Accommodation and age-dependent eye model based on in vivo measurements / Modelo de ojo variable con la acomodación y la edad, basado en medidas in vivo

Purpose: To develop a flexible model of the average eye that incorporates changes with age and accommodation in all optical parameters, including entrance pupil diameter, under photopic, natural, environmental conditions. Methods: We collated retrospective in vivo measurements of all optical parameters, including entrance pupil diameter. Ray-tracing was used to calculate the wavefront aberrations of the eye model as a function of age, stimulus vergence and pupil diameter. These aberrations were used to calculate objective refraction using paraxial curvature matching. This was also done for several stimulus positions to calculate the accommodation response/stimulus curve. Results: The model predicts a hyperopic change in distance refraction as the eye ages (+0.22 D every 10 years) between 20 and 65 years. The slope of the accommodation response/stimulus curve was 0.72 for a 25 years-old subject, with little change between 20 and 45 years. A trend to a more negative value of primary spherical aberration as the eye accommodates is predicted for all ages (20-50 years). When accommodation is relaxed, a slight increase in primary spherical aberration (0.008μm every 10 years) between 20 and 65 years is predicted, for an age-dependent entrance pupil diameter ranging between 3.58 mm (20 years) and 3.05 mm (65 years). Results match reasonably well with studies performed in real eyes, except that spherical aberration is systematically slightly negative as compared with the practical data. Conclusions: The proposed eye model is able to predict changes in objective refraction and accommodation response. It has the potential to be a useful design and testing tool for devices (e.g. intraocular lenses or contact lenses) designed to correct the eye's optical errors

Objetivo: Desarrollar un modelo flexible de ojo medio que incorpore los cambios en función de la edad y la acomodación en todos los parámetros ópticos, incluyendo el diámetro de pupila de entrada, en condiciones ambientales fotópicas y naturales. Métodos: Recopilamos medidas retrospectivas in vivo de todos los parámetros ópticos, incluyendo el diámetro de pupila de entrada. Se usó un trazado de rayos para calcular las aberraciones de frente de onda del modelo ocular en función de la edad, vergencia de estímulo y diámetro de la pupila. Se utilizaron dichas aberraciones para calcular la refracción objetiva mediante el criterio de curvatura paraxial. Esto se realizó también para diversas posiciones del estímulo, para calcular la curva de respuesta acomodativa. Resultados: El modelo predice un cambio hipermetrópico en la refracción de lejos a medida que el ojo envejece (+ 0,22 D cada 10 años) entre los 20 y los 65 años. La pendiente de la curva de respuesta acomodativa fue de 0,72 para un sujeto de 25 años, con pocos cambios entre los 20 y los 45 años. Se predice una tendencia hacia un valor más negativo de la aberración esférica primaria a medida que el ojo acomoda, en todas las edades (de 20 a 50 años). Con la acomodación relajada, se predice un ligero incremento de la aberración esférica primaria (0,008 μm cada 10 años) entre los 20 y los 65 años, para un diámetro de pupila de entrada dependiente de la edad que oscila entre 3,58 mm (20 años) y 3,05mm (65 años). Los resultados concuerdan razonablemente bien con los estudios realizados en ojos reales, exceptuando que la aberración esférica es ligera y sistemáticamente menor en comparación a los datos experimentales. Conclusiones: El modelo de ojo propuesto es capaz de predecir los cambios de la refracción objetiva y la respuesta acomodativa. Tiene el potencial de ser una herramienta útil de diseño y prueba de elementos correctores (e.j.: lentes intraoculares o lentes de contacto) de los errores ópticos del ojo

Optical quality for keratoconic eyes with conventional RGP lens and simulated, customised contact lens corrections: a comparison.

PURPOSE: To compare monochromatic aberrations of keratoconic eyes when uncorrected, corrected with spherically-powered RGP (rigid gas-permeable) contact lenses and corrected using simulations of customised soft contact lenses for different magnitudes of rotation (up to 15°) and translation (up to 1mm) from their ideal position. METHODS: The ocular aberrations of examples of mild, moderate and severe keratoconic eyes were measured when uncorrected and when wearing their habitual RGP lenses. Residual aberrations and point-spread functions of each eye were simulated using an ideal, customised soft contact lens (designed to neutralise higher-order aberrations, HOA) were calculated as a function of the angle of rotation of the lens from its ideal orientation, and its horizontal and vertical translation. RESULTS: In agreement with the results of other authors, the RGP lenses markedly reduced both lower-order aberrations and HOA for all three patients. When compared with the RGP lens corrections, the customised lens simulations only provided optical improvements if their movements were constrained within limits which appear to be difficult to achieve with current technologies. CONCLUSIONS: At the present time, customised contact lens corrections appear likely to offer, at best, only minor optical improvements over RGP lenses for patients with keratoconus. If made in soft materials, however, these lenses may be preferred by patients in term of comfort.