A new type of spectacle lens was developed incorporating a thin layer of a novel polymer with a light-programmable
refractive index. The refractive index change can be used to change the optical power of the lens. One of the
applications of this new lens is the correction of high-order aberrations of the human eye. A feasibility study was
conducted to determine whether such wavefront-guided high-order correcting spectacle lenses can be 1) accurately
manufactured, and 2) improve vision of human subjects. The ocular wavefront of 30 subjects was measured with a Z-ViewTM diffractive aberrometer. A vision correcting high-order zone canceling the subjects' ocular wavefront was
"programmed" directly into pairs of wavefront-guided spectacle lenses (WFGSL). The lenses could be successfully
manufactured to an average Zernike rms accuracy of 81% (range 70% to 90%). Comparison was made against identical
spectacles without the high-order zone. Double-masked vision tests included high and low-contrast visual acuity, and
contrast sensitivity. The subject was allowed only a few minutes of adaptation time to the spectacles. While some
experienced a dramatic improvement in vision, this was not observed for all subjects, in particular for subjects with
small amounts of high-order aberrations. We speculate that more consistent vision improvement can be achieved by 1)
determining a subject's candidacy for WFGSL based on the subject's ocular aberrations, 2) correcting only selected
aberrations, 3) manufacture with higher purity and accuracy, and 4) lengthening the adaptation period before testing
each lens.
Based on the Talbot self-imaging principle, a diffraction-based wavefront sensor, the Z-ViewTM wavefront sensor, has been developed at Ophthonix Inc. According to the Talbot effect, a periodic grating can be self-imaged at certain distances behind the grating, commonly known as Talbot distances, without the aid of any imaging device. The fidelity of the Talbot image to the grating pattern is affected by the wavefront aberration in the illumination beam. Therefore, the wavefront distortion can be retrieved through numerical analysis of the Talbot image. Unlike the well-known Shack-Hartmann wavefront sensor, where a group of pixels on the camera is responsible for only one wavefront data point, each camera pixel in the Z-View wavefront sensor has a corresponding wavefront data. The Z-View wavefront sensor measures the wavefront at 1024 x 1048 data points, and can achieve a dynamic range of wavefront curvature of 20 diopters. The Z-View wavefront sensor has been successfully used for wavefront sensing in ophthalmic aberrometry, adaptive optics, and lensometry at Ophthonix.
A novel wavefront sensor (Z-ViewTM) using a two dimensional diffractive grating has been developed at Ophthonix, Inc. Based on the Talbot self-imaging theory, a CMOS camera is placed behind the grating to capture the first Talbot image of the aberrated wavefront. This captured Talbot image is analyzed to recover the wavefront aberration. The diffractive grating wavefront sensor has been used in Ophthonix's Z-View Aberrometer, an objective refractive vision assessment system which is now commercially used in optometrist's offices/clinics across the United States of America. Coupled with a deformable mirror and other auxiliary optics systems, Z-View wavefront sensor forms the A-View adaptive optic vision correction system at Ophthonix. This A-View system is used to study the effect of complete wavefront correction in human vision, and has potential application in prescribing Ophthonix's wavefront-guided iZonTM lenses. In this paper, the wavefront sensing principle of this novel diffractive wavefront sensor and its applications will be discussed.
High order aberrations in human eye can deteriorate visual acuity and contrast sensitivity. Such aberrations can not be corrected with traditional low-order (defocus and astigmatism) spectacles or contact lenses. A state-of-the-art adaptive optics vision correction system was developed using Ophthonix's Z-View diffractive wavefront sensor and a commercial miniature deformable mirror. While being measured and corrected by this system, the patient can also view a Snellen chart or a Contrast Sensitivity chart through the system in order to experience the vision benefits both in visual acuity and contrast sensitivity. Preliminary study has shown the potential that this system could be used in a doctor's office to provide patients with a subjective feel of the objective high order prescription measured on Z-View.
In the eye, the retinal nerve fibers transmit the visual signal from the photoreceptors to the brain. In certain diseases, i.e., glaucoma, these nerve fibers are damaged, resulting in impaired vision or blindness. The retinal nerve fiber layer consists of parallel structures of diameter smaller than the wavelength of light. Therefore, this qualifies it as a form birefringent structure, capable of changing the state of polarization of light double passing it. The amount of change in the state of polarization (retardation) can be assessed with a polarimeter and is proportional to the thickness of the nerve fiber layer at the measurement location. A scanning laser polarimeter (Nerve Fiber AnalyzerTM) is described that employs a low power near infra-red laser beam to illuminate the human retina. In normal eyes, a thick retinal nerve fiber layer was measured in the superior and inferior regions of the peripapillary retina. In glaucoma eyes, this normal nerve fiber layer thickness distribution was found to be disturbed. The measured retinal nerve fiber directions indicated that the retinal nerve fiber layer around the optic nerve head of a normal eye is radially symmetrical.
The assessment of the condition of the retinal nerve fiber layer plays an important role for the early detection of blinding eye diseases like glaucoma. We describe the application of a scanning laser polarimeter for quantitative measurements of the retinal nerve fiber layer thickness in vivo. The measuring beam of the scanning laser polarimeter is focused on the retina and penetrates the birefringent nerve fiber layer. The retardation of the light double- passing the nerve fiber layer is proportional to its thickness and is measured at 256 by 256 positions within a field of view of 15 by 15 degrees. The measurement time is less than 1 second. During the measurement, the polarization effects of the anterior segment of the human eye are canceled by a cornea polarization compensator. The retinal retardation values are displayed as a color coded map of the retinal nerve fiber layer thickness distribution.
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