To determine the impact of the equivalent refractive index (ERI) on intraocular lens (IOL) power ... more To determine the impact of the equivalent refractive index (ERI) on intraocular lens (IOL) power prediction for eyes with previous myopic laser in situ keratomileusis (LASIK) using custom ray tracing. AMO B.V., Groningen, the Netherlands, and the Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA. Retrospective data analysis. The ERI was calculated individually from the post-LASIK total corneal power. Two methods to account for the posterior corneal surface were tested; that is, calculation from pre-LASIK data or from post-LASIK data only. Four IOL power predictions were generated using a computer-based ray-tracing technique, including individual ERI results from both calculation methods, a mean ERI over the whole population, and the ERI for normal patients. For each patient, IOL power results calculated from the four predictions as well as those obtained with the Haigis-L were compared with the optimum IOL power calculated after cataract surgery. The study...
A high-resolution method that allows direct measurements of the intercenter cone distance in the ... more A high-resolution method that allows direct measurements of the intercenter cone distance in the living human fovea is proposed. The experimental technique is similar to that used in stellar speckle interferometry. It is based on the recording and posterior processing of coherent short-exposure images of a small area of the central fovea. By using this optical-digital procedure, we have obtained what are to our knowledge the first objective measurements in vivo of the cone spacing in the human fovea. The reconstruction of the whole spatial information of the cone mosaic would also be possible by further improvements reconstruction algorithms.
Second-harmonic generation microscopy of photocurable polymer intrastromal implants in ex-vivo corneas
Biomedical Optics Express, 2015
A custom adaptive-optics (AO) multiphoton microscope was used to visualize the corneal stroma aft... more A custom adaptive-optics (AO) multiphoton microscope was used to visualize the corneal stroma after the insertion of a photocurable polymer material. A lamellar pocket was created and a certain amount of polymer in liquid form was injected. This turned into a rigid film after UV irradiation. Intact eyes were used as control. Tomographic and regular second harmonic generation (SHG) microscopy images were recorded from both control and corneas with polymer implants. In control corneas, the SHG signal decreased uniformly with depth. However, treated corneas exhibited an abrupt loss of SHG signal at the implant location. The use of AO increased the SHG levels and improved the visualization of the stroma, not only at deeper corneal layers but also beneath the implant. Moreover, the absence of SHG signal from the implant allowed its geometrical characterization (thickness and location). This technique offers a potential tool for non-invasive analysis of morphological changes in the cornea after surgery or treatment, and might be useful in future clinical environments.
A Polychromatic High Sensitivity Double-Pass System to Measure Intraocular Scattering
Frontiers in Optics 2007/Laser Science XXIII/Organic Materials and Devices for Displays and Energy Conversion, 2007
ABSTRACT
Adaptive Optics in Ocular Optical Coherence Tomography
Biological and Medical Physics, Biomedical Engineering, 2012
We have designed an intraocular telescope for the posterior chamber of the human eye of patients ... more We have designed an intraocular telescope for the posterior chamber of the human eye of patients with age related macular degeneration. The basic design is composed of two decentered high optical power lenses ( + 66D and -66D) inducing a 3° prismatic effect to project a magnified central field of view into a healthier location off the central fovea. Aspheric surfaces were used to ensure a compromise between good optical quality and high tolerance to the final axial position of both lenses after surgery. With this particular design, the telescope affords an extended range of depth of focus, high tolerance to different axial lengths of the eye and robustness against typical values of astigmatism and higher order aberrations. The final design has been manufactured in a foldable material and is compact enough to facilitate surgical implantation. This telescope is a simple but promising intraocular visual aid for AMD patients.
Quality of vision in patients who have undergone corneal refractive surgery depends upon the opti... more Quality of vision in patients who have undergone corneal refractive surgery depends upon the optimal centration of the procedures used. The center of the pupil is used as a reference point in some corneal ablation procedures. The achromatic axis would be a more sensible option from an optical point of view, but it is not as readily detectable. As an alternative, other refractive techniques, like the small aperture corneal inlay for presbyopia correction, use the corneal reflex (first Purkinje image). To assess the relative position of these two marks, we developed a new instrument to simultaneously measure both the first Purkinje image (PI) and the intersection of the achromatic axis with the pupil plane. The apparatus records images of the pupil and the PI when illuminated with a circle of infrared light-emitting diodes. A second optical path allows determination of the achromatic axis by using a subjective method. Both the positions of the PI and the achromatic axis intersection a...
We have developed a new optical procedure to determine the optimum power of intraocular lenses (I... more We have developed a new optical procedure to determine the optimum power of intraocular lenses (IOLs) for cataract surgery. The procedure is based on personalized eye models, where biometric data of anterior corneal shape and eye axial length are used. A polychromatic exact ray-tracing through the surfaces defining the eye model is performed for each possible IOL power and the area under the radial MTF is used as a metric. The IOL power chosen by the procedure maximizes this parameter. The IOL power for 19 normal eyes has been determined and compared with standard regression-based predictions. The impact of the anterior corneal monochromatic aberrations and the eye's chromatic aberration on the power predictions has been studied, being significant for those eyes with severe monochromatic aberrations, such as post-LASIK cataract patients, and for specific IOLs with low Abbe numbers.
Journal of refractive surgery (Thorofare, N.J. : 1995), 2007
To assess the performance and optical limitations of standard, aspheric, and wavefront-customized... more To assess the performance and optical limitations of standard, aspheric, and wavefront-customized intraocular lenses (IOLs) using clinically verified pseudophakic eye models. White light pseudophakic eye models were constructed from physical measurements performed on 46 individual cataract patients and subsequently verified using the clinically measured contrast sensitivity function (CSF) and wavefront aberration of pseudophakic patients implanted with two different types of IOLs. These models are then used to design IOLs that correct the astigmatism and higher order aberrations of each individual eye model's cornea and to investigate how this correction would affect visual benefit, subjective tolerance to lens misalignment (tilt, decentration, and rotation), and depth of field. Physiological eye models and clinical outcomes show similar levels of higher order aberration and contrast improvement. Customized correction of ocular wavefront aberrations with an IOL results in contra...
ABSTRACT An abstract is unavailable. This article is available as HTML full text and PDF.
<title>Binocular adaptive optics visual simulator: understanding the impact of aberrations on actual vision</title>
Ophthalmic Technologies XX, 2010
A novel adaptive optics system is presented for the study of vision. The apparatus is capable for... more A novel adaptive optics system is presented for the study of vision. The apparatus is capable for binocular operation. The binocular adaptive optics visual simulator permits measuring and manipulating ocular aberrations of the two eyes simultaneously. Aberrations can be corrected, or modified, while the subject performs visual testing under binocular vision. One of the most remarkable features of the apparatus
<title>Adaptive optics using a liquid crystal spatial light modulator for ultrahigh-resolution optical coherence tomography</title>
Ophthalmic Technologies XVI, 2006
Adaptive optics using a liquid crystal spatial light modulator for ultrahigh-resolution optical c... more Adaptive optics using a liquid crystal spatial light modulator for ultrahigh-resolution optical coherence tomography. [Proceedings of SPIE 6138, 61380Y (2006)]. Enrique J. Fernández, Boris Povazay, Boris M. Hermann, Angelika ...
Adaptive optics visual simulator
Journal of refractive surgery (Thorofare, N.J. : 1995)
To develop a prototype instrument that uses adaptive optics to introduce virtually any desired ab... more To develop a prototype instrument that uses adaptive optics to introduce virtually any desired aberration profile in a subject's eye. At the same time, the instrument could be used to evaluate the subject's spatial vision for each controlled aberration profile. This "aberration testing station" or "visual simulator" allows us to study the relationship between specific aberrations and visual quality. The apparatus uses infrared light to measure the wavefront aberration of the system plus the eye with a Hartmann-Shack wavefront sensor. Defocus is added (or removed) with a computer-controlled, motorized optometer, while higher order aberrations are introduced by a 37-channel membrane deformable mirror. A parallel viewing channel is used for visual testing with the instrument. Visual acuity, contrast sensitivity, and other visual tests are performed under normal viewing for each desired aberration profile. The range of defocus that can be added is nearly unli...
Journal of refractive surgery (Thorofare, N.J. : 1995)
Despite the fact that ocular aberrations blur retinal images, our subjective impression of the vi... more Despite the fact that ocular aberrations blur retinal images, our subjective impression of the visual world is sharp, which suggests that the visual system compensates for subjective influence. If the brain adjusts for specific aberrations of the eye, vision should be clearest when looking through a subject's typical wave aberration rather than through an unfamiliar one. We used adaptive optics techniques to control the eye's aberrations in order to evaluate this hypothesis. We used adaptive optics to produce point spread functions (PSFs) that were rotated versions of the eye's typical PSF by angles in 45 degrees intervals. Five normal subjects were asked to view a stimulus with their own PSF or with a rotated version, and to adjust the magnitude of the aberrations in the rotated case to match the subjective blur of the stimulus to that seen when the wave aberration was in typical orientation. The magnitude of the rotated wave aberration required to match the blur with t...
Corneal small aperture inlays provide extended depth of focus as a solution to presbyopia. As thi... more Corneal small aperture inlays provide extended depth of focus as a solution to presbyopia. As this procedure is becoming more popular, it is interesting to compare its performance with traditional approaches, such as monovision. Here, binocular visual acuity was measured as a function of object vergence in three subjects by using a binocular adaptive optics vision analyzer. Visual acuity was measured at two luminance levels (photopic and mesopic) under several optical conditions: 1) natural vision (4 mm pupils, best corrected distance vision), 2) pure-defocus monovision ( + 1.25 D add in the nondominant eye), 3) small aperture monovision (1.6 mm pupil in the nondominant eye), and 4) combined small aperture and defocus monovision (1.6 mm pupil and a + 0.75 D add in the nondominant eye). Visual simulations of a small aperture corneal inlay suggest that the device extends DOF as effectively as traditional monovision in photopic light, in both cases at the cost of binocular summation. H...
The extent to which monocular visual performance of subjects with normal amounts of ocular aberra... more The extent to which monocular visual performance of subjects with normal amounts of ocular aberrations can be improved with adaptive optics (AO) depends on both the pupil diameter and the luminance for visual testing. Here, the benefit of correction of higher order aberrations for binocular visual performance was assessed over a range of luminances for natural light-adapted pupil sizes with a binocular AO visual simulator. Results show that binocular aberration correction benefits for visual acuity and contrast sensitivity increase with decreasing luminances. Also, the advantage of binocular over monocular viewing increases when visual acuity becomes worse. The findings suggest that binocular summation mitigates poor visual performance under low luminance conditions.
Eye models are valuable tools that can help delineate the role of anatomical parameters on visual... more Eye models are valuable tools that can help delineate the role of anatomical parameters on visual performance and guide the design of advanced ophthalmic instrumentation. We propose an optically accurate wide-field schematic eye that reproduces the complete aberration profile of the human eye across a wide visual field. The optical performance of the schematic eye is based on experimentally measured wavefront aberrations taken with a four mm pupil for the central 80°of the horizontal meridian (101 eyes) and 50°of the vertical meridian (10 eyes). Across the entire field of view, our model shows excellent agreement with the measured data both comprehensively and for low-order and high-order aberrations. In comparison to previous eye models, our schematic eye excels at reproducing the aberrations of the retinal periphery. Also unlike previous models, tilt and decentering of the gradient refractive index crystalline lens, which arose naturally through the optimization process, permits our model to mimic the asymmetries of real human eyes while remaining both anatomically and optically correct. Finally, we outline a robust reverse building eye modeling technique that is capable of predicting trends beyond those defined explicitly in the optimization routine. Our proposed model may aid in the design of wide-field imaging instrumentation, including optical coherence tomography, scanning laser ophthalmoscopy, fluorescence imaging, and fundus photography, and it has the potential to provide further insights in the study and understanding of the peripheral optics of the human eye.
Aberration generation by contact lenses with aspheric and asymmetric surfaces
Journal of refractive surgery (Thorofare, N.J. : 1995)
We explored the potential of aberration correction in the human eye by using a new generation of ... more We explored the potential of aberration correction in the human eye by using a new generation of soft contact lenses with aspheric and asymmetric surfaces. Soft contact lens samples were designed with one asymmetrical surface (front) and one spherical (back) to produce predetermined amounts of desired pure defocus, astigmatism, trefoil, coma, and spherical aberration. Contact lens wavefront aberrations were measured ex vivo using a Fizeau-Tolanski interferometer and compared with the in vivo wavefronts obtained by subtracting the aberrations of the eye with and without the contact lenses. These second set of measurements were obtained using a Shack-Hartmann sensor. We found that an aberration-free contact lens sample induced in the eye a small amount of residual aberration. We obtained a good match between the ex vivo and in vivo wavefront measurements for most of the samples of the contact lenses. The aberrations generated by soft contact lenses on the eye were predictable. Rotatio...
Second Harmonic Generation (SHG) imaging is a non-invasive technique sensitive to local anisotrop... more Second Harmonic Generation (SHG) imaging is a non-invasive technique sensitive to local anisotropy that provides useful information on microscopic structures . SHG process is mostly directional rather than isotropic, with a preferred SHG signal in the forward direction. This means that SHG imaged structures will strongly depend on the recording configurations within the microscope [2]. Moreover, polarized light has been shown to be important when visualizing different features of samples containing collagen . The aim of this work is to model the spatial distribution of SHG signal from collagen fibers for incident elliptically polarized states located along a vertical meridian on the Poincaré sphere. The beam was assumed to be focused on a horizontal collagen fiber through a microscope objective.
Uploads
Papers by Pablo Artal