Background: Preterm birth potentially plays an important role in visual development. Studies have shown that frequency of myopia, astigmatism, anisometropia, strabismus, and amblyopia in children born preterm is higher than term children.
Objective: The aim is to study different types of refractive errors in children under-five years of age born preterm and term.
Methods: Comparative cross-sectional study was carried out among 64 children aged 5 years or less. Age, gender, and social status were noted. Children were subjected to refraction according to their age. Detailed anterior segment and posterior segment examination as per the cooperation of the child was conducted with torch light or slit-lamp examination with Ziess, Appasamy AARU 2000. Visual acuity was examined with appropriate methods suitable for age.
Results: Fifty percent were preterm and 50% were term. About 50% were male and 50% were female. The most common refractive error was hypermetropia (42%). Among those with compound types of refractive errors, the most common was compound myopic astigmatism ≥2 diopters (17%). Compound types of refractive error were significantly more (62.5%) among the preterm compared to 31.2% among term; significantly more (91.7%) among those born <32 weeks of gestation compared to 45% and 45.5% among those born between 33 and 36 weeks and born >36 weeks of gestational, respectively; significantly more (88.9%) among low birth weight babies compared to 40% among normal birth weight babies. Age and gender were not significantly associated with compound types of refractive errors (P > 0.05).
Conclusion: Most common refractive error was hypermetropia. Among those with compound types of refractive errors, the most common was compound myopic astigmatism ≥2 diopters. Being preterm, born at the gestational age of <32 weeks and low birth weight were significant risk factors for compound types of refractive errors.
Keywords: Anisometropia, gestation, preterm, refractive error
|How to cite this URL:|
Sindhura JL, Muduthanapally C, Murthy L R, Das S, Dubey RS. Study of different types of refractive errors in under-five children born preterm versus full term. MRIMS J Health Sci [Epub ahead of print] [cited 2023 Mar 30]. Available from: http://www.mrimsjournal.com/preprintarticle.asp?id=362532
| Introduction|| |
Preterm birth is a major cause of morbidity and also increases the risk of death from other perinatal conditions. However, recent advances in neonatology have led to dramatic improvements in survival rates. With more preterm infants surviving the neonatal and perinatal periods, the focus has begun to shift toward improving long-term functional outcomes for these high-risk infants.
Preterm birth potentially plays an important role in visual development in two ways. First, premature exteriorization removes the visual system from the nurturing intrauterine environment during a period of rapid maturation. The immature visual system is unnaturally subjected to external visual stimulation and its tissues can no longer depend on the placental maternal-to-fetal transfer of essential nutrients. While the basic organization of the structures of the visual system appears to be specified innately, substantial immaturity is present in both preterm and term infants. Postnatal visual experience and nutrition can modify the fine structure and function of the visual system. Second, the overall immaturity of the preterm infant, along with the many systemic associations and complications of preterm birth places the infant at significant risk for permanent visual impairment.,
Studies have shown that the frequency of myopia, astigmatism, anisometropia, strabismus, and amblyopia in children born preterm is higher than term children. Although the mechanism of myopia development in preterm children is not yet clear, various studies have suggested that myopia may be related to increased corneal astigmatism, decreased anterior chamber depth, and increased lens refractive power or it may have developed due to structural changes caused by laser therapy.,,
This study is done to study different types of refractive errors in children under-five years of age born preterm and term.
| Materials and Methods|| |
This comparative cross-sectional study was done in the Department of Ophthalmology, Malla Reddy Institute of Medical Sciences, in collaboration with the departments of Paediatrics, Obstetrics, and Gynaecology during 18 months, i.e., from January 2020 to June 2021. Sixty-four children up to the age of 5 years who had approached the outpatient department of ophthalmology were included in the study after it was given clearance by the institutional ethics committee and obtained assent form from the parents.
Children up to 5 years of age, both male and female, were included in the study. Children of age more than 5 years, or with retinopathy of prematurity (ROP), children having visual impairments due to other ocular morbidities or suffering from acute illness such as fever, etc., were excluded from the study. Parents who did not wish to participate or had any objections were excluded from the study.
Demographic details, such as age, gender, and social status, were noted. Children were subjected to refraction according to their age. Detailed anterior segment and posterior segment examination as per the cooperation of the child was conducted with torch light or slit lamp examination with Ziess, Appasamy AARU 2000.
In preverbal children, Retinoscopy under cycloplegia using photo refractor and streak retinoscope (Heine beta 200 retinoscope) was done. Verbal children were subjected to visual acuity tests using Snellen's chart, and subsequently, retinoscopy under cycloplegia using streak retinoscope, and automated refraction with Topcon KR 8900 would be performed.
The child would be sitting at 6-m distance in a room equipped with Snellen's chart. One eye of the child was occluded would be asked to recognize the figure on the picture chart or read the alphabets or E or C chart where the child would be asked to tell the direction or Allen's card test was used. Accordingly, the visual acuity would be noted down as 6/60, 6/9 or CF from 3-m, 1-m.
All children were subjected to cycloplegic refraction where 0.5% cyclopentolate eye drops 45 times with a gap of 20 min between each drop was instilled in children <5 years or 1% atropine eye ointment applied two times a day for 3 days was administered and the case was reviewed on the 4th day in children of age group <3 years. Later, automated refraction was performed in the dilated pupil, after which streak retinoscopy was performed, and refraction was noted.
Data were collected and tabulated in M. S. Excel, and an appropriate statistical test was applied. Mean, standard deviation, range, and upper and lower confidence limit were calculated for noncategorical data like age. Proportions were computed for categorical data and the Chi-square test was applied. P value was calculated, and P < 0.05 was considered statistically significant.
| Results|| |
In the present study, out of 64 children included, 50% were born preterm and 50% were born at term. About 50% were male and 50% were female. Among preterm, based on Gestational age in weeks, 37.5% were in less than or equal to 32 weeks and 62.5% were in less than or equal to 36 weeks. Based on birth weight in preterm, 44.4% and 55.6% were of low birth weight among <32 weeks' gestation and 3236 weeks' gestation, respectively [Table 1].
|Table 1: Distribution of study subjects as per sociodemographic variables|
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In the present study, 42% had simple hypermetropia, 11% were diagnosed with simple myopia, 17% had compound myopic astigmatism ≥2 diopters, 16% with compound myopic astigmatism <2 diopters, 9% with compound hypermetropic astigmatism <2 diopters, 3% with compound hypermetropic astigmatism ≥2 diopters, and 2% with anisometropia [Table 2].
|Table 2: Distribution of study subjects as per different types of refractive errors|
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He prevalence of compound types of refractive error was 62.5% among preterm babies compared to only 31.2% among term babies. This difference was statistically significant (P < 0.05). The prevalence of compound types of refractive error was 91.7% among those born before 32 weeks of gestation compared to only 45% and 45.5% among those were born between 33 and 36 weeks and born beyond 36 weeks of gestational, respectively. This difference was found to be statistically significant (P < 0.05). The prevalence of compound types of refractive error was 88.9% among the low birth weight babies compared to only 40% among the normal birth weight babies. This difference was found to be statistically significant (P < 0.05). Age and gender were not found to be significantly associated with the compound types of refractive errors (P > 0.05) [Table 3].
|Table 3: Association between various factors and compound types of refractive errors|
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| Discussion|| |
Refractive errors are common in the neonatal period following full-term and preterm birth. Full-term neonates commonly demonstrate high levels of hypermetropia and astigmatism that reduce rapidly during the 1st year of life. Ingram et al. found this process, known as emmetropization, to be complete in 82% of full-term infants by 12 months of age. Emmetropization has also been described for preterm infants who tend to be more myopic and astigmatic at birth than full-term infants.
In 2020, Kaplan et al. conducted a study to compare the refractive measures of preterm and full-term children aged 1-year-old where 52 eyes of 26 preterm children and 44 eyes of 22 term children were included in the study. Myopia in preterm with ROP (45%) was higher than the term (16%) and preterm without ROP (38%), and the rate of hyperopia in term (52%) was quite higher than preterm (13%) and preterm with ROP (10%). The percentage of astigmatism was significantly higher in preterm (85%) and preterm with ROP (53%) than in term (25%). The study concluded that refractive errors are more often in preterm infants, even in the absence of ROP.
In the present study, among 32 preterm children included, 16% had simple myopia, 22% had simple hypermetropia, 28% had compound myopic astigmatism less than or equal to or more than two diopters, 3% each had Compound hypermetropic astigmatism <2 diopters and anisometropia. A study of refractive errors in cryotreated children was not taken up here.
Kaya et al. observed that the proportion of refractive errors was more in the severe ROP group compared to mild or no ROP in all age groups. Uprety et al., in a study from Nepal, found that as age increased, the incidence of astigmatism and anisometropia increased. Other studies like one which was carried out in the year 2000 also reported more prevalence of myopia in children who were born prematurely. We also observed similar findings in the present study.
A higher prevalence of myopia among children was reported by O'Connor et al. in the year 2002. Compared to the present study, the age group used by the author was 1 year more. Two studies, reported that the prevalence of myopia was more in children who were preterm. We also observed similar findings. O'Connor et al. noted that being preterm was an important risk factor for hypermetropia >3D. Compared to the present study findings, Darlow et al. found lower rates of hypermetropia of 1D or more as well as lower rates of astigmatism. This difference may be attributed to the photo-refraction technique used was different in these two studies.
Fledelius in 1990 reported that prematurity was an important risk factor for anisometropia. It was also found to be common in children born before 32 weeks of gestation when compared to full-term children. Ozdemir et al. found that the incidence of low spherical equivalent was more common in children born at an early gestational age and in children with low birth weight. However, they did not find any association between postmenstrual age and astigmatism. Shapiro et al. noted that there was no difference in the results of the refraction among preterm and term babies. But anisometropia was significantly more in children born at a low gestational age and low birth weight.
Among 32 term children included in the present study, 6% each had simple myopia and compound myopic astigmatism more than or equal to 2 diopters and Compound hypermetropic astigmatism more than or equal to 2 diopters, 63% had simple hypermetropia, 16% had Compound hypermetropic astigmatism <2 diopters. Myopia with astigmatism <2 diopters was seen in 16.7% and myopia with astigmatism ≥2 diopters was seen in 66.7% of the children whose gestational age was ≤32 weeks in the study and this finding was statistically significant with P < 0.0001. It was observed that low birth weight had a significant correlation with astigmatism. Akova-Budak et al. observed that the prevalence of myopia was more in children with low birth weight compared to children with normal or higher birth weight. In one study, they reported that there is a positive association between birth size and ocular dimensions. However they did not study about the refraction and their study population was children aged 79 years, whereas we had children up to 5 years of age. Similarly, a study which was carried out in 2014, noted that refraction is not related to gestational age or birth size. This study was among 415 year children.
In 2016, Bhatti et al. in their cross-sectional study to test the hypothesis that the structural contributions to myopia in preterm and full-term born children are different, where 93 children ranging from ages 2 to 13 who had myopia ≥−3 diopters in at least one eye were examined with A-scans. The anterior chamber depth in myopic eyes in preterm was shallower than in myopic eyes if full term. The lens thickness measurements were thicker among myopic preterm than myopic full terms. Finally, the axial length of myopic eyes in full term was longer than that of myopic eyes in preterm, P = 0.01. In the present study, a scan was not performed, and also, it did not include children aged above 5 years for comparison.
Corneal curvature was steeper, a shorter white-to-white distance was observed in adults with low birth weight adjusted for age and sex.
| Conclusion|| |
Among preterm children, incidence of simple myopia in preterm was observed more in <1-year age group, Simple hypermetropia was observed more in <4 and <5 years' age group, and incidence of compound myopic astigmatism less than or equal to or more than two diopters was more in <2 years' age group. Among term children, Simple hypermetropia was observed more in <1 year's age group, followed by <4 years' age group. CHA <2 diopters were observed more in <1-year age group, followed by <3 years' age group. Type of refractive error and gestational age showed the significant prevalence of myopia with astigmatism in preterm compared to terms (P < 0.05). Type of refractive error and Birth weight showed a significant difference between the groups as the P value was calculated to be <0.05. LBW group showed more myopia with astigmatism and anisometropia.
ROP, refractive error, strabismus, and cortical visual impairment, other forms of visual impairment that have been reported for the preterm population, including nystagmus, glaucoma, optic nerve hypoplasia, and eye movement and reading disorders, if screened at the right time with proper intervention may reduce the burden of ocular morbidity in these children and will improve the quality of life.
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Conflicts of interest
There are no conflicts of interest.
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Department of Ophthalmology, Malla Reddy Institute of Medical Sciences, Suraram, Hyderabad, Telangana
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2], [Table 3]