Hope you will able to help me with this question. I have conducted a research regarding refractive errors. According to my results I have a total number of 150 children with different refractive errors. Among these 150, I have 50 children with myopia, 40 with astygmastismus and 20 with hypermetropia. The rest are anisometropians. Anisometropia is not a type of refractive error. So this is like a trick question...
Would it be better if I wrote instead of 150 children (300 eyes) and then count different refractive errors in each eye separately. This way I wont have anisometropias.
Hope you can help
As ever, it depends on the questions you're asking. If you're simply describing what you have observed, and clearly present the data, then to some extent it doesn't matter. But you probably want to detail information on aniso in your population.
Be careful too about the per person vs per eye issue. There's some recent discussion of this in Bunce et al (2014) Br J Ophthalmol 98:408-412
I'm not an expert in ophtalmology but it seems that if one eye has any refractive (or non-refractive) error, the second should have the same error too (Certainly, sphere-cyl-angle are different, say Left: Sph -5, Cyl-3, 163o , Right Sph-4.5, Cyl- 3.5, 148o). But I've never seen a situation when refraction and imaging performance strongly differ for both eyes. So I think the result should be the same either for 150 childrens or 300 eyes?
In my opinion Refraction could be divided on Emmetropia -Normal Eye and Refractive Errors , named Anysometropia, which includes Myopia, Hyperopia and Astigmatism
Regarding patients and eyes, you will discuss eyes separately, since it could be a different refraction on both eyes, types of astigmatism, etc. In addition you could also calculate separatly astigmatismus cases based on it's classfication - simple myopic or hyperopic, compound myopic vs. hyperopic, mixed,
Good lluck to you in your research.
I would go for 300 eyes and this way avoid anisometropia issue. It seems that there is a confusion between ametropia, which reffers to any type of refractive error of the eye, and anisometropia, which reffers to differences in refractive error higher than 2D between OD and OS. Good luck with your research !
Anisometropia, where the refractive error differs in the two eyes, is an important condition (that can lead to amblyopia in children for example) and should be discussed. As Paul mentioned previously, be careful about using data from both eyes of one subject as they are not independent data. I suggest you read the following paper, which is very good and has free access:
Armstrong RA Statistical guidelines for the analysis of data obtained from one or both eyes. Ophthalmic Physiol Opt 2013, 33: 7–14.
http://onlinelibrary.wiley.com/doi/10.1111/opo.12009/abstract
David provides the citation and information for you.
Although the two eyes may have different errors (and this is common), you can't treat them as independent.
thank you very much for you answers.
Best regards from Bosnia and Herzegovina
The question regarding anisometropia has been answered, but for some ideas on presentation of refractive error data you might find it helpful to look at the recent paper on the prevalence of refractive errors in Europe https://www.researchgate.net/publication/273785252_Prevalence_of_refractive_error_in_Europe_the_European_Eye_Epidemiology_E3_Consortium
Article Prevalence of refractive error in Europe: the European Eye E...
I think that depending on you objectives, you can go either way and there won't be any breeches at all
Thinking about your research publication, I would describe all 300 eyes instead
I do same work with my master student several years before. ..i agreed with previous comments. ...just i add something related to mixed astigmatism as it is myopia in one meridian and hypermetropic in the other one so that is why some studies uses spherical equivalent to pass this problem...
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