Time Course and Predictors of Amblyopia Improvement with 2 Hours of Daily Patching

Introduction

For children with amblyopia secondary to strabismus and/or anisometropia, many clinicians initiate treatment with spectacles alone, if needed.^{2, 3} When amblyopic-eye improvement stops after a period with spectacles wear only, prescribing 2 hours of daily patching is often the next step.^{3, 4} Our purpose was to evaluate the amount and time course of amblyopia improvement with 2 hours of prescribed daily patching in children age 3 to <8 years, and to determine predictors of visual acuity (VA) improvement and amblyopia resolution.

Methods

Analyses were limited to children 3 to <8 years of age with strabismic and/or anisometropic amblyopia and no prior amblyopia treatment except spectacles (if needed) who participated in the run-in phase of a clinical trial (protocol at www.pedig.net).¹ Prior to enrollment, children requiring spectacles wore them for ≥ 16 weeks or until there was no improvement in amblyopic-eye VA between 2 consecutive visits. At enrollment, 2 hours of daily patching was prescribed for ≥ 12 weeks until there was no improvement in amblyopic-eye VA between 2 consecutive visits ≥ 6 weeks apart, confirmed by a retest. We analyzed VA outcomes for 196 children who had minimum follow-up of 11 weeks (135 with moderate amblyopia 20/50 to 20/80 and 61 with severe amblyopia 20/100 to 20/400). We evaluated the relationship between improvement at best VA during run-in phase follow-up and baseline factors of age, amblyopic-eye VA, and amblyopia cause (strabismus, anisometropia, or both) by fitting an analysis of covariance model. We used logistic regression to evaluate the relationship between these baseline factors and achieving amblyopia resolution (amblyopic-eye VA of 20/25 or better and ≤ 1 line interocular difference).

Results

The median duration of prescribed patching until there was no improvement in amblyopic-eye acuity was 20.2 weeks (20.0 weeks and 22.1 weeks in moderate and severe amblyopia groups, respectively), ranging from 11.0 to 50.3 weeks. Children with moderate amblyopia improved an average of 2.9 logMAR lines (95% confidence interval (CI) = 2.7, 3.2), and those with severe amblyopia improved an average of 4.9 lines (95% CI = 4.4, 5.4) (Table 1). Amblyopic-eye VA improved to 20/25 or better and was within one line of the fellow eye for 33% (95% CI = 25%, 42%) with moderate amblyopia and 11% (95% CI = 5%, 22%) with severe amblyopia. Nearly half of children with either moderate (47%) or severe (48%) amblyopia achieved their best run-in phase amblyopic-eye VA 12 weeks (8 to <14 weeks) after initiating patching. Greater amblyopic-eye acuity improvement was associated with worse baseline VA (p<0.001) and younger age (p=0.03) at enrollment, but not with amblyopia cause (p=0.47) (Table 1). Better amblyopic-eye VA at enrollment was the only predictor of achieving amblyopia resolution (Table 2).

Table 1.

Visual acuity improvement (lines) according to enrollment factors for the overall cohort and by amblyopia severity

	Amblyopia severity at enrollment						Overall (N=196)
	20/50-20/80 (N=135)			20/100-20/400 (N=61)						P-value* (Overall)
	N	Mean	Std	N	Mean	Std	N	Mean	Std
Overall	135	2.9	1.5	61	4.9	2.0	196	3.5	1.9
Age at Enrollment (Years)
3 to <4	13	3.2	1.3	10	6.2	2.6	23	4.5	2.5
4 to <5	44	3.2	1.7	13	5.2	2.2	57	3.6	2.0
5 to <6	37	2.9	1.6	23	4.1	1.4	60	3.4	1.6	0.03
6 to <7	21	2.5	1.1	8	4.3	1.3	29	3.0	1.4
7 to <8	20	2.8	1.2	7	6.0	1.6	27	3.6	1.9
Amblyopia Cause
Strabismus	33	3.3	1.5	13	4.7	2.4	46	3.7	1.9
Anisometropia	67	2.8	1.5	25	4.8	1.5	92	3.4	1.7	0.47
Anisometropia/Strabismus	35	2.8	1.3	23	5.2	2.3	58	3.7	2.1
Enrollment Amblyopic Eye Visual Acuity
≥ 20/200	0	0	0	13	6.1	2.6	13	6.1	2.6
20/160	0	0	0	12	5.3	1.7	12	5.3	1.7
20/125	0	0	0	16	4.6	1.6	16	4.6	1.6
20/100	0	0	0	20	4.2	1.7	20	4.2	1.7	<0.001
20/80	29	3.4	1.8	0	0	0	29	3.4	1.8
20/63	52	3.3	1.3	0	0	0	52	3.3	1.3
20/50	54	2.3	1.2	0	0	0	54	2.3	1.2

Std = Standard deviation

^*Based on an analysis of covariance model using data from the overall cohort to evaluate amblyopic-eye visual acuity improvement (lines) since enrollment, adjusting for age (years) at enrollment as a continuous factor, enrollment amblyopic-eye visual acuity (logMAR) as a continuous factor and amblyopia cause.

Table 2.

Relationship between amblyopia resolution (20/25 or better amblyopic-eye visual acuity and ≤ 1 line interocular difference) and enrollment factors

	Overall	Resolved
	N	N	%	Odds Ratio (95% CI)*	P-Value*
Overall	196	52	27%
Amblyopia Severity at Enrollment
Moderate (20/50 to 20/80)	135	45	33%	3.89 (1.61, 9.37)	0.003
Severe (20/100 to 20/400)	61	7	11%	Reference
Enrollment Age (Years)
3 to <4	23	8	35%
4 to <5	57	19	33%
5 to <6	60	14	23%	0.76 (0.57, 1.02)§	0.06
6 to <7	29	4	14%
7 to <8	27	7	26%
Amblyopia cause
Strabismus	46	16	35%	2.06 (0.81, 5.22)	0.31
Anisometropia	92	25	27%	1.43 (0.63, 3.28)
Strabismus/Anisometropia	58	11	19%	Reference

^*Based on a logistic regression model of amblyopia resolution as the dependent variable that included amblyopia severity at enrollment, age at enrollment as a continuous variable (years) and amblyopia cause as the explanatory factors.

^§Odds ratio for age variable based on a change of 1 year in age

Discussion

Children in this study were treated with 2 hours daily patching until no improvement between two visits, but as previously reported, no improvement from a previous exam is insufficient to establish maximum or stable VA.^{1, 3} Nonetheless, our data show that 2 hours of daily patching often leads to robust VA improvement, and younger children tend to improve more with patching. Children with worse VA when starting patching tend to improve more, but those with better baseline VA are more likely to achieve amblyopia resolution. Taken together with results from prior studies, we conclude it is reasonable to initiate patching at a dosage of 2 hours each day, even for children with severe amblyopia.⁵ If there is no improvement between 2 visits, reasonable options include increasing the prescribed patching dose to 6 hours per day¹ or continuing 2 hours of prescribed patching, knowing that VA stability is not established by no improvement from the previous visit.