Cataract is one of the leading treatable causes of visual impairment in children.1 It is estimated that congenital cataract is responsible for approximately 5% to 20% of childhood blindness globally. Although there might be variability from country to country, the incidence is about 1 in 250 births.2 Congenital cataract can be unilateral or bilateral. Opacity can vary in size and location, and opacifications can range in severity from a small white spot to involving the entire lens. Regardless of etiology, cataracts that occlude the optical axis and hinder vision must be treated early for normal visual development.
The most severe complication of congenital cataract is permanent visual impairment. Occlusion of the optical axis because of lens opacity during a sensitive period of visual development could result in permanent amblyopia and nystagmus. Unilateral cataracts have worse visual prognoses than bilateral cataracts. Even minimal opacity might cause severe amblyopia in some cases.
In addition to an appropriate surgical intervention to clear the visual axis, the use of aphakic spectacles, contact lenses, or intraocular lens (IOL) implantation is necessary for good visual development.
Most eye growth occurs in the first year of life.3 Changes in the globe’s axial length (AL) occur in three phases. The first phase (from birth to 2 years) is the rapid growth stage. The AL increases by approximately 4.0 mm in the first 6 months and by approximately 2.0 mm in the next 6 months of life. The growth rate slows in the second (2 to 5 years) and third (5 to 13 years) phases, with elongation of only 1.0 mm in each phase.
The aim of the present study was to analyze the effect of lens status on AL in patients who underwent surgery for unilateral and bilateral congenital cataract.
Patients and methods
The records of patients who were treated and followed for congenital cataract in the Ophthalmology Department of Yüzüncü Yıl University School of Medicine, between January 1996 and January 2016, were retrospectively analyzed. The study was conducted in accordance with the Declaration of Helsinki and with approval of the Yüzüncü Yıl University School of Medicine Ethics Committee.
Patients with unilateral or bilateral congenital cataract occluding the optical axis who were followed for at least 5 months were included in the study. Patients with trauma-related cataract, glaucoma, microphthalmia, nanophthalmos, and other anterior segment pathologies were excluded. Six of the patients were missing preoperative or postoperative measurements for one eye and were included in the study only with their measured eye.
All patients initially underwent lensectomy and/or anterior vitrectomy and posterior capsulotomy, as appropriate for their age. Postoperatively, the patients were prescribed aphakic spectacles or contact lenses after a retinoscopic examination. Secondary IOL implantation was performed at approximately 2 to 3 years of age. Some patients with late presentation for cataract or with unilateral cataract underwent a single operation including lensectomy plus IOL implantation and/or posterior capsulotomy with anterior vitrectomy. Ocular examinations and AL measurements were performed preoperatively and postoperatively. The AL was measured using ultrasound biometry (EchoScan-US 1800, Nidek Co., Ltd.). The intraocular pressure (IOP) measurements were recorded preoperatively and postoperatively. The number of measurements that were performed with an applanation tonometer were 7 preoperatively and 21 postoperatively. The remaining measurements were performed with digital palpation of the globe and evaluated as normal limits.
The patients were separated into three groups: bilateral aphakic, bilateral pseudophakic, and unilateral. Patients who underwent cataract extraction and IOL implantation in separate operations were included in both the bilateral aphakic and bilateral pseudophakic groups. The unilateral group was subdivided into the operated cataract eyes (unilateral aphakic and unilateral pseudophakic) and unoperated fellow phakic eyes. The patients’ ages, follow-up periods, and preoperative and postoperative AL measurements were evaluated.
The statistical analyses were performed with SPSS software (version 23.0, IBM Corp.). The normality of data distribution within the groups was assessed with the Kolmogorov-Smirnov test. The Student t test and Mann-Whitney U test were used for pair-wise comparisons of the groups. The preoperative and postoperative AL measurements were compared using a paired-samples t test and the Wilcoxon test. The assessment of AL changes by age at surgery was done with a Pearson correlation test and a simple linear regression analysis. A P value less than 0.05 was considered statistically significant.
The study comprised 168 eyes of 87 patients. The bilateral aphakic group included 49 eyes of 25 patients (18 [72%] boys and 7 [28%] girls). The mean age at the time of cataract surgery was 8.17 months ± 10.65 (SD) (range 1 to 48 months). The bilateral pseudophakic group included 103 eyes of 54 patients (32 [59.26%] boys and 22 [40.74%] girls). The mean age of this group at time of cataract surgery was 42.47 ± 43.81 months (range 3 to 168 months). The unilateral operated cataract group included 40 eyes of 20 patients (11 [55%] boys and 9 [45%] girls). Their mean age at time of cataract surgery was 42.47 ± 43.81 months (range 3 to 168 months). Table 1 shows the preoperative and postoperative AL and changes in AL in each group. A comparison of the preoperative and postoperative AL revealed a statistically significant increase in all groups (P = .001 for each group) (Table 1).
In the unilateral cataract group, 4 (20%) of the 20 patients were unilateral aphakic, whereas 16 (80%) were unilateral pseudophakic. When aphakic eyes were compared with fellow phakic eyes in the unilateral aphakic group, there were no significant differences in preoperative AL, postoperative AL, change in AL, or monthly growth rate (Table 2). Comparison of pseudophakic and fellow phakic eyes in the unilateral pseudophakic group showed no significant difference in preoperative AL or change in AL; however, there were significant differences in the final AL and monthly growth rate (Table 2).
When eyes in the unilateral aphakic and the bilateral aphakic groups were compared, no statistically significant differences were observed in terms of age at surgery, preoperative and postoperative AL, follow-up duration, change in AL, or monthly growth rate (Table 3).
Comparison eyes in the unilateral pseudophakic and bilateral pseudophakic groups also revealed no statistically significant differences in terms of age at surgery, preoperative and postoperative AL, follow-up duration, change in AL, or monthly growth rate (Table 4).
Table 5 shows the monthly growth rate and changes in AL according to age at surgery in the bilateral aphakic, bilateral pseudophakic, and unilateral operated cataract groups. All groups showed statistically significant negative correlations between age at surgery and AL change and between age at surgery and monthly growth rate (P < .05).
The mean preoperative IOP was 14 ± 2.8 mm Hg and the mean postoperative IOP was 13.9 ± 2.9 mm Hg in patients who could be measured by an applanation tonometer.
During ocular development in a healthy newborn, the AL, corneal diameter, and corneal curvature radius increase with age.3 As the cornea flattens, there is a decrease in keratometry values. The index of refraction of the pediatric lens also decreases with age. Hussain et al.4 examined the changes in AL in healthy pediatric eyes and found that the mean AL was 16.8 mm at birth, rapidly increased to about 20.0 mm at 1 year of age, and was approximately 21.0 mm at age 4 years.
Apart from the physiological axial elongation in the eye, AL is also influenced by genetic and environmental factors.5 It was demonstrated that intensive work at close distances increases axial elongation and that axial elongation and progression of myopia continue even in students in their 20s who study intensively. Previous studies have shown that visual deprivation induces axial elongation and myopia in the eyes of neonatal animals.6,7 In their work on chickens, Papastergiou et al.8 found that although ocular reactivity to visual form deprivation continues in 1-year-old chickens, both growth stimulation and myopic shift in the refraction are reduced compared with recently hatched chicks. They found that the neurochemical changes in the visually impaired eyes of the 1-year-old chickens were in parallel with those in recently hatched chicks. These findings suggest that the deprivation model could be used to model human myopia predisposition.
Congenital cataract is among the leading causes of deprivation amblyopia.9 Successful treatment of amblyopia depends on early diagnosis and treatment of the cataract. Lensectomy and posterior capsulotomy with anterior vitrectomy are the preferred surgical methods to ensure long-term clearance of the visual axis.10 IOL implantation can be done either in the same session as lensectomy or as a secondary procedure. Postoperatively, the immediate priority is to correct refractive errors using spectacles or contact lenses.
In a study of monkeys that underwent unilateral lensectomy, the AL measured between 8 months and 26 months using A-mod ultrasound was found to be shorter in the aphakic eyes compared with the unoperated eyes.11 In a study by Wilson et al.,12 the AL of unilateral congenital cataract patients was measured at first presentation and at 5 years of age. Although some of the operated patients had concurrent IOL implantation, others were fitted postoperatively with aphakic contact lenses. The initial and final AL were significantly shorter in the cataractous and operated eyes compared with fellow eyes. There was no significant difference between the initial and final AL. In addition, there was no significant difference between patients with contact lenses and IOLs with regard to initial AL, final AL, or change in AL.12 In the patients with unilateral cataract in our study, there were no significant differences between the operated eye and fellow phakic eyes in terms of initial AL (P = .13) or final AL (P = .25) (Table 1). However, the change in AL between the initial and final examinations and the monthly growth rate were significantly greater in the unoperated fellow eyes compared with the operated eyes (P < .05). These results are consistent with those reported in the literature.
In a study by Lambert et al.,13 monkeys underwent unilateral lensectomy after which some received an IOL implant whereas others were left aphakic. Examinations at 5 weeks and 1 year showed shorter ALs in the aphakic and pseudophakic eyes compared with the fellow phakic eyes. The difference in length was more pronounced in the pseudophakic eyes. In another study, an evaluation of 47 eyes of 33 patients who had IOL implantation in the first year of life revealed no significant difference in mean axial elongation between the unilateral pseudophakic and fellow phakic eyes (P = .59).14 In the present study, there was no statistically significant difference in preoperative AL, final AL, change in AL, or monthly growth rate between eyes with unilateral cataract that were left aphakic and the patients’ fellow eyes (Table 3). In unilateral cataract patients who had IOL implantation, comparison of the pseudophakic and fellow phakic eyes showed no significant differences in preoperative AL and change in AL; however, the final AL and the monthly growth rate were significantly lower (P < .05). This difference was consistent with the literature.
In another study, lensectomy with IOL implantation was performed on one of the cataractous eyes of 25 children aged 4 to 10 years with bilateral cataract.15 When compared with the other cataractous eye, the axial elongation based on initial and final measurements was significantly less in the pseudophakic eye (P < .05). In a study investigating changes in AL after congenital cataract surgery, Vasavada et al.16 found that unilateral pseudophakic patients aged 1 year or younger had a significantly higher rate of axial elongation compared with bilateral pseudophakic patients (25.53% versus 18.50%, P = .001). However, another study comparing axial elongation in unilateral and bilateral pseudophakic eyes did not show a statistically significant difference.17 When we compared bilateral and unilateral pseudophakic patient groups at similar ages (P > .05) in our study, there was a significant difference in preoperative AL (P = .039), but no significant differences in follow-up period, final AL, change in AL, or monthly growth rate (P > .05).
In a study comparing bilateral and unilateral cataracts, 18 patients with unilateral cataract and 20 with bilateral cataract underwent cataract surgery.18 The eyes were left aphakic and contact lenses were prescribed. Eyes with unilateral cataract tended to already have relatively longer ALs before surgery. After 4 to 8 years, a third of the eyes were found to be clearly above normal, meaning their AL values were above the normal range. Eyes with bilateral cataract, on the other hand, were found to be shorter than normal, especially when operated in the first 6 months of life. In 4 to 8 years of follow-up, the degree of microphthalmia was found to have increased. In this study, patients with unilateral and bilateral cataract were compared with age-matched healthy children. Our comparison of bilateral and unilateral aphakic patients at similar ages revealed no statistically significant differences in preoperative AL, follow-up period, final AL, change in AL, or monthly growth rate (P > .05).
Vasavada et al.16 reported a significant negative correlation between age and rate of axial elongation. Similarly, there was a significant negative correlation between age at surgery and change in AL and monthly growth rate in our study (P < .05).
IOP is potentially one of the major factors affecting the globe growth. Kiefer et al.19 found a positive correlation between IOP and AL in congenital glaucoma. In our study, no glaucoma occurred after cataract surgery. Although IOP measurements in our study were evaluated in normal limits, one of the limitations of that study is that IOP was not measured in all patients by an applanation tonometer.
A limitation of our study was that keratometric and refractive parameters could not be assessed because of the lack of patient data. The use of digital palpation in most of the IOP measurements was one of the limitations of the study. Another limitation of this study was the small sample sizes in the unilateral cataract group and its subgroups.
Various factors can affect axial elongation. In the present study, we observed a smaller increase in AL in pseudophakic eyes compared with phakic eyes. This difference in elongation might result from a defocused image falling on the retina because of a lack of accommodation and its effect on the scleral structure. Experimental studies are required to further clarify this phenomenon.
What Was Known
- Most eye growth occurs in the first year of life.
- Intensive work at close distances increases axial elongation and that causes progression of myopia.
- There results of axial length (AL) changes in aphakic, pseudophakic, and unoperated eyes in the literature vary.
What This Paper Adds
- The final ALs and monthly growth rates were lower in pseudophakic eyes compared with phakic eyes in patients with unilateral congenital cataract.
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None of the authors has a financial or proprietary interest in any material or method mentioned.