Continued monitoring after amblyopia treatment advised

Prompt detection, immediate re-treatment and good patient adherence may decrease risk for deteriorating visual acuity.

A prolonged risk for deterioration of visual acuity persists for at least 2 years after termination of amblyopia treatment, a study suggested.

“We recommend a follow-up time of 2 years after cessation of treatment for all treated patients with amblyopia,” Christine De Weger, MSc, first author of the study, said in an e-mail interview with Ocular Surgery News.

There are exceptions, however. According to Dr. De Weger, sometimes patients should be monitored for longer than 24 months, such as when they have not used optical correction despite having high ametropia or when another risk factor such as increasing anisometropia has developed since ending treatment for amblyopia.

The study, published in the Journal of Pediatric Ophthalmology & Strabismus, sought to establish a time interval for monitoring visual acuity as well as risk factors associated with amblyopia recurrence.

“It is possible to prevent amblyopia recurrence if loss of visual acuity is detected in time and re-treatment is started immediately and performed with good compliance,” Dr. De Weger said.

Methods, contradictions in literature

The study included 282 patients aged 7 years to 13 years who underwent treatment for anisometropic amblyopia (42%), strabismic amblyopia (48%), or a combined form of amblyopia, strabismus and anisometropia (10%). After cessation of treatment, follow-up exams occurred for a median interval of 3.9 years.

Deterioration of visual acuity was denoted by a decrease of one or more Snellen lines. For statistical analysis, Snellen visual acuity was then converted to logMAR values. A loss in visual acuity of 2 logMAR or more signified amblyopia recurrence. Re-treatment generally occurred after a loss of one Snellen line was established by repeated measurement during the same session.

According to the study, contradictions exist in the literature regarding risk factors and recurrence rates of amblyopia, which range from 13% to 75%.

Dr. De Weger said that the inconsistent findings may be caused by several factors, including varying ages of patients at cessation of treatment, varying numbers of patients, varying adherence rates, uncertainty as to whether maintenance treatment was applied, inconsistency in monitoring patients after treatment, varying follow-up times, differing study designs and selection bias.

Results, risks for recurrence

Recurrence of amblyopia occurred in six patients (2.1%), and adherence during both primary treatment and re-treatment was found to be poor in this group. All six did not use spectacles despite high hypermetropia in combination with astigmatism.

A drop in Snellen visual acuity of at least one line occurred in 77 patients (27.3%). Of these, 38 (49%) eventually lost two Snellen lines as a result of poor adherence to re-treatment, and 39 (51%) were able to reverse deterioration to a loss of zero Snellen lines through moderate to good adherence.

All patients with deterioration experienced visual loss within the first 2 years after cessation of amblyopia treatment. They were re-treated for a median of 7 months and were evaluated afterward over a median period of 3.3 years.

Nineteen patients discontinued follow-up evaluations after their first deterioration, which the study authors believe may have decreased the reported risk of amblyopia recurrence from 8.9% to 2.1%. Dr. De Weger and colleagues also suggested that the study’s low reported risk of recurrence may have resulted from its design; immediately after documentation of visual deterioration, patients received re-treatment.

The study authors discovered a positive correlation between the duration of treatment and the long-term stability of visual acuity, a finding that was not prevalent in the literature.

“In our study, the duration of amblyopia treatment was not determined by the gain of visual acuity but by the age of the patient. … So, the duration of treatment in our study may be much longer than that of studies in which cessation of treatment was determined by the attained visual acuity,” Dr. De Weger said.

Multivariate analysis corrected for duration of treatment, enabling the study authors to determine the factors that were independently associated with the risk of amblyopia recurrence: visual acuity of the amblyopic eye at initial treatment, esotropia of 4° or less at initial treatment, the tendency for deterioration upon weaning off occlusion treatment, and increased anisometropia due to emmetropization of the dominant eye during follow-up.

Patient adherence

The study found that timely re-treatment and good patient adherence can restore visual acuity. Dr. De Weger is currently planning a prospective study centered on patients who were encouraged to continue using the treated amblyopia eye and, in cases of ametropia, to use the treated eye along with optical correction.

“Using the treated amblyopic eye is preventing that eye from permanent suppression and regressing to deep central suppression. … The longer suppression exists, the deeper the suppression and the worse the amblyopia may become,” Dr. De Weger said.

A key limitation to this study was the subjectivity of measuring patient adherence. The use of patching and spectacles was reported by parents and then interpreted and graded by an orthoptist.

“I encourage my patients at termination of follow-up visits after amblyopia treatment to continue looking with the treated amblyopic eye by covering the fellow eye once in a while. This means activating the renewed visual pathways,” Dr. De Weger said, stressing the importance of adherence. – by Michelle Pagnani

Reference:

• De Weger C, Van Den Brom HJ, Lindeboom R. Termination of amblyopia treatment: when to stop follow-up visits and risk factors for recurrence. J Pediatr Ophthalmol Strabismus. 2010;47(6):338-346.

• Christine De Weger, MSc, can be reached at Wilhemina Ziekenhuis Assen, Poli-oogheelkunde, Postbus 30001, 9400 RA Assen, Netherlands; e-mail: c.deweger@home.nl.
• Disclosure: No products or companies are mentioned that would require financial disclosure.

This study encourages a longer follow-up period after cessation of amblyopia treatment by demonstrating that a real risk exists for patients who discontinue patching. The results are consistent with the anecdotal experience of many pediatric ophthalmologists, but it is beneficial to have such outcomes formally documented. Overall, it suggests that we maintain refractive correction in order to neutralize the underlying cause of amblyopia and maintain follow-up monitoring in case of vision loss. In clinical practice, one must prescribe patching for as long as necessary but not any longer, because the mother of the child typically serves as cheerleader, enforcer and encourager. This study provides the scientific basis for not terminating a patching routine too early, because it reminds both the doctor and family of the real possibility for visual regression. Knowing there is at least a one-in-four chance of vision loss tends to motivate.

– Anthony P. Johnson, MD
OSN Pediatrics/Strabismus Board Member