Myopia, commonly known as nearsightedness, is becoming increasingly prevalent in children worldwide. As parents seek effective ways to manage their child's myopia, it’s essential to understand the tools and technologies available.
Among these, optical biometry for axial length measurement plays a critical role. Accurate measurement of axial length is key to monitoring and controlling myopia progression. This article will explain why optical biometry is superior to other methods and why relying on algorithms to estimate axial length from refraction and keratometry is not effective.
Understanding Myopia and Axial Length
Myopia occurs when the eye grows too long from front to back, resulting in light focusing in front of the retina instead of directly on it. This excessive axial length is the primary anatomical change associated with myopia. As myopia progresses, the axial length continues to increase, which can lead to a higher risk of developing severe eye conditions later in life, such as retinal detachment, glaucoma, and myopic maculopathy.
Why Axial Length Measurement Matters
Monitoring axial length is essential for managing myopia effectively. Unlike refractive error, which can fluctuate and be influenced by other factors, axial length provides a more stable and direct measurement of the eye's growth. Tracking changes in axial length allows eye care professionals to assess the effectiveness of myopia management interventions, such as orthokeratology, atropine eye drops, and multifocal contact lenses. This data is crucial for making informed decisions about treatment adjustments.
The Limitations of Estimating Axial Length from Refraction and Keratometry
In the past, some practitioners relied on algorithms to estimate axial length based on refraction (the prescription for glasses or contact lenses) and keratometry (measurements of the corneal curvature). However, this method has significant limitations:
Inaccuracy in Growing Eyes: Estimations from refraction and keratometry are not reliable in children whose eyes are still growing and changing. The relationship between refractive error and axial length is not linear and can vary widely among individuals. For example, two children with the same refractive error can have different axial lengths, leading to inaccurate assessments.
Ignoring the Posterior Segment: These algorithms typically focus on the anterior segment of the eye (cornea and lens) and do not account for changes in the posterior segment, where axial elongation primarily occurs. This omission can lead to an underestimation of axial length and, consequently, myopia progression.
Lack of Precision: Estimation methods lack the precision needed for managing myopia progression. Small changes in axial length can be significant in terms of risk for developing high myopia and associated complications. Optical biometry provides the accuracy necessary to detect these small changes and adjust treatment accordingly.
Optical Biometry: The Gold Standard
Optical biometry is a non-invasive, highly accurate method for measuring the axial length of the eye. Using low-coherence interferometry or swept-source optical coherence tomography (OCT), these devices measure the entire length of the eye from the cornea to the retina with micrometer precision.
Key advantages of optical biometry include:
High Precision: Optical biometry devices can measure axial length with incredible accuracy, detecting changes as small as 0.01 mm. This level of precision is essential for monitoring myopia progression over time and making informed decisions about treatment.
Comprehensive Measurement: Unlike estimation methods, optical biometry measures the entire eye, including both the anterior and posterior segments. This comprehensive measurement provides a more accurate assessment of myopia progression.
Consistency: Optical biometry offers consistent results, which are crucial for long-term monitoring. This consistency allows for better comparison of data over time, helping to track the effectiveness of myopia management strategies.
Other Methods of Measuring Axial Length: A Comparative Analysis
Other methods, such as ultrasound biometry, have also been used to measure axial length. However, these methods have limitations when compared to optical biometry:
Ultrasound Biometry: While ultrasound biometry is effective, it requires direct contact with the eye, which can be uncomfortable for children and may cause measurement variability due to pressure on the eye. Additionally, ultrasound has a lower resolution than optical biometry, leading to less precise measurements.
Partial Coherence Interferometry (PCI): PCI, a form of optical biometry, is highly accurate but can be affected by cataracts or other media opacities. Newer optical biometry technologies, such as swept-source OCT, overcome these limitations by providing clearer images through opaque media.
Conclusion
For parents of children undergoing myopia management, understanding the importance of accurate axial length measurement is crucial. Optical biometry stands out as the gold standard for this purpose, offering unparalleled accuracy and consistency. Relying on algorithms that estimate axial length from refraction and keratometry or using less precise methods can lead to inaccurate assessments and suboptimal myopia management. By ensuring that your child’s eye care includes regular axial length measurement with optical biometry, you are taking a vital step in protecting their long-term eye health.
References
Ohno-Matsui, K., Wu, P. C., Yamashiro, K., Vutipongsatorn, K., Fang, Y., & Cheung, C. M. G. (2021). IMI Pathologic Myopia. Investigative Ophthalmology & Visual Science, 62(5), 5-7. doi:10.1167/iovs.62.5.5.
Flitcroft, D. I. (2012). The complex interactions of retinal, optical and environmental factors in myopia aetiology. Progress in Retinal and Eye Research, 31(6), 622-660. doi:10.1016/j.preteyeres.2012.06.004.
Read, S. A., Collins, M. J., & Vincent, S. J. (2014). Light exposure and eye growth in childhood. Investigative Ophthalmology & Visual Science, 55(10), 7046-7053. doi:10.1167/iovs.14-14986.
Tideman, J. W. L., Polling, J. R., & Voortman, T. (2018). Axial length growth and the risk of developing myopia in European children. Acta Ophthalmologica, 96(3), 301-309. doi:10.1111/aos.13525.
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