Extended depth of focus contact lenses for presbyopia

BCLA CLEAR Presbyopia: Management with contact lenses and spectacles

This paper seeks to outline the history, market situation, clinical management and product performance related to the correction of presbyopia with both contact lenses and spectacles. The history of the development of various optical forms of presbyopic correction are reviewed, and an overview is presented of the current market status of contact lenses and spectacles. Clinical considerations in the fitting and aftercare of presbyopic contact lens and spectacle lens wearers are presented, with general recommendations for best practice. Current options for contact lens correction of presbyopia include soft simultaneous, rigid translating and rigid simultaneous designs, in addition to monovision. Spectacle options include single vision lenses, bifocal lenses and a range of progressive addition lenses. The comparative performance of both contact lens and spectacle lens options is presented. With a significant proportion of the global population now being presbyopic, this overview is particularly timely and is designed to act as a guide for researchers, industry and eyecare practitioners alike.

Light sheet fluorescence microscopy using axi-symmetric binary phase filters

Light sheet fluorescence microscopy (LSFM) has become an indispensable tool in biomedical studies owing to its depth-sectioning capability and low photo-bleaching. The axial resolution in LSFM is determined mainly by the thickness of the illumination sheet, and a high numerical-aperture lens is thus preferred in the illumination to increase the axial resolution. However, a rapid divergence of the illumination beam limits the effective field-of-view (FoV), that provides high-resolution images. Several strategies have been demonstrated for FoV enhancement, which involve the use of Bessel or Airy beams, for example. However, the generation of these beams requires complicated optical setup or phase filters with continuous phase distributions, which are difficult to manufacture. In contrast, a binary phase filter (BPF) comprising concentric rings with 0 or π phases produces a response similar to its continuous original and is easy to realize. Here, we present a novel form of LSFM that integrates BPFs derived from two representative axi-symmetric aberrations, including phase axicon and spherical aberrations, to improve the imaging performance. We demonstrate that these BPFs significantly increase the FoV, and those derived from axicon generate self-reconstructing beams, which are highly desirable in imaging through scattering specimens. We validate its high-contrast imaging capability over extended FoV by presenting three-dimensional images of microspheres, imaginal disc of Drosophila larva, and Arabidopsis.

Perceived image quality with simulated segmented bifocal corrections

Bifocal contact or intraocular lenses use the principle of simultaneous vision to correct for presbyopia. A modified two-channel simultaneous vision simulator provided with an amplitude transmission spatial light modulator was used to optically simulate 14 segmented bifocal patterns (+ 3 diopters addition) with different far/near pupillary distributions of equal energy. Five subjects with paralyzed accommodation evaluated image quality and subjective preference through the segmented bifocal corrections. There are strong and systematic perceptual differences across the patterns, subjects and observation distances: 48% of the conditions evaluated were significantly preferred or rejected. Optical simulations (in terms of through-focus Strehl ratio from Hartmann-Shack aberrometry) accurately predicted the pattern producing the highest perceived quality in 4 out of 5 patients, both for far and near vision. These perceptual differences found arise primarily from optical grounds, but have an important neural component.

Dependence of depth of focus on spherical aberration of optical systems

This paper presents a theoretical analysis and computation of aberration coefficients of the third and fifth order of transverse spherical aberration of an optical system, which generates a ray bundle with a diameter of a geometric-optical circle of confusion smaller than a predetermined limit value. Equations were derived for the calculation of aberration coefficients of an optical system, which satisfy given conditions, and for the determination of the maximum possible depth of focus for given conditions.

On the use of the supporting quadric method in the problem of the light field eikonal calculation

A new iterative technique for calculating the eikonal function of a light field providing the focusing into a set of points is introduced. This technique is a modification of the supporting quadric method widely used for design of reflecting and refracting optical surfaces for generating prescribed illuminance distributions at given discrete set of points. As an example, we design a refractive optical element which focuses an incident beam into a set of points with energy pattern forming an image of a keyboard of a calculator. It is shown that the proposed technique is well-suited for the design of diffractive optical elements producing continuous intensity distributions within the scalar theory of diffraction. It is also shown that the calculated eikonal function is a good initial guess when designing diffractive optical elements using the iterative Gerchberg-Saxton algorithm.

Assessment of imaging with extended depth-of-field by means of the light sword lens in terms of visual acuity scale

We present outcomes of an imaging experiment using the refractive light sword lens (LSL) as a contact lens in an optical system that serves as a simplified model of the presbyopic eye. The results show that the LSL produces significant improvements in visual acuity of the simplified presbyopic eye model over a wide range of defocus. Therefore, this element can be an interesting alternative for the multifocal contact and intraocular lenses currently used in ophthalmology. The second part of the article discusses possible modifications of the LSL profile in order to render it more suitable for fabrication and ophthalmological applications.

Developments in the correction of presbyopia I: spectacle and contact lenses

PURPOSE

To outline the refractive problems associated with presbyopia and to review the basis and relative merits of currently-available methods for their correction, with detailed consideration of spectacle and contact lens approaches.

CONTENTS

In the developed world, most of the present population will spend roughly half their lives as presbyopes. The well-known presbyopic changes with age in amplitude of accommodation and required near addition are briefly reviewed, together with the less widely acknowledged slow drifts that occur in distance refraction. The desirability of restoring to presbyopes clear vision for objects at any distance, ideally corresponding to vergences within the range of at least 0 to -5 D, in any viewing direction, is stressed. A general outline is given of possible corrective methods. Methods which satisfy the needs of a 50 year-old may not be suitable for the 80 year-old. Corrections may involve both fixed- and variable-focus lens systems, and surgical methods which modify the optics of the cornea, replace the crystalline lens with different fixed optics, or attempt to at least partially restore active accommodation. Some more recent methods of spectacle and contact lens correction are described in more detail. Particular attention is given to recent commercially-developed spectacles in which the corrective power can be varied actively by either mechanical (liquid-filled deformable lenses or Alvarez lenses) or electrical (liquid crystal lenses) means to allow objects at different distances to be seen clearly. Contact lens corrections show less progress and are still preferred only by a minority of older patients, most of whom are early presbyopes.

SUMMARY

The rising proportion of presbyopes in the population, covering an age span of around 40 years, represents both a problem for those concerned with giving their patients the best vision possible at both far and near viewing distances and a commercial opportunity. Traditional single-vision distance and near, bifocal, and progressive spectacle lens solutions, together with contact lens modalities for presbyopic correction, are being challenged by a variety of new approaches. It remains to be seen whether the latter will receive wide acceptance in practice.

Aspheric spectacles for correcting presbyopia with myopia and astigmatism

The aim of this paper is to propose a method for designing aspheric spectacles capable of realizing good optical performance at both far and near vision for presbyopia. We have experimentally measured wavefront aberrations and axial lengths for eight myopic eyes. In consideration of the field of view (FOV), the rotation of the eyeball, and a small amount of accommodation retained for presbyopia, we constructed individual eye models and optimized all the spectacle-eye systems for visible wavelengths by Zemax's simulation. Finally, we evaluated the image quality by the modulation transfer function (MTF) and visual acuity (VA) with different pupil sizes (2, 2.8, 4 mm). Results show that when the pupil size is 2 mm or 2.8 mm, the spectacles designed for the full FOV (0° and ±4° FOV) provide a strong ability to transfer low contrast at both far and near vision, and the VA for all reaches 0.8, and up to 1.1 for eyes NO. 1, NO. 5, NO. 6, and NO. 8 for the 0° FOV. As the pupil size increases to 4 mm, the VA for all comes to 0.6 for the full FOV, indicating that presbyopia is able to acquire a good visual resolution at both far and near vision by the designed aspheric spectacles. Furthermore, we verified the visual continuity of the spectacle-eye systems by studying intermediate vision, which demonstrates that the method used in our design is accurate and practicable.

Cortical adaptation and visual enhancement

Passive ophthalmic optic devices correct refractive defects of the eye but are not designed to employ neural adaptation processes. An extended depth of focus technology is implemented on conventional refractive devices, such as spectacles and contact lenses, and its testing is described. This technology is capable of simultaneously correcting all refractive errors, such as myopia, hyperopia, presbyopia, regular/irregular astigmatism, as well as their combinations. This is achieved by exploiting the capacity of the visual system for adaptation to contrast as well as its capability of creating a coherent continuous visual field out of discrete lines of sight.

Intraocular omni-focal lens with increased tolerance to decentration and astigmatism

PURPOSE

To measure the optical performance of an extended depth of focus (EDOF) intraocular lens (IOL), which provides an imaging solution for near, intermediate, and distance ranges, and to compare its optical performance to available bifocal IOLs with various extents of decentration and astigmatism aberrations.

METHODS

A special profile that performs interference principle-based focal extension is engraved on the top of a monofocal rigid IOL. An optical bench based on the L&B eye model was used to test the performance in comparison with the bifocal AcrySof ReSTOR SA60D3 lens (Alcon Laboratories Inc).

RESULTS

The imaging performances at near, intermediate, and distance ranges were mapped. Different decentration parameters and amount of astigmatism aberration were tested. In numerical simulations and the experimental bench, the EDOF IOL was demonstrated to have good visual acuity in near, intermediate, and distance ranges as well as reduced sensitivity to decentration of up to 0.75 mm and the capability of correcting astigmatism aberrations of up to 1.00 diopter.

CONCLUSIONS

Extended depth of focus technology is capable of providing clear and focused vision at near, intermediate, and distance ranges. Its high quality imaging is obtained under large decentration conditions and residual astigmatism. This capability broadens the potential use of the technology beyond its application as a simultaneous multifocal lens.

Predicting clinical visual acuity of presbyopia treatments

PURPOSE

To predict the potential clinical visual acuity of different presbyopia treatments.

METHODS

The defocus transfer function (DTF) is a mathematical technique for simultaneously illustrating the optical transfer function for all levels of defocus. Through-focus clinical visual acuity measurements were superimposed onto the DTF to determine the corresponding retinal contrast and map out a modulation threshold curve. The process is performed for an apodized diffractive and a zonal refractive intraocular lens, as well as an opaque annular ring implant that extends depth of focus.

RESULTS

Clinical visual acuity measurements appear to track contours on the DTF. The elevation of these contours changes as a function of spatial frequency, with the general trend being that for higher spatial frequencies, more retinal contrast is needed to achieve a given level of visual acuity. The presence of these contours suggests a minimum level of retinal contrast is needed to achieve a given visual acuity, and if this threshold is exceeded, the presbyopia treatment can provide the corresponding acuity clinically.

CONCLUSIONS

The DTF provides a global view of ocular performance for all object distances. The disparate technologies investigated all gave similar modulation threshold curves. These results suggest that the modulation threshold curve can be used to predict potential visual acuity of other multifocal lens designs and methods for treating presbyopia.