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Published thesis:Amblyopia related 首頁 > 英文版 > Published thesis:Amblyopia related

Improvement of Visual Acuity in Children with Refractive Amblyopia

Treated with Rotated Prism Combined with Near Activity     

Ke-Hung Chien, MD, Chao-Chyun Lin, MD, Jiann-Torng Chen, PhD

Po-Liang Chen, MD

 

Running title: Amblyopia Treated with Rotated Prism and Near Activity

 

Department of Ophthalmology,

Tri-Service General Hospital,

National Defense Medical Center,

Taipei, Taiwan, Republic of China

 

*Corresponding author: Po-Liang, Chen, MD.

 Department of Ophthalmology,

Tri-Service General Hospital,

National Defense Medical Center,

No. 325, Sec. 2, Cheng Gong Road, Taipei, 114,

Taiwan, Republic of China.

TEL: +886-2-87927165;

FAX: +886-2-87927164;

E-mail: ddff36@yahoo.com.tw

 

ABSTRACT

 

PurposeTo evaluate the effect of a new modality on improving visual acuity (VA) in patients with refractive amblyopia.

 

MethodsRetrospective and interventional case series. Medical records of one hundred and twenty children with refractive amblyopia treated with the modality consisted of rotated prisms, plus lens and near activities were analyzed from Jan 2001 through Jan 2006. Characteristics such as Improvement of VA in amblyopic eyes and resolution of amblyopia (visual acuity6/7.5 or difference2 line in logMAR) were assessed in patients without (group P) and with spectacle correction (group P+G).

 

ResultsAmong the patients, the mean VA of the amblyopic eyes improved from 0.22 logMAR to 0.03 logMAR (1.9 lines) in group P and from 0.24 logMAR to 0.09 logMAR (1.5 lines) in group P+G after treatment (P<0.001). Resolution of amblyopia was achieved in 62 of 65 patients (95.4%) in group P and 36 of 55 patients (65.5%) in group P+G. The mean time of amblyopic resolution was 4.56 weeks (7.40 sessions) in group P and 3. 77 weeks (6.23 sessions) in group P+G (P=0.035). Among the whole group, age, baseline refraction error and baseline VA differed significantly between amblyopia resolution group (success) and visual acuity stabilization group (failed). And we found that better baseline VA in both groups and younger age in group P may help in predicting their amblyopic resolution.

 

Conclusions VA can be improved with rotated prisms, plus lens and near activities in children with refractive amblyopia with or without refractive correction. VA improvement was better in group P but sooner in group P+G. The VA improvements by this modality were smaller because of their better initial VA. However, the time to resolution of amblyopia was faster compared with other modalities. Rotated prisms combined with near acuity might provide an alternative treatment in children with refractive amblyopia.

 

 

INTRODUCTION

Amblyopia is the disorder that consists of functional abnormalities, such as visual acuity (VA) reduction, contrast sensitivity impairment, spatial distortion, abnormal spatial interaction and contour interaction. Refractive amblyopia, either anisometropia or isometropia, results from relative high refractive errors in one or both eyes which made blurred retinal images. The presumed mechanism is pattern vision deprivation. Children carry their risk in developing amblyopia if untreated within their critical period. From previous studies, optimal spectacle correction is a major component in improving visual function in patients of anisometropic amblyopia1, 2. Besides, patching or penalization of the sound eye is often conjunct to the anisometropic amblyopia therapy. However, patching often carries relative high failure rate due to low compliance in some patients.

Besides patching, penalization and refractive correction, there are handful methods to reverse amblyopia. Perceptual learning improves visual performance by repeating basic tasks and it revealed comparable effects in amblyopic therapy with patching3. In this retrospective study, we adopted a new modality combined rotated prisms, plus lens, and near activities and would like to realize its efficacy on patients of refractive amblyopia.

 

MATERIALS AND METHODS

The study protocol complied with the requirement of the Institution of Review Board of the Tri-Service General Hospital. Medical records of pediatric patients who underwent amblyopic therapy by this modality between Jan 2001 and Jan 2006 in the ophthalmology department of Tri-Service General Hospital were reviewed.

Patients were recruited in this study if they met the inclusion and exclusion criteria. The major inclusion criteria consisted of children 3 to 11 years old; best-corrected visual acuity of better than 6/60 but inferior to 6/7.5 in the amblyopic eye; cycloplegic refractive error in each eye of 6.00 diopters (D) or more of myopia, 2.00 D or more of astigmatism, 4.00 D or more of hypermetropia, or both; no other concurrent amblyopia treatment other than spectacles. We excluded some patients because of too short following-up period to reach definition for amblyopia resolution or failure, ocular diseases that could result in reduced visual acuity, or existence of strabismus.

We conducted the new modality which contains 2 sets of lens for “flippers” for our visual training program. Set A was constructed with +0.5 diopter (D) plus lens and 5.0 D prism whereas set B included +1.0 D plus lens with 2.0 D base-in prism.

When objects performed their training for near activities between 2.5 and 3.0 meters in distance such as watching television, this modality was switched to only adopt set A for function. The training program which lasted for 50 minutes constituted from +0.5 D plus lens and 5.0 D base-down prism for 6 seconds followed by +0.5 D plus lens and 5.0 D base-in prism for another 9 seconds (Table 1) (Figure 1).       

When another training was performed in closer distance ranging from 30 to 60 cm, set A and B were worked together for 50 minutes while we added +1.50 D plus lens in front of eyes when used for reading purpose (distance 30 cm) and +0.5 D plus lens when used in playing computer games (distance 60 cm). In the initial 6 seconds of this training, there was only set A lens in +0.5 D plus lens and 5.0 D base-down cylinders. And in the following 14 seconds, set A and B were used together with +1.5 D plus lens with 7.0 D base-in prism (+0.5 D plus lens with 2.0 D base-in prism in set A and +1.0 D plus lens with 2.0 D base-in prism in set B).   

Patients were then grouped into group P for patients who did not wear spectacles and group P+G for patients who received spectacle correction in the same time. All patients underwent visual training programs about twice a week. Their visual acuity and cycloplegic refraction error during each training session were recorded.

Primary end point of this study was their differences of visual acuity less than 0.2 logMAR in the amblyopic eye of anisometropic amblyopia patients and visual acuity better than 0.1 logMAR in either amblyopic eye of isometropic patients. Secondary end point was that the amblyopic eye did not gain > 0.1 logMAR improvement in 6 consecutive visits and the objects were referred to the failed group.   

Data were analyzed with the software SPSS version 13.0 for Windows (SPSS Inc, Chicago, IL, USA). We conducted a t-test for comparing characteristics between groups and a P value 0.05 was considered significant. A regression analysis was adopted to evaluate the factor which can concordant with the improvement rate of the visual acuity among the groups.

 

RESULTS

One hundred and twenty children with refractive amblyopia and received therapy were enrolled. There were 35 children in anisometropic amblyopia and 85 children in isometropia in this study. Finally, we reported the study results of 205 eyes (120 children) who including 6 of myopic amblyopia, 24 of hypermetropic amblyopia, 147 of astigmatic amblyopia and 28 of mixed refractive amblyopia. Their mean age was 5.7 years old. The mean VA of the amblyopic eyes at baseline was 0.23 logMAR with ranging from 0.10 to 1.00 logMAR. The mean refractive errors were -1.10 D in spherical equivalent. The baseline characteristics of these patients are listed in Table 2. 

Based upon the concurrent spectacle correction or not, we grouped the patients into 2 subgroups. The first group was group P and there were 115 amblyopic eyes in 65 patients without spectacle correction in this group. And the second group, Group P+G which consisted of patients with spectacle correction was formed by 90 amblyopic eyes in 55 patients.  

Amblyopia resolved with final VA < 0.1 logMAR in the amblyopic eye or interocular VA difference2 lines in logMAR in 98 patients of our study (81.7%). The mean VA of the amblyopic eyes improved significantly from 0.23 logMAR at baseline to 0.06 logMAR after VA stabilized with mean improvement amplitude was 0.17 logMAR. The mean time to resolution of amblyopia was 4.3 weeks with ranging from 1.0 to 13.0 weeks. The mean sessions of visual training to resolution were 7.0 sessions (ranging from 1 to 35 times) (Table 3). There was average -0.026 D increased after therapy without significance (P=0.23).

In group P, mean visual acuity improved from 0.22 to 0.03 logMAR with 1.9 lines improvement. Amblyopia resolved in 62 out of 65 patients (95.4%) and they on average took 4.56 weeks (about 7.40 sessions) to achieve resolution. Better baseline visual acuity and young age may predict resolution in this group (P=0.01, P=0.02, respectively). Mean refraction error addition of +0.004 D was noted in this group.

Our modality provided amblyopia resolution in 36 out of 55 patients (65.5%) with mean improvement of 1.5 lines from 0.24 logMAR to 0.09 logMAR in group P+G. Among these 36 patients, the mean time to resolution in group P+G was 3.77 weeks or 6.23 sessions. In addition, better baseline visual acuity was the only predictor to resolution (P=0.00), -0.064 D of mean refraction error addition was noted.

Between the success and failed groups, age, baseline refraction error and baseline VA showed significant differences (P=0.001, 0.004, 0.000, respectively). In the failed group, their mean basline VA was 0.35 logMAR with mean improvement was 0.12 logMAR.

 

DISCUSSION

The mainstream of refractive amblyopia therapy is refractive correction with patching, penalization or their combination. Refractive correction alone has been proved to offer 3.9 lines improvement at first year in the patients of bilateral moderate and severe refractive amblyopia2. Patching and penalization are well-known adjunctions to treat amblyopia. However, social stigma and anxiety of patching in younger children and impeding daily activities in older children limited its compliance and then poorer application. In previous studies, efficacy and dosage of patching are reviewed to increase its compliance in such patients4. Our previous study showed that comparable results between patching and perceptual learning3, and perceptual learning via a modality in combination with or without spectacle correction for amblyopia was conducted in this study. Among this retrospective study, we enrolled 205 eyes with anisometropic and isometropic amblyopia and adopted a new modality which consists of plus lenses, rotated prisms and near activity. Visual acuity improvement and resolution time of amblyopia were analysed according to two different groups with and without spectacles.

The mean visual acuity improvement of our study was 0.16 logMAR which was smaller than previous studies. Though there was no study on similar modality before, visual acuity improvements by perceptual learning are 2.5 lines3, 5 in untreated amblyopic eyes. We believe that our study revealed different results which may contribute to different inclusion criteria and baseline VA. In our study, we included patients of mild amblyopia whose mean baseline VA was 0.23 logMAR while patients with strabismus or deprivation amblyopia were excluded.

Perceptual learning is defined to improve visual performance by repeating simple tasks. The definite pathway remains inconclusive but it is shown to affect visual function in turn with the fast component which affects higher level of processing and consequently linked to sensory unit after repeated tasking and then slow component that involves in the low-level processing within the sensory units. These links may be weakened or strengthened according to the activities6. Polat et al analyzed their adult patients treated by the Gabor patch stimuli and found that 68% patients gained their visual improvement over average 45 sessions with mean improvement of 0.25 logMAR5. And from our previous study, perceptual learning may provide 2.5 lines VA improvements in 76% patients of anisometropia amblyopia either in adults or children3. Visual training by ocular exercise via a combination of spherical lens, prism and different fixation distance shift is initial conducted by optometrists to treat accommodate and vergence disorders7. They provided 70% to 100% cure rates either for accommodative or vergence disorders. Our study offered 81.7% cure rate in refractive amblyopia in the premises of excluding vergence or accommodative disorder. In our study, there was no significant refraction error addition after therapy in either group and we believed that the modality which improved VA after ocular exercise induced by rotated prism with plus lens may involve perceptual learning pathways.

Since perceptual learning is made of several sessions that must be performed in one period of time as one session. In our study, 50 minutes per day offered sufficient favorable results and it could be performed either at home or at office. Stewart and his coworkers proposed the dose-response rate for patching in patients aged between 3 and 8 years is around 0.1 logMAR for every 120 hours of patching8, and latter they suggested that age may influence the dose-response rate in amblyopia therapy9. According to this conclusion, it may take about 200 hours to achieve mean improvement of 0.17 logMAR. However, our patients spent almost 7 hours in Group P and 6 hours in Group P+G to resolution. Besides mild to moderate amblyopia in our patients, we thought that young age and perceptual learning played some roles in the results.

Compliance of amblyopia therapy remains another concern regarding its success. Loudon et al. stated that poor parental fluency in the national language, a low level of education, and poor baseline visual acuity may lead to low compliance and then failure of therapy10. To improving success rate, intense supervising occlusion treatment and parental education do great help11.  The traditional patching failed in some patients due to social stigma or anxiety but perceptual learning may also fail due to boring simple tasks3. Our study conducted the modality that could be applied in daily activities in different setting such as watching television, reading, doing homework and playning interactive games provided relative high compliance.

Since myopia has relative high prevalence in East Asian of 22.4% at age 6 and 64.1% at age 1212, several factors including genes, environment or near work are thought to be in relation. Near work (< 30 cm ) and longer working time (> 30 minutes) may related to more refraction error13 while performing near activities with patching is proved beneficial in treating amblyopia14. Our modality was performed in near activities at distance from 30 cm to 3.0 meters by different settings and there was no significant refraction error addition noted after therapy.

We believed that the improvement in VA may result from several factors. First, we thought the improvement was accounted for by the increased blood flow in the extraocular and ciliary muscles during eye exercise. Consequently, accommodative amplitudes increased and then visual performance was reinforced. Second, interactive activities consisted of watching favorite television programs, playing interactive computer games and doing homework increased compliance compared with repetitive simple tasks which children may feel bored soon. Third, patients enrolled in our study were belonged to mild to moderate amblyopia (most baseline visual acuity ranged from 0.4 to 0.1 logMAR) compared with moderate to severe amblyopia in previous studies. 

    Compared with previous studies mainly on children who did not receive any amblyopia treatment before, we enrolled patients who received treatment of spectacle correction. There were 1.5 lines improvement to the amblyopic eyes in Group P+G. In our previous study, no patients of residual amblyopia showed improvement after 4 months of therapy15, and most patients in our study gained their improvement in the first 8 weeks (Table 2). In patients with residual amblyopia from therapies, our modality may aid in further improvement.

    There were some limitations in our study. First, there was absence of control group. As a perceptual learning, parents often requested this therapy and were not willed to participate in the control group. Second, relative short observation period was not enough to measure the retention effect of this amblyopia therapy. 90% patients lose their mean VA in 0.05 logMAR in first year5 and 92% patients lose 0.02 logMAR after 8-month therapy in our experience3, we may need at least one year following period to measure this effect. Third, there is relative better baseline VA compared with other studies. Further clinical study will be needed to evaluate this modality in refractive amblyopia.

    In conclusion, our study result showed the good result of this modality in refractive amblyopia therapy. VA improved more in Group P than in Group P+G while patients with spectacle correction gained their resolution in sooner pattern. Patients with better baseline visual acuity could expect their greater odds in amblyopia resolution. The modality combined rotated prism, plus lens and near activities may provide an effective alternative choice to treat refractive amblyopia.   

 

REFERENCES

1.         Steele AL, Bradfield YS, Kushner BJ, France TD, Struck MC, Gangnon RE. Successful treatment of anisometropic amblyopia with spectacles alone. J Aapos. 2006;10:37-43

2.         Wallace DK, Chandler DL, Beck RW, Arnold RW, Bacal DA, Birch EE, Felius J, Frazier M, Holmes JM, Hoover D, Klimek DA, Lorenzana I, Quinn GE, Repka MX, Suh DW, Tamkins S, Pediatric Eye Disease Investigator G, Wallace DK, Chandler DL, Beck RW, Arnold RW, Bacal DA, Birch EE, Felius J, Frazier M, Holmes JM, Hoover D, Klimek DA, Lorenzana I, Quinn GE, Repka MX, Suh DW, Tamkins S, Pediatric Eye Disease Investigator G. Treatment of bilateral refractive amblyopia in children three to less than 10 years of age. American Journal of Ophthalmology. 2007;144:487-496

3.         Chen PL CJ, Fu JJ. A pilot study of anisometropia amblyopia improved in adults and children by perceptual learning: An alternative treatment to patching. Ophthal Physiol Opt. 2008;28:1-7

4.         Repka MX, Beck RW, Holmes JM, Birch EE, Chandler DL, Cotter SA, Hertle RW, Kraker RT, Moke PS, Quinn GE, Scheiman MM. A randomized trial of patching regimens for treatment of moderate amblyopia in children. Arch Ophthalmol. 2003;121:603-611

5.         Polat U, Ma-Naim T, Belkin M, Sagi D, Polat U, Ma-Naim T, Belkin M, Sagi D. Improving vision in adult amblyopia by perceptual learning. Proceedings of the National Academy of Sciences of the United States of America. 2004;101:6692-6697

6.         Sagi D, Tanne D, Sagi D, Tanne D. Perceptual learning: Learning to see. Current Opinion in Neurobiology. 1994;4:195-199

7.         Ciuffreda KJ, Ciuffreda KJ. The scientific basis for and efficacy of optometric vision therapy in nonstrabismic accommodative and vergence disorders. Optometry (St Louis, Mo ). 2002;73:735-762

8.         Stewart CE, Moseley MJ, Stephens DA, Fielder AR. Treatment dose-response in amblyopia therapy: The monitored occlusion treatment of amblyopia study (motas). Invest Ophthalmol Vis Sci. 2004;45:3048-3054

9.         Stewart CE, Stephens DA, Fielder AR, Moseley MJ. Modeling dose-response in amblyopia: Toward a child-specific treatment plan. Invest Ophthalmol Vis Sci. 2007;48:2589-2594

10.       Loudon SE FM, Looman CW, et al. Predictors and a remedy for noncompliance with amblyopia therapy in children measured with the occlusion dose monitor. Invest Ophthalmol Vis Sci. 2006;47:4393-4400

11.       El-Ghrably IA LD, Gnanaraj L. Does compliance with amblyopia management improve following supervised occlusion treatment? Eur J Ophthalmol. 2007;17:823

12.       Cheng D, Schmid KL, Woo GC. Myopia prevalence in chinese-canadian children in an optometric practice. Optom Vis Sci. 2007;84:21-32

13.       Ip JM, Saw SM, Rose KA, Morgan IG, Kifley A, Wang JJ, Mitchell P. Role of near work in myopia: Findings in a sample of australian school children. Invest Ophthalmol Vis Sci. 2008;49:2903-2910

14.      Holmes JM, Edwards AR, Beck RW, Arnold RW, Johnson DA, Klimek DL, Kraker RT, Lee KA, Lyon DW, Nosel ER, Repka MX, Sala NA, Silbert DI, Tamkins S. A randomized pilot study of near activities versus non-near activities during patching therapy for amblyopia. J Aapos. 2005;9:129-136

15.       Chen PL, Chen JT, Tai MC, Fu JJ, Chang CC, Lu DW, Chen P-L, Chen J-T, Tai M-C, Fu J-J, Chang C-C, Lu D-W. Anisometropic amblyopia treated with spectacle correction alone: Possible factors predicting success and time to start patching. American Journal of Ophthalmology. 2007;143:54-60

 

 


 

TABLES

 

TABLE 1. Setting of the modality in different purpose

 

Set A

Set B

Net effect

Original

setting

0.5 D plus lens

5.0 D prism

1.0 D plus lens

2.0 D prism

 

Watching

Television

(2.5-3.0 m)

6 seconds –

0.5 plus lens

5.0 D prism (base-down)

No work

6 seconds –

0.5 plus lens

5.0 D prism (base-down)

9 seconds –

0.5 plus lens

5.0 D prism (base-in)

No work

9 seconds –

0.5 plus lens

5.0 D prism (base-in)

Reading

(30 cm)

Add 1.5 D

6 seconds –

0.5 plus lens

5.0 D prism (base-down)

No work

6 seconds –

2.0 plus lens

5.0 D prism (base-down)

14 seconds –

0.5 plus lens

5.0 D prism (base-in)

14 seconds –

1.0 D plus lens

2.0 D prism

(base-in)

14 seconds –

3.0 D plus lens

7.0 D prism (base-in)

Playing computer games

(60 cm)

Add 0.5 D

6 seconds –

0.5 plus lens

5.0 D prism (base-down)

No work

6 seconds –

1.0 plus lens

5.0 D prism (base-down)

14 seconds –

0.5 plus lens

5.0 D prism (base-in)

14 seconds –

1.0 D plus lens

2.0 D prism

(base-in)

14 seconds –

2.0 D plus lens

7.0 D prism (base-in)

D = diopters

 

 

 

 

 

 


 

 


TABLE 2. Baseline Characteristics of Study Cohort of Patients (n=205)

Characterisitcs

N (%)

Male

101 (49)

Age (years)

 

 Mean (SD)

5.7 (1.4)

 Range

3.0 to 11.0

 3 to 4

8 (3.9)

 4 to 5

56 (27.3)

 5 to 6

70 (34.1)

 6 to 7

36 (17.6)

 7 to 8

18 (8.8)

 8 to 9

12 (5.9)

 9 to 10

2 (1.0)

 10 to 11

3 (1.5)

Visual acuity

 

Mean logMAR (SD)

0.23 (0.12)

Range

0.10 to 1.00

 0.10 to 0.20

86 (42.0)

 0.20 to 0.30

50 (24.4)

 0.30 to 0.40

40 (19.5)

 0.40 to <0.50

 0.50 to <0.70

 0.70 to 1.00

20 (9.8)

6 (2.9)

3 (1.5)

Type of refractive amblyopia

 

 Myopia

6 (2.9)

 Hypermetropia

24 (11.7)

 Astigmatism

147 (71.7)

 Mixed

28 (13.7)

Spherical equivalent (D)

 

 Mean (SD)

-1.10 (3.5)

 Range

-13.88 to 6.75

-7.00

15 (3.5)

-7.00 to -4.00

7 (0.6)

-4.00 to 0.00

115 (82.9)

0.00 to 4.00

52 (7.1)

 4.00 to 7.00

16 (5.9)

D = diopters, logMAR = logarithm of the minimum angle of resolution, SD = standard deviation

 

 

 

 

 

 


 

 

TABLE 3.  Resolution of Amblyopic Eyes after Treatment

 

All Patients

(170 eyes)

Group P

(110 eyes)

Group P+G

(60 eyes)

Improvement from baseline

(logMAR line)

 

 

 

<1 line

9

2

7

1 to <2 lines

99

61

38

2 to <3 lines

36

29

7

3 lines

26

18

8

Mean (SD)

1.7 (0.9)

1.9 (0.8)

1.5 (0.9)

 

 

 

 

Time to resolution

 

 

 

<4 weeks

92

54

38

4 to <8 weeks

54

34

20

8 weeks

24

22

2

 

 

 

 

Sessions to resolution

 

 

 

<7 times

98

59

38

7 to < 14 times

59

37

21

14 times

13

14

1

logMAR = logarithm of the minimum angle of resolution

 


 

FIGURE LEGENDS

Figure 1

One patient used this modality in doing homework (A), playing computer games (B), and watching television (C).

 

     

 

 



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