|Year : 2012 | Volume
| Issue : 2 | Page : 85-88
Myopic shift in pediatric pseudophakia: Long-term follow-up
Talal Althomali1, Abdulaziz H Awad2
1 Department of Surgery, College of Medicine, Taif University, Riyadh, Saudi Arabia
2 Department of Surgery, King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia
|Date of Web Publication||13-Sep-2012|
Department of Surgery, College of Medicine, Taif University, PO Box 795, 21944, Taif
Source of Support: None, Conflict of Interest: None
Purpose: To evaluate the rate of myopic shift during 3.5 years in children with pseudophakia at a tertiary eye care hospital. Materials and Methods: A retrospective review of the medical records was conducted for children aged 1-9 years who underwent cataract extraction with intraocular lens (IOL) implantation in order to evaluate initial and annual postoperative refractions. Adjusted estimates of the rate of refractive shift related to patient characteristics were based on a generalized estimating equation model of spherical equivalent refractive error over time, taking into account time-related correlations within the data. Results: A total of 138 eyes of 117 subjects were included in the study. A statistically significant shift in refractive error over time was found in the myopic direction (P < 0.001) Significant interaction was present, indicating that age at time of surgery influenced the rate of myopic shift, but only in children with traumatic etiology. A myopic shift of -0.66 diopters/year was calculated in patients with cataracts of nontraumatic etiology. In those with traumatic cataracts, the rate of myopic shift was -0.85 diopters/year, with a decrease 0.13 diopters/year for each year of increasing age at time of surgery. Conclusion: Our findings suggest a trend toward myopia in pseudophakic children. This was particularly true in children with cataracts of traumatic origin. The strategy of aiming for a hyperopia in order to offset some of the expected myopia may be a reasonable one. Further work is required to develop the necessary nomograms.
Keywords: Children, myopic shift, pseudophakia, Saudi Arabia
|How to cite this article:|
Althomali T, Awad AH. Myopic shift in pediatric pseudophakia: Long-term follow-up. Saudi J Health Sci 2012;1:85-8
| Introduction|| |
There is an increasing acceptance of intraocular lens (IOL) implantation as a means of correcting pediatric aphakia. There is also an increasing concern about the change in refraction as a child's eye grows and, consequently, the optimal IOL power to utilize in those growing eyes. Several approaches have been recommended, at times in sharp contradiction to one other. The majority recommend some form of undercorrection for an anticipated myopic shift; ,,,,,,, however, hyperopic shift has also been reported.  To date, there are few large long-term reported studies of documented refractions in children with pseudophakic eyes. At the King Khaled Eye Specialist Hospital (KKESH), a tertiary eye care facility, pediatric IOLs have been used in older children (9 years and above) since 1989 and in children as young as 1 year since 1993. Despite the multi-physician practice at KKESH, with varying opinions and approaches regarding the optimal IOL power at time of surgery, the consistently documented refractions and frequent follow-ups served as an excellent data source for the authors to evaluate long-term refractive trends in these patients. This study was undertaken to evaluate the rate of myopic shift in young children with pseudophakia by assessing variables that might influence changes in refraction.
| Materials and Methods|| |
The Institutional Review Board's approval was obtained for this study. Chart reviews were undertaken for all children aged between 1 and 9 years who underwent cataract extraction with primary or secondary IOL implantation between late 1992 and early 1996 at the KKESH and with follow-up for at least 2 years postoperatively. The following data were extracted from the medical records: age of patient, refractive measurements and cataract etiology. All patients included in the study were contacted and brought back to our clinic for a complete ophthalmic examination, including repeat keratometry measurements and axial length of each eye.
The Sanders-Retzlaff-Kraff (SRK) II formula was used to calculate the IOL power. Data collected indicated that IOLs of varying A-constants and differing types were used. To avoid these variables, the refractive error obtained closest to 2 months post surgery was used as the baseline postoperative refractive error. Follow-up refractions at 6-months interval postoperatively and annually thereafter were compared with the baseline postoperative refraction. Evaluation of the refractive shift between eyes of the 21 bilateral cases during follow-up showed a correlation coefficient of -0.18. Given the small negative correlation observed, all eyes of all subjects were included in the overall analysis.
IOP measurements were documented from the preoperative visit or prior to surgery while under general anesthesia. Postoperative IOP was documented and a final IOP measurement was obtained from each subject during attendance at the last follow-up clinic.
Best corrected visual acuity was assessed using an E-game chart in a 20-foot lane with one eye occluded (in most patients) or by blurring the other eye with a +5.00 lens when manifest or latent nystagmus was noted. In most cases, retinoscopy was performed 30 minutes after instillation of 1% cyclopentolate and 2.5% phenylephrine drops. In older children, manifest refractions were performed with subjective refinement.
Adjusted estimates of the rate of refractive shift related to patient characteristics were based on a generalized estimating equation (GEE) model of spherical equivalent refractive error over time, taking into account time-related correlations within the data. Statistical analyses were applied to all data using the Stata 6.0 statistical software package (Stata Corporation, College Station, TX, USA). Univariate analysis of continuous variables was done using Student's t-test and one-way analysis of variance (ANOVA). Multivariate analysis using a generalized GEE model of spherical equivalent refractive error over time was used to investigate the association between refractive shift and initial axial length or presence of amblyopia.
| Results|| |
A total of 138 eyes of 117 subjects were included in this study. Mean age at time of surgery was 5.1 (range 1.2-9) years; n = 78(67%) were males and n = 39 (33%) were females.
Visual acuity before surgery and at final follow-up examination is depicted in [Figure 1]. The figure shows a large overall increase in visual acuity seen at the final follow-up visit versus the results obtained preoperatively.
|Figure 1: Distribution of visual acuity before surgery and at final follow-up (n = 138)|
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Myopic shift was greatest in children with traumatic cataracts [Table 1] and in children who were younger at the time of surgery [Table 2]. Evaluation of the mean myopic shift during follow-up, stratified by cataract etiology and age at surgery, suggested that the effect of age on the amount of myopic shift is greater in those with traumatic cataract [Table 3], [Figure 2]. No significant differences in follow-up period between subgroups were present that could account for these results. Multivariate analysis using a GEE model of spherical equivalent refractive error over time revealed no significant association between refractive shift and initial axial length, or presence of amblyopia.
|Figure 2: Mean myopic shift during follow-up by age and cataract etiology|
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|Table 1: Mean age, follow-up and myopic shift in subjects by cataract etiology (n = 138)|
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|Table 2: Mean follow-up, myopic shift and change in axial length in subjects by age category (n = 138)|
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|Table 3: Mean myopic shift by cataract etiology and patient age at time of surgery (n = 138)|
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Investigation of interaction between time since surgery, younger age at time of surgery and traumatic etiology of cataract were all significantly associated with increasing refractive shift in the myopic direction [Table 4]. A statistically significant shift in refractive error in the myopic direction was observed in our subjects during follow-up (P < 0.02). The distribution of change in refractive error is shown in [Figure 3]. This figure highlights the gradual progression toward myopia in our pseudophakic patients. It also shows the greater rate of myopic shift seen in traumatic versus nontraumatic cases.
|Table 4: Adjusted estimates of the rate of refractive shift associated with clinical factors following pediatric cataract extraction with IOL implantation (n = 138)|
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| Discussion|| |
While multiple factors may play a part in the refractive state of an eye (genetics, age, keratometry, axial length, amblyopia, visual acuity, time between onset of cataract and surgery, cataract etiology and time to correct the residual refractive error), these variables, which are impossible to standardize, may limit the conclusions from any study on myopic shift in pediatric aphakia, or pseudophakia.
Our results show a consistent myopic shift, more obvious at a younger age, with a simultaneous increase in axial length. This is in agreement with other reports in the literature. ,, This trend of myopia in pseudophakia is the result of normal eye growth. Dahan and Drusedau demonstrated that pseudophakic eyes show the most growth (axial elongation) during the first 2 years of life, and continue to grow slowly up to the age of 8 years. This is the same pattern of elongation seen in normal phakic eyes.  Our results show that the myopic shift is consistent with this growth pattern, and confirms that younger children experience more of a myopic shift than do older children, because younger eyes elongate more. It is probable that the operated eye shows a larger myopic shift than the unoperated fellow eye. This is because the IOL power is fixed, while the lens power in the phakic eye changes to compensate for the axial elongation.
[Figure 3] clearly shows the greater myopic shift in eyes with traumatic cataract compared with eyes with nontraumatic (congenital/developmental) cataract. It is possible that eyes with nontraumatic cataract may elongate differently from eyes with traumatic cataract, perhaps because congenital/developmental eyes are frequently shorter than normal at the time of cataract surgery. The reduced axial length may be secondary to the blurring of the retinal image experienced during early infancy, or, alternatively, these cases may have intrinsic abnormalities that alter ocular growth.
Our data strongly supports the goal of hyperopia in young children at the time of surgery in anticipation of a significant myopic shift over time. Both cataract etiology and age at time of surgery should be considered when determining the degree of initial hyperopic correction that is desirable. The development of a nomogram based upon a larger set of data is needed to assist surgeons in selecting the optimal IOL power for each patient. Having stated that, one should always keep in mind that the selection of IOL power is very much patient specific. Two main factors may influence the choice of IOL power: (1) the surgeon - this study involved analyzing data from patients over many years in a large eye hospital. Thus, there were many different surgeons - some aimed for emmetropia, others aimed for undercorrection according to age and others undercorrected by 1 diopter at the time of surgery. Furthermore, the condition of the other eye (high hyperopia or myopia, etc.) may have influenced the surgeons' choice of IOL power. (2) The parents - some parents may have preconceived strong opinions on the potential use of contact lenses or glasses to correct the residual hyperopia.
| Conclusion|| |
Our findings suggest a trend toward myopia in pseudophakic children. This was particularly true in children with cataracts of traumatic origin. The strategy of undercorrecting to offset some of the expected myopia may be a reasonable one. Further work is necessary to develop the required nomograms.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4]