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The Significance of Measuring Axial Length in Myopia

by | Jul 1, 2023 | Manuscripts | 0 comments

Sapam Bishwamitra Singh, B.Optom

M.Optometry (Student), Bansara Institute of Ophthalmic Sciences, Shillong-India.

 

Introduction

Myopia is defined as short sightedness or “When accommodation is at rest, parallel light beams from infinity concentrate in front of the retina”.(1) In India, the most frequent cause of vision impairment and the second most important factor in preventable blindness are untreated refractive errors. The most typical side effect of Myopic retinopathy is permanent vision loss. To prevent blindness, it is important to manage the onset and development of myopia. One of the most significant elements impacting refractive errors is ocular biometrics.(2) One of the most common avoidable causes of blindness worldwide is refractive error.(3) According to the World Health Organization’s “VISION 2020: The Right to Sight: A Global Initiative to Eliminate Avoidable Blindness” report.(4) Among refractive errors, myopia is the most common form. In the future, myopia is predicted to make up 50% of the projected global population in 2050.(5) Myopia can be 80–90% prevalent in the population of people aged 17–18 in various Asian nations.(6)

Individuals who have high or severe forms of myopia are more likely to develop glaucoma, lacquer cracks, retinal detachment, chorioretinal atrophy, and other ocular problems.(7)

Axial length

The distance between the corneal surface and an inference peak that corresponds to the retinal pigment epithelium/membrane Bruch’s is known as the axial length (AL).(8-9) The typical axial length of a fully developed new-borns’ eye is 16–18 mm, whereas it is 22–25 mm in adults.(10-12) AL is used clinically to estimate the power of intraocular lenses (IOLs) before cataract and refractive surgery, (13) for the purpose of identifying eye diseases like staphyloma,(14) to determine the retinal detachment risk.,(15) and research on myopia also measure the structural and dimensional components.(16)

Axial length and myopia

Myopia is produced by an imbalance between the optical power and length of the eye. Myopia in youngsters develop and worsen because of excessive axial eye lengthening. (17-22) Although the relationship between the two is not linear and does not persist throughout childhood, there is a significant correlation between an individual’s degree of myopia and the length of their eye. (19,23) To assess the severity of myopia in their patients, ophthalmologists and optometrists now use optical partial coherence interferometry and equipment for reading ultrasonic velocity. Most people concur that AL is the main factor influencing refractive error.(24) According to Warrier et al. (25), these variations were due to population effects. For instance, close work was more intense in the younger age group, a factor enhancing AL likely caused by a defocus-induced disturbance of emmetropization.(26) To stop the child’s eyes from getting too long is the major goal of myopia management therapy. This is because, despite having shorter eyes and lower myopia, the risk for related ocular pathology is higher the longer the eye. (27-33)

Axial length measurement and cycloplegic refraction

Cycloplegic (“damp”) refraction is a standard practice in children who already have myopia. (34-36) Based on current data, a 1 dioptre change in refractive error corresponds to a 0.28mm increase in AL for children aged 6 to 7 years, and a 1 dioptre change corresponds to a 0.32mm increase in AL for children aged 12 to 13 years. (19,37) 1 dioptre equals 0.35 to 0.40mm in adults. (19,38) According to Cruickshank and Logan (19), children of any age with mild myopia have an increase in AL of 0.32mm for every dioptre change in refractive error, compared to children with moderate myopia who have an increase in AL of 0.58mm. AL and cycloplegic refraction are the normative tests used to assess the efficacy of myopia control treatments at its commencement. (39,40)

Conclusion

For the therapy of childhood myopia, precise prescription of refractive error is crucial. Without cycloplegic refraction, we run the danger of prescribing over-minus the child. The sole metric that may be used to assess the development of myopia is axial length. Axial length measures and cycloplegic refraction measurements are both required to assess a child’s myopia and/or its progression. Axial length measurement can be used to assess a patient’s risk of developing myopia, their risk of developing related disease, and the efficacy of their current myopia valid measure.

 

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