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Biometry characteristics in congenital cataract patients before surgery in a tertiary eye care centre in Nepal

Purpose To evaluate the anterior segment biometry characteristics in congenital cataract patients before undergoing surgery in a tertiary eye care centre. Methods We retrospectively reviewed the charts of congenital cataract patients aged less than 15 years who had undergone the congenital cataract surgery from Jan-Dec, 2015. 451 eyes of 351 patients were reviewed. The eyes were examined using an autorefract-keratometer, applanation A-scan and parameters like keratometry, axial length, corneal astigmatism were noted. Results The mean age at the surgery was 92.4 ± 4.13 months (range 6 months to 15 years). The ratio of boys to girls was 2.34:1. The mean axial length was 21.94 ± 1.94 mm. Girls had shorter axial length than boys (21.53 mm vs 22.11 mm, p = 0.01). The axial length in the cataractous eyes in bilateral cases was significantly smaller than that in the unilateral cases (21.46 mm vs 22.55 mm, p < 0.0001).The mean keratometry was 44.12 ± 2.6 D. Girls had larger mean keratometry value than boys (44.71 vs 43.88, p = 0.0032). Keratometry values were higher in cataractous eyes in bilateral cases than in the unilateral cases (44.61 D vs 43.51 D, p < 0.0001). The mean corneal astigmatism was 1.49 ± 1.13 D. The prevalence of the corneal astigmatism of 2.0 D or more was 25.5%. The with-the-rule astigmatism was the most frequent type (62.53%). Girls had higher mean astigmatism than boys (p = 0.0122). The mean corneal astigmatism was higher in the cataractous eyes in bilateral cases than in the unilateral cases (p = 0.0094). Conclusions The axial length, mean keratometry and corneal astigmatism in congenital cataract patients varied with age, gender, and laterality. The data on biometry characteristics of Nepalese pediatric patients provided in the present study are of clinical significance and hence greatly enhance the guidelines for treatment decisions, IOL power calculations and management of congenital cataract patients.


Introduction
With the recent advances in the surgical techniques and progresses in pediatric cataract surgery, primary implantation of intraocular lens has been the standard of care for the congenital and childhood cataract. 1 Biometry of the eye is an essential step for calculation of intraocular lens power. The calculation of IOL power in pediatric population is prone to errors due to technical difficulties in measuring biometric parameters in children and use of IOL power calculation formulas designed for adult patients which are based on adult biometry data. In newborns or non-cooperative children the biometric measurements need to be performed under general anesthesia. Autokeratometers are commonly used for the biometric measurements of such children, but they are still not available in most medical centers in the developing countries, where congenital cataract is a leading cause of childhood blindness. 2,3 Keratometric measurements may not be accurate in clinical conditions, such as presence of corneal opacities or posttraumatic deformations. In such situations, error may occur if adult average keratometric values are taken for the IOL power calculations. So for the accurate calculation of IOL power in pediatric eyes, the biometry data from the pediatric eyes are necessary.
Several previous studies have reported the biometry data like axial length, anterior chamber depth and lens thickness in children with clear lens 4,5,6 and in cataractous eyes of Caucasian and African-american children. 7 Similarly the corneal curvature and axial length data in Caucasian children with cataractous eye 8 , keratometry in pediatric eyes with cataract 9,10 , anterior segment biometry characteristics in Chinese congenital cataract patients 11 have been reported.
We retrospectively evaluated a large series of pediatric eyes with congenital cataract with the objective to report the axial length, keratometry measurements and astigmatism in pediatric cataractous eyes measured with the applanation A-scan and an autorefract-keratometer.

Materials and methods
The retrospective review of the charts of all patients who had undergone the congenital cataract surgery at or before 15 years of age at the pediatric ophthalmology clinic of Sagarmatha Choudhary Eye Hospital, Lahan between January 2015 and December 2015 was done. All the Nepalese congenital cataract cases which were diagnosed before surgery and lacked other ocular abnormalities like corneal diseases, subluxated lens, glaucoma and nystagmus were included. The eyes in which the axial length or keratometry values were not available at the time of cataract surgery were excluded. The axial length was measured with the applanation A-scan technique and keratometry was done using a handheld autorefract-keratometer, Retinomax K-plus 3 at the time of general anesthesia.
The cataractous eyes of unilateral cases and both eyes of bilateral cases were included in the analysis. Data collected include age at the time of surgery, gender, laterality of cataract, axial length, keratometry and corneal astigmatism.
Absolute frequency (n) and relative frequency (%) were used to analyze qualitative variables, and mean and standard deviation (mean ± SD) were used to analyze quantitative variables. The t-test for independent samples was used to analyze the variables of cataractous eyes. A P-value <0.05 was considered statistically significant.

Results
Four hundred and fifty one eyes of 351 patients were reviewed. A unilateral cataract was present in 56.41% (198/351), and the remaining 43.59% (153/351) had bilateral cataract. The mean age at surgery was 92.4 ± 4.13 months (range 6 months to 15 years). The ratio of boys to girls was 2.34:1 (246:105).
The mean axial length was 21.94 ± 1.94 mm (range 16.12-32.58 mm). The mean axial length was higher in the cataractous eyes in boys (22.11 ± 2.02 mm) than that in girls (21.53 ± 1.73 mm) (p = 0.01, 95% CI = 0.14 to 1.02). However, the mean axial length comparisons among the males and females according to age distribution was found to be significant in age group between 11-15 years (p = 0.007, 95% CI = 0.26-1.60) and not in other age groups as shown in Table 1. The axial length in the cataractous eyes in bilateral cases (21.46 ± 2.05 mm) was significantly smaller than in the unilateral cases (22.55 ± 1.63 mm) (p <0.0001, 95% CI = 0.7037 to 1.4763). There was no difference between the mean axial length of right eyes and left eyes (p = 0.9135). The axial length measurements in the cataractous eyes by age group, gender and laterality is provided in Table 1.

Discussions
Biometry of the eye is a crucial step for the IOL power calculation. The pediatric IOL power calculations however are based on formulas which are designed for adult eyes and are formulated based on adult biometry data. The biometry data based on the pediatric eyes are hence essential to design IOL power calculation formulas specifically for the pediatric population. The biometry characteristics and prevalence of preoperative corneal astigmatism are essential for proper planning and management of congenital cataracts. The studies with large cohort of congenital cataract patients are however less, perhaps due to low incidence of congenital cataract, lack of proper equipments, difficulty in    examinations or lack of awareness of importance of such data. In this study, we report the biometry characteristics of the large cohort of congenital cataract patients in Nepal. Previous studies have reported the axial length and corneal curvature data in cataractous eyes of Caucasian and African-american children 7 , axial length, anterior chamber depth (ACD) and lens thickness (LT) in noncataractous pediatric eyes. 4,5,6 It has been reported that the growth of the eye is influenced by visual experience and visual deprivation leads to elongation of eye. 12,13 In this study we used applanation A-scan to determine the axial length values in pediatric cataractous eyes. We found that the eyes with bilateral cataract had significantly smaller axial length than those with unilateral cataract (Table 1, 21.53 vs 22.11, p = 0.0001), similar to reports by Trivedi and Wilson 7 , Rasooly et al. 13 and Lorenz et al. 14 Sex-linked differences in axial length was found similar to that reported in literature 4,15 , the girls having shorter axial length than boys (Table 1, 21.53 mm vs 22.11 mm, p = 0.01). The axial length at age less than 1 year was significantly different from all other age categories (Table 1). We could not adequately determine the rate of axial growth or the age at which axial length growth stabilizes since this was not a longitudinal study.
Keratometry values have been previously reported in noncataractous pediatric eyes 16,17 as well as in cataractous pediatric eyes. 8,9,10,11 Trivedi and Wilson 8 investigated keratometry in 299 pediatric eyes with cataracts of white and African Americans and reported that the average keratometry value was 45.39 D, with steeper keratometry in girls than in boys and in unilateral cases than in bilateral cases. Gordon and Donzis 18 reported the average keratometry value of full-term infants as 45.2 D. Shrestha and Shrestha 10 in a study of keratomeric readings in 80 bilateral congenital cataracts from Nepal have reported mean keratometry value of 44.8 D in operated eyes and 44.7 D in fellow eyes. Another keratometry study in Thai children from newborn to the age of ten found that the keratometry reading was consistent in all age groups in the range of 43-44 D. 19 In the present study, the mean keratometry value was 44.12 D. We found that infants have a steeper keratometry than older children and girls have steeper keratometry compared to boys, which is consistent with the previous findings. 8,17,18 In additions, our study show significantly steeper mean keratometry readings in bilateral congenital cataract cases than those of cataractous eyes in unilateral involvement (p <0.0001) which contradicts previous findings. 8 The difference in age composition or different ethnicities may cause these discrepancies.
In the present study, the mean corneal astigmatism in congenital cataract patients was 1.49 D. More than one fourth of the cases (25.5%) had astigmatism of 2 D or more indicating the high prevalence of corneal astigmatism in the congenital cataract patients. Previous studies have shown the prevalence of corneal astigmatism of 2 D or more to be 65.7% in Japanese congenital cataract patients 20 and 39.25% in Chinese congenital cataract patients. 11 Most of the patients had with-the-rule astigmatism similar to other studies. 11,20 We also found that the mean corneal astigmatism was higher in the bilateral congenital cataract cases than the affected eyes of the unilateral congenital cataract cases which is probably due to abnormal development of the eyes. 21 This is the first study on the biometry characteristics and prevalence of corneal astigmatism in congenital cataract patients in Nepal. The knowledge of anterior segment biometry characteristics as well as corneal astigmatism measured before surgery can thus improve the management guidelines of congenital cataracts.
There were some limitations to this study. We used the applanation A-scan ultrasound biometry for the axial length measurements in this study. Applanation ultrasound remains a commonly used method worldwide, especially in developing countries like Nepal due to familiarity with the technique and cost. The acquisition of both ultrasonography data as well as keratometry data in paediatric patients is difficult because of the technical difficulties and the need for general anesthesia in newborns and uncooperative children. However, applanation ultrasound biometry has been reported to have comparative accuracy and equal or better results with optical biometry in previous comparative studies. [22][23][24] Also, compared to immersion A-scan biometry with non-contact to cornea, we used applanation A-scan biometry, which requires the ultrasound probe to be placed in contact with the corneal surface. The compression of cornea is unavoidable in applanation biometry making the axial length measurement more variable compared to other non-contact biometries. 25

Conclusion
The axial length, mean keratometry and corneal astigmatism in congenital cataract patients varied with age, gender, and laterality. The data on biometry characteristics of Nepalese pediatric patients provided in the present study are of clinical significance and hence greatly enhance the guidelines for treatment decisions, IOL power calculations and management of congenital cataract patients.

17.74%
with-the-rule against-the-rule oblique Fig. 3. Types of corneal astigmatism in the entire sample of congenital cataract patients.