One-year follow-up of clinical convergence measures in children enrolled in the Convergence Insufficiency Treatment Trial—Attention and Reading Trial

Abstract

Purpose

To assess the long-term stability of clinical measures of convergence (near point of convergence [NPC] and positive fusional vergence [PFV]) in participants enrolled in the Convergence Insufficiency Treatment Trial-Attention and Reading Trial (CITT-ART) who received 16 weeks of office-based vergence/accommodative therapy.

Methods

A total of 310 children, 9–14 years old, with symptomatic convergence insufficiency were enrolled in CITT-ART. Some 270 completed both their 16-week primary outcome visit followed by a 1-year follow-up visit. Of those 270, 181 (67%) were randomised to the vergence/accommodative therapy. Of the 181 in the vergence/accommodative group, 121 (67%) reported not receiving any additional treatment after the 16-week primary outcome visit. The mean change in NPC, PFV and percentages of children classified by the predetermined success criteria of convergence (normal NPC [<6 cm] and/or improved by ≥4 cm; normal PFV [passing Sheard's criterion and base-out break >15Δ] and/or improved by ≥10Δ) were compared at the 16-week primary outcome visit and 1 year later.

Results

Of the 121 who returned for their 1-year follow-up visit, there was no significant change in mean adjusted NPC (reduction of −0.2 cm; 95% CI: −1.0 to 0.5 cm) at 1 year. There was a statistically significant decrease in mean-adjusted PFV (−4.7∆; 95% CI: −6.5 to −2.8Δ) at 1 year. There were similar percentages of participants classified as ‘normal’ (p = 0.30), ‘normal and/or improved’ (p > 0.50) and ‘normal and improved’ (p > 0.14) based on NPC and PFV at the 1-year visit compared with the 16-week primary outcome visit.

Conclusion

The improvements in NPC and PFV following 16 weeks of vergence/accommodative therapy (with no reported additional treatment thereafter) in children with symptomatic convergence insufficiency persisted 1-year post-treatment.

Key points

• Improvements in the near point of convergence and positive fusional vergence measurements found after office-based vergence/accommodative therapy in children with convergence insufficiency were maintained 1 year after ending treatment.

• 92% of children treated for convergence insufficiency had a normal or improved near point of convergence 1 year after completion of office-based vergence/accommodative therapy.

• 91% of children treated for convergence insufficiency still had normal and/or improved fusional convergence 1 year after completion of office-based vergence/accommodative therapy.

INTRODUCTION

Office-based vergence/accommodative therapy with home reinforcement (hereafter termed vergence/accommodative therapy) is a common treatment for children with symptomatic convergence insufficiency.1 Vergence/accommodative therapy for children with convergence insufficiency has resulted in robust improvements in clinical measures of near point of convergence (NPC) and positive fusional vergence (PFV) after 12 or 16 weeks of treatment.2,3 Less is known about the long-term stability of these improvements in the convergence measures.

Only a few previous investigations have assessed the long-term stability of clinical findings after completing office-based therapy for convergence insufficiency. These studies used different therapy techniques,4 were in adult populations5,6 or had few participants return for long-term follow-up.7 The only study we are aware of that addressed this question in a large cohort of children who received similar therapy was the Convergence Insufficiency Treatment Trial (CITT).8 In CITT, the significant improvements observed in the NPC of participants in the office-based vergence/accommodative therapy group at the 12-week primary outcome visit were maintained at the 1-year follow-up visit (NPC mean change = 0.5 cm, 95% CI: −1.6 to −4.9 cm; PFV mean change = 0.6Δ, 95% CI: +2.6 to +6.20Δ).8

In the more recent Convergence Insufficiency Treatment Trial Attention and Reading Trial (CITT-ART), children with symptomatic convergence insufficiency were randomised to either office-based vergence/accommodative therapy or placebo therapy. At the 16-week primary outcome visit, the NPC and PFV measures along with symptoms improved significantly after vergence/accommodative therapy. While symptom improvement was similar between the active therapy and placebo groups, the active therapy group had a significantly greater improvement in NPC and PFV.3 The present investigation aimed to determine if the improvements in NPC and PFV were sustained 1 year after the vergence/accommodative therapy was completed in participants who did not receive any additional treatment other than prescribed maintenance therapy for 3 months.

METHODS

The CITT-ART study was supported through a cooperative agreement with the National Eye Institute of the US National Institutes of Health and was conducted according to the tenets of the Declaration of Helsinki. The institutional review boards of participating sites approved the protocol and Health Insurance Portability and Accountability Act (HIPAA) authorisation-compliant consent and assent forms. Written assent and consent were obtained from each participant and their parent (or legal guardian), respectively. Study oversight was provided by an independent data and safety monitoring committee. The study is registered at www.clinicaltrials.gov (CITT-ART: NCT02207517). The design and results of CITT-ART have been published elsewhere3,9,10 and are only partially described herein.

Eligibility

CITT-ART enrolled 310 children between 9 and 14 years of age who had symptomatic convergence insufficiency defined as: (1) a near exodeviation at least 4∆ greater than at distance fixation, (2) a receded (≥6 cm) NPC, (3) insufficient PFV (i.e., convergence amplitudes) at near, defined as failing Sheard's criterion (base-out blur [or break if no blur] less than twice the near heterophoria) or positive fusional vergence at near ≤15∆ base-out break, (4) a score of ≥16 on the convergence insufficiency symptom survey (CISS).3,9,10 Eligible participants were randomised in a 2:1 ratio to vergence/accommodative therapy or placebo therapy, respectively. For the vergence/accommodative therapy group, a 16-week programme of weekly, 60-min, office-based therapy was administered by study-certified therapists and home reinforcement therapy was prescribed.9–11

Follow-up after completion of therapy (16-week primary outcome) in CITT-ART

All participants were to return for a 1-year follow-up visit after the office-based therapy programme was discontinued at the CITT-ART 16-week outcome visit. The management of participants after the outcome visit depended on whether they remained symptomatic. Participants who were deemed asymptomatic (score of <16 on the CISS) at the end of their office-based treatment programme were prescribed home maintenance therapy of 15 min once per week for 3 months, after which therapy was discontinued. Maintenance therapy procedures consisted of one gross convergence technique (e.g., Brock string, 3-dot card) and one fusional vergence technique (e.g., eccentric circles, lifesaver cards).10 If participants were still symptomatic (score of ≥16 on the CISS) at the 16-week primary outcome visit, they were offered additional treatment at the discretion of the investigator. Because additional treatment was not in the protocol or standard among sites, participants who reported additional treatment were not included in this analysis. A subset of participants did not report whether they received additional treatment after the 16-week primary outcome visit, and thus, they were also not included in the analysis. Since the CITT-ART study found that the improvement in the CISS scores was not statistically different between the vergence/accommodative therapy and placebo groups,3 CISS scores were not included in this analysis. The participants who were included in this analysis comprised those who were randomised to vergence/accommodative therapy, completed their 16-week primary outcome visit, returned for the 1-year follow-up visit and reported that they received no additional therapy or treatment after the primary outcome visit. Participants who received additional treatment or were randomised to placebo therapy were not included in this analysis.

Clinical measures of convergence

Certified examiners used consistent techniques to measure NPC and PFV at all visits. Participants wore their optical correction (if prescribed) for all testing. Participants with distance visual acuity of 6/9 or worse at the 1-year follow-up visit underwent refraction and were tested through their best-corrected lenses. NPC break was measured using a Gulden Ophthalmics Near Point Rule (guldenophthalmics.com) with the edge of the rule placed on the participant's forehead, in between the eyebrows and above the nose. The target was a single column of 6/9 letters at 40 cm that was moved slowly towards the participant at a speed of 1–2 cm/s until the participant reported diplopia or the examiner observed a loss of fusion. NPC was measured three times to the nearest 0.5 cm, with at least 10-s intervals between measurements and the three measures were averaged.

PFV was measured with a horizontal prism bar with 1∆ base-out initially placed before an eye and then slowly (speed of approximately 2Δ/s) introducing increasing magnitudes of prism while participants viewed a single column of 6/9 letters at 40 cm. The examiner paused at each prism increment to confirm that the letters were still ‘single and clear’. Participants were told to report when the letters became blurred or when they broke into two (became double). If no diplopia was reported, examiners noted the magnitude of the prism where the participant appeared to lose fusion. The PFV measure was the participant's subjective blur report, or if there was no report of blur, then the break point (participant's report of diplopia or loss of fusion noted by the examiner) was used. PFV was measured three times, separated by at least 30-s intervals and the three measures were averaged.

Statistical methods

All statistical analyses were completed using SAS Version 9.4 (sas.com). A conservative estimate of p = 0.001 was used to adjust for the multiple comparisons reported herein. Initial two-sample t-tests (for interval-scaled characteristics) and chi-square tests (for nominal or ordinal characteristics) were used to compare participants who completed and those who missed the 1-year follow-up visit. A general linear model with repeated measures was used to obtain estimates of mean change (from treatment completion to 1 year) for both NPC break and PFV. The baseline and outcome clinical measures were used as covariates and an unstructured variance/covariance matrix was assumed. The percentages of participants in the vergence/accommodative therapy group falling into each success criterion (see Success Criterion for Convergence Measures) were calculated for the 1-year visit and compared with the same outcomes from the 16-week visit using the McNemar test.

After the study was completed, the coordinating centre discovered 10 ineligible participants who had not met the original PFV eligibility criteria. Three of these 10 participants met the eligibility criteria of the present study (assigned to office-based vergence/accommodative therapy, completed the 16-week primary outcome visit, returned for the 1-year follow-up visit and reported completing no additional therapy) and thus were included in the analyses. Sensitivity analyses performed with these three participants excluded showed a negligible impact on the observed changes in NPC and PFV.

Success criterion for convergence measures

Post-treatment, each participant's success was assessed based on predefined criteria that were used at the 16-week primary outcome examination. Success was determined by the extent of improvements (i.e., reached normal value, improved by a given magnitude) observed for the NPC or PFV measures.3 For NPC, normal was defined as <6 cm and improved was defined as a decrease (improvement) of at least 4 cm. For PFV, normal was defined as passing Sheard's criterion (i.e., compensating vergence range is at least twice the heterophoria) and having a base-out break finding >15Δ, whereas improved was defined as an increase of at least 10Δ.

An additional classification was created for instances where participants might not have reached the predetermined normal values but still demonstrated improvement in their clinical findings. For example, a participant might have been enrolled with an NPC break value of 15 cm and showed a clinically large improvement to 6.5 cm but did not reach the normal criteria of NPC (≤6 cm). This would fall under the success criteria of receded NPC [≥6 cm] but improved ≥4 cm. In another instance, a participant might have been classified with a normal NPC (e.g., 4.5 cm), but began the study at 7.0 cm. This participant reached a normal outcome but with a smaller change in their NPC value. This participant would be classified as normal NPC (<6 cm) but improved <4 cm. The most robust classification was normal NPC and improved ≥4 cm. All three of these classifications represent success measures that address different components of NPC and how it is interpreted clinically. A final classification of: normal NPC and/or improved ≥4 cm consisted of all three of the previously listed success criteria.

The same classification system was used for PFV. The first classification was insufficient PFV but improved ≥10Δ, which would be someone who did not pass Sheard's criterion and had a base-out to break finding <15Δ, but improved ≥10Δ, which is clinically meaningful.3 The next classification would be a normal PFV (passing Sheard's criterion and a base-out break finding > 15Δ) but improved < 10Δ. The third success classification would be: normal PFV and improved ≥ 10Δ. Combining all three success criteria results in the success criterion classification of normal PFV and/or improved ≥ 10Δ.

RESULTS

Patient follow-up

Of the original RCT participants who were enrolled (n = 310), 303 completed their 16-week primary outcome visit. Of those who completed this visit, 89% (270/303) returned for their 1-year follow-up visit, with 91% (181 of 199) in the vergence/accommodative therapy group returning. The long-term effect of vergence/accommodative therapy reported herein uses the 121 (out of 181; 67%) who did not receive additional treatment between the 16-week primary outcome visit and the 1-year follow-up visit (Table 1). Of those excluded from the analyses, 24 reported additional treatment and 36 did not report whether additional treatment was received and so were not analysed. There did not appear to be meaningful differences in the demographic and clinical characteristics of participants randomised to vergence/accommodative therapy used to investigate the long-term effects and those who were excluded from the analyses (Table 1). Subjects who reported receiving additional treatment after the primary outcome visit (n = 24) had significantly higher CISS scores (mean difference of 8.3 points, p < 0.0001) and were approximately 3Δ more exophoric at near (p = 0.02) at the primary outcome visit as compared to those who did not report additional treatment.

TABLE 1.

Clinical and demographic characteristics of participants in the vergence/accommodative group based on Year 1 completion status.

Characteristic	Analyseda (n = 121)	Not analysedb (n = 60)	p-Value
Age (years) (mean [95% CI])	10.7 (10.4, 11.0)	11.0 (10.6, 11.5)	0.14
Female, n (%)	74 (61)	35 (58)	0.71
Hispanic or Latino, n (%)	54 (45)	11 (18)	<0.001
Race, n (%)			0.51
Black or African American	25 (21)	16 (27)
White	78 (65)	38 (63)
Other	18 (15)	6 (10.0)
Asymptomatic at week 16 (CISS score < 16), n (%)	61 (50)	26 (43)	0.37
Normal near point of convergence at week 16 (break < 6 cm), n (%)	102 (84)	55 (92)	0.17
Normal positive fusional vergencec at week 16, n (%)	104 (86)	52 (87)	0.90
Exodeviation at distance (Δ) [mean (95% CI)]
Baseline study visit	2.1 (1.6, 2.6)	2.1 (1.4, 2.8)	0.97
16-week outcome visit	2.3 (1.8, 2.8)	2.9 (1.9, 3.8)	0.29
Exodeviation at near (Δ) (mean [95% CI])
Baseline study visit	9.7 (9.0, 10.5)	10.4 (9.4, 11.4)	0.30
16-week outcome visit	7.6 (6.7, 8.6)	9.4 (8.2, 10.7)	0.03
Near point of convergence break (cm) (mean [95% CI])
Baseline study visit	13.4 (12.1, 14.7)	15.4 (13.0, 17.7)	0.12
16-week outcome visit	4.1 (3.4, 4.9)	3.6 (3.1, 4.1)	0.19
Normal near point of convergence at week 16 (break < 6 cm), n (%)	102 (84)	55 (92)	0.17
Positive fusional vergence blur/break (Δ) (mean [95% CI])
Baseline study visit	11.6 (10.9, 12.3)	10.9 (9.6, 12.1)	0.28
16-week outcome visit	34.2 (32.3, 36.2)	35.3 (32.6, 38.0)	0.52
Normal positive fusional vergencec at week 16, n (%)	104 (86)	52 (87)	0.90

Abbreviations: CISS, convergence insufficiency symptom score; Δ, prism dioptre.

^a Participants randomised to vergence/accommodative therapy, completed their 16-week primary outcome visit, returned for the 1-year follow-up visit and reported that they received no additional treatment after the primary outcome visit.

^b Participants randomised to vergence/accommodative therapy, completed their 16-week primary outcome visit, returned for the 1-year follow-up visit but reported receiving additional treatment (n = 24) or did not report whether additional treatment was received (n = 36).

^c Normal positive fusional vergence defined as mean base-out break greater than 15Δ and passed Sheard's criterion (base-out blur ≥ twice near heterophoria).

Clinical measures of convergence

Table 2 presents NPC and PFV values (mean ± SD) at baseline, 16-week primary outcome visit and the 1-year follow-up visit, with the adjusted mean change (95% CI) for the vergence/accommodative therapy group. The adjusted mean reduction in NPC from the primary outcome to the 1-year follow-up of −0.2 cm (95% CI: −1.0 cm to 0.5 cm) was not statistically significant (p = 0.50). The adjusted mean change in PFV of −4.7∆ (95% CI: −6.5∆ to −2.8∆) represented a statistically significant decline (p < 0.0001).

TABLE 2.

Mean (standard deviation [SD]) and mean adjusted change for near point of convergence (break, cm) and positive fusional vergence (blur^a, Δ) at baseline, 16-week (primary outcome visit) and 1-year (long-term follow-up) for participants assigned to vergence/accommodative therapy who reported no additional therapy after the 16-week outcome visit (n = 121).

Study visit	Near point of convergence (npc)—break (cm) mean (SD)	Positive fusional vergence (pfv)—blura (Δ) mean (SD)
Baseline (n = 121)	13.4 (7.4)	11.6 (3.9)
16-week outcomeb (n = 120)	4.1 (3.9)	34.2 (10.7)
1-year follow-upb (nnpc = 120, npfv = 121)	4.5 (3.4)	29.4 (10.6)
Change from 16-week outcome to 1-year follow-upc	−0.3 (95% CI: −1.0 to 0.5)	−4.7 (95% CI: −6.5 to 2.8)

Abbreviation: Δ, prism dioptre.

^a Break if no blur reported.

^b One participant had a missing near point of convergence (cm) and positive fusional vergence (Δ) at week 16; one participant had a missing near point of convergence (cm) at the 1-year examination.

^c Adjusted for mean response at baseline and the 16-week examination.

Success criteria for convergence outcomes

There was little difference in the percentage of participants meeting the success criteria between the 16-week primary outcome visit and the 1-year follow-up visit (i.e., either a normal or improved clinical convergence measure) for both NPC and PFV (Table 3). Ninety-four percent of participants (113 of 120) had a ‘normal and/or improved’ NPC at the 16-week outcome visit compared with 92% (110 of 120) at the 1-year follow-up visit (p = 0.53). There were 86 participants (out of 120, 72%) with ‘normal and improved’ NPC at the 16-week outcome visit compared with 80 (out of 120, 67%) at the 1-year follow-up visit (p = 0.37). A similar percentage of participants were classified as having ‘normal and/or improved’ PFV at both the 16-week primary outcome (93%; 111 of 120) and 1-year visit follow-up visit (91%; 110 of 121; p = 0.78). There were 99 participants (out of 120; 83%) with ‘normal and improved’ PFV at the 16-week outcome visit compared with 92 (out of 121; 76%) at the 1-year follow-up visit (p = 0.14). At the 1-year follow-up visit, 9% (10 out of 120) of participants in the vergence/accommodative therapy group did not reach any of the three predetermined success criteria for NPC and 9% (11 out of 121) did not reach any of the three success criteria for PFV (Table 3). Of the 94 (out of 120; 78%) participants with both ‘normal’ NPC and PFV at the 16-week primary outcome visit, 79 (84%) also had both ‘normal’ NPC and PFV at the 1-year follow-up visit (p = 0.30).

TABLE 3.

Percentage (number) of participants assigned to vergence/accommodative therapy who reported no additional therapy after the 16-week outcome visit classified as normal or improved for each clinical outcome measure at the 16-week and 1-year follow-up study visits.

Near point of convergence (NPC) break (cm)
Study visit	Receded NPC but improved ≥4 cm	Normal NPCa but improved <4 cm	Normal NPCa and improved ≥4 cm	Normal NPCa and/or improved ≥4 cmb
16-week outcome (n = 120c)	9% (n = 11)	13% (n = 16)	72% (n = 86)	94% (n = 113)
1-year follow-up (n = 120d)	8% (n = 10)	17% (n = 20)	67% (n = 80)	92% (n = 110)

Positive fusional vergence blur or breake (Δ)
Study visit	Insufficient PFV but improved ≥ 10Δ	Normal PFVf but improved < 10Δ	Normal PFVf and improved ≥ 10 Δ	Normal PFVf and/or improved ≥ 10Δ
16-week outcome (n = 120c)	6% (n = 7)	4% (n = 5)	83% (n = 99)	93% (n = 111)
1-year follow-up (n = 121)	8% (n = 10)	7% (n = 8)	76% (n = 92)	91% (n = 110)

Abbreviations: PFV, positive fusional vergence; Δ, prism dioptre.

^aNormal NPC: break < 6 cm.

^bTotal of three preceding columns.

^cOne participant has missing NPC (cm) and PFV (Δ) at the 16-week examination.

^dOne participant has missing NPC (cm) at the 1-year examination.

^eBreak if no blur reported.

^fNormal PFV: passing Sheard's Criterion and having a base-out break >15Δ.

DISCUSSION

The mean NPC and PFV of 9- to 14-year-old children with symptomatic convergence insufficiency who completed 16 weeks of office-based vergence/accommodative therapy remained clinically normal 1 year after treatment cessation. The slight decrease in NPC of 0.2 cm was not statistically or clinically significant. The decrease in PFV of 4.7Δ was statistically significant but not clinically meaningful, as PFV remained normal or improved in 91% of participants with a mean PFV of 29.4Δ at the 1-year follow-up visit.

These study findings are similar to the long-term outcomes found in the CITT for participants randomised to office-based vergence/accommodative therapy for 12 weeks, but this study included more participants (121 versus 32) who were seen 1 year following the cessation of treatment.8 In CITT, the mean adjusted NPC at 1 year improved by 0.2 cm (95% CI: −0.9 to 1.3 cm). The PFV improved by 3.0Δ (95% CI: 0.04–5.9Δ), similar to the results from this study. This change was statistically significant but not clinically meaningful.8 In the subset of participants in the present study who did not receive any treatment after the 16-week outcome visit (n = 121), the mean adjusted NPC worsened by 0.2 cm (95% CI: −1.0 to 0.5 cm) and the PFV decreased by 4.7 ∆ (95% CI: −6.5 to −2.8∆). Like the results found for the CITT study, the mean adjusted change in NPC was not statistically significant, although the change in PFV was significant; however, the changes in both studies were not clinically meaningful (≤10Δ determined a priori to be clinically meaningful). The findings of the present study are similar to those of a non-controlled study by Shin et al.7 where 9- to 13-year-old children with symptomatic convergence insufficiency or combined convergence insufficiency with accommodative insufficiency received 12 weeks of office-based vergence/accommodative therapy. They found that 17 of the 20 (85%) children maintained improved clinical measures of NPC and PFV 1 year later.

This study had many strengths, including the randomised study design, study-certified investigators following a rigorous therapy protocol, the use of masked examiners and a high retention rate. A limitation is that one-third of the original trial participants were excluded because they either received additional treatment or did not report whether additional treatment was received between treatment cessation and their 1-year follow-up visit.

CONCLUSION

Improvements in NPC and PFV were maintained in children with convergence insufficiency who were randomised to vergence/accommodative therapy in the CITT-ART study, completed both the primary outcome and 1-year follow-up visits and reported receiving no additional treatment during the 1-year interval.

AUTHOR CONTRIBUTIONS

Ann M. Morrison: Conceptualization (supporting); investigation (supporting); visualization (equal); writing – original draft (lead); writing – review and editing (lead). Marjean T. Kulp: Conceptualization (equal); funding acquisition (lead); investigation (equal); methodology (equal); project administration (lead); supervision (equal); writing – original draft (supporting); writing – review and editing (supporting). Susan A. Cotter: Conceptualization (equal); funding acquisition (lead); investigation (lead); methodology (equal); project administration (lead); supervision (equal); writing – review and editing (supporting). Mitchell M. Scheiman: Conceptualization (lead); funding acquisition (lead); investigation (lead); methodology (lead); project administration (lead); supervision (lead); writing – review and editing (equal). Erin C. Jenewein: Investigation (supporting); methodology (supporting); visualization (supporting); writing – review and editing (equal). Tawna L. Roberts: Investigation (supporting); methodology (supporting); visualization (supporting); writing – review and editing (equal). G. Lynn Mitchell: Conceptualization (equal); data curation (lead); formal analysis (lead); funding acquisition (lead); methodology (equal); project administration (lead); supervision (equal); visualization (equal); writing – review and editing (equal). L. Eugene Arnold: Investigation (equal); writing – review and editing (supporting). Dashaini Retnasothi: Data curation (supporting); visualization (supporting); writing – original draft (supporting); writing – review and editing (supporting). Annette Bade: Methodology (supporting); writing – review and editing (supporting). Richard Hertle: Conceptualization (equal); funding acquisition (equal); investigation (equal); methodology (equal); writing – review and editing (supporting). Eric Borsting: Investigation (supporting); writing – review and editing (supporting).

FUNDING INFORMATION

This work was supported by the National Eye Institute of National Institutes of Health, Department of Health and Human Services (grant number 5U10EY022599 to MMS, 5U10EY022601 to GLM, 5U10EY022595 to SC, 5U10EY022592 to MK, 5U10EY022586 to ES, 5U10EY022600 to RH, 5U10EY022587 to MG, 5U10EY022596 to RC, 5U10EY022594 to KH and 5U10EY022591 to ST). The funding organisation had no role in the design or conduct of this research.

CONFLICT OF INTEREST STATEMENT

The authors report no conflicts of interest and have no proprietary interest in any of the materials mentioned in this article.