Do Peripheral Refraction and Aberration Profiles Vary with the Type of Myopia? - An Illustration Using a Ray-Tracing Approach

Abstract

Myopia is considered to be the most common refractive error occurring in children and young adults, around the world. Motivated to elucidate how the process of emmetropization is disrupted, potentially causing myopia and its progression, researchers have shown great interest in peripheral refraction. This study assessed the effect of the myopia type, either refractive or axial, on peripheral refraction and aberration profiles. METHODS: Using customized schematic eye models for myopia in a ray tracing algorithm, peripheral aberrations, including the refractive error, were calculated as a function of myopia type. RESULTS: In all the selected models, hyperopic shifts in the mean spherical equivalent (MSE) component were found whose magnitude seemed to be largely dependent on the field angle. The MSE profiles showed larger hyperopic shifts for the axial type of myopic models than the refractive ones and were evident in -4 and -6 D prescriptions. Additionally, greater levels of astigmatic component (J180) were also seen in axial-length-dependent models, while refractive models showed higher levels of spherical aberration and coma. RESUMENSe considera que la miopía es el error refractivo más frecuente a nivel mundial en niños y en adultos jóvenes. Con el objetivo de esclarecer de qué modo se ve perturbado el proceso de emetropización, potencialmente dando lugar a la aparición de miopía y a su progresión, los investigadores se han mostrado muy interesados en estudiar la refracción periférica. Este estudio evalúa en qué medida la refracción periférica y los perfiles de aberración dependen del tipo de miopía predominante, ya sea refractiva o axial. MÉTODOS:Partiendo de modelos de ojo esquemáticos adaptados al caso de la miopía y utilizando un algoritmo de trazado de rayos, se calcularon las aberraciones periféricas, incluyendo el error refractivo, en función del tipo de miopía. RESULTADOS: En todos los modelos estudiados, se observó un cambio o desplazamiento hipermetrópico en el equivalente esférico medio (EEM), cuyo valor parecía depender mayormente del ángulo analizado (excentricidad). En los perfiles de EEM se aprecia que dicho desplazamiento hipermetrópico es mayor para los modelos de miopía de tipo axial que para los de tipo refractivo, diferencia que se hace evidente en los casos correspondientes a -4 D y a -6 D. Además, se observó que el coeficiente asociado al término de astigmatismo (J180) presentaba un valor más alto en los modelos con un mayor peso de la miopía axial, mientras que en los modelos predominantemente refractivos se obtuvieron mayores niveles de aberración esférica y de coma. CONCLUSIONES: Este estudio ha concluido que aquellos ojos miopes donde prima la componente axial pueden presentar un mayor riesgo de progresión que ojos miopes que tengan errores refractivos similares pero donde prime la componente refractiva. Esta predicción surge de los resultados teóricos obtenidos en modelos de ojos utilizando un algoritmo de trazado de rayos, por lo que necesitan ser confirmados experimentalment...

Changes in Peripheral Refractive Profile after Orthokeratology for Different Degrees of Myopia

“…[12][13][14] Bakaraju et al have suggested that the risk for myopia progression could be higher in axial myopias compared to refractive ones according to their peripheral refractive pattern. 15 Interestingly, pioneer work from Cho and coauthors found a positive and statistically significant correlation between baseline spherical equivalent refraction and vitreous chamber depth elongation in the orthokeratology group such that the higher the baseline myopia the lower the myopic progression. Conversely, the opposite was found in the control group of spectacle wearers.…”

Ocular higher-order aberrations and axial eye growth in young Hong Kong children

“…While defocus and astigmatism (lower-order aberrations) can be corrected with conventional spectacles or contact lenses, other optical imperfections described as higher-order aberrations (HOAs) cannot be corrected using traditional optical corrections and have the potential to alter retinal image quality 12 , 13 which may provide cues to the retina 14 , and possibly lead to the development of myopia 15 . Numerous studies have investigated the relationships between HOAs and age 16 – 21 , axial length 22 , 23 , refractive error 24 , accommodation 13 , 25 , and ethnicity 24 , 26 , 27 .…”

Peripheral Refraction in Myopic Patients After Orthokeratology

“…[14][15][16] Bakaraju et al have suggested that the risk for myopia progression could be higher in axial myopias compared to refractive ones according to their peripheral refractive pattern. 17 Despite these findings, the characterization of peripheral refraction after corneal reshaping has only been addressed by a limited number of studies. 18 In the work of Charman et al, the authors showed for the first time the actual changes in off-axis refraction induced by ortho-k treatment.…”