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1From the Centre for Paediatric Epidemiology, Institute of Child Health, London, United Kingdom; the 2Department of Ophthalmology and Visual Sciences Unit, Great Ormond Street Hospital, London, United Kingdom; and the 3Division of Epidemiology, Institute of Ophthalmology, London, United Kingdom.
| Abstract |
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METHODS. All children aged less than 16 years in the United Kingdom who had newly diagnosed congenital/infantile cataract in a 12-month period during 19951996 (the British Congenital/infantile Cataract Study) were traced through their managing ophthalmologists. Outcome data were collected at least 6 years after diagnosis, by using specifically designed questionnaires. Ordinal regression analysis identified factors associated with postoperative acuity.
RESULTS. Of 153 children who had surgery, complete data were available in 122 (85%). Median age at follow-up was 7 and 6.91 years, respectively, for bilateral and unilateral disease. Median age at surgery was 4.57 months in bilateral and 2.99 months in unilateral cases, with 40% and 45%, respectively, of children operated on by 3 months. Median (range) postoperative acuity was 6/18 (6/5, no perception of light) in bilateral and 6/60 (6/5, no perception of light) in unilateral disease. Poor compliance with occlusion was the factor most strongly associated with poorer acuity in both unilateral and bilateral disease: the odds of worse vision in unilateral cataract were 7.92 times greater with <50% versus 100% compliance (95% CI 1.6837.26). In bilateral disease, odds of worse vision were reduced with each month of decreasing age at surgery (0.98, 95% CI 0.940.99), but increased by the presence of additional medical conditions (3.53, 95% CI 1.0811.44) and the presence of postoperative ocular complications (2.94, 95% CI 1.386.51).
CONCLUSIONS. These findings support a secular improvement in postoperative acuity in bilateral, and to a lesser extent, unilateral disease. Nevertheless early detection of congenital cataract through effective newborn screening and improving concordance with occlusion both remain priorities. Further improvements in outcomes in unilateral disease are necessary before parents can be advised universally that treatment will achieve a functionally useful "spare" eye.
However, to date, outcomes of congenital and infantile cataract and their associations have generally been reported only in case series, which are intrinsically prone to selection bias and confounding, and they have also often been based on relatively short-term follow-up. Few questions about the treatment of congenital and infantile cataract have been addressed through randomized controlled trials.10 11 12 Clinical factors postulated to be important to visual outcome in children are age at diagnosis and surgery, type of refractive correction, type of cataract surgery, compliance with occlusion regimen, etiology of cataract, presence of nonophthalmic disorders, development of capsular opacity or secondary membrane, and serious ocular postoperative complications.2 6 7 8 9 13 14 15 16 17 Despite recent, and continuing, changes in the management of congenital/infantile cataract, there has been very limited large-scale, population-based research on outcomes. We report long-term postoperative visual acuity in a unique nationally representative group of children with congenital/infantile cataract, together with the factors associated with poor vision.
| Methods |
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Statistical Analysis
From the extant literature described earlier2 13 14 15 16 17 the factors considered, a priori, to be of interest in relation to visual outcome were age at presentation, time since presentation, age at cataract surgery, time since cataract surgery, compliance with occlusion regimen, type of cataract surgery, type of refractive correction, primary IOL implantation, etiology of cataract, presence of nonophthalmic disorders, development of capsular opacity or secondary membrane and serious postoperative complications.
First, any statistical relationships between these potential predictors were investigated. Then, ordinal logistic regression analyses were undertaken to investigate the associations between these factors and postoperative visual acuity. Initially, the effect of each factor was investigated (univariate analysis). Then, the independent effects of each significant factor, taking into account all other significant factors (i.e., joint effects) were investigated (multivariate analyses). We analyzed unilateral and bilateral cases separately because of the inherent differences in terms of factors related to amblyopia and visual outcomes. Furthermore, for children with bilateral cataract, the correlation of acuity outcomes from the same individual was accounted for by the use of two-level hierarchical models (level 1 is the eye and level 2 is the child).23 Analysis was undertaken on computer using commercial software (Stata, 2003; Stata Corp., College Station, TX). Results are presented with 95% confidence intervals (CIs).
To ensure reliable and stable acuity measures, as well as the capture of major postoperative complications, we excluded 12 children for whom follow-up data were available only until the age of 5 years. Snellen acuity measures were used in the analysis, as most (82%) children had vision recorded in this format by the use of standard crowded Snellen charts, with the remainder (71 children, 18%) tested with standard crowded logMAR (logarithm of the minimum angle of resolution) charts. Furthermore, Snellen measurements are made on an ordinal scale that readily incorporates the more extreme categorical outcomes (hand movements, perception of light, nonperception of light) to be included in the analysis. Thus, acuity measures recorded as logMAR (71 children, 18%) were transposed to Snellen notation. Clinicians were asked to report compliance with occlusion and their method of assessment (parental report, diaries or log books, or other means). They also reported the percentage of intended occlusion achieved, as a categorical variable (<50%, 50%, 75%, or 100%), which was used in the analysis of the effect of compliance.
The study adhered to the tenets of the Declaration of Helsinki, was approved by the Great Ormond Street Hospital/Institute of Child Health local research ethics committee, and complied with extant research governance requirements.
| Results |
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The median age at surgery of the children with bilateral cataract was 4.57 months (range, 5 days at 12.12 years), with 40% operated on by 3 months. The median age at surgery of the children with unilateral cataract was 2.99 months (15 days to 5.66 years), with 45% operated on by 3 months. The types of cataract surgery undertaken are shown in Table 1 . Lensectomy and vitrectomy was marginally more common than lens aspiration in both bilateral and unilateral cases. Ninety-nine children with bilateral cataract who had both extracted had the same procedure in each eye (Figure 1) .
In the children with bilateral cataract, 73 (34%) of 212 eyes had primary IOLs, and in the children with unilateral cataract, 14 (35%) of 40 had primary IOLs. Median age (range) at surgery for primary IOL implantation in children with bilateral cataracts, by eye, was 4.39 years (range, 0.0812.12), and the median age of implantation in children with unilateral cataract was younger (2.84 years; range, 0.254.78). Only 12 eyes underwent implantation at ages younger than 2 years.
Forty-eight eyes of 38 children had serious postoperative ocular complications, as shown in Table 2 , which included glaucoma, retinal detachment, and endophthalmitis. In addition, 9 of 40 eyes of children with unilateral cataract and 34 of 212 eyes of children with bilateral cataract showed postoperative capsular/secondary membranes.
The classification of the underlying or associated factors for congenital cataract at the last follow-up visit is shown in Table 3 .
In unilateral cases, there was a strong statistical correlation between age at presentation and age at surgery (P
0.005; Spearmans correlation coefficient, 0.89), as well as an association between age at presentation and compliance (P = 0.05; Kruskal-Wallis score, 10.04). In bilateral cases, there were associations between age at cataract surgery and compliance (P = 0.04; Kruskal-Wallis score, 8.39), as well as serious postoperative complications (P
0.005; Mann-Whitney score, 3.04). The implications of these statistical associations for the analyses are discussed later.
Table 4 presents the findings of the preliminary univariate analysis and Table 5 the findings of the subsequent multivariate analyses of the associations between the factors of interest and visual acuity in bilateral cataract. These are depicted as the odds that the acuity in an eye will be in a worse category, in the presence of the factor of interest (categoric predictors) or with a unit change in the factor (numeric predictors) and after taking account of the within-person correlation between eyes. Several specific variables, when assessed individuallythat is, before taking into account any other factors (univariate analysis)were associated with visual outcome (Table 4) . These included age at presentation and surgery, having an isolated cataract, type of cataract surgery, having primary IOL implantation, compliance with occlusion, presence of other medical conditions, and occurrence of postoperative capsular opacification.
Table 5 shows that age at cataract surgery, compliance with the occlusion regimen, the presence of other medical conditions, and the presence of serious postoperative complications were all independently associated with acuity outcome.
The odds of being in a worse visual acuity category were reduced with each month of decreasing age at surgery. By contrast, the odds of being in a worse visual acuity category were greater for those children with additional medical condition(s) compared with those without and also were greater for those with a postoperative complication than those without. In addition, the odds of achieving a worse VA with 50% compliance were much greater than with 100% compliance. That the finding of compliance of less than 50% was not similarly significantly associated (at the 5% level) may reflect the smaller sample size of this subgroup, together with the statistical correlation between age at cataract surgery and compliance described earlier.
Tables 6 and 7 present the findings of the univariate and multivariate analyses, respectively, of the associations between the factors of interest and visual acuity in unilateral cataract. Several specific variables, when assessed individuallythat is, before taking into account any other factors (univariate analysis)were associated with visual outcome (Table 6) . These included age at presentation, primary IOL implantation, compliance with occlusion, and occurrence of postoperative capsular opacification. Notably, as shown in Table 7 , after adjustment for differences in compliance, no other factors were significantly associated with outcome, perhaps because of the associations described earlier between age at presentation and both compliance and age at surgery, as well as between age at surgery and serious postoperative complications. Thus, for completeness, as age at presentation is considered a key determinant of visual outcomes (and was significantly associated in the univariate analysis), it was retained in the final model, for which the findings are presented in Table 7 .
| Discussion |
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Potential limitations of the study include the nonstandardization of surgical techniques and occlusion protocols, together with the use of outcomes data, which although collected systematically, were reported by a large number of ophthalmologists. However, as children were managed by individuals with special expertise in congenital cataract, and data were validated independently in a 16% subsample, the findings can be viewed as reporting reliable functional outcomes. Furthermore, the nature and size of the population studied offers unique advantages in relation to minimizing selection bias and increasing precision.
Direct comparisons with previous studies, comprising case series rather than whole populations, is not straightforward because of inherent methodological differences. Nonetheless, in broad terms, acuity outcomes in the present study are toward the better end of the ranges that have been reported previously for bilateral cataract,24 25 26 27 and are also generally better than those historically described for unilateral disease.14 25 28 These findings, in particular in relation to unilateral cataract, are consistent with a recent secular trend of improving visual outcomes.29 This trend is likely to be accounted for by a combination of improved management of amblyopia (through earlier detection and surgery, increased emphasis on occlusion and better methods for correction of postoperative refractive error) occurring in parallel with advances in surgical techniques, instrumentation, and materials.
It is noteworthy that half of all children with bilateral disease in the present study achieved a level of acuity (6/18) that is conventionally considered the threshold for mainstream schooling, using printed media and with only minimal extra help.25 This finding should help inform parents of children with congenital cataract who are embarking on treatment and has implications for educational resource allocation. By contrast, only one in five children with unilateral cataract achieved this level of vision in the treated eye. Thus, despite appropriate surgery and amblyopia treatment, these children may fail to realize the useful "spare" eye that clinicians and parents often consider to be main goal of treating unilateral disease.30 We therefore suggest continued circumspection in advising families considering treatment for their children with unilateral cataract, where that is the major consideration.
It is notable that compliance with occlusion (i.e., concordance with prescribed treatment) was the factor most strongly associated with visual outcome in bilateral as well as unilateral disease, although the strength of this association was greater for the latter. This reflects the important impact of competitive inhibition in addition to that of stimulus/form deprivation per se in unilateral (or sometimes in very asymmetrical bilateral) disease.7 9 16 We recognize that because compliance was not objectively measured, but rather was assessed through direct parental questioning and validation of clinical notes, recall bias and other potential sources of error may have resulted in overestimation of the amount of occlusion achieved.31 32 More reliable measurement of compliance would be achieved by using an occlusion dose monitor (a modified occlusion patch connected to a data logger),31 32 which would be recommended in future prospective investigations. Nevertheless, the fact that the association between compliance and acuity could be elicited and quantified, even with the less refined measure of compliance obtained by routine assessment in usual clinical practice, attests to its significance.2 24 33 There is an extensive body of literature regarding dose and duration of occlusion in the management of congenital cataract.7 13 14 15 16 17 However, the barriers to effective initiation and maintenance of occlusion remain significant. They are also relatively underresearched, although a clinically important association between poor compliance and social deprivation has been reported.34 Increased input by orthoptists into supporting occlusion and actively enabling parents embarking on treatment to speak with others who have successfully managed it have both been recommended for children with other forms of amblyopia.35 These may also be appropriate for children with congenital cataract. Providing written information for parents regarding the critical period, the importance of occlusion, and the potential negative effects of not treating amblyopia have also been shown to be beneficial in improving compliance.36 There remains a need for investigations that combine objective assessment of occlusion achieved (rather than that prescribed), together with quantitative and qualitative approaches to capturing child and parental experiences of occlusion over timefor example, through questionnaire instruments such as the Amblyopia Treatment Index37 and/or the Protective Motivation Theory Questionnaire.35
Our study quantifies the established association of better outcome with earlier surgery in children with bilateral cataract. Although this association was not replicated in the statistical model for unilateral disease, this may be accounted for by the correlation between age at surgery and age at presentation and, in turn, the latter variables further association with compliance. Previous reports in the literature have recommended early surgery, albeit at different points, less than 8 weeks.25 26 38 Early detection is crucial for timely surgical intervention.25 In the United Kingdom, screening for ophthalmic disorders is undertaken within a broader context of a national program of child health surveillance. The recommendations of the National Screening Committee (NSC) of the United Kingdom about screening for visual deficits and ophthalmic disorders39 are consistent with recent guidelines elsewhere.40 It is advised that all newborns be assessed for media opacities by examination of the pupillary red reflex, inspection of the eyes, and inquiries about visual behavior. A repeat examination is advised at 6 to 10 weeks. However, the need for improvements in the training of screening pediatricians is recognized.19 41 Routine monitoring and audit of the screening program at a national level could help to ensure that standards are maintained. Routine examination has also been recommended in children with a known family history of hereditary cataracts, to ensure prompt detection. This approach also requires professional awareness of the need to respond actively to parental concerns.39
Although surgery for visually significant cataract must be within the critical period, to prevent amblyopia, complications also have been shown to increase with earlier surgery.42 In this study, there was a significant association between age at surgery and serious postoperative complications, echoing the findings of other studies.25 26 27 These postoperative complications were associated with a poorer visual outcome. There is a need therefore to balance the timing of surgery to prevent amblyopia with the best time to minimize postoperative complications. The point of equilibrium is unknown. A prospective trial in which children could be randomized to surgery at different ages within the critical period in which treatment is likely to be most effective (by convention currently considered to be up to 8 weeks of age in dense unilateral and approximately 12 weeks in bilateral disease), could address the key question of the optimum timing.
That the presence of other nonophthalmic disorders was associated with poorer visual acuity in bilateral disease in the present study is consistent with prior reports24 26 and is likely to reflect additional causes of poor vision, such as learning impairment or cerebral visual impairment and difficulties of acuity assessment in some children.
As primary IOL implantation was undertaken in only 12 eyes of children
2 years old in our study, reflecting prevailing management practices in 19951996, there is limited statistical power for investigations of the outcomes of this approach, which is increasingly advocated by some for infants with cataract. It remains to be shown through population-based studies and randomized clinical trials that IOL implantation offers additional visual benefits without increased risk of complication.
We suggest that our findings provide evidence of recent improvement over time in the visual prognosis in bilateral, and to a lesser degree, unilateral cataract, in children in industrialized countries. This improvement has been achieved through earlier detection and referral of affected children for appropriate surgical, medical, and optical treatment. Nevertheless, there is room for further improvement, which will necessitate continued implementation of existing effective screening and treatment strategies together with research-based innovation in these areas, to achieve the international goal of reducing the burden of avoidable childhood visual impairment due to congenital cataract.
| Appendix 1 |
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| Acknowledgements |
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| Footnotes |
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Supported by a grant from the Guide Dogs for the Blind Association. Research at the Institute of Child Health and Great Ormond Street Hospital for Children National Health Service (NHS) Trust benefits from research and development funding received from the NHS Executive.
Submitted for publication August 30, 2005; revised December 6, 2005, and March 27, May 11, and May 18, 2006; accepted August 15, 2006.
Disclosure: M. Chak, None; A. Wade, None; J.S. Rahi, None
The publication costs of this article were defrayed in part by page charge payment. This article must therefore be marked "advertisement" in accordance with 18 U.S.C.
1734 solely to indicate this fact.
Corresponding author: Jugnoo Sangeeta Rahi, Centre for Paediatric Epidemiology, Institute of Child Health, 30 Guilford Street, London WC1N 1EH, UK; j.rahi{at}ich.ucl.ac.uk.
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