1. Investigative Ophthalmology & Visual Science. 2008: 49(10); 4427-36
Associations between Aniosmetropia, Amblyopia, and Reduced Stereoacuity in a School-Aged Population with a High Prevalence of Astigmatism
Velma Dobson, Hoseph M. Miller, Candice E. Clifford- Donaldson & Erin M. Harvey
Ap. 박미라/ R4. 이경민

2. Previous Study/ Purpose
Introduction

3. Introduction(1)
Children who have anisometropia are known to be at risk of amblyopia.
The greater the magnitude of the anisometropia, the more severe the amblyopia tends to be.
Because anisometropic amblyopia is treatable in childhood, eye care professionals advocate methods for detection of anisometropia in young children.

4. Introduction(2) Problems of previous study
Variability in the criteria used to define anisometropia
Lack of data relating type & amount of anisometropia to presence of amblyopia
Ignore the effect of cylinder anisometropia
Ignore the effect of differences in cylinder axis between eyes

5. Introduction (3) Limitation Use of variety of VA chart
Use of Titmus SA test : monocular & binocular cues
Population relatively few cylinder anisometropia
Failure to include pt. with cylinder anisometropia, interocular differences in cylinder axis>10°
Glass effect
Selection bias

6. Introduction(4) Purpose of this study
To describe the relation between magnitude of anisometropia and interocular acuity difference, stereoacuity, and the presence of amblyopia in shcool-aged members with a high prevalence of astigmatism.
Allows assessment of the role of astigmatism and astigmatic axis as risk factors for the development of amblyopia

7. Subjects/ Procedures/ Data analysis
Methods

8. Subjects 1047 children 4 ~ 13 years of age
Attended elementary school (kindergarten through 6th grade) on the society (about 5 schools were selected)

9. Procedure (1) : Eye exam
Assessment of eye alignment : cover & uncover test at distance and near.
Assessment of distance VA at 4m with ETDRS logMAR charts
Measurement of refractive error 40 to 60 min. after instillation of one drop of proparacaine and 2 drops of cyclopentolate
Estimate confirmed by retinoscopy
Examination of external eye
Fundus examination

10. Procedure (2) : VA & SA Eyeglasses VA : using ETDRS logMAR chart at 4m
VA<20/20 in one or both eyes
Hyperopia >2.5D on any merdian
Myopia >0.75D on any merdian
Astigmatism>1.0D in one or both eyes
Anisometropia>1.5D SE
VA : using ETDRS logMAR chart at 4m
Rt eye: chart 1, Lt eye: chart 2
SA : using random dot test at 40cm

11. Data Analysis: Clincal notation
4 groups
Isometropic (ISO)
SE hyperopic anisometropia(SHA)
SE myopic anisometropia(SMA)
Cylinder anisometropia(CA)

12. Data Analysis: Vector notation
Method of Thibos et al
M(SE)
J0(power in vertical/ horizontal merdian)
0.5D of J0= 1.0D of cylinder at 90°
J45(power in oblique merdian)
0.5D of J45= 1.0D of cylinder at 45°

13. Fourier Approach of Thibos’
Spherical (S); Cylinder magnitude (C), Axis (α)
 Spherical equivalent(M) + Jackson cross cylinder component
Fourier analysis : complex waveform
Sum of harmonically related sine waves and cosine waves, plus a constant
Conversion from the polar Fourier form [M, Jxα] to the rectangular Fourier form [M,J0, J45]
J0=J cos(2α), J45=J sin(2α)
Conversion from the convention form to the rectangular Fourier form
M=S+C/2
J0=C/2 cos2(β-90)=-C/2 cos2β, J0=C/2 sin2(β-90)=-C/2 sin2β
Power Vectors : An Application of Fourier Analysis to the Description and Statistical Analysis of Refractive error
Optometry & Visual Sciencs, 1997; 74(6):

14. Data Analysis: Vector notation
Method of Harris
Vector dioptric difference(VDD)
Single No. representing the vector distance between 2 refractions.
1.41VDD= 1.0D SE difference without Dc.
Minimal anisometropia group
Interocular difference of <0.35VDD

15. Comparison with Harris’s notation
Refractive error  Expression as matrix with Vector h (h1,h2, h3)
Spherical (S); Cylinder magnitude (C), Axis (α)
Mean & Variance calculation as matrix calculation.
h1=S+C sin2α =M+J0
h2=-√2Csinαcosα = J45√2
h3= S+Ccos2α =M-J0
The mean and variance of samples of dioptric powers : the basic calculations
Clinical & Experimental Optometry, 1990; 73: 89-92

16. Data Analysis ANOVA with post hoc analysis with Bonferroni correction
VA & SA results as function of amount of anisometropia
Χ2 analysis with post hoc analysis with Bonferroni correction
Amblyopia prevalence as a function of amount of ansiometropia

17. Results Subject populations/ Anisometropia & Best corrected IAD
Amblyopia/ Anisometropia & Best corrected SA
Effect of previous glass wear
Results

18. Results : Subject population
Exclusion : 25 childeren  left sample of 972
Cataract, traumatic injury, strabismus, lid abnormlities, iris abnormalities, refused dilating drops, developmental delay, Hx of amblyopia, F/U loss
Astigmatism
≥1D : 415 of 972 children(42.7%), ≥2D : 267 children(27.5%)
Axis
Rt. Eye : with the rule with ≥1D astigmatism in all 362
Lt. eye : with the rule with ≥1D astigmatism in 351 & against the rule in 1child.
No oblique axis

19. Results : Anisometropia & BCIAD(1)
Significant effect of amount of anisometropia in the SHA & CA group, but not in the SMA group.
Within SHA groups: SE anisometropia ≥1.0D had significantly greater mean IAD than did in ISO group
Within CA groups : Cylinder anisometropia≥3.0D had significantly greater mean IAD than did in ISO group

20. Results : Anisometropia & BCIAD(2)
In Thibos’ method : no single group that different from the minimal anisometropia group in IAD
In Harris’ method : significant effect of amount of anisometropia
1.41 ~2.12 VDD, 2.12~2.83VDD, ≥2.83VDD

21. Results : Amblyopia(1)
Significant effect in amblyopia prevalence in the SHA & CA group, but not in the SMA group.
Within SHA groups: SE anisometropia ≥1.0D had significantly greater amblyopia prevalence than did in ISO group
Within CA groups : Cylinder anisometropia≥2.0D had significantly greater amblyopia prevalence than did in ISO group

22. Results : Amblyopia(2)
In the whole groups, significant relation between prevalence of amblyopia & amount of anisometropia in both J0/J45 and VDD
Post Hoc analysis
In Thibos’ method : no single group higher than minial anisometropia
In Harris’ method : higher than minimal anisometropia in ~2.12 VDD,
2.12~2.83VDD, ≥2.83VDD

23. Results : Anisometropia & BCSA(1)
SA: 48.6 arc sec.
Significant effect of amount of anisometropia in the SHA, SMA & CA groups
SHA group: SA worse in SE anisometropia ≥0.5D than minimal aniso.
SMA group: SA worse in SE anisometropia ≥0.5D than minimal aniso.
CA group : SA worse in SE anisometropia ≥0.5D than minimal aniso

24. Results : Anisometropia & BCSA(2)
SA: 47.7 arc sec
SA: 48.6 arc sec
Significant effect of amount of anisometropia in both J0/J45 and VDD
Post Hoc analysis
In Thibos’ method : SA worse in J0/J45 anisometropia≥0.25D than ISO
In Harris’ method : SA worse than minimal anisometropia in 0.71~1.41
VDD, 1.41 ~2.12 VDD, 2.12~2.83VDD, ≥2.83VDD

25. Results : Effect of previous glasses wear
Responses on the parental questionnaire concerning previous glasses wear : 959 of 972 study (98.7%)
Glasses wearing : reduce amblyopia in aniometropia patients.
Similar to results for the entire group of children.
Significant relation between the amount of anisometropia and the mean IAD in CA group & VDD termed calculation
Significant relation between the amount of anisometropia and SA for all groups
Significant relation between the amount of anisometropia and the prevalence of amblyopia in CA group and J0/J45 & VDD termed calculation

26. discussion

27. Discussion(1) Similarities with previous studies
Nonastigmatic, hyperopic children with ≥1.0D of anisometropia showed significantly increased mean IAD
Nonastigmatic, myoic children with ≥1.0D of anisometropia did not show significant increase in mean IAD
The amount of anisometropia that resulted in decreased best corrected SA was identical with the amount of anisometropia that produced an increase in mean IAD & in prevalence of amblyopia

28. Discussion(2) Differences from previous studies
In cylinder anisometropes
Previous study : significant increase in IAD with >1.5D anisometropia
This study : significant increase in IAD with >3.0D anisometropia
Due to lower threshold for amblyopia
Anisometropia using 2-vector based methods
Include cylinder axis & magnitude both
Thibos’ method : relate only to cylinder & axis anisometropia
In Harris’ method : reflect anisometropia based on sphere, cylinder & axis value

29. Discussion(3) Strengths of this study Large, school-based study
Population : high % of children with astigmatism
Measurement of refractive errors
CPR Retinomax autorefractor Retinoscopy
BCVA measured by ETDRS chart
Contains logMAR spacing of optotypes
BCSA measured by random dot SA test
Sample with no or minimal anisometropia
Isometropic baseline data
1st large sample data relating vector-method calculation of anisometropia to data on IAD, SA & presence of amblyopia
Include cylinder axis in calculations.

30. Discussion(4) Limitations of this study
Many of the subjects with higher amounts of anisometropia had a Hx. Of spectacle wear
Underestimated prevalence of amblyopia
Overestimated the amount of anisometropia to produce amblyopia
Differences in the variability of recognition acuity vs SA results
Long examination time led to inattentiveness
Absence of against-the-rule & oblique axis astigmatism in the subject population
Relatively small No. Of subjects with myopic anisometropia ≥1.0D

31. Thank You for Your Attentions!