Centre for Vision in the Developing World

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Research Publications

You can explore previous publications and posters from the Centre by browsing the list below. Be sure to check back regularly for new publications.

Papers

Self correction of refractive error among young people in rural China: results of cross sectional investigation
M. Zhang, R. Zhang, M. He, W. Liang, X. Li, L. She, Y. Yang, G.E. MacKenzie, J. D. Silver, L. Ellwein, B. Moore, N. Congdon, BMJ (2011)
Abstract:
Objective: To compare outcomes between adjustable spectacles and conventional methods for refraction in young people.
Design: Cross sectional study.
Setting: Rural southern China.
Participants: 648 young people aged 12-18 (mean 14.9 (SD 0.98)), with uncorrected visual acuity ≤6/12 in either eye.
Interventions: All participants underwent self refraction without cycloplegia (paralysis of near focusing ability with topical eye drops), automated refraction without cycloplegia, and subjective refraction by an ophthalmologist with cycloplegia.
Main outcome measures: Uncorrected and corrected vision, improvement of vision (lines on a chart), and refractive error.
Results: Among the participants, 59% (384) were girls, 44% (288) wore spectacles, and 61% (393/648) had 2.00 dioptres or more of myopia in the right eye. All completed self refraction. The proportion with visual acuity ≥6/7.5 in the better eye was 5.2% (95% confidence interval 3.6% to 6.9%) for uncorrected vision, 30.2% (25.7% to 34.8%) for currently worn spectacles, 96.9% (95.5% to 98.3%) for self refraction, 98.4% (97.4% to 99.5%) for automated refraction, and 99.1% (98.3% to 99.9%) for subjective refraction (P=0.033 for self refraction v automated refraction, P=0.001 for self refraction v subjective refraction). Improvements over uncorrected vision in the better eye with self refraction and subjective refraction were within one line on the eye chart in 98% of participants. In logistic regression models, failure to achieve maximum recorded visual acuity of 6/7.5 in right eyes with self refraction was associated with greater absolute value of myopia/hyperopia (P < 0.001), greater astigmatism (P=0.001), and not having previously worn spectacles (P=0.002), but not age or sex. Significant inaccuracies in power (≥1.00 dioptre) were less common in right eyes with self refraction than with automated refraction (5% v 11%, P < 0.001).
Conclusions: Though visual acuity was slightly worse with self refraction than automated or subjective refraction, acuity was excellent in nearly all these young people with inadequately corrected refractive error at baseline. Inaccurate power was less common with self refraction than automated refraction. Self refraction could decrease the requirement for scarce trained personnel, expensive devices, and cycloplegia in children’s vision programmes in rural China.
Correspondence to: N Congdon ncongdon1@gmail.com
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The Child Self-Refraction Study - Results from Urban Chinese Children in Guangzhou
M. He, N. Congdon, G.E. MacKenzie, Y. Zeng, J.D. Silver, L. Ellwein, Opthalmology, Vol 118 (2011)
Abstract:
Objective: To compare visual and refractive outcomes between self-refracting spectacles (Adaptive Eye- care, Ltd, Oxford, UK), noncycloplegic autorefraction, and cycloplegic subjective refraction.
Design: Cross-sectional study.
Participants: Chinese school-children aged 12 to 17 years.
Methods: Children with uncorrected visual acuity 6/12 in either eye underwent measurement of the logarithm of the minimum angle of resolution visual acuity, habitual correction, self-refraction without cycloplegia, autorefraction with and without cycloplegia, and subjective refraction with cycloplegia.
Main Outcome Measures: Proportion of children achieving corrected visual acuity 6/7.5 with each modality; difference in spherical equivalent refractive error between each of the modalities and cycloplegic subjective refractive error.
Results: Among 556 eligible children of consenting parents, 554 (99.6%) completed self-refraction (mean age, 13.8 years; 59.7% girls; 54.0% currently wearing glasses). The proportion of children with visual acuity 6/7.5 in the better eye with habitual correction, self-refraction, noncycloplegic autorefraction, and cycloplegic subjective refraction were 34.8%, 92.4%, 99.5% and 99.8%, respectively (self-refraction versus cycloplegic subjective refraction, 0.001). The mean difference between cycloplegic subjective refraction and noncyclople- gic autorefraction (which was more myopic) was significant (–0.328 diopter [D]; Wilcoxon signed-rank test 0.001), whereas cycloplegic subjective refraction and self-refraction did not differ significantly (–0.009 D; Wilcoxon signed-rank test P 0.33). Spherical equivalent differed by 1.0 D in either direction from cycloplegic subjective refraction more frequently among right eyes for self-refraction (11.2%) than noncycloplegic autore- fraction (6.0%; P 0.002). Self-refraction power that differed 1.0 D from cycloplegic subjective refractive error (11.2%) was significantly associated with presenting without spectacles (P 0.011) and with greater absolute power of both spherical (P 0.025) and cylindrical (P 0.022) refractive error.
Conclusions: Self-refraction seems to be less prone to accommodative inaccuracy than noncycloplegic autorefraction, another modality appropriate for use in areas where access to eye care providers is limited. Visual results seem to be comparable. Greater cylindrical power is associated with less accurate results; the adjustable glasses used in this study cannot correct astigmatism. Further studies of the practical applications of this modality are warranted.
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Reproducibility of sphero-cylindrical prescriptions
G. E. Mackenzie, Ophthalmic and Physiological Optics, Vol 28 (2008)
Abstract:
"Purpose: To investigate the reproducibility of the sphero-cylindrical prescriptions provided by 40 optometrists.
Methods: Forty registered optometrists were randomly selected from the cities of Oxford and Westminster in the UK to perform a sphero-cylindrical refraction on an asymptomatic 29-year-old male subject. The 95% limits of reproducibility for each component of refraction were assessed and are presented together with scatterplots, distribution ellipsoids and polar profiles of dioptric power.
Results: The mean stigmatic (spherical equivalent) refraction for the right eye was -0.83 D (S.D. = 0.28 D) with 95% limits of agreement -1.38 and -0.28 D. The 95% reproducibility limits for stigmatic data [1.96 (root 2) (S.D)] was 0.78 D. The average inter-ocular difference in the stigmatic components of refraction was -0.044 D (S.D. = 0.20 D) but estimates ranged from -0.50 to +0.50 D. Mean ortho- and oblique antistigmatic refractions were -0.23 D (S.D. = 0.084 D) and -0.14 D (S.D. = 0.086 D) respectively.
Conclusions: The findings of this paper suggest that refractions performed by multiple optometrists on a single eye will differ in their stigmatic component by over 0.78 D on average not more than once in 20 refractions. The reproducibility of refractions reported here, approximately twice as variable as those reported under repeatability conditions, has profound implications for the analysis of refractive data collected by multiple optometrists over the course of replication, longitudinal and epidemiological studies."
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Self-optimised vision correction with adaptive spectacle lenses in developing countries
M. G. Douali and J. D. Silver, Ophthalmic and Physiological Optics, Vol 24 (2004)
Abstract:
"It is estimated by the World Health Organization that about 1 billion people in the developing world would benefit immediately from distance vision and near vision correction if it were available to them. Here we address this problem and provide a solution by correcting vision in the field with adaptive liquid-filled variable focus lenses. We describe the details of the lens and present the results of a series of experiments performed in Ghana, Nepal, Malawi and South Africa that demonstrate that it is possible by simple means to self-determine and obtain correct refraction using such lenses."
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How to use an adaptive optical approach to correct vision globally
J.D. Silver, M.G. Douali, A.S. Carlson and L. Jenkin, South African Optometrist, Vol 63 (2003)
Abstract:
"It is estimated that about one billion people in the Developing World would benefit immediately from distance vision and near vision correction if it were available to them. Here we address this problem by correcting vision in the field with adaptive liquid filled variable focus lenses, and test whether it is possible by simple means to determine and obtain correct refraction using such lenses."
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