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The effects of hyperopic and astigmatic ametropia on stereoacuity by Titmus stereo test
Taiwan Journal of Ophthalmology 2 (2012) 22e24
Contents lists available at SciVerse ScienceDirect
Taiwan Journal of Ophthalmology journal homepage: www.e-tjo.com
Original article
The effects of hyperopic and astigmatic ametropia on stereoacuity by Titmus stereo test Ju-Wen Yang a, Tien-Yi Huang b, Ko-Jen Yang a, Jiahn-Shing Lee c, Wan-Chen Ku a, Ling Yeung a, Pei-Hsuan Wu d, Yi-Fang Lin a, Chi-Chin Sun a, e, * a
Department of Ophthalmology, Chang Gung Memorial Hospital, Keelung, Taiwan Ryan Eye Clinic, Taoyuan, Taiwan Department of Ophthalmology, Chang Gung Memorial Hospital, Linkou, Taiwan d Department of Public Finance, Meiho Institute of Technology, Pingtung, Taiwan e Department of Chinese Medicine, Chang Gung University, Kwei-shan, Taoyuan, Taiwan b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 August 2011 Received in revised form 7 November 2011 Accepted 16 November 2011 Available online 9 January 2012
Purpose: Using the Titmus stereo test to examine the association between hyperopic ametropia including hyperopia, astigmatism, anisometropia, and stereoacuity in a school-aged population. Methods: We measured cycloplegic autorefraction, best corrected monocular visual acuity and best corrected stereoacuity in a population of 4- to 13-year-old school-aged children (Keelung, Taiwan) after obtaining proper informed consent. Children with amblyopia (best-corrected visual acuity inferior to 20/25) or strabismus were excluded from the study. The effects of the severity of hyperopia, astigmatism, and anisometropia on stereoacuity revealed by the Titmus stereo test were analyzed. Results: One hundred and seventeen children (51 boys and 66 girls; mean age ¼ 7.32 years, range ¼ 4e13 years) with hyperopia were enrolled into the study. The mean spherical error was þ1.48 1.30 diopters (D) (range ¼ þ0.25 to þ6.50D). The mean astigmatism was -1.22 1.04 D (range ¼ 0 to -3.50 D). They received the Titmus stereo test. A spherical error > þ3.00 D and spherical equivalent > þ3.00 D showed a strong association with decreased stereoacuity in the Titmus stereo test (p ¼ 0.000). The degree of astigmatism or astigmatic anisometropia was not significantly correlated with the stereopsis in the test. Conclusion: The Titmus stereo test revealed a good quantification of the stereoacuity. A spherical error > þ3.00 D, and a spherical equivalent > þ3.00D were all associated with a significantly reduced stereoacuity in school-aged children. Copyright Ó 2011, The Ophthalmologic Society of Taiwan. Published by Elsevier Taiwan LLC. All rights reserved.
Keywords: ametropia astigmatism depth perception hyperopia stereopsis
1. Introduction Stereopsis is a binocular sensation of relative depth1 that reaches adult levels at approximately 5 years of age.2 Stereoacuity influences the performance of fine visuomotor actions and spatial representation in preschool children. Hrisos et al. found that reduced stereoacuity was associated with poor performance on tasks assessing hand-eye coordination and visuomotor skills.3 Two types of stereopsis tests can be applied in analysis: contour and random dot tests.4 The Titmus stereo test is one of the commonly used contour tests. It assesses a range of disparities from
* Corresponding author. Department of Ophthalmology, Chang Gung Memorial Hospital, 6F, 222 Mai-Jin Road, An-Le District, Keelung City, Taiwan. E-mail address: [email protected] (C.-C. Sun).
3000 to 40 seconds of arc. The Titmus stereo test is useful in quantifying the performance of stereopsis. Normal development of the stereopsis is based on good binocular vision. If the visual acuity of both eyes reaches 20/25 or better, the stereopsis would achieve an average of 43 seconds of arc measured by the Titmus test.5 It is well known aniseikonia, amblyopia, strabismus, nystagmus, aphakia, monovision or monofixation syndrome will impair the development of stereopsis. Unilateral visual impairment is associated with reduced stereoacuity.3 However, the association between refractive factors and stereoacuity development has rarely been addressed. The purpose of this study is to examine how hyperopia, astigmatism, anisometropia, spherical anisometropia, and astigmatic anisometropia affect the development of stereoacuity. We applied the Titmus stereo test in a suburban community sample of 4 to 13 year-old children in Taiwan.
2211-5056/$ e see front matter Copyright Ó 2011, The Ophthalmologic Society of Taiwan. Published by Elsevier Taiwan LLC. All rights reserved. doi:10.1016/j.tjo.2011.11.004
J.-W. Yang et al. / Taiwan Journal of Ophthalmology 2 (2012) 22e24
2. Methods
23
Table 2 The distribution of the refractive error and the participants.
2.1. Participants
Group
Number
Median
76 27 14
þ0.63 þ2.13 þ4.00
50 44 23
þ0.75 þ2.31 þ4.44
41 14 62
0.00 -0.75 -1.75
83 20 14
0.00 -1.00 -1.63
76 17 24
-0.25 -0.875 -1.75
94 10 13
-0.25 -0.75 -2.00
Sphere (D)
The study was held from August 2007 to August 2008. In total, 117 hyperopic children of both sexes were enrolled in this prospective study, approved by an institutional review board, with proper consent from the parents of each participant. We excluded the patients with strabismus, amblyopia, nystagmus and ocular disease such as congenital cataract, glaucoma, retinopathy of prematurity, ocular trauma history, mental retardation or neurologic disorder. After cycloplegic refraction with 2% cyclopentolate eyedrops, best-corrected visual acuity (BCVA) was tested. We excluded children with BCVA below 20/25. To eliminate the cases with suppression, a Worth-4-Dot test was performed. Participants with poor comprehension of the test were also excluded. The Titmus test was performed by the same technician (Yi-Fang Lin). In the test, we asked the patient to wear the polarized glasses. The test was performed at a distance of 40 cm. We recorded the stereoacuity in seconds of arc according to the result of the best distinguished stereogram. It ranged from 40 to 3000 seconds of arc. 2.2. Statistical analysis For analyzing the differences between the groups of refractive error and the Titmus stereoacuity, we used the Kruskal-Wallis test. A p value of < 0.05 was considered significant. The Dunnett test for two-pair comparisons was applied in comparing the stereoacuity in the subgroups of the refractive error. A linear regression test was performed to evaluate the effects of the variables in the Titmus test. 3. Results One hundred and seventeen children (51 boys and 66 girls, aged 4 to 13 years) were included in the study. The mean age was 7.32 years. The profiles of refractive error are summarized in Table 1. The spherical equivalent was defined as D of sphere plus D of astigmatism/2. The spherical error and the spherical equivalent were categorized into three groups: þ0.25 w þ1.50 D, þ1.75 w þ3.00 D, and > þ3.00 D. The degree of astigmatism, anisometropia, spherical anisometropia, and astigmatic anisometropia was also grouped into 0 w -0.50 D, -0.75 w -1.00 D, and > -1.00 D. The distribution of respective refractive components is shown in Table 2. All the participants received the Titmus stereo test. The performances of stereoacuity obtained by the Titmus test between the clusters of each group divided by different refractive errors were then compared. Table 3 listed the results of statistical analyses of the stereoacuity by the test among the different groups of refractive error. A significant correlation was noted between different groups of spherical error, spherical equivalent, and stereoacuity by the Titmus test, suggesting that a severity of hyperopia > þ3.00 D affected stereopsis performance among school-aged children (Table 3). By contrast, the degree of astigmatism or astigmatic anisometropia
Table 1 The profile of the mean refractive errors of the participants.
Sphere Spherical equivalent Spherical anisometropia Anisometropia Astigmatism Astigmatic anisometropia
þ0.25 w þ1.50 þ1.75 w þ3.00 > þ3.00 Spherical equivalent (D) þ0.25 w þ1.50 þ1.75 w þ3.00 > þ3.00 Astigmatism (D) 0 w -0.50 -0.75 w -1.00 < -1.00 Astigmatic anisometropia (D) 0 w -0.50 -0.75 w -1.00 < -1.00 Anisometropia (D) 0 w -0.50 -0.75 w -1.00 < -1.00 Spherical anisometropia (D) 0 w -0.50 -0.75 w -1.00 < -1.00
was not significantly associated with reduced stereoacuity in this study. No significant correlation was found between groups of anisometropia, spherical anisometropia, astigmatism, astigmatic anisometropia, and stereoacuity in the Titmus test. A linear regression test was performed in the Titmus test. The results are summarized in Table 4, further confirming only the sphere and spherical equivalent were significantly related to decreased stereopsis by the Titmus test.
Table 3 Summary of the stereoacuity by Titmus test among groups of different refractive error. Data were analyzed by the nonparametric procedure of a Kruskal-Wallis test, followed by a Dunnett test for two-pair comparisons. The factors of sphere and spherical equivalent had a significant effect in the Titmus test (p value < 0.01). We also compared the subgroups in the sphere and spherical equivalent. The data in subgroups (c and f) > þ3.00D showed the significance. Group
Median/mean p rank (seconds of arc)
Sphere (D)
0.00** (a) þ0.25 w þ1.50 50/52.37 (b) þ1.75 w þ3.00 80/60.39 (c) > þ3.00 100/92.32
Spherical equivalent (D) (d) þ0.25 w þ1.50 50/53.50 (e) þ1.75 w þ3.00 50/55.51 (f) > þ3.00 100/77.63 Astigmatism (D) 0 w -0.50 -0.75 w -1.00 < -1.00
50/59.06 70/62.50 50/58.17
0 w -0.50 -0.75 w -1.00 < -1.00
50/56.82 80/67.15 80/60.29
0 w -0.50 -0.75 w -1.00 < -1.00
50/55.29 80/61.15 80/69.23
0 w -0.50 -0.75 w -1.00 < -1.00
50/56.50 70/59.45 100/76.73
Astigmatic anisometropia (D)
Range (diopter, D)
þ1.48 1.30 þ2.09 1.54 þ0.49 0.65 þ0.69 0.88 -1.22 1.04 -0.47 0.59
þ0.25 w þ6.50 þ0.25 w þ7.06 0 w þ3.25 0 w þ4.50 0 w -3.50 0 w -3.00
0.18
Spherical anisometropia (D)
* p < 0.05, ** p < 0.01.
(d) V.S. (f)** (e) V.S. (f)* 0.90
0.44
Anisometropia (D)
Mean (diopter, D)
(a) V.S. (c)** (b) V.S. (c)** 0.00**
0.11
24
J.-W. Yang et al. / Taiwan Journal of Ophthalmology 2 (2012) 22e24 Table 4 The effects of the variables in the Titmus test were analyzed using linear regression test. A p value < 0.05 with 95% confidence intervals was considered statistically significant. p Age Sphere Spherical equivalent Astigmatism Astigmatic anisometropia Anisometropia Spherical anisometropia
0.80 0.00* 0.00* 0.32 0.49 0.15 0.06
stereoacuity, from 3000 to 40 seconds of arc. However, it may have the disadvantage of monocular cue on low-grade tests. Secondly, since we did not test the stereoacuity with the correcting glasses, therefore, the performance of stereoacuity after refractive correction was unknown. Further study may help to identify the role of wearing glasses in improving the normal development of stereoacuity. In summary, the Titmus stereo test revealed good quantification of stereoacuity. Hyperopia (> þ3.00 D) and spherical equivalent (> þ3.00 D) were all associated with a significantly reduced stereoacuity in school-aged children.
* p < 0.01.
References 4. Discussion The association between hyperopia and poor stereopsis has been found by previous studies.6, 7 In particular, if the esotropia developed in the high hyperopia group, a few of them showed stereopsis.8 We examined the refractive factors in the development of stereoacuity. Spherical error or spherical equivalent > þ3.00 D was associated with reduced stereoacuity in the Titmus test. Our results were in accordance with those obtained by Gawecki and Adamski, who found that almost complete loss of stereopsis was noted in patients with spherical hypermetropia > þ3.00 D.9 Children with hyperopia are more frequently treated for prevention of amblyopia. In this study, we found a significantly reduced stereoacuity in the hyperopic group > þ3.00 D. Children with hyperopia > þ3.00 D may require refractive correction to help the normal development of stereoacuity. However, no significant reduced stereoacuity was found in the group of spherical anisometropia or astigmatic anisometropia. The statistical insignificance is perhaps related to the limited case number and the design of this study. Ljubica and Jelena reported more than half (57.8%) of the amblyopia group were patients with strabismic (35%) and ametropic (22.8%) amblyopia. Further, in patients with severe amblyopia, esotropia or greater hyperopic astigmatism, impaired stereopsis was noticeable.10 Anisometropia and astigmatic anisometropia were strongly related to amblyopia and strabismus in past reports.11,12 However, we excluded children with amblyopia and strabismus from this study, which were related to the impaired stereopsis. We believe that the effect of anisometropia in reducing stereopsis is greater in the general population. The prevalence of hyperopia was reported to be from 12.8% to 38.0% in school-aged children in different countries.13e20 Because hyperopia was associated with an increased risk of amblyopia and strabismus, optical correction was usually suggested for children with hyperopia > þ5.00D in the past.21 The ophthalmologists would consider prescribing spectacles in non-strabismic children at 1, 3 and 5 years of age for hyperopia of þ4.50 D, þ3.00 D and þ2.50 D, respectively.22 In our study, we found hyperopia > þ3.00 D was associated with impaired stereoacuity. Therefore, spectacle prescription for hyperopia > þ3.00 D should be considered. There are some limitations in this study. Firstly, the Titmus stereo test is a contour test, which can be used in quantifying
1. Raymond van EE, Casper J. Erkelens. Stability of binocular depth perception with moving head and eyes. Vision Res 1996;36:3827e42. 2. Hong SW, Park SC. Development of distant stereoacuity in visually normal children as measured by the Frisby-Davis distance stereotest. Br J of Ophthalmol 2008;92:1186e9. 3. Hrisos S, Clarke MP, Kelly T, Henderson J, Wright CM. Unilateral visual impairment and neurodevelopmental performance in preschool children. Br J of Ophthalmol 2006;90:836e8. 4. Sherry L, Fawcett. An evaluation of the agreement between contour-based circles and random dot-based near stereoacuity tests. JAAPOS 2005;9:572e8. 5. Levy NS, Glick EB. Stereoscopic perception and Snellen visual acuity. Am J Ophthalmol 1974;78:722e4. 6. von Noorden GK, Avilla CW. Accommodative convergence in hypermetropia. Am J Ophthalmol 1990;110:287e92. 7. Mai GH. Stereoacuity and ametropia. Zhonghua Yan Ke Za Zhi 1993;29:280e2 [in Chinese, English abstract]. 8. Dobson V, Sebris SL. Longitudinal study of acuity and stereopsis in infants with or at-risk for esotropia. Invest Ophthalmol Vis Sci 1989;30:1146e58. 9. Gawecki M, Adamski J. Anisometropia and stereopsis. Klin Oczna 2004;106: 561e3 [in Polish, English abstract]. 10. Dorn Ljubica, Petrinovi c-Doresi c Jelena. Stereoscopic visual acuity in strabismic and ametropic/refractive amblyopia. Acta Clin Croat 2008;47:67e72. 11. Huynh SC, Wang XY, Ip J, Robaei D, Kifley A, Rose KA, et al. Prevalence and associations of anisometropia and aniso-astigmatism in a population based sample of 6 year old children. Br J Ophthalmol 2006;90:597e601. 12. Birch EE, Fawcett SL, Morale SE, Weakley Jr DR, Wheaton DH. Risk factors for accommodative esotropia among hypermetropic children. Invest Ophthalmol Vis Sci 2005;46:526e9. 13. Eballe AO, Bella LA, Owono D, Mbome S, Mvogo CE. Eye disease in children aged 6 to 15 years: a hospital-based study in Yaounde. Sante 2009;19:61e6 [in French, English abstract]. 14. Czepita D, Mojsa A, Zejmo M. Prevalence of myopia and hyperopia among urban and rural schoolchildren in Poland. Ann Acad Med 2008;54:17e21. 15. Ip JM, Robaei D, Kifley A, Wang JJ, Rose KA, Mitchell P. Prevalence of hyperopia and associations with eye findings in 6- and 12-year-olds. Ophthalmology 2008;115:678e85. 16. Czepita D, Mojsa A, Ustianowska M, Czepita M, Lachowicz E. Prevalence of refractive errors in schoolchildren ranging from 6 to 18 years of age. Ann Acad Med 2007;53:53e6. 17. Jeddi Blouza A, Loukil I, Mhenni A, Khayati L, Mallouche N, Zouari B. Management of hyperopia in children. J Fr Ophtalmol 2007;30:255e9 [in French, English abstract]. 18. Czepita D, Zejmo M, Mojsa A. Prevalence of myopia and hyperopia in a population of Polish schoolchildren. Ophthalmic Physiol Opt 2007;27:60e5. 19. Czepita D, Goslawski W, Mojsa A. Occurrence of hyperopia among students ranging from 6 to 18 years of age. Klin Oczna 2005;107:96e9 [in Polish, English abstract]. 20. Kleinstein RN, Jones LA, Hullett S, Kwon S, Lee RJ, Friedman NE, et al. CLEERE study group. Refractive error and ethnicity in children. Arch Ophthal 2003;121: 1141e7. 21. Wutthiphan S. Guidelines for prescribing optical correction in children. J Med Assoc Thai 2005;88:163e9. 22. Farbrother JE. Spectacle prescribing in childhood: a survey of hospital optometrists. Br J Ophthalmol 2008;92:392e5.
Contents lists available at SciVerse ScienceDirect
Taiwan Journal of Ophthalmology journal homepage: www.e-tjo.com
Original article
The effects of hyperopic and astigmatic ametropia on stereoacuity by Titmus stereo test Ju-Wen Yang a, Tien-Yi Huang b, Ko-Jen Yang a, Jiahn-Shing Lee c, Wan-Chen Ku a, Ling Yeung a, Pei-Hsuan Wu d, Yi-Fang Lin a, Chi-Chin Sun a, e, * a
Department of Ophthalmology, Chang Gung Memorial Hospital, Keelung, Taiwan Ryan Eye Clinic, Taoyuan, Taiwan Department of Ophthalmology, Chang Gung Memorial Hospital, Linkou, Taiwan d Department of Public Finance, Meiho Institute of Technology, Pingtung, Taiwan e Department of Chinese Medicine, Chang Gung University, Kwei-shan, Taoyuan, Taiwan b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 August 2011 Received in revised form 7 November 2011 Accepted 16 November 2011 Available online 9 January 2012
Purpose: Using the Titmus stereo test to examine the association between hyperopic ametropia including hyperopia, astigmatism, anisometropia, and stereoacuity in a school-aged population. Methods: We measured cycloplegic autorefraction, best corrected monocular visual acuity and best corrected stereoacuity in a population of 4- to 13-year-old school-aged children (Keelung, Taiwan) after obtaining proper informed consent. Children with amblyopia (best-corrected visual acuity inferior to 20/25) or strabismus were excluded from the study. The effects of the severity of hyperopia, astigmatism, and anisometropia on stereoacuity revealed by the Titmus stereo test were analyzed. Results: One hundred and seventeen children (51 boys and 66 girls; mean age ¼ 7.32 years, range ¼ 4e13 years) with hyperopia were enrolled into the study. The mean spherical error was þ1.48 1.30 diopters (D) (range ¼ þ0.25 to þ6.50D). The mean astigmatism was -1.22 1.04 D (range ¼ 0 to -3.50 D). They received the Titmus stereo test. A spherical error > þ3.00 D and spherical equivalent > þ3.00 D showed a strong association with decreased stereoacuity in the Titmus stereo test (p ¼ 0.000). The degree of astigmatism or astigmatic anisometropia was not significantly correlated with the stereopsis in the test. Conclusion: The Titmus stereo test revealed a good quantification of the stereoacuity. A spherical error > þ3.00 D, and a spherical equivalent > þ3.00D were all associated with a significantly reduced stereoacuity in school-aged children. Copyright Ó 2011, The Ophthalmologic Society of Taiwan. Published by Elsevier Taiwan LLC. All rights reserved.
Keywords: ametropia astigmatism depth perception hyperopia stereopsis
1. Introduction Stereopsis is a binocular sensation of relative depth1 that reaches adult levels at approximately 5 years of age.2 Stereoacuity influences the performance of fine visuomotor actions and spatial representation in preschool children. Hrisos et al. found that reduced stereoacuity was associated with poor performance on tasks assessing hand-eye coordination and visuomotor skills.3 Two types of stereopsis tests can be applied in analysis: contour and random dot tests.4 The Titmus stereo test is one of the commonly used contour tests. It assesses a range of disparities from
* Corresponding author. Department of Ophthalmology, Chang Gung Memorial Hospital, 6F, 222 Mai-Jin Road, An-Le District, Keelung City, Taiwan. E-mail address: [email protected] (C.-C. Sun).
3000 to 40 seconds of arc. The Titmus stereo test is useful in quantifying the performance of stereopsis. Normal development of the stereopsis is based on good binocular vision. If the visual acuity of both eyes reaches 20/25 or better, the stereopsis would achieve an average of 43 seconds of arc measured by the Titmus test.5 It is well known aniseikonia, amblyopia, strabismus, nystagmus, aphakia, monovision or monofixation syndrome will impair the development of stereopsis. Unilateral visual impairment is associated with reduced stereoacuity.3 However, the association between refractive factors and stereoacuity development has rarely been addressed. The purpose of this study is to examine how hyperopia, astigmatism, anisometropia, spherical anisometropia, and astigmatic anisometropia affect the development of stereoacuity. We applied the Titmus stereo test in a suburban community sample of 4 to 13 year-old children in Taiwan.
2211-5056/$ e see front matter Copyright Ó 2011, The Ophthalmologic Society of Taiwan. Published by Elsevier Taiwan LLC. All rights reserved. doi:10.1016/j.tjo.2011.11.004
J.-W. Yang et al. / Taiwan Journal of Ophthalmology 2 (2012) 22e24
2. Methods
23
Table 2 The distribution of the refractive error and the participants.
2.1. Participants
Group
Number
Median
76 27 14
þ0.63 þ2.13 þ4.00
50 44 23
þ0.75 þ2.31 þ4.44
41 14 62
0.00 -0.75 -1.75
83 20 14
0.00 -1.00 -1.63
76 17 24
-0.25 -0.875 -1.75
94 10 13
-0.25 -0.75 -2.00
Sphere (D)
The study was held from August 2007 to August 2008. In total, 117 hyperopic children of both sexes were enrolled in this prospective study, approved by an institutional review board, with proper consent from the parents of each participant. We excluded the patients with strabismus, amblyopia, nystagmus and ocular disease such as congenital cataract, glaucoma, retinopathy of prematurity, ocular trauma history, mental retardation or neurologic disorder. After cycloplegic refraction with 2% cyclopentolate eyedrops, best-corrected visual acuity (BCVA) was tested. We excluded children with BCVA below 20/25. To eliminate the cases with suppression, a Worth-4-Dot test was performed. Participants with poor comprehension of the test were also excluded. The Titmus test was performed by the same technician (Yi-Fang Lin). In the test, we asked the patient to wear the polarized glasses. The test was performed at a distance of 40 cm. We recorded the stereoacuity in seconds of arc according to the result of the best distinguished stereogram. It ranged from 40 to 3000 seconds of arc. 2.2. Statistical analysis For analyzing the differences between the groups of refractive error and the Titmus stereoacuity, we used the Kruskal-Wallis test. A p value of < 0.05 was considered significant. The Dunnett test for two-pair comparisons was applied in comparing the stereoacuity in the subgroups of the refractive error. A linear regression test was performed to evaluate the effects of the variables in the Titmus test. 3. Results One hundred and seventeen children (51 boys and 66 girls, aged 4 to 13 years) were included in the study. The mean age was 7.32 years. The profiles of refractive error are summarized in Table 1. The spherical equivalent was defined as D of sphere plus D of astigmatism/2. The spherical error and the spherical equivalent were categorized into three groups: þ0.25 w þ1.50 D, þ1.75 w þ3.00 D, and > þ3.00 D. The degree of astigmatism, anisometropia, spherical anisometropia, and astigmatic anisometropia was also grouped into 0 w -0.50 D, -0.75 w -1.00 D, and > -1.00 D. The distribution of respective refractive components is shown in Table 2. All the participants received the Titmus stereo test. The performances of stereoacuity obtained by the Titmus test between the clusters of each group divided by different refractive errors were then compared. Table 3 listed the results of statistical analyses of the stereoacuity by the test among the different groups of refractive error. A significant correlation was noted between different groups of spherical error, spherical equivalent, and stereoacuity by the Titmus test, suggesting that a severity of hyperopia > þ3.00 D affected stereopsis performance among school-aged children (Table 3). By contrast, the degree of astigmatism or astigmatic anisometropia
Table 1 The profile of the mean refractive errors of the participants.
Sphere Spherical equivalent Spherical anisometropia Anisometropia Astigmatism Astigmatic anisometropia
þ0.25 w þ1.50 þ1.75 w þ3.00 > þ3.00 Spherical equivalent (D) þ0.25 w þ1.50 þ1.75 w þ3.00 > þ3.00 Astigmatism (D) 0 w -0.50 -0.75 w -1.00 < -1.00 Astigmatic anisometropia (D) 0 w -0.50 -0.75 w -1.00 < -1.00 Anisometropia (D) 0 w -0.50 -0.75 w -1.00 < -1.00 Spherical anisometropia (D) 0 w -0.50 -0.75 w -1.00 < -1.00
was not significantly associated with reduced stereoacuity in this study. No significant correlation was found between groups of anisometropia, spherical anisometropia, astigmatism, astigmatic anisometropia, and stereoacuity in the Titmus test. A linear regression test was performed in the Titmus test. The results are summarized in Table 4, further confirming only the sphere and spherical equivalent were significantly related to decreased stereopsis by the Titmus test.
Table 3 Summary of the stereoacuity by Titmus test among groups of different refractive error. Data were analyzed by the nonparametric procedure of a Kruskal-Wallis test, followed by a Dunnett test for two-pair comparisons. The factors of sphere and spherical equivalent had a significant effect in the Titmus test (p value < 0.01). We also compared the subgroups in the sphere and spherical equivalent. The data in subgroups (c and f) > þ3.00D showed the significance. Group
Median/mean p rank (seconds of arc)
Sphere (D)
0.00** (a) þ0.25 w þ1.50 50/52.37 (b) þ1.75 w þ3.00 80/60.39 (c) > þ3.00 100/92.32
Spherical equivalent (D) (d) þ0.25 w þ1.50 50/53.50 (e) þ1.75 w þ3.00 50/55.51 (f) > þ3.00 100/77.63 Astigmatism (D) 0 w -0.50 -0.75 w -1.00 < -1.00
50/59.06 70/62.50 50/58.17
0 w -0.50 -0.75 w -1.00 < -1.00
50/56.82 80/67.15 80/60.29
0 w -0.50 -0.75 w -1.00 < -1.00
50/55.29 80/61.15 80/69.23
0 w -0.50 -0.75 w -1.00 < -1.00
50/56.50 70/59.45 100/76.73
Astigmatic anisometropia (D)
Range (diopter, D)
þ1.48 1.30 þ2.09 1.54 þ0.49 0.65 þ0.69 0.88 -1.22 1.04 -0.47 0.59
þ0.25 w þ6.50 þ0.25 w þ7.06 0 w þ3.25 0 w þ4.50 0 w -3.50 0 w -3.00
0.18
Spherical anisometropia (D)
* p < 0.05, ** p < 0.01.
(d) V.S. (f)** (e) V.S. (f)* 0.90
0.44
Anisometropia (D)
Mean (diopter, D)
(a) V.S. (c)** (b) V.S. (c)** 0.00**
0.11
24
J.-W. Yang et al. / Taiwan Journal of Ophthalmology 2 (2012) 22e24 Table 4 The effects of the variables in the Titmus test were analyzed using linear regression test. A p value < 0.05 with 95% confidence intervals was considered statistically significant. p Age Sphere Spherical equivalent Astigmatism Astigmatic anisometropia Anisometropia Spherical anisometropia
0.80 0.00* 0.00* 0.32 0.49 0.15 0.06
stereoacuity, from 3000 to 40 seconds of arc. However, it may have the disadvantage of monocular cue on low-grade tests. Secondly, since we did not test the stereoacuity with the correcting glasses, therefore, the performance of stereoacuity after refractive correction was unknown. Further study may help to identify the role of wearing glasses in improving the normal development of stereoacuity. In summary, the Titmus stereo test revealed good quantification of stereoacuity. Hyperopia (> þ3.00 D) and spherical equivalent (> þ3.00 D) were all associated with a significantly reduced stereoacuity in school-aged children.
* p < 0.01.
References 4. Discussion The association between hyperopia and poor stereopsis has been found by previous studies.6, 7 In particular, if the esotropia developed in the high hyperopia group, a few of them showed stereopsis.8 We examined the refractive factors in the development of stereoacuity. Spherical error or spherical equivalent > þ3.00 D was associated with reduced stereoacuity in the Titmus test. Our results were in accordance with those obtained by Gawecki and Adamski, who found that almost complete loss of stereopsis was noted in patients with spherical hypermetropia > þ3.00 D.9 Children with hyperopia are more frequently treated for prevention of amblyopia. In this study, we found a significantly reduced stereoacuity in the hyperopic group > þ3.00 D. Children with hyperopia > þ3.00 D may require refractive correction to help the normal development of stereoacuity. However, no significant reduced stereoacuity was found in the group of spherical anisometropia or astigmatic anisometropia. The statistical insignificance is perhaps related to the limited case number and the design of this study. Ljubica and Jelena reported more than half (57.8%) of the amblyopia group were patients with strabismic (35%) and ametropic (22.8%) amblyopia. Further, in patients with severe amblyopia, esotropia or greater hyperopic astigmatism, impaired stereopsis was noticeable.10 Anisometropia and astigmatic anisometropia were strongly related to amblyopia and strabismus in past reports.11,12 However, we excluded children with amblyopia and strabismus from this study, which were related to the impaired stereopsis. We believe that the effect of anisometropia in reducing stereopsis is greater in the general population. The prevalence of hyperopia was reported to be from 12.8% to 38.0% in school-aged children in different countries.13e20 Because hyperopia was associated with an increased risk of amblyopia and strabismus, optical correction was usually suggested for children with hyperopia > þ5.00D in the past.21 The ophthalmologists would consider prescribing spectacles in non-strabismic children at 1, 3 and 5 years of age for hyperopia of þ4.50 D, þ3.00 D and þ2.50 D, respectively.22 In our study, we found hyperopia > þ3.00 D was associated with impaired stereoacuity. Therefore, spectacle prescription for hyperopia > þ3.00 D should be considered. There are some limitations in this study. Firstly, the Titmus stereo test is a contour test, which can be used in quantifying
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