|Year : 2018 | Volume
| Issue : 1 | Page : 16-19
Pattern of wavefront aberrations in Indian children with ametropia
Kaushik Murali, C Vidhya
Department of Pediatric Ophthalmology, Sankara Eye Hospital, Bengaluru, Karnataka, India
|Date of Web Publication||18-Jan-2018|
Sankara Eye Hospital, Old-Airport Road, Kundalahalli Gate, Bengaluru - 560 037, Karnataka
Source of Support: None, Conflict of Interest: None
Purpose: The aim of this study was to evaluate the distribution of wavefront aberrations in Indian children with refractive errors and to determine the correlation between the degree of refractive error and aberration. Materials and Methods: A prospective study was conducted on 216 eyes of 108 consecutive children attending the outpatient clinic. Based on refractive error, the children were allocated to five groups: “Emmetropic,” “hyperopic,” “simple astigmatism,” “compound astigmatism,” and “myopic” group. Lower order aberrations (LOAs) and higher order aberrations (HOAs) were analyzed within and between the groups. Results: Mean age of the children was 10.9 years. Of the total 216 eyes, 40 eyes had emmetropia, 52 had simple astigmatism, 54 had compound astigmatism, 43 had myopia, and 27 had hyperopia. In all the groups, increase in spherical equivalent was associated with increase in LOAs of defocus and astigmatism and the root mean square (RMS) of total HOAs. In comparison with the “emmetropic” group, all other groups showed a significant increase in LOAs (P < 0.001) and RMS of total HOAs (P < 0.001), with the “compound astigmatism” group showing higher values. Spherical aberrations were found to be associated with simple astigmatism, compound astigmatism (P = 0.008), and myopia (P = 0.041). Statistical analysis was done using analysis of variance applying Bonferroni correction factor and Pearson's correlation coefficient. Conclusions: Ametropic eyes are associated with HOAs. Indian children were found to have higher values of aberrations when compared to other races. Practitioners may need to factor this while treating children for refractive errors.
Keywords: Aberrations, ametropia, coma, spherical aberrations, trefoil
|How to cite this article:|
Murali K, Vidhya C. Pattern of wavefront aberrations in Indian children with ametropia. J Clin Ophthalmol Res 2018;6:16-9
|How to cite this URL:|
Murali K, Vidhya C. Pattern of wavefront aberrations in Indian children with ametropia. J Clin Ophthalmol Res [serial online] 2018 [cited 2018 Sep 23];6:16-9. Available from: http://www.jcor.in/text.asp?2018/6/1/16/223572
Wavefront aberrations are optical imperfections of the eye that prevent light from focusing perfectly on the retina, resulting in defects in the visual image. Aberrations are divided into lower order aberrations (LOAs) of first and second order and higher order aberrations (HOA) of third order and above. HOAs can produce vision disturbances such as difficulty seeing at night, glare, halos, blurring, and starburst patterns.
Since there is no published literature on the distribution of HOAs in Indian children with various refractive errors, we undertook this study. A secondary objective was to determine any correlation between the degree of refractive error and aberrations.
| Materials and Methods|| |
A prospective study was conducted on 216 eyes of 108 consecutive children (in the age group of 4 to18 years) attending the pediatric ophthalmology outpatient clinic of our hospital in the month of June 2016. All patients were examined for uncorrected visual acuity and best-corrected visual acuity (BCVA) using age appropriate charts and thereafter converted to logMAR followed by tests of binocularity and were refracted. A slit lamp examination was conducted to rule out conditions affecting the cornea and tear film, media opacities, previous surgery or trauma.
HOAs were measured by an aberrometer (iDesign Advanced WaveScan Studio) in a dark room after 30 min of application of 1% cyclopentolate eye drops and tropicamide plus eye drops applied 5 min apart, after getting the informed consent from the parents. By applying cycloplegic agents to the eyes, we tried to negate the effects of variable accommodation in children which can alter the results. The aberrometer uses a Fourier reconstruction algorithm and Hartmann-Shack technology. Measurements were repeated three times for each eye and the best image was selected by a single experienced optometrist. Analysis was based on a pupil size of 4 mm. Root mean square (RMS) values were calculated from Zernike coefficients. LOAs of defocus and astigmatism and HOAs of coma, trefoil, spherical aberrations, and RMS of total HOAs were calculated.
Exclusion criteria included history of corneal surgery or trauma, children using contact lenses, corneal scar, keratoconus, or any fundus changes which could alter vision. Children with BCVA of <6/12 were also excluded as the amblyopic eyes might harbor variable aberrations. Approval was obtained from the Institutional Ethics Committee.
Children were divided into five groups depending on the refractive error; “emmetropic” group, “hyperopic” group, “simple astigmatism” group, “compound astigmatism” group, and “myopic” group. Refractive error was described in terms of spherical equivalent (SE). Eyes with SE refractive errors within ± 0.25 diopter (D) were categorized as emmetropic: Myopic group – spherical power >0.5D: Hyperopic group – spherical power ≥+0.5D: Simple astigmatism group – spherical power −0 and cylindrical power >0.5D: Compound astigmatism-spherical power >0.5D with cylindrical power >0.5D.
In all the groups, eyes with SE <2D were analyzed with the >2D. The LOA and HOA were analyzed within and between the groups.
Analysis of data was carried out using the analysis of variance applying Bonferroni correction factor. A two-sided P ≤ 0.05 was considered statistically significant. Pearson's correlation coefficient was used to assess the correlations between pairs of quantitative variables. All the results were expressed as mean ± standard deviation.
| Results|| |
A total of 216 eyes of 108 children were studied. Mean age of children was 10.9 years (range 4 to18 years). There were 52 males (48%) and 56 females (52%) [Table 1].
|Table 1: Mean values of age, number of eyes, and spherical equivalent and in each groups|
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In all the groups, increase in SE was associated with increase in LOAs of defocus and astigmatism, and RMS of total HOAs [Chart 1] and [Chart 2]. In the “simple astigmatism” group and “myopic” group, spherical aberrations showed statistically significant changes with the increase in SE (P = 0.04). [Chart 1] shows comparison of the RMS of total HOA with the SE in “simple astigmatism” group: [Chart 2] shows correlation of SE with the RMS of total HOA in the “compound astigmatism” group. In comparison with the “emmetropic” group, all other groups showed a significant increase in the LOAs (P < 0.001) and RMS of total HOAs (P < 0.001 for all).
The “compound astigmatism” group showed a statistically significant change in the spherical aberration (P = 0.041). RMS of total HOAs was statistically higher in the “compound astigmatism” group in comparison with the “simple astigmatism” group (P = 0.04) and the “myopic” group (P = 0.001). Comparison of the “hyperopic” and “myopic” group showed no difference in the parameters.
In all the groups, eyes with >2D SE had a statistically significant increase in the RMS of total HOAs (P = 0.001) when compared to the eyes with <2D.
Comparing all the groups, the RMS values were highest in the “compound astigmatism” group followed by “myopic” and “hyperopic,” then by “simple astigmatic” groups.
[Chart 3] depicts comparison of the mean coefficient of aberration values of the various parameters in the five groups.
| Discussion|| |
Wavefront aberrations can be recorded through various technologies and are designated through Zernike polynomials. Aberrations are measured by a RMS value which represents the ocular aberrations in micrometers (μm). The third- and fourth-order aberrations are the most prevalent HOAs in the human eye. Refractive errors that cause an image defocus (LOAs) are usually corrected with spectacle lenses. The presence of wavefront aberrations could affect not only the emmetropisation of the eye but could also affect the image quality and development of amblyopia. With advancements in lens technology, it is possible to correct these HOAs if the overall quality of life is affected. It is therefore important to understand how these aberrations affect visual quality and are correlated to other characteristics in children.
This study is a first of its kind to compare the various refractive errors in the eyes of Indian children, especially dividing them into simple and compound astigmatism.
Previous studies on refractive errors , have not analyzed myopic astigmatism separately from simple myopia. Classification into simple and compound astigmatism in this study has been noteworthy as results showed that compound astigmatism have higher values of aberrations than myopes.
HOAs have been proposed to vary among different racial populations across the world. Our study in Indian children shows higher RMS of total HOAs than the studies done on Pakistanis, Chinese, and Cauasians ,, [Table 2]. This might be due to differences in measurements across different pupil sizes in different studies.
|Table 2: Higher order aberrations in various racial populations as shown by various studies|
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In our study, we investigated ocular HOAs in patients with myopia, hyperopia, and astigmatism. The main focus was on coma (third order aberrations) and spherical aberrations (fourth order aberrations), as these were the most significant components of HOAs in children and have been thought to be amblyogenic.,
Marcos et al. reported that the RMS of wavefront aberrations in high myopia has statistically significant positive correlation with refractive error. He et al. proposed that myopic patients have greater HOAs compared to emmetropes. Karimian et al. showed that SE refractive error was significantly correlated with RMS of spherical aberration in patients with myopia. They also found that spherical- and coma-like aberrations were the HOAs associated with astigmatism, increasing myopia, and age.
In concordance with these studies our study also found the significant correlation of LOAs and the RMS of total HOAs with amount of refractive error not only in myopia but also in all the groups. The spherical aberrations were found to be the significant HOAs associated with myopia and astigmatism and might be the reason for degrading the retinal image quality in these children.
Kirwan et al. in his study on HOA's in children showed increased ocular aberrations in myopic eyes. They postulated that the higher level of ocular aberrations was a stimulus for inducing myopia. Our study found that the RMS of HOAs was higher in children with compound astigmatism and higher for refractive errors >2D SE. As the refractive errors increases, the optical imperfections (e.g., in the form of corneal or lens curvatures) in the eye changes, probably leading to the increased HOAs. It is thus probably needed to understand if these children with higher refractive errors must be specifically treated with some customized glasses or contact lenses that correct HOAs.
The variations of the results we got in our study compared to other studies ,,, may be due to the measurements done at the pupillary size of 4 mm, the limited age group, and smaller sample size. The children with higher refractive errors will require long-term follow-up to rule out conditions such as keratoconus which again are associated with higher HOA values.
While prescription of glasses may restore vision, our results show that children with higher refractive errors > 2D could have HOA's which could affect retinal image quality. Considering the increasing incidence of refractive errors in the Indian population, treating ophthalmologists need to be aware of HOA's. Whether these HOAs change with the growth, needs more prospective studies. The possibility of HOAs increasing refractive error, due to their ability to degrade the retinal images, requires further randomized controlled trials.
| Conclusions|| |
The existing knowledge concerning the clinical significance of HOAs, their relationship to the visual function, and the potential effectiveness of correcting HOAs encouraged us to study HOAs in children. Ametropic eyes and especially compound astigmatism are associated with HOA, especially in higher refractive errors of >2D SE. Indian children were found to have higher values of aberrations when compared to other races. Practitioners may need to factor this while treating children for refractive errors.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]