raised by the study that one has to ask if the study is valid or even worth publishing in the first place. However, the PEDIG investigators are some of the best of the best in clinical research. In addition, it is difficult to question the statistics behind the results of the study as these are straight forward and transparent.
A host of issues can be raised regarding the subjects in the study, a very heterogeneous group with different histories of treatment and experience. Further, a major drawback in many PEDIG studies is the lack of documentation regarding compliance of patching therapy. The PEDIG investigators rely on the parents undertaking the prescribed hours of patching therapy without actually objectively documenting that the hours of patching reported by the parents is really the number of hours that the child was patched. For example, in one study by this reviewer (Dr. Leguire), we found that parents typically patch for two hours less than prescribed by their child’s eye doctor. If children are not patched the hours that the investigators think that the child is patched, this would complicate interpretation of the study findings. In addition, children are notorious at not wearing their patch as prescribed. For example, one celebrated case documented in the Eye Clinic at Columbus Children’s hospital: An amblyopic child was being patch full time (about 8 hours per day); yet, after several months the child was not responding to therapy. An investigation revealed the cause of the lack of improvement – once the child was on the school bus he removed his patch from the good eye and placed it on the amblyopic eye so he could see. The teacher reported that the child was compliant in wearing his patch all day long. On the return bus trip the child would remove the patch from his amblyopic eye and place it back on the good eye. At home, the mother saw that the child was also compliant in wearing the patch all day long.
One thing is certain; children with amblyopia must be followed closely by their eye doctor and not only during treatment but also after successful treatment to ensure that if the amblyopia does return that it can be dealt with in a timely manner.