Anatomical changes of the growing crystalline lens influence its refractive development, including power and spherical aberration. We have recently developed a new instrument that characterizes both the optical and biometric properties of the lens in-vitro by merging Ray-Tracing Aberrometry (RTA) with three-dimensional OCT imaging. In this abstract, we describe the application of the RTA to the measurement of lens spherical aberration.
Experiments were performed on 54 isolated human lenses (age: 0.25 to 56 years). The system was programmed to sequentially deliver the probing beam through the lens using a raster scan pattern of 13 × 13 transversal positions spaced 0.5 mm apart. Exit rays were imaged after exiting the tissue chamber at 9 different axial positions (ΔZ = 0 mm to 8 mm) in 1 mm intervals. A total of 1,521 spot images were acquired per lens. All data was automatically analyzed using custom software we developed in MATLAB. Exit ray slopes over a 6 mm pupil were used to determine Zernike wavefront coefficients up to the sixth order. The 4th order Zernike coefficient Z[4,0] was used to measure primary spherical aberration (SA). The results suggest that spherical aberration of the growing lens becomes more negative before adulthood and less negative after around age 30. The data is consistent with results from in-vivo studies that suggest the lens spherical aberration becomes less negative in older lenses (>30 years).
Age-related changes in the crystalline lens shape and refractive index gradient produce changes in dioptric power and high-order aberrations that influence the optics of the whole eye and contribute to a decrease in overall visual quality. Despite their key role, the changes in lens shape and refractive index gradient with age and accommodation and their effects on high-order aberrations are still not well understood. The goal of this project was to develop a combined laser ray tracing (LRT) and optical coherence tomography (OCT) system to measure high-order aberrations, shape and refractive index gradient in non-human primate and human lenses. A miniature motorized lens stretching system was built to enable imaging and aberrometry of the lens during simulated accommodation. A positioning system was also built to enable on- and off-axis OCT imaging and aberrometry for characterization of the peripheral defocus of the lens. We demonstrated the capability of the LRT-OCT system to produce OCT images and aberration measurements of crystalline lens with age and accommodation in vitro. In future work, the information acquired with the LRT-OCT system will be used to develop an accurate age-dependent lens model to predict the role of the lens in the development of refractive error and aberrations of the whole eye.
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