Major Articles The incidence and visual acuity outcomes of children identified with ametropic amblyopia by vision screening Mohammed Aftab Maqsud, MMedSci, MSc,a and Gemma E. Arblaster, MSc, BMedSci (Hons) Orthopticsb,c PURPOSE METHOD
RESULTS
CONCLUSIONS
To determine the incidence of ametropic amblyopia within a vision screening program’s population and report the visual acuity outcomes of children identified with the condition. The medical records of children who underwent vision screening as their first assessment at 4-5 years of age between September 1, 2005 and August 31, 2006, were retrospectively reviewed. Children referred with #0.30 logMAR in each eye with at least 1 year of follow-up had their hospital notes reviewed and data on final visual acuity, refractive error, and follow-up period collected. A total of 33 children identified as having ametropic amblyopia with a follow-up of at least 1 year. The incidence of ametropic amblyopia was 2%-3.2%, depending on the definition used. The mean visual acuity achieved after treatment was 0.12 logMAR, which is significantly less than the age-appropriate mean of 0.00 logMAR (P \ 0.01). Ametropic amblyopia responds to treatment, but most children demonstrate persistent reduced visual acuity at age 7 years. The incidence of ametropic amblyopia within a routine vision screening population shows that significant numbers fail to self-present. ( J AAPOS 2015;19:104-107)
A
metropic amblyopia is defined as a bilateral condition that occurs when there is a high degree of refractive error and therefore blur in each eye.1,2 Ametropic amblyopia may develop if there is hyperopia of $4 D, myopia of $8 D, or astigmatism of $2 D.1,3,4 Ametropic amblyopia is a condition given little priority on the assumption that this condition will self-present,5-7 and the condition has received less research attention than unilateral amblyopia.6-8 Ametropic amblyopia responds well to refractive correction; however, it is unclear whether affected individuals reach age-appropriate vision levels, and the time required for maximum improvement is unknown.3,4,9 The purpose of this study was to determine the incidence of ametropic amblyopia in a vision screening program in the UK and to report the visual
Author affiliations: aOrthoptic Department, Hull Royal Infirmary, Hull, United Kingdom; b Academic Unit of Ophthalmology and Orthoptics, University of Sheffield, Sheffield, United Kingdom; cOrthoptic Department, Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, United Kingdom Submitted September 30, 2013. Revision accepted October 31, 2014. Published online March 28, 2015. Correspondence: Mohammed Aftab Maqsud, MMedSci, MSc, Orthoptic Department, Hull Royal Infirmary, Anlaby Road, Hull, HU3 2 JZ. (email: mohammed.maqsud@hey. nhs.uk). Copyright Ó 2015 by the American Association for Pediatric Ophthalmology and Strabismus. 1091-8531/$36.00 http://dx.doi.org/10.1016/j.jaapos.2014.10.023
104
acuity outcomes after treatment in children identified with the condition.
Subjects and Methods The research was conducted in accordance with the Declaration of Helsinki and ethical approval was obtained from Hull and East Yorkshire NHS Trust. The medical records of all children aged 4-5 years referred from a routine vision screening program over a period of 1 year, September 1, 2005, to August 31, 2006, were retrospectively reviewed to identify children with visual acuity #0.300 logMAR in each eye and refractive error of .4.00 D spherical equivalent or .1.50 D of astigmatism in each eye. Visual acuity was measured by orthoptists using the Keeler crowded logMAR test or the crowded logMAR Kay picture test. Cycloplegic retinoscopy and fundus and media examination were performed by a pediatric ophthalmologist or optometrist; full refractive correction was always prescribed. Ideally visual acuity would have been assessed immediately following spectacle correction of the refractive error in order to diagnose ametropic amblyopia; however, this was not possible. Visual acuity was routinely assessed 6 weeks after full-time spectacle wear. At this 6-week review, ametropic amblyopia was diagnosed if corrected visual acuity of 0.200 logMAR was not achieved in each eye. This level was chosen as an acceptable level of visual acuity for children 4-5 years of age.8 If visual acuity of 0.200 logMAR was achieved in each eye, the participant did not fulfill the
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Table 1. Initial and final visual acuity, and refractive error results for all participants Type of refractive error
Number
Mean SE, D
Standard deviation, D
Range of SE, D
Mean initial visual acuity, logMAR
Hyperopia Astigmatism Hyperopia and astigmatism Myopia
13 12 8 0
5.19 1.43 6.20 -
1.06 1.11 1.45 -
4.00-7.50 0.00-3.00 3.50-8.13 -
0.553 0.452 0.591 -
D, diopter; SE, spherical equivalent. criteria for ametropic amblyopia and was excluded. The inclusion criteria were no previous ocular treatment, a minimum follow-up of 1 year, good attendance, and good treatment compliance as reported by the parent or guardian. The following data was collected: visual acuity, refractive error, duration of follow-up, presence of strabismus, and whether occlusion therapy was required. Outcome was defined as the final recorded visual acuity. Visual acuity outcomes were compared to normal visual acuity for children of a similar age, identified as 0.000 logMAR using the Keeler crowded logMAR test.10 The primary treatment for all participants was full refractive correction with instructions for full-time glasses wear. Occlusion was only prescribed in cases where participants had complied with full-time glasses wear through their refractive adaptation period but an interocular difference of .0.200 logMAR persisted. Departmental protocols were followed before occlusion therapy was considered, including correct dispensing of spectacles; treatment compliance, as reported by parents; subjective refraction for those considered to be overplussed; further investigation if visual acuity failed to improve or worsened; and consideration of whether latent nystagmus was present through observation by the examiner, ophthalmoscopy, or assessment of visual acuity with both eyes open. Participants who missed two consecutive appointments were considered noncompliant and excluded. A minimum sample of 27 was required to ensure 80% power for the study using G*Power software (Institute for Experimental Psychology, Dusseldorf).11 To assess whether ametropic amblyopic patients achieved age-appropriate visual acuity a single sample t test was used. An independent t test was used to analyze whether treatment influenced final visual acuity. Different refractive errors were compared using a one-way analysis of variance test; these refractive groups were defined as follows: hyperopia, hyperopia $4.00 D spherical equivalent \1.50 D cylinder; astigmatism, \2.00 D but .1.50 D; hyperopia and astigmatism: $2.00 D and .1.50 D; myopia, $6.00 D.
Results Vision screening was offered to 2,468 children and performed on 2,240 children during the study period. Of those who did not pass routine vision screening, 78 (3.5%) failed because of reduced (uncorrected) visual acuity in each eye. Of these, 33 failed to meet the refractive criteria and were excluded, including 2 with pathology (1 bilateral lens opacities, 1 fine latent nystagmus) and 6 with low myopia whose visual acuity improved at their
Journal of AAPOS
first visit following refractive correction. A further 12 were later excluded as they were deemed noncompliant with treatment. Prior to exclusions for poor treatment compliance, 45 participants fulfilled the study visual acuity and refractive criteria for ametropic amblyopia giving an incidence of 2.0%. A total of 33 participants (21 males, 12 females) met the inclusion criteria; mean age was 4 years, 7months, standard deviation 5 months (range, 4-5.83 years). One child who had recently relocated to the area started treatment at 5 years 11 months. Of the 33 children, 5 had a manifest deviation. Clinical findings are summarized in e-Supplement 1 (available at jaapos. org); refractive findings are summarized in Table 1. Uncorrected visual acuity in the better eye ranged from 0.300 to 0.875 logMAR (mean with standard deviation, 0.46 0.17 logMAR). The interocular difference in visual acuity ranged from 0.000 to 0.600 logMAR (mean, 0.15 0.16 logMAR). A summary of initial and final visual acuity for all eyes can be seen in Figure 1. Five children had an esotropia of 8–25 D; cosmesis was acceptable in all cases and none underwent strabismus surgery. Nine participants underwent unilateral occlusion therapy; 1 for strabismic amblyopia, 5 for anisometropic amblyopia, and 3 for strabismic and anisometropic amblyopia. The mean visual acuity outcome for ametropic amblyopic patients (excluding those requiring unilateral occlusion therapy for strabismic amblyopia) was 0.12 0.08 logMAR, which was statistically significant compared to the age-appropriate visual acuity of 0.0 logMAR (P \ 0.01). The improvement in visual acuity over time is shown in Figure 2. Of 33 children, 17 (50%) achieved visual acuity of 0.20 logMAR in each eye at 30 weeks’ refractive correction; 25 (75%), at 60 weeks; and 30 (90%), at 60 weeks. No correlation was found between age of initial refractive correction and final visual acuity (r 5 0.08; P . 0.05). Those prescribed glasses before 4 years and 7 months showed no statistical difference in visual acuity outcomes from those prescribed glasses after 4 years and 7 months (P . 0.05). No difference was found in visual acuity outcomes between the different refractive groups (P . 0.05). No correlation was found between visual acuity at referral and the amount of (spherical equivalent) refractive error (P . 0.05) or between the amount of refractive error and final visual acuity (r 5 0.01; P . 0.05). Of the 12 participants (mean age, 4.58 0.33 years; range, 4-5.08 years) excluded from the study because of poor treatment compliance or poor attendance, none had
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FIG 1. Initial visual acuity at referral of all participants; the improvement in visual acuity following refractive correction; and improvement following occlusion therapy in those participants where it was required.
strabismus. The mean visual acuity outcome in the better eye was 0.13 0.1 logMAR. Mean follow-up was 10 3 months.
Discussion In this study, children with ametropic amblyopia failed to reach normal visual acuity levels by age 7 years following correction of their refractive error between the ages of 4 and 5 years (mean, 0.12 logMAR: P \ 0.01). Whether this difference is functionally important is debatable and it is possible that the visual acuity could improve beyond the age of 7 years.10 The 2% incidence of ametropic amblyopia in this study was higher than other published figures of 0.5%, 0.2%, and 0.6%.3,4,9 One reason for this variance may be that this study investigated a group for which there were no previous concerns.7,8
Wallace and colleagues3 assessed children 3-10 years of age with similar refractive error. The mean visual acuity achieved in the better-seeing eye in our study (0.17 logMAR) compares well with the vision achieved with both eyes open (0.16 logMAR) reported by Wallace and colleagues.3 In their study, 74% of children achieved visual acuity of 20/25 (0.1 logMAR) after 1 year; however, only 31% of participants in our study achieved this visual acuity level at 1 year. This difference may be due to methodology: Wallace and colleagues3 measured vision with both eyes open, which has been shown to give a higher threshold visual acuity measure.10 In the present study, refractive correction was the sole treatment for 73% (24/33) of childen, whereas 27% (9/33) also required a period of unilateral occlusion therapy, which is comparable to the 36% reported by Klimek and colleagues.12
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Visual acuity in the better eye was between 0.3-0.875 logMAR yet did not cause any concern to parents as assumed may be the case.1,7,8 Following refractive correction 2% were later diagnosed as having ametropic amblyopia. Visual acuity gradually improved in those with ametropic amblyopia, yet 50% did not achieve the expected normal level of visual acuity (0.00 logMAR) at age 7.2,3,15 The impact of reduced levels of vision in children and the longer-term outcomes in ametropic amblyopia warrant further study.
Acknowledgements The authors thank their colleagues Alexandra Lindstrom and Sandra Medforth as well as Mr. Jim Innes, whose patients were reviewed for the study. References
FIG 2. Improvement in visual acuity over time for participants who had had refractive correction as their sole treatment.
Visual acuity improved gradually, with a mean improvement of 0.12 logMAR over a mean period of 50 weeks. Improvement in visual acuity after this time is thought to occur at a rate expected secondary to a function of age or learning effects.6 It has been hypothesized that this gradual improvement is a reflection of the gradual development of the visual cortex and lateral geniculate body once a focused image is achieved with refractive correction.13,14 Age at which treatment commenced in the present study did not significantly affect final visual acuity (P . 0.05).3,4,15 The power of this analysis however was low (13%), and the study analysis was not robust, because the age range of the participants was limited to age 4-5 years. Although age at first refractive correction failed to influence the final visual acuity, it is unclear whether an upper age limit exists by which treatment must commence. Some studies suggest the later presentation of ametropic amblyopia accounts for the disappointing outcomes and advocate identification and treatment of high hyperopia before 3 years of age.12,16,17 In the present study 15% of participants (5/33) had manifest strabismus, compared with 84% of all individuals with high hyperopia.12,18 High hyperopic individuals can have reduced amplitudes of accommodation, which may contribute to their lack of emmetropization and a lower incidence of manifest strabismus in ametropic amblyopia. In those in whom strabismus does develop, Edelman and Borchert hypothesize individuals may have enough accommodation to cause strabismus but not enough to eliminate blur.15 Within this vision screening cohort 3.5% of children were identified with reduced visual acuity in each eye.
Journal of AAPOS
1. Taylor K, Powell C, Hatt, et al. Interventions for unilateral and bilateral refractive amblyopia. Cochrane Database Syst Rev, http:// onlinelibrary.wiley.com/doi/10.1002/14651858.CD005137/full; 2012. Accessed 14/07/12. 2. Hubel D, Wiesel T. The period of susceptibility to the physiological effects of unilateral eye closure in kittens. J Physiol 1970;206:419-36. 3. Wallace DK, Chandler DL, Beck RW, et al. Treatment of bilateral refractive amblyopia in children three to less than 10 years of age. Am J Ophthalmol 2007;144:487-96. 4. Ziylan S, Yabas O, Zorlutuna N, et al. Isoametropic amblyopia in highly hyperopic children. Acta Ophthalmol Scand 2007;85:111-13. 5. AAO. Vision screening for infants and children. (2007) http://onetext. aao.org/CE?Practice Guidlines/ClinicalStatements-Content.aspx? cid50ad11e02–6a8b-437e-8d01-f45eb18bc0b6 Accessed 14/08/12. 6. Carlton J, Kamon J, Czoski-Murray C, et al. The clinical effectiveness and cost-effectiveness of screening programmes for amblyopia and strabismus in children up to the age of 4-5 years: a systematic review and economic evaluation. Health Technol Assess 2008;12. iii, xi-194. 7. Pattison B, Plymat K. Vision Screening of school children: should it be continued? Contemp Nurse 2001;10:163-71. 8. UK NSC. Vision Screening in Children aged 4-5 years- an evidence review (2013). http://www.screening.nhs.uk/vision-child Accessed March 1, 2014. 9. Fern K. Visual acuity outcome in Isoametropic Hyperopia. Optom Vis Sci 1989;66:649-58. 10. Manny R, Hussein M, Gwiazda J, et al. Repeatability of ETDRS visual acuity in children. Invest Ophthalmol Vis Sci 2003;44:3294-300. 11. Faul F, Erdfelder E, Lang A, et al. G*Power 3: a flexible statistical power analysis program for the social, behavioural and biomedical sciences. Behav Res Methods 2007;39:175-91. 12. Klimek D, Cruz O, Scott W, et al. Isoametropic amblyopia due to high hyperopia in children. J AAPOS 2004;8:310-13. 13. Timney B, Mitchell D, Giffin F. The development of vision in cats after extended periods of dark-rearing. Exp Brain Res 1978;31:547-60. 14. Regal D, Boothe R, Teller D, et al. Visual acuity and visual responsiveness in dark-reared monkeys. Vision Res 1976;16:523-30. 15. Edelman P, Borchert M. Visual outcome in high hypermetropia. J AAPOS 1997;1:147-50. 16. Kirk V, Clausen M, Armitage M. Preverbal photoscreening for amblyogenic factors and outcomes in amblyopia treatment: early objective screening and visual acuities. Arch Ophthalmol 2008;125:489-92. 17. Hunter D. Treatment of amblyopia in older children. Arch Ophthalmol 2005;123:557-8. 18. Atkinson J, Braddick O, Robier B, et al. Two infant vision screening programmes: prediction and prevention of strabismus and amblyopia from photo and video-refractive screening. Eye (Lond) 1996;10: 189-98.
RESULTS
CONCLUSIONS
To determine the incidence of ametropic amblyopia within a vision screening program’s population and report the visual acuity outcomes of children identified with the condition. The medical records of children who underwent vision screening as their first assessment at 4-5 years of age between September 1, 2005 and August 31, 2006, were retrospectively reviewed. Children referred with #0.30 logMAR in each eye with at least 1 year of follow-up had their hospital notes reviewed and data on final visual acuity, refractive error, and follow-up period collected. A total of 33 children identified as having ametropic amblyopia with a follow-up of at least 1 year. The incidence of ametropic amblyopia was 2%-3.2%, depending on the definition used. The mean visual acuity achieved after treatment was 0.12 logMAR, which is significantly less than the age-appropriate mean of 0.00 logMAR (P \ 0.01). Ametropic amblyopia responds to treatment, but most children demonstrate persistent reduced visual acuity at age 7 years. The incidence of ametropic amblyopia within a routine vision screening population shows that significant numbers fail to self-present. ( J AAPOS 2015;19:104-107)
A
metropic amblyopia is defined as a bilateral condition that occurs when there is a high degree of refractive error and therefore blur in each eye.1,2 Ametropic amblyopia may develop if there is hyperopia of $4 D, myopia of $8 D, or astigmatism of $2 D.1,3,4 Ametropic amblyopia is a condition given little priority on the assumption that this condition will self-present,5-7 and the condition has received less research attention than unilateral amblyopia.6-8 Ametropic amblyopia responds well to refractive correction; however, it is unclear whether affected individuals reach age-appropriate vision levels, and the time required for maximum improvement is unknown.3,4,9 The purpose of this study was to determine the incidence of ametropic amblyopia in a vision screening program in the UK and to report the visual
Author affiliations: aOrthoptic Department, Hull Royal Infirmary, Hull, United Kingdom; b Academic Unit of Ophthalmology and Orthoptics, University of Sheffield, Sheffield, United Kingdom; cOrthoptic Department, Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, United Kingdom Submitted September 30, 2013. Revision accepted October 31, 2014. Published online March 28, 2015. Correspondence: Mohammed Aftab Maqsud, MMedSci, MSc, Orthoptic Department, Hull Royal Infirmary, Anlaby Road, Hull, HU3 2 JZ. (email: mohammed.maqsud@hey. nhs.uk). Copyright Ó 2015 by the American Association for Pediatric Ophthalmology and Strabismus. 1091-8531/$36.00 http://dx.doi.org/10.1016/j.jaapos.2014.10.023
104
acuity outcomes after treatment in children identified with the condition.
Subjects and Methods The research was conducted in accordance with the Declaration of Helsinki and ethical approval was obtained from Hull and East Yorkshire NHS Trust. The medical records of all children aged 4-5 years referred from a routine vision screening program over a period of 1 year, September 1, 2005, to August 31, 2006, were retrospectively reviewed to identify children with visual acuity #0.300 logMAR in each eye and refractive error of .4.00 D spherical equivalent or .1.50 D of astigmatism in each eye. Visual acuity was measured by orthoptists using the Keeler crowded logMAR test or the crowded logMAR Kay picture test. Cycloplegic retinoscopy and fundus and media examination were performed by a pediatric ophthalmologist or optometrist; full refractive correction was always prescribed. Ideally visual acuity would have been assessed immediately following spectacle correction of the refractive error in order to diagnose ametropic amblyopia; however, this was not possible. Visual acuity was routinely assessed 6 weeks after full-time spectacle wear. At this 6-week review, ametropic amblyopia was diagnosed if corrected visual acuity of 0.200 logMAR was not achieved in each eye. This level was chosen as an acceptable level of visual acuity for children 4-5 years of age.8 If visual acuity of 0.200 logMAR was achieved in each eye, the participant did not fulfill the
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Table 1. Initial and final visual acuity, and refractive error results for all participants Type of refractive error
Number
Mean SE, D
Standard deviation, D
Range of SE, D
Mean initial visual acuity, logMAR
Hyperopia Astigmatism Hyperopia and astigmatism Myopia
13 12 8 0
5.19 1.43 6.20 -
1.06 1.11 1.45 -
4.00-7.50 0.00-3.00 3.50-8.13 -
0.553 0.452 0.591 -
D, diopter; SE, spherical equivalent. criteria for ametropic amblyopia and was excluded. The inclusion criteria were no previous ocular treatment, a minimum follow-up of 1 year, good attendance, and good treatment compliance as reported by the parent or guardian. The following data was collected: visual acuity, refractive error, duration of follow-up, presence of strabismus, and whether occlusion therapy was required. Outcome was defined as the final recorded visual acuity. Visual acuity outcomes were compared to normal visual acuity for children of a similar age, identified as 0.000 logMAR using the Keeler crowded logMAR test.10 The primary treatment for all participants was full refractive correction with instructions for full-time glasses wear. Occlusion was only prescribed in cases where participants had complied with full-time glasses wear through their refractive adaptation period but an interocular difference of .0.200 logMAR persisted. Departmental protocols were followed before occlusion therapy was considered, including correct dispensing of spectacles; treatment compliance, as reported by parents; subjective refraction for those considered to be overplussed; further investigation if visual acuity failed to improve or worsened; and consideration of whether latent nystagmus was present through observation by the examiner, ophthalmoscopy, or assessment of visual acuity with both eyes open. Participants who missed two consecutive appointments were considered noncompliant and excluded. A minimum sample of 27 was required to ensure 80% power for the study using G*Power software (Institute for Experimental Psychology, Dusseldorf).11 To assess whether ametropic amblyopic patients achieved age-appropriate visual acuity a single sample t test was used. An independent t test was used to analyze whether treatment influenced final visual acuity. Different refractive errors were compared using a one-way analysis of variance test; these refractive groups were defined as follows: hyperopia, hyperopia $4.00 D spherical equivalent \1.50 D cylinder; astigmatism, \2.00 D but .1.50 D; hyperopia and astigmatism: $2.00 D and .1.50 D; myopia, $6.00 D.
Results Vision screening was offered to 2,468 children and performed on 2,240 children during the study period. Of those who did not pass routine vision screening, 78 (3.5%) failed because of reduced (uncorrected) visual acuity in each eye. Of these, 33 failed to meet the refractive criteria and were excluded, including 2 with pathology (1 bilateral lens opacities, 1 fine latent nystagmus) and 6 with low myopia whose visual acuity improved at their
Journal of AAPOS
first visit following refractive correction. A further 12 were later excluded as they were deemed noncompliant with treatment. Prior to exclusions for poor treatment compliance, 45 participants fulfilled the study visual acuity and refractive criteria for ametropic amblyopia giving an incidence of 2.0%. A total of 33 participants (21 males, 12 females) met the inclusion criteria; mean age was 4 years, 7months, standard deviation 5 months (range, 4-5.83 years). One child who had recently relocated to the area started treatment at 5 years 11 months. Of the 33 children, 5 had a manifest deviation. Clinical findings are summarized in e-Supplement 1 (available at jaapos. org); refractive findings are summarized in Table 1. Uncorrected visual acuity in the better eye ranged from 0.300 to 0.875 logMAR (mean with standard deviation, 0.46 0.17 logMAR). The interocular difference in visual acuity ranged from 0.000 to 0.600 logMAR (mean, 0.15 0.16 logMAR). A summary of initial and final visual acuity for all eyes can be seen in Figure 1. Five children had an esotropia of 8–25 D; cosmesis was acceptable in all cases and none underwent strabismus surgery. Nine participants underwent unilateral occlusion therapy; 1 for strabismic amblyopia, 5 for anisometropic amblyopia, and 3 for strabismic and anisometropic amblyopia. The mean visual acuity outcome for ametropic amblyopic patients (excluding those requiring unilateral occlusion therapy for strabismic amblyopia) was 0.12 0.08 logMAR, which was statistically significant compared to the age-appropriate visual acuity of 0.0 logMAR (P \ 0.01). The improvement in visual acuity over time is shown in Figure 2. Of 33 children, 17 (50%) achieved visual acuity of 0.20 logMAR in each eye at 30 weeks’ refractive correction; 25 (75%), at 60 weeks; and 30 (90%), at 60 weeks. No correlation was found between age of initial refractive correction and final visual acuity (r 5 0.08; P . 0.05). Those prescribed glasses before 4 years and 7 months showed no statistical difference in visual acuity outcomes from those prescribed glasses after 4 years and 7 months (P . 0.05). No difference was found in visual acuity outcomes between the different refractive groups (P . 0.05). No correlation was found between visual acuity at referral and the amount of (spherical equivalent) refractive error (P . 0.05) or between the amount of refractive error and final visual acuity (r 5 0.01; P . 0.05). Of the 12 participants (mean age, 4.58 0.33 years; range, 4-5.08 years) excluded from the study because of poor treatment compliance or poor attendance, none had
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FIG 1. Initial visual acuity at referral of all participants; the improvement in visual acuity following refractive correction; and improvement following occlusion therapy in those participants where it was required.
strabismus. The mean visual acuity outcome in the better eye was 0.13 0.1 logMAR. Mean follow-up was 10 3 months.
Discussion In this study, children with ametropic amblyopia failed to reach normal visual acuity levels by age 7 years following correction of their refractive error between the ages of 4 and 5 years (mean, 0.12 logMAR: P \ 0.01). Whether this difference is functionally important is debatable and it is possible that the visual acuity could improve beyond the age of 7 years.10 The 2% incidence of ametropic amblyopia in this study was higher than other published figures of 0.5%, 0.2%, and 0.6%.3,4,9 One reason for this variance may be that this study investigated a group for which there were no previous concerns.7,8
Wallace and colleagues3 assessed children 3-10 years of age with similar refractive error. The mean visual acuity achieved in the better-seeing eye in our study (0.17 logMAR) compares well with the vision achieved with both eyes open (0.16 logMAR) reported by Wallace and colleagues.3 In their study, 74% of children achieved visual acuity of 20/25 (0.1 logMAR) after 1 year; however, only 31% of participants in our study achieved this visual acuity level at 1 year. This difference may be due to methodology: Wallace and colleagues3 measured vision with both eyes open, which has been shown to give a higher threshold visual acuity measure.10 In the present study, refractive correction was the sole treatment for 73% (24/33) of childen, whereas 27% (9/33) also required a period of unilateral occlusion therapy, which is comparable to the 36% reported by Klimek and colleagues.12
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Maqsud and Arblaster
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Visual acuity in the better eye was between 0.3-0.875 logMAR yet did not cause any concern to parents as assumed may be the case.1,7,8 Following refractive correction 2% were later diagnosed as having ametropic amblyopia. Visual acuity gradually improved in those with ametropic amblyopia, yet 50% did not achieve the expected normal level of visual acuity (0.00 logMAR) at age 7.2,3,15 The impact of reduced levels of vision in children and the longer-term outcomes in ametropic amblyopia warrant further study.
Acknowledgements The authors thank their colleagues Alexandra Lindstrom and Sandra Medforth as well as Mr. Jim Innes, whose patients were reviewed for the study. References
FIG 2. Improvement in visual acuity over time for participants who had had refractive correction as their sole treatment.
Visual acuity improved gradually, with a mean improvement of 0.12 logMAR over a mean period of 50 weeks. Improvement in visual acuity after this time is thought to occur at a rate expected secondary to a function of age or learning effects.6 It has been hypothesized that this gradual improvement is a reflection of the gradual development of the visual cortex and lateral geniculate body once a focused image is achieved with refractive correction.13,14 Age at which treatment commenced in the present study did not significantly affect final visual acuity (P . 0.05).3,4,15 The power of this analysis however was low (13%), and the study analysis was not robust, because the age range of the participants was limited to age 4-5 years. Although age at first refractive correction failed to influence the final visual acuity, it is unclear whether an upper age limit exists by which treatment must commence. Some studies suggest the later presentation of ametropic amblyopia accounts for the disappointing outcomes and advocate identification and treatment of high hyperopia before 3 years of age.12,16,17 In the present study 15% of participants (5/33) had manifest strabismus, compared with 84% of all individuals with high hyperopia.12,18 High hyperopic individuals can have reduced amplitudes of accommodation, which may contribute to their lack of emmetropization and a lower incidence of manifest strabismus in ametropic amblyopia. In those in whom strabismus does develop, Edelman and Borchert hypothesize individuals may have enough accommodation to cause strabismus but not enough to eliminate blur.15 Within this vision screening cohort 3.5% of children were identified with reduced visual acuity in each eye.
Journal of AAPOS
1. Taylor K, Powell C, Hatt, et al. Interventions for unilateral and bilateral refractive amblyopia. Cochrane Database Syst Rev, http:// onlinelibrary.wiley.com/doi/10.1002/14651858.CD005137/full; 2012. Accessed 14/07/12. 2. Hubel D, Wiesel T. The period of susceptibility to the physiological effects of unilateral eye closure in kittens. J Physiol 1970;206:419-36. 3. Wallace DK, Chandler DL, Beck RW, et al. Treatment of bilateral refractive amblyopia in children three to less than 10 years of age. Am J Ophthalmol 2007;144:487-96. 4. Ziylan S, Yabas O, Zorlutuna N, et al. Isoametropic amblyopia in highly hyperopic children. Acta Ophthalmol Scand 2007;85:111-13. 5. AAO. Vision screening for infants and children. (2007) http://onetext. aao.org/CE?Practice Guidlines/ClinicalStatements-Content.aspx? cid50ad11e02–6a8b-437e-8d01-f45eb18bc0b6 Accessed 14/08/12. 6. Carlton J, Kamon J, Czoski-Murray C, et al. The clinical effectiveness and cost-effectiveness of screening programmes for amblyopia and strabismus in children up to the age of 4-5 years: a systematic review and economic evaluation. Health Technol Assess 2008;12. iii, xi-194. 7. Pattison B, Plymat K. Vision Screening of school children: should it be continued? Contemp Nurse 2001;10:163-71. 8. UK NSC. Vision Screening in Children aged 4-5 years- an evidence review (2013). http://www.screening.nhs.uk/vision-child Accessed March 1, 2014. 9. Fern K. Visual acuity outcome in Isoametropic Hyperopia. Optom Vis Sci 1989;66:649-58. 10. Manny R, Hussein M, Gwiazda J, et al. Repeatability of ETDRS visual acuity in children. Invest Ophthalmol Vis Sci 2003;44:3294-300. 11. Faul F, Erdfelder E, Lang A, et al. G*Power 3: a flexible statistical power analysis program for the social, behavioural and biomedical sciences. Behav Res Methods 2007;39:175-91. 12. Klimek D, Cruz O, Scott W, et al. Isoametropic amblyopia due to high hyperopia in children. J AAPOS 2004;8:310-13. 13. Timney B, Mitchell D, Giffin F. The development of vision in cats after extended periods of dark-rearing. Exp Brain Res 1978;31:547-60. 14. Regal D, Boothe R, Teller D, et al. Visual acuity and visual responsiveness in dark-reared monkeys. Vision Res 1976;16:523-30. 15. Edelman P, Borchert M. Visual outcome in high hypermetropia. J AAPOS 1997;1:147-50. 16. Kirk V, Clausen M, Armitage M. Preverbal photoscreening for amblyogenic factors and outcomes in amblyopia treatment: early objective screening and visual acuities. Arch Ophthalmol 2008;125:489-92. 17. Hunter D. Treatment of amblyopia in older children. Arch Ophthalmol 2005;123:557-8. 18. Atkinson J, Braddick O, Robier B, et al. Two infant vision screening programmes: prediction and prevention of strabismus and amblyopia from photo and video-refractive screening. Eye (Lond) 1996;10: 189-98.
