Largedynamic-range Shack-Hartmann wavefront sensor for highly aberrated eyes

Abstract. A conventional Shack-Hartmann wavefront sensor has a limitation that increasing the dynamic range usually requires sacrificing measurement sensitivity. The prototype large-dynamic-range Shack-Hartmann wavefront sensor presented resolves this problem by using a translatable plate with subapertures placed in conjugate with the lenslet array. Each subaperture is the same size as a lenslet and they are arranged so that they overlap every other lenslet position. Three translations of the plate are required to acquire four images to complete one measurement. This method increases the dynamic range by a factor of two with no subsequent change in measurement sensitivity and sampling resolution of the aberration. The feasibility of the sensor was demonstrated by measuring the higher order aberrations of a custom-made phase plate and human eyes with and without the plate

Effect of Airflow Exposure on the Tear Meniscus

Purpose. To compare the effect of airflow exposure on the tear meniscus and blink frequency in normal and evaporative dry eye subjects. Methods. In 9 normal subjects and 9 short tear breakup time (SBUT) dry eye subjects, lower tear meniscus height (TMH) and area (TMA) and blink frequency were measured with anterior segment optical coherence tomography (OCT) before and after 5 minutes of airflow exposure (1.5 ± 0.5 m/s). Results. In SBUT dry eyes, both TMH and TMA decreased significantly (P = 0.027, P = 0.027) with a significant increase of blink frequency after airflow exposure, while significant increase in TMA was found in normal eyes. Conclusion. Measurement of the tear meniscus with anterior segment OCT seems to be useful as a noninvasive and objective method for evaluating the effect of airflow on tear film

Comparison of Higher-Order Aberration and Contrast Sensitivity in Monofocal and Multifocal Intraocular Lenses

PURPOSE: The visual performance of pseudophakic eyes depends on the type of intraocular lenses (IOLs) that are implanted. Aspherical and multifocal IOLs have recently been developed to improve visual quality after cataract surgery, but multifocal IOLs can be associated with decreased contrast sensitivity (CS), halos, and glare. This study compares the visual performance of monofocal and multifocal IOLs by measurement of higher-order aberrations (HOAs) and CS values. MATERIALS AND METHODS: HOAs and CS values of 42 eyes with implanted monofocal IOLs and 40 eyes with implanted multifocal IOLs were measured preoperatively and more than 6 months after surgery. In the multifocal IOL group, HOAs and CS values were also measured with addition of a trial lens of -0.5 diopter (D) to evaluate the compensatory effect on spherical aberration. RESULTS: CS values of the multifocal IOL group were significantly lower than those of the monofocal IOL group for all spatial frequencies tested (p<0.01), and the spherical aberration was significantly higher in the multifocal IOL group than in the monofocal IOL group (p<0.001). Addition of a -0.5 D lens to the multifocal IOL group decreased the difference in CS between the two groups (p=0.003). CONCLUSION: Increased spherical aberration may contribute to lower CS in the multifocal IOL group. In such cases, CS can be improved by addition of a -0.5 D lens to compensate for the spherical aberration.ope

Neural Compensation for Long-term Asymmetric Optical Blur to Improve Visual Performance in Keratoconic Eyes

The authors examined whether the neural visual system compensates for long-term visual experience with a blurred retinal image, resulting in improved visual performance in keratoconic eyes

Interaction between optical and neural factors affecting visual performance

Thesis (Ph. D.)--University of Rochester. Institute of Optics, 2012.The human eye suffers from higher order aberrations, in addition to conventional spherical and cylindrical refractive errors. Advanced optical techniques have been devised to correct them in order to achieve superior retinal image quality. However, vision is not completely defined by the optical quality of the eye, but also depends on how the image quality is processed by the neural system. In particular, how neural processing is affected by the past visual experience with optical blur has remained largely unexplored. The objective of this thesis was to investigate the interaction of optical and neural factors affecting vision. To achieve this goal, pathological keratoconic eyes were chosen as the ideal population to study since they are severely afflicted by degraded retinal image quality due to higher order aberrations and their neural system has been exposed to that habitually for a long period of time. Firstly, we have developed advanced customized ophthalmic lenses for correcting the higher order aberration of keratoconic eyes and demonstrated their feasibility in providing substantial visual benefit over conventional corrective methodologies. However, the achieved visual benefit was significantly smaller than that predicted optically. To better understand this, the second goal of the thesis was set to investigate if the neural system optimizes its underlying mechanisms in response to the long-term visual experience with large magnitudes of higher order aberrations. This study was facilitated by a large-stroke adaptive optics vision simulator, enabling us to access the neural factors in the visual system by manipulating the limit imposed by the optics of the eye. Using this instrument, we have performed a series of experiments to establish that habitual exposure to optical blur leads to an alteration in neural processing thereby alleviating the visual impact of degraded retinal image quality, referred to as neural compensation. However, it was also found that chronic exposure to poor optics caused neural insensitivity to fine spatial detail thus adversely limiting the achievable visual benefit when improving the eye‘s optical quality. Finally, we demonstrated that the altered, but plastic visual system could be re-adapted to improved optics such that it partially recovers its normal mechanism. These findings not only provide vast clinical implications for advanced customized vision correction methodologies for normal, pathologic and presbyopic eyes but also vital scientific insight into the neural processing of the visual system in response to the aberrated optics of the eye

Investigation of corneal biomechanical and optical behaviors by developing individualized finite element model

Thesis (Ph. D.)--University of Rochester. Department of Mechanical Engineering, 2019.The biomechanics of the cornea has a significant impact on its optical behavior. Alterations in corneal biomechanics lead to abnormalities in the surface topography and affect ocular aberrations that degrade retinal image quality. The goal of this thesis work is aimed towards investigating the interaction of corneal biomechanical and optical behaviors through development of an individualized corneal model based on the finite element method that accounts for the large variations in corneal geometry and material properties. The goal of the thesis can be divided into four specific aims. First, we investigated the biomechanical and optical behaviors of a healthy normal cornea at various IOPs through numerical simulations based on a widely accepted anisotropic hyperelastic FE model. We conducted a sensitivity analysis based on a powerful experimental/statistical technique, the DOE method. The biomechanical and optical responses of the cornea to IOP elevation as well as the relative contribution of multiple geometrical and material parameters to corneal biomechanical and optical behaviors were evaluated. We found that the radius of curvature of the cornea was the most important geometric parameter that contributes to both biomechanical and optical behaviors of the cornea. For material parameters, corneal apical displacement was influenced nearly evenly by matrix stiffness, fiber stiffness and nonlinearity. However, the corneal optical aberrations were primarily affected by the matrix stiffness and the distribution of collagen fibril dispersion. These findings have important implications for future theoretical and experimental studies of the cornea, especially for the development of an individualized cornea model. Second, we proposed new methods for material characterization of individual corneas. We aimed to characterize a complete set of material parameters for developing an individualized 3-D anisotropic hyperelastic corneal model, which provides accurate prediction of the interrelation between corneal biomechanics and optics of a specific cornea. We proposed novel methods mainly focusing on the individual quantification of three challenging material parameters, including collagen fiber stiffness, collagen fiber nonlinearity and collagen fibril dispersion using optical information of the cornea to overcome the traditional challenges in corneal material characterization. The new material characterization method could also be beneficial for future development of an in vivo individualized biomechanical model of the cornea and the investigation of the impact of corneal biomechanics on patient’s visual performance for clinical applications. Third, we evaluated the clinical significance of corneal biomechanical modeling in one of the important clinical applications, laser refractive surgery. An accurate prediction of the biomechanical response of the cornea to tissue ablation would help to predict postoperative surgical outcomes, which can be taken into account in developing new surgical paradigms for obtaining optimal surgical outcomes. The predictive ability of our biomechanical model was evaluated by simulating myopic corrections in PRK surgery. Our findings suggest that both of the spatial variation in collagen fibril dispersion and the depth-dependent extrafibrillar matrix stiffness play a significant role in the postoperative biomechanical and optical outcomes. Characterization of these two material features helps to predict more accurate trend of the HOAs induced by the surgical process. Lastly, we explored a novel method to induce in vivo IOP elevation for potential future development of an in vivo corneal model. Our new material characterization methods require a measurement of corneal optical behavior at varied IOP levels. Therefore, we investigated the potential of developing an in vivo individualized corneal model for clinical applications by developing an efficient and non-contract method to control IOP elevation in vivo. For the first time, we showed that in vivo IOP can be temporarily elevated and controlled in an innovative, safe, non-contact way using an inversion table. The research presented in this thesis helps to gain understandings of the biomechanical and optical responses of individual corneas to various intraocular pressures and to corneal surgery, such as laser vision correction. Furthermore, the capabilities and techniques described in the thesis may be applied to investigate underlying mechanisms, diagnosis and treatments of other clinically important ophthalmic pathologies such as keratoconus, post-refractive ectasia and glaucoma