Peripheral Image Quality Research Articles

Retinal capillary and choriocapillaris assessment using a beam modifier optical coherence tomography angiography module to increase lateral optical resolution.

To assess a new optical coherence tomography angiography (OCTA) technology and its contribution to retinal vascularization and choriocapillaris (CC) exploration. A new module, named "Beam expander" (BE), which increases the lateral resolution of OCTA, was used in combination with a prototype software in the PLEX® Elite 9000 Swept-Source OCT instrument (ZEISS, Dublin, CA). This prospective study involved 22 healthy subjects imaged with and without BE. Qualitative analysis of superficial capillary plexus (SCP), deep capillary complex (DCC) retinal and CC angiograms were performed. Perfusion density (PD), vessel density (VD), and foveal avascular zone (FAZ) measurements were also compared. Qualitative analysis of single SCP and DCC retinal angiograms acquired with BE showed significantly better vessel sharpness (respectively, p = 0.0002, and p<0.0001), and greater peripheral image quality (p = 0.028 and p = 0.007) compared to standard OCTA images. Mean VD of whole retina single scans was significantly higher for BE angiograms compared to classic angiograms (28.16 ±1.29 mm-1 and 23.36 ±0.92 mm-1, respectively, p<0.0001). Repeatability of VD, PD and FAZ raw size were found to be similar between the two methods (intraclass correlation coefficient: 0.671, 0.604 and 0.994 with BE versus 0.764, 0.638 and 0.990 without BE). CC image quality was found to be significantly superior with BE, and flow deficits were more visible in all BE scans compared to standard scans. An increase in lateral resolution of the OCT beam resulted in higher quality of retinal and choriocapillaris OCTA images in healthy subjects. These results provide significant insights into the future OCTA imaging enhancements.

Comparison of optical myopia control interventions: effect on peripheral image quality and vision.

This study compares the effects on peripheral vision and image quality of four myopia control interventions: a) Perifocal spectacles/ArtOptica, b) Stellest spectacles/Essilor), c) MiyoSmart spectacles/Hoya and d) MiSight contact lenses/CooperVision. Five subjects participated with habitual or no correction as reference. Three techniques were used: 1) Hartmann-Shack sensors for wavefront errors, 2) double-pass imaging system for point-spread-functions (PSF), and 3) peripheral acuity evaluation. The results show that multiple evaluation methods are needed to fully quantify the optical effects of these myopia control interventions. Perifocal was found to make the relative peripheral refraction (RPR) more myopic in all subjects and to interact with the natural optical errors of the eye, hence showing larger variations in the effect on peripheral vision. MiSight had a smaller effect on RPR, but large effect on peripheral vision. Stellest and MiyoSmart also showed small effects on RPR but had broader double-pass PSFs for all participants, indicating reduced retinal contrast. Reduction in peripheral retinal contrast might thereby play a role in slowing myopia progression even when the peripheral refraction does not turn more myopic.

Peripheral optical anisotropy in refractive error groups.

This study investigated differences in peripheral image quality with refractive error. Peripheral blur orientation is determined by the interaction of optical aberrations (such as oblique astigmatism) and retinal shape. By providing the eye with an optical signal for determining the sign of defocus, peripheral blur anisotropy may play a role in mechanisms of accommodation, emmetropisation and optical myopia control interventions. This study investigated peripheral through-focus optical anisotropy and image quality and how it varies with the eye's refractive error. Previously published Zernike coefficients across retinal eccentricity (0, 10, 20 and 30° horizontal nasal visual field) were used to compute the through-focus modulation transfer function (MTF) for a 4 mm pupil. Image quality was defined as the volume under the MTF, and blur anisotropy was defined as the ratio of the horizontal to vertical meridians of the MTF (HVRatio). Across the horizontal nasal visual field (at 10, 20 and 30°), the peak image quality for emmetropes was within 0.3D of the retina, as opposed to myopes whose best focus was behind the retina (-0.1, 0.4 and 1.5D, respectively), while for hyperopes it lay in front of the retina (-0.5, -0.6 and -0.6D). At 0.0D (i.e., on the retina), emmetropes and hyperopes both exhibited horizontally elongated blur, whereas myopes had vertically elongated blur (HVRatio=0.3, 0.7 and 2.8, respectively, at 30° eccentricity). Blur in the peripheral retina is dominated by the so-called "odd-error" blur signals, primarily due to oblique astigmatism. The orientation of peripheral blur (horizontal or vertical) provides the eye with an optical cue for the sign of defocus. All subject groups had anisotropic blur in the nasal visual field; myopes exhibited vertically elongated blur, perpendicular to the blur orientation of emmetropes and hyperopes.

Commentary: Renewed interest in off-axis retinoscopy and peripheral refraction for it's role in control of myopia progression.

We all know that vision is a combination of optical input and neural processing. Traditionally, retinoscopy has remained the benchmark for the assessment of refractive errors for the optical input that is perceived by the eye and then processed by the brain. Conventionally, it has always been known that “on the visual axis” (on-axis) retinoscopy gives a more accurate estimate of refractive error compared to retinoscopy that is done off the visual axis (off-axis). However, in practical terms, retinoscopy is frequently performed slightly off the visual axis and there are situations in which on the visual axis retinoscopy is difficult or even impossible. These include retinoscopy in uncooperative children or when the subject has been anesthetized. Chaurasiya et al.[1] in their current study on “refractive changes during off-the-axis retinoscopy in myopia” and many other researchers, over the years have tried to quantify the error in the quantum of refractive error when this is measured with “off-axis” retinoscopy in routine clinical practice. Ferree et al.[2] in 1931 measured peripheral refraction with the Zeiss parallax refractometer (Carl Zeiss, Jena, Germany). Rempt et al.[3] was the first to perform eccentric retinoscopy and introduced the skiagram to categorize different peripheral refractive error patterns. Jackson et al.[4] examined off the visual axis retinoscopy in eight adults (spherical equivalent <±2.5 D) who had undergone cycloplegia. The degrees of the eccentricity of up to 20° along the temporal horizontal field were examined and they found a myopic shift of 5% in spherical equivalent and an increase in cylindrical power of 3% for every degree of eccentricity. In the present study, the authors have noted an increase in myopic shift with approximately 7 and 18% for 10 and 20° of eccentricity, respectively, in the mean spherical equivalent refraction of 10° myopic patients. What is traditionally believed and agreed upon is that the error in refraction, which is noted in off-axis retinoscopy, is generally small and clinically insignificant when the deviation of axis and the quantum of refractive error is small, and more often than not, this error is eliminated in the process of subjective refraction which follows retinoscopy. However, this error in retinoscopy can become significant if the deviation of the axis of retinoscopy from the visual axis is large or if the quantum of refraction being measured is large, for example, as in high myopia.[5] Of late, there has been renewed interest in the measurement of peripheral refraction as it is increasingly believed that peripheral refractive defocus plays a role in myopia progression by inducing axial growth of the eye. Animal studies have shown that depending on the location of the image relative to the retina, axial elongation can be stopped or triggered. Experiments in chickens and monkeys whose vision were defocused either with negative spectacle lenses (hyperopic defocus) or positive lenses (myopic defocus), showed that their visual system was altering their refractive state by accelerating or slowing axial elongation in order to compensate for the imposed defocus.[6] This applies both in the fovea and in the periphery of the retina. Originally, it was believed that only foveal optical errors could regulate eye growth, but it is now believed that peripheral image quality can also modify ocular growth even in the presence of a sharp foveal image. This is the reason that many researchers have advocated the use of bifocal or progressive addition lenses (PAL) for children as a strategy to retard the progression of myopia, but as of now, there is no consensus regarding their clinical efficacy.[7] Studies with PAL have typically shown a small but clinically insignificant effect on slowing myopia progression as noted in Cochrane review 2020.[8] A meta-analysis noted small reductions in myopia progression (0.25 D) and axial elongation (−0.12 mm).[9] So, there is indeed a value in studying the variation of refractive error assessment between the on-axis and off-axis retinoscopy but more work needs to be done to have more clarity regarding the clinical application of this work, especially in control of myopia progression.

Peripheral image quality in pseudophakic eyes.

The purpose of this work was to evaluate peripheral image quality in the pseudophakic eye using computational, physical, and psychophysical methods. We designed and constructed a physical model of the pseudophakic human eye with realistic dimensions using a corneal phantom and a board-only camera that was pivoted around an axis that matched the anatomical center of a human retina, assuming a radius of curvature of 12 mm, while it was submersed in a 23.4 mm long water filled chamber to emulate human ocular axial length. We used this optical setup to perform direct recording of the point spread function (PSF) and the associated retinal images for a commercial intraocular lens (IOL). Additionally, psychophysical tests were carried out to investigate the impact of the off-axis astigmatism in peripheral visual performance, where spectacle-induced astigmatism simulated the pseudophakic conditions in healthy subjects. Our findings using the physical eye model confirm the existence of large amounts of astigmatism in the periphery of the pseudophakic eye. The psychophysical tests revealed a significant reduction of detection sensitivity in the peripheral visual field. The latter suggests that off-axis astigmatism in patients implanted with IOLs may have performance and safety implications for activities requiring efficient peripheral vision.

2-D Peripheral image quality metrics with different types of multifocal contact lenses

To evaluate the impact of multifocal contact lens wear on the image quality metrics across the visual field in the context of eye growth and myopia control. Two-dimensional cross-correlation coefficients were estimated by comparing a reference image against the computed retinal images for every location. Retinal images were simulated based on the measured optical aberrations of the naked eye and a set of multifocal contact lenses (centre-near and centre-distance designs), and images were spatially filtered to match the resolution limit at each eccentricity. Value maps showing the reduction in the quality of the image through each optical condition were obtained by subtracting the optical image quality from the theoretical physiological limits. Results indicate that multifocal contact lenses degrade the image quality independently from their optical design, though this result depends on the type of analysis conducted. Analysis of the image quality across the visual field should not be oversimplified to a single number but split into regional and groups because it provides more insightful information and can avoid misinterpretation of the results. The decay of the image quality caused by the multifocal contacts alone, cannot explain the translation of peripheral defocus towards protection on myopia progression, and a different explanation needs to be found.

Effect of induced transverse chromatic aberration on peripheral vision

Transverse chromatic aberration (TCA) is one of the largest optical errors affecting the peripheral image quality in the human eye. However, the effect of chromatic aberrations on our peripheral vision is largely unknown. This study investigates the effect of prism-induced horizontal TCA on vision, in the central as well as in the 20° nasal visual field, for four subjects. Additionally, the magnitude of induced TCA (in minutes of arc) was measured subjectively in the fovea with a Vernier alignment method. During all measurements, the monochromatic optical errors of the eye were compensated for by adaptive optics. The average reduction in foveal grating resolution was about 0.032 ± 0.005 logMAR/arcmin of TCA (mean ± std). For peripheral grating detection, the reduction was 0.057 ± 0.012 logMAR/arcmin. This means that the prismatic effect of highly dispersive spectacles may reduce the ability to detect objects in the peripheral visual field.

Comparison of the Optical Image Quality in the Periphery of Phakic and Pseudophakic Eyes

The natural lens may provide some compensatory optical effect in the periphery. When it is substituted by an IOL during cataract surgery, the quality of the peripheral optics will be modified. We compared the peripheral image quality in the eyes of patients with one eye implanted with a monofocal IOL and the fellow eye still with the natural precataract lens. We used a scanning peripheral Hartmann-Shack wavefront sensor to measure the central 80° of visual angle along the horizontal meridian. Twelve patients with ages ranging between 65 to 81 years were evaluated. The results of the phakic and pseudophakic eyes were compared using the spherical equivalent, astigmatism, higher order aberrations, and the Strehl ratio. The statistical differences at each angle between the two eyes were evaluated. In the eyes implanted with IOLs, the peripheral mean spherical equivalent was slightly more myopic than in the phakic eyes, although the differences were only significant for some angles. Astigmatism increased much faster in the periphery for the pseudophakic eyes as compared with the phakic eyes. The mean values were significantly different from 9° and 17° outwards at the temporal and nasal retina, respectively. As an example, at 30°, eyes implanted with IOLs presented 1.5 diopters (D) of additional astigmatism. The higher order aberrations were not significantly different between the two groups. Eyes implanted with monofocal IOLs present more astigmatism in the periphery than the healthy older eyes. This suggests that the crystalline lens provides a beneficial effect to partially compensate off-axis astigmatism. The degradation of the peripheral retinal image may reduce the pseudophakic patient's performance in common visual tasks.

Evaluating the peripheral optical effect of multifocal contact lenses

Multifocal soft contact lenses have been used to decrease the progression of myopia, presumably by inducing relative peripheral myopia at the same time as the central image is focused on the fovea. The aim of this study was to investigate how the peripheral optical effect of commercially available multifocal soft contact lenses can be evaluated from objective wavefront measurements. Two multifocal lenses with high and low add and one monofocal design were measured over the ±40° horizontal field, using a scanning Hartmann-Shack wavefront sensor on four subjects. The effect on the refractive shift, the peripheral image quality, and the depth of field of the lenses was evaluated using the area under the modulation transfer function as the image quality metric. The multifocal lenses with a centre distance design and 2dioptres of add induced about 0.50dioptre of relative peripheral myopia at 30° in the nasal visual field. For larger off-axis angles the border of the optical zone of the lenses severely degraded image quality. Moreover, these multifocal lenses also significantly reduced the image quality and increased the depth of field for angles as small as 10°-15°. The proposed methodology showed that the tested multifocal soft contact lenses gave a very small peripheral myopic shift in these four subjects and that they would need a larger optical zone and a more controlled depth of field to explain a possible treatment effect on myopia progression.

Measuring ocular aberrations and image quality in peripheral vision with a clinical wavefront aberrometer

Background: Clinical aberrometers are accurate, robust instruments for measuring wavefront aberrations for foveal vision but several practical concerns arise when performing aberrometry of the peripheral field. The purpose of this study was to evaluate these concerns experimentally using a physical eye model.Methods: A physical model eye was constructed to provide a stable test case that resembled a human eye. Aberrations were measured with a commercial Shack‐Hartmann aberrometer along lines‐of‐sight ranging from zero to 45° of eccentricity. Commercial software for wavefront reconstruction and Zernike analysis was adapted for use with elliptical entrance pupils encountered off‐axis.Results: Pupil dimensions estimated from the array of Shack‐Hartmann spots captured by the wavefront sensor followed geometrical optics predictions up to 30° eccentricity. With careful attention to detail, aberration analysis over an elliptical pupil was verified with alternative software. Retinal image quality declined slowly as eccentricity increased due to the eye model's spherical aberration. The total RMS computed from Zernike coefficients overestimated the total RMS computed based on the wavefront error of the elliptical pupil.Conclusion: Measurement of off‐axis wavefront aberrations of a model eye over a restricted range of eccentricities is possible with the COAS clinical wavefront aberrometer and auxiliary lenses to correct astigmatism. When central image quality is good, the off‐axis aberrations will have a powerful effect on peripheral image quality. When central image quality is poor, the additional effect of off‐axis aberrations will be minor.

Theoretical analysis of peripheral imaging after excimer laser corneal refractive surgery for myopia

Purpose To explore theoretically the retinal point images in the peripheral fields of eyes that have had excimer laser refractive surgery. Setting University research laboratory. Methods Model eyes were based on Navarro’s finite schematic eye, the eyes being made myopic by an increase in axial length. To simulate photorefractive keratectomy (PRK), the anterior shape and thickness of the cornea were modified. Variables included pupil size, ablation zone size, preexisting refractive error, and the addition of a blending zone. Image-quality criteria for each retinal point image were its size and the angular separation of the centroids of those parts of the image produced by rays passing through ablated and unablated corneal zones. Results In the peripheral visual field, the boundary between the ablated and unablated cornea caused a separation of the retinal image of a single point into 2 parts. The separation increased with the preexisting refractive error. Image quality was correspondingly reduced by ablation. As pupil size increased, the field angle at which the retinal image doubling first occurred decreased. Increasing the diameter of the ablation zone or using a blending zone increased the angle at which the doubling first occurred, and the blending zone improved image quality considerably. Chromatic effects appeared to be relatively unimportant. Conclusions This analysis provides further evidence of the disadvantages of small central ablation zones in excimer laser refractive surgery and of the advantages of well-designed blending zones in improving postsurgical peripheral image quality. Image quality in the peripheral field of the pseudoemmetropic post-PRK eye is generally worse than in a naturally emmetropic eye, even though the axial image quality may be similar.

Biconcave Contact Lenses: A Critical Analysis of Their Optical Properties

The purpose of this experiment was to compare biconcave contact lenses with other contact lenses already used for observation and irradiation of the retina and choroid. The optical performance of different biconcave lenses is described in terms of magnification, resolution, and field of view. The optical properties of the eye were taken into account using the Gullstrand's model of the human eye. The performance of biconcave contact lenses represents a compromise between that of Goldmann's and wide angle indirect contact lenses. An upright image, with good peripheral image quality and an intermediate field of view is characteristic of such design. In addition, laser irradiation with large spot sizes is less hazardous when using such negative contact lenses compared to positive lenses of the same absolute refractive power. Biconcave contact lenses qualify as a complement to planoconcave lenses for chorioretinal observation and irradiation tasks. For the same magnification factor, the field of view is smaller than that obtained with indirect contact lenses but the image degradation in the periphery of the retina is reduced.