Axial Length
轴向长度的增长和欧洲儿童近视发展的风险
概括
作为一个孩子的眼睛生长,最后眼睛形状和their final refractive correction is influenced by a mix of genetics, the environment and what the child does with their time, and continued eye growth increases risk of becoming highly myopic in later life. Being able to identify what stage of growth a child is at by assessing their growth against a reliable percentile chart would be valuable in trying to predict future level myopia of myopia in a child and guide interventions towards reducing rate of eye growth.
This population-based study set out to produce a percentile growth chart for axial length based on the data collected from European children and adults, and in doing so they found a stronger correlation between the refractive error and axial length in myopes compared to the same measurements in emmetropes. A significant relationship was also found in myopes between spherical equivalent refraction and both corneal curvature and axial length. The authors conclude that percentile growth charts of AL can be used as a key predictor for monitoring paediatric eye growth.
Clinical relevance
- The spherical equivalent (SE) was significantly related to the corneal radius (CR) and, on average, myopic children had steeper CR compared to emmetropes and hyperopes. This was confirmed by the same finding from the adult subjects.
- Compared to emmetropes and hyperopes, myopic children had a faster eye growth rate and a myopic shift seemed to occur at approx. 9yrs old.
- 轴向长度findings suggest that if a child seems to be moving up through the percentile groups, there is a good chance they will become myopic.
- What percentile a child is at when aged 6yrs could be a good predictor of their myopia by age 9yrs old.
- 所有这些发现都可以帮助眼部护理从业人员确定那些在实践中查看儿童的SE，CR和年龄时具有较高快速发展风险的人。
- 如果我们在实践中需要参考增长图表，那么它可以更轻松地向父母和患者展示孩子的进展可能是什么。
Limitations and future research
Tideman等人意识到他们的研究的某些方面可能会影响他们的结果：
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- The Generation R study (children aged 6-9yrs old) and the Rotterdam study (adults of 57yrs old) were both carried out on the Netherlands, while the ALSPAC study involved 15yr olds in UK. The authors admitted this may have geographical differences.
- There was no data for 20-25yr olds to bridge the gap in between the ages of the cohorts. This could mean that the growth curve trends could be under-estimated for 15yr olds.
- There was a difference in the instruments used to measure AL. Although this could have introduced a slight difference, the authors felt it shouldn’t be significant enough to change the results
- The authors also suggested that a follow-up of children after 2010 could reveal if they have a steeper growth curve compared to those from their study.
- An interesting finding was that height may be linked to axial length growth. The authors found a strong correlation with height and AL growth for 6yrs olds. There was slightly less for 9yr olds but it was still a significant correlation. However, they found there was no difference with the refractive error for boys or girls, suggesting no gender difference. Future research may explore this further and confirm if axial length growth may have a proportional link to height growth rates.
Association Of Axial Length With Risk Of Uncorrectable Visual Impairment For Europeans With Myopia
概括
在许多发达的近视越来越频繁countries and we now know it isn’t simply a matter of poor vision which we ‘fix’ with spectacles or contact lenses. It can lead to myopic maculopathy, glaucoma, cataract and retinal detachment and having 'high' myopia increases these risks further. These eye conditions can all potentially lead to reduced vision at best and blindness at worst. As myopia increases, the eye’s total axial length has been seen to increase too, and it is this elongation which leaves the eye at risk from ocular pathologies.
构成“高”近视的分类可能会有所不同。世界卫生组织（WHO）决定在2015年的阈值-5.00d且更强的阈值（1）。出于他们的研究目的，Tideman等人将参与者分类为高度近视，当时他们的球形等效（SE）为-6.00D，轴向长度（AXL）为26mm或更多。
This study used cross-sectional data collected from population-based studies undertaken by the Rotterdam study (I, II & III) and the Erasmus Rucphen Study. These results were combined with case-control data from the Myopia Study, with participants across all studies being 25 years or older. The authors wished to explore a link between visual impairment as a result of increased AXL, refractive error and to be able to apply this to the wider population.
Clinical relevance
It’s all about the risk
- We can see how myopia is likely to be a leading cause of blindness in the near future after the study findings suggest that “visual impairment will increase 7- to 13-fold by 2055 in high-risk areas”.
- We can also be more aware of an individual’s risk when we can see that those with an AXL of 26mm or greater. Those with longer axial length had a higher chance of having myopic-linked vision impairment - this increased from a 3.8% chance if the AXL was less than 26mm to a 25% chance if the AXL was 26mm or longer. An AXL of 30mm or longer was associated with a 90% chance of vision impairment in their lifetime due to complications from myopia.
- Eye Care Professionals are in a prime position to communicate this robust information we have on the risks associated with increased myopia and what their options are to reduce that risk.
- Start considering myopia management early.
- The participants who were most at risk of visual impairment were in the older age group and they had therefore had longer eyes and higher myopia for a longer time.
- Don’t forget the lower myopes!
- We need to consider all myopes as potentially being at risk of axial elongation and an increasing risk of impairment later in life, as we know from this and other studies that those who ‘only’ have -1.00D refractive error will already have double the risk of myopic maculopathy and posterior sub-capsular cataract compared to an emmetrope.(2)
Limitations and future research
This is a robust analysis taking in the data of more than 15,000 individuals, across multiple studies. The key area for future research is to measure how myopia control interventions for today's generation influence their rates of pathology and vision impairment in the future. This is a very long-term question, as our current generation of children with access to myopia management will need to age another 50-60 years before their outcomes could be compared to the ages analyzed in this paper. To this point, the authors recognized that their calculated risk estimates will become overstated with adoption of (successful) myopia strategies to slow myopia progression.
Race specific studies:The authors made predictions of varying prevalence for different countries, but these were based on values originally gathered from Europeans and they were aware this may not be directly applicable to other ethnicities. They were able to allow for this by using reported prevalence estimates for each country. At the time of publishing (2016), Tideman et al were unaware of any likely ethnic differences and felt confident they were making feasible predictions. Similar research across different ethnicities would help determine whether this observation holds true.
Changes in prevalence:这项研究表明，当他们看着参与者的几十年出生时，尤其是从1920年开始，近视向近视的转变，年轻人组的近视患病率较高（25年至60年）。这表明人口随着时间的流逝而变得越来越近视，随着年龄的增长，损害的机会随之增加。作者预测，到2055年，在欧洲，视觉问题的风险将增加2至3倍，在新加坡有3至5倍的机会，在大韩民国的3至6倍。这是基于他们的发现，在他们的分析中包括2012年的最后一项研究。从那时起，近视病理的可能性可能会超出他们的期望。进一步的后续研究可以验证这是否发生了重大改变。
Myopia Progession
Accommodation Is Unrelated To Myopia Progression In Chinese Myopic Children
概括
Although the relationship between accommodation and myopia has been widely investigated, disagreement remains on whether accommodative lag (under-accommodation) plays a part in myopia progression. The proposed mechanism being that the resultant hyperopic defocus stimulates axial length growth towards reduce the lag in focus. A contributing factor towards this conjecture is differences in adopted methodology, which the authors of the set out to address.
By implementing analysis across a continuous range of accommodation between 0 and 6.00D, and including distance accommodation facility, the authors found no association between both measurement conditions leading them to conclude that lag of accommodation has no influence on rate of myopia progression.
This study adds weight to the argument that accommodation lag has no influence on myopia progression, however, even though complex and thorough analysis was conducted, there remain many differences to real world viewing conditions, meaning the jury is still out on whether or not myopia progression is influenced by accommodation lag.
Clinical relevance
- 这项研究的一个有趣的观察结果是，在平均研究队列年龄（0.61d/yr）时，比Donovan等人（0.48D/YR）发现的近视进程率更快。1Leading the authors to suggest that应该给予更多关注年轻的近视，其近视迅速发展，因此更有可能在后来的近视中变高.
- Results from this study indicate that accommodation lag has no influence on rate of myopia progression, at least in a Chinese population. However, the results should not be considered as definitive due to differences between study measurement protocols and real world conditions.
Limitations and future research
- Accommodation lag, while measured using an accurate system and carefully analysed, does not necessarily replicate actual accommodation lag under normal conditions:
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- Accommodation lag was measured under monocular conditions, meaning that blur was the only stimulus to accommodation – this does not match real world viewing where binocular fusion also acts as a stimulus to accommodation.
- Accommodation was measured dynamically – the near fixation target focus demand was being continuously moved during the measurement process. This does not replicate static focus stimulus distance, i.e. when reading a book.
- Refraction was subjective maximum plus and did not include cycloplegia, which is the current gold standard in a research setting.
- This study involved Chinese children only due to the geographic setting so outcomes cannot be necessarily extrapolated to be representative of children from other ethnicities or countries.
- Most myopia progression data were retrospective, meaning that any potential additional influential factors may not necessarily be similar across all participants. The authors argue that applying a Gompertz function to the data helps alleviate against this potential for error.
- The authors were aware that different times spent concentrating at near wasn’t measured and therefore a conclusion on effect of accommodation-induced hyperopic defocus can’t be deduced.
- Measurements were conducted in a clinical environment with controlled lighting and deliberately chosen working distances doesn’t necessarily translate to how children might read at home.
Prevalence of Myopia
Prevalence Of Myopia Among Disadvantaged Australian Schoolchildren
概括
This retrospective cross sectional analysis of disadvantaged Australian school children reveals:
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- Lower overall prevalence of myopia than emmetropia and hyperopia
- Higher prevalence of myopia in older children
- No change in overall myopia prevalence between 2014 and 2018, but double the prevalence when compared to study data from 1976
Clinical relevance
- The children included in this study were predominantly from rural areas which in comparison to children living in urban areas conceivably means:
- Greater time spent outdoors
- Less time spent on digital devices
- Lower expectations from education
- This research only captures data from a snapshot in time, however it reveals that while prevalence of myopia was higher in older compared to younger children as expected, myopia prevalence remained low, with most older children (14 & 15 yrs) being emmetropic.
- Study outcomes add further weight to the suggestion that environmental factors such as outdoor lifestyle and early age educational pressures may have an impact on prevalence of myopia.
Limitations and future research
- Non cycloplegic retinoscopy refraction was undertaken, which could potentially bias towards slightly more myopic refractions
- The authors indicate that the measured lower prevalence of myopia, compared to that reported in studies on other Australian locations, suggests the need for including questions on socioeconomic status, education and outdoor activity in myopia prevalence studies.
