We read the article published by Fieß, et al (1) with considerable interest and laud them on their study and the large cohort. Considerable work has been done earlier, which looks at factors associated with refractive errors, however few studies document association with birth weight. Keeping this in mind, we feel that there are a few points requiring further clarity in this article.
The authors mention their inability to control for factors such as paternal refractive error and family history. However, previous studies not only discuss the paternal refractive error and family history, but also expand the affecting factors to include the number of myopic parents. (2) In the study design described by Höhn et al. where comprehensive information on living conditions and birth weight was collected via computer-assisted telephone interviews, (3) information on number of myopic parents could also have been collected, and would have proven to be an important covariate in the analysis.
The authors also report that 8369 participants provided birth weight data, of which 45 were excluded due to unreliable self-reported data [<1000g (n=7) or >6000g (n=38)]. However, tables 2 and 3 report analysed results based on 8369 participants not 8324 (after exclusion of the 45). Even though 45 is an insignificant number, and does not affect the results as such, this aspect of the results needs further clarity.
We read the article published by Fieß, et al (1) with considerable interest and laud them on their study and the large cohort. Considerable work has been done earlier, which looks at factors associated with refractive errors, however few studies document association with birth weight. Keeping this in mind, we feel that there are a few points requiring further clarity in this article.
The authors mention their inability to control for factors such as paternal refractive error and family history. However, previous studies not only discuss the paternal refractive error and family history, but also expand the affecting factors to include the number of myopic parents. (2) In the study design described by Höhn et al. where comprehensive information on living conditions and birth weight was collected via computer-assisted telephone interviews, (3) information on number of myopic parents could also have been collected, and would have proven to be an important covariate in the analysis.
The authors also report that 8369 participants provided birth weight data, of which 45 were excluded due to unreliable self-reported data [<1000g (n=7) or >6000g (n=38)]. However, tables 2 and 3 report analysed results based on 8369 participants not 8324 (after exclusion of the 45). Even though 45 is an insignificant number, and does not affect the results as such, this aspect of the results needs further clarity.
Lastly, while the authors mention, further factors that affect BCVA and refractive errors such as amount of outdoor activity, near work in childhood and adolescence, prematurity (4,5) and gestational age, the non-inclusion of these possible confounders in their analysis makes it difficult to plan public health interventions based on these results. In the present form, the results of association of birth weight with myopic refractive error are significant but emphasise the need for further studies which control for gestational age, prematurity and other factors mentioned above, while studying the association, so that the effect can be isolated to birth weight. Public health interventions can then be planned accordingly.
We appreciate the opportunity to be able to discuss our views on the subject and the article in question.
References
1. Fieß A, Schuster AK, Nickels S, et al, Association of low birth weight with myopic refractive error and lower visual acuity in adulthood: results from the population-based Gutenberg Health Study (GHS), British Journal of Ophthalmology 2019;103:99-105.
2. Jones LA, Sinnott LT, Mutti DO, Mitchell GL, Moeschberger ML, Zadnik K. Parental history of myopia, sports and outdoor activities, and future myopia. Invest Ophthalmol Vis Sci. 2007;48(8):3524-32.
3. Höhn R, Kottler U, Peto T, et al. The ophthalmic branch of the Gutenberg Health Study: study design, cohort profile and self-reported diseases. PLoS One. 2015;10(3):e0120476. Published 2015 Mar 16. doi:10.1371/journal.pone.0120476
4. Cook A, White S, Batterbury M, et al. Ocular growth and refractive error development in premature infants without retinopathy of prematurity. Invest Ophthalmol Vis Sci. 2003;44:953–960.
5. Fieß A, Kölb-Keerl R, Knuf M, et al. Axial Length and Anterior Segment Alterations in Former Preterm Infants and Full-Term Neonates Analyzed With Scheimpflug Imaging. Cornea 2017;36:821–7.
We thank Dr. Tobon for his comments regarding our recently published article on refractive errors frequency in Colombia.1
Initially he referred to the exclusion of the participants with less than 20/40 of distance corrected vision. The explanation of the application of this criterium was that, since as it has been shown, reproducibility of manifest refraction is less in patients with bad distance corrected visual acuity, and in this study we needed to have a very reliable manifest refraction examination.2
However, we believe that Dr. Tobon highlights a very interesting point, which is worth analyzing in more detail. Ours and other studies that have analyzed the prevalence of refractive errors in a population have excluded eyes with other ocular conditions, including amblyopia. For example, in the study conducted in Mexico by Gomez-Salazar et al, which included a very large sample (more than 670,000 patients), they excluded patients with amblyopia.3 This made it impossible to analyze the frequency of amblyopia or anisometropia.
In our study we excluded those patients with less than 20/40 of distance corrected visual acuity in any eye. Unfortunately, we did not keep the information on those patients excluded, and therefore we cannot determine the exact number or diagnosis of those cases. For future studies we will record such information.
With regard to the second query of Dr. Tobon, we decided not to use cyclopegic refraction in this study, performed...
We thank Dr. Tobon for his comments regarding our recently published article on refractive errors frequency in Colombia.1
Initially he referred to the exclusion of the participants with less than 20/40 of distance corrected vision. The explanation of the application of this criterium was that, since as it has been shown, reproducibility of manifest refraction is less in patients with bad distance corrected visual acuity, and in this study we needed to have a very reliable manifest refraction examination.2
However, we believe that Dr. Tobon highlights a very interesting point, which is worth analyzing in more detail. Ours and other studies that have analyzed the prevalence of refractive errors in a population have excluded eyes with other ocular conditions, including amblyopia. For example, in the study conducted in Mexico by Gomez-Salazar et al, which included a very large sample (more than 670,000 patients), they excluded patients with amblyopia.3 This made it impossible to analyze the frequency of amblyopia or anisometropia.
In our study we excluded those patients with less than 20/40 of distance corrected visual acuity in any eye. Unfortunately, we did not keep the information on those patients excluded, and therefore we cannot determine the exact number or diagnosis of those cases. For future studies we will record such information.
With regard to the second query of Dr. Tobon, we decided not to use cyclopegic refraction in this study, performed around our country, because this additional intervention would have required more complex logistical necessities, ethical requirements. Since the participants would have been exposed to an additional risk,4 although small, it should have been expressly indicated in the informed consent, and accepted by the potential participants (or in the case of the children by the parents or guardians), issue that at a given moment could have decreased the confidence of the population and made it more difficult to recruit patients in certain areas of the country, distant from our usual care center, being us a group of researchers not known in those areas to which we move for the study. Instead, we decided to perform a sequential examination by experienced optometrists: first a non-cycloplegic retinoscopy, making it as static as possible by requesting the patients to keep the fixation in a distant object in order to relax the accommodation and secondly, we carried out a careful manifest refraction. The results of the latter were the one taken into account in the study. If there was a discrepancy between the retinoscopy and the manifest refraction, the optometrist rechecked the patient. As other experts have indicated (see the explanation by Marsh-Tootle and Frazier), this approach is valid, but as we recognized it, it could be considered a weakness of our study. It is correct that despite the meticulousness in performing these non-cycloplegic examinations, we could have overestimated the frequency of myopia and underestimated that of hyperopia, especially in patients with ages between 8 and 11 years.
REFERENCES
1. Galvis V, Tello A, Otero J, et al. Prevalence of refractive errors in Colombia: MIOPUR study. Br J Ophthalmol 2018;102:1320-3.
2. Leinonen J, Laakkonen E, Laatikainen L. Repeatability (test-retest variability) of refractive error measurement in clinical settings. Acta Ophthalmol Scand 2006;84:532-6.
3. Gomez-Salazar F, Campos-Romero A, Gomez-Campaña H, et al. Refractive errors among children, adolescents and adults attending eye clinics in Mexico. Int J Ophthalmol 2017;10:796-802.
4. Bhatia SS, Vidyashankar C, Sharma RK, et al. Systemic toxicity with cyclopentolate eye drops. Indian Pediatr 2000;37:329-31.
5. Marsh-Tootle WL, Frazier MG. Infants, toddlers and children. Borish's Clinical
Refraction. 2nd edn. Philadelphia: Buiterworth Heinemann Elsevier, 2006:1415–6.
Dear Editor,
We read the article published by Fieß, et al (1) with considerable interest and laud them on their study and the large cohort. Considerable work has been done earlier, which looks at factors associated with refractive errors, however few studies document association with birth weight. Keeping this in mind, we feel that there are a few points requiring further clarity in this article.
The authors mention their inability to control for factors such as paternal refractive error and family history. However, previous studies not only discuss the paternal refractive error and family history, but also expand the affecting factors to include the number of myopic parents. (2) In the study design described by Höhn et al. where comprehensive information on living conditions and birth weight was collected via computer-assisted telephone interviews, (3) information on number of myopic parents could also have been collected, and would have proven to be an important covariate in the analysis.
The authors also report that 8369 participants provided birth weight data, of which 45 were excluded due to unreliable self-reported data [<1000g (n=7) or >6000g (n=38)]. However, tables 2 and 3 report analysed results based on 8369 participants not 8324 (after exclusion of the 45). Even though 45 is an insignificant number, and does not affect the results as such, this aspect of the results needs further clarity.
Lastly, while the authors mention, furt...
Show MoreWe thank Dr. Tobon for his comments regarding our recently published article on refractive errors frequency in Colombia.1
Show MoreInitially he referred to the exclusion of the participants with less than 20/40 of distance corrected vision. The explanation of the application of this criterium was that, since as it has been shown, reproducibility of manifest refraction is less in patients with bad distance corrected visual acuity, and in this study we needed to have a very reliable manifest refraction examination.2
However, we believe that Dr. Tobon highlights a very interesting point, which is worth analyzing in more detail. Ours and other studies that have analyzed the prevalence of refractive errors in a population have excluded eyes with other ocular conditions, including amblyopia. For example, in the study conducted in Mexico by Gomez-Salazar et al, which included a very large sample (more than 670,000 patients), they excluded patients with amblyopia.3 This made it impossible to analyze the frequency of amblyopia or anisometropia.
In our study we excluded those patients with less than 20/40 of distance corrected visual acuity in any eye. Unfortunately, we did not keep the information on those patients excluded, and therefore we cannot determine the exact number or diagnosis of those cases. For future studies we will record such information.
With regard to the second query of Dr. Tobon, we decided not to use cyclopegic refraction in this study, performed...
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