Peripheral Optical Quality Research Articles

Wide-field optical eye models for emmetropic and myopiceyes.

Ocular wavefront aberrations are used to describe retinal image formation in the study and modeling of foveal and peripheral visual functions and visual development. However, classical eye models generate aberration structures that generally do not resemble those of actual eyes, and simplifications such as rotationally symmetric and coaxial surfaces limit the usefulness of many modern eye models. Drawing on wide-field ocular wavefront aberrations measured previously by five laboratories, 28 emmetropic (-0.50 to +0.50 D) and 20 myopic (-1.50 to -4.50 D) individual optical eye models were reverse-engineered by optical design ray-tracing software. This involved an error function that manipulated 27 anatomical parameters, such as curvatures, asphericities, thicknesses, tilts, and translations-constrained within anatomical limits-to drive the output aberrations of each model to agree with the input (measured) aberrations. From those resultant anatomical parameters, three representative eye models were also defined: an ideal emmetropic eye with minimal aberrations (0.00 D), as well as a typical emmetropic eye (-0.02 D) and myopic eye (-2.75 D). The cohorts and individual models are presented and evaluated in terms of output aberrations and established population expectations, such as Seidel aberration theory and ocular chromatic aberrations. Presented applications of the models include the effect of dual focus contact lenses on peripheral optical quality, the comparison of ophthalmic correction modalities, and the projection of object space across the retina during accommodation.

Poster Session: Peripheral blur may provide the eye with a cue for the sign of defocus.

The sign of defocus is used by the retina to guide emmetropization. However, the means by which the eye determines whether light is focused in front of, or behind the retina, remains elusive. In the current study, we propose a new cue for the sign of defocus: the orientation of the anisotropic peripheral blur. Previously published [1] population averages of wavefront aberrations across the horizontal visual field in hyperopes, emmetropes and myopes were used to assess peripheral optical quality and blur orientation. Due to the large magnitudes of off-axis astigmatism and coma, the peripheral retinal image quality was dominated by anisotropic blur, whose direction was also correlated with refractive error (vertically elongated peripheral blur in myopic eyes and horizontally elongated peripheral blur in emmetropic and hyperopic eyes). The differences in groups may be due to the interaction between peripheral wavefront aberrations and globe shape (i.e. peripheral axial length). We also found an interaction between longitudinal chromatic aberration and off-axis astigmatism, wherein peripheral blur orientation is wavelength dependent, raising additional questions pertaining to the nature of chromatic cues. The orientation of peripheral blur may provide the retina with an optical cue for the sign of defocus, potentially playing an important role in emmetropization. [1] Romashchenko et al., "Peripheral refraction and higher order aberrations." Clin Exp Optom 103.1 (2020): 86-94.

Individualized modeling for the peripheral optics of the human myopic eye.

Individualized optical modelling of the eye is a useful tool to estimate optical properties of the eye from a set of geometrical parameters. In the context of myopia research, it is important to understand not only the on-axis (foveal) optical quality, but also the peripheral profile. This work describes a method to extend on-axis individualized eye modeling to the peripheral retina. Using measurements of corneal geometry, axial distances, and central optical quality from a group of young adults, a crystalline lens model was built to help reproduce the peripheral optical quality of the eye. Subsequent individualized eye models were generated from each of the 25 participants. These models were used to predict the individual peripheral optical quality over the central 40 degrees. Outcomes of the final model were then compared to the actual measurements of peripheral optical quality in these participants, measured with a scanning aberrometer. A high agreement was found between the final model and measured optical quality for the relative spherical equivalent and J0 astigmatism.

Inverted meniscus intraocular lens as a better optical surrogate of the crystalline lens.

Current intraocular lenses (IOLs) are designed to substitute the cataractous crystalline lens, optimizing focus at the fovea. However, the common biconvex design overlooks off-axis performance, leading to a reduced optical quality in the periphery of the retina in pseudophakic patients compared to the normal phakic eye. In this work, we designed an IOL to provide better peripheral optical quality, closer in that respect to the natural lens, using ray-tracing simulations in eye models. The resulting design was a concave-convex inverted meniscus IOL with aspheric surfaces. The curvature radius of the posterior surface was smaller than that of the anterior surface by a factor that depended on the IOL power. The lenses were manufactured and evaluated in a custom-built artificial eye. Images of a point source and of extended targets were directly recorded at various field angles with both standard and the new IOLs. This type of IOL produces superior image quality in the whole visual field, being a better surrogate for the crystalline lens than the commonly used thin biconvex intraocular lenses.

Peripheral optical quality and myopia progression in children

Peripheral optical quality and myopia progression in children

Relative peripheral defocus and myopic progression in children

Dear Editor, Yamaguchi and colleagues [1] investigated peripheral optical quality and determined its relationship with axial elongation and myopic progression in children. On the basis that a “progressing group” of seven children had more initial hyperopic relative peripheral defocus than a “non-progressing” group of 22 children, despite both groups having similar initial central refractions and axial lengths, they concluded that progression of axial myopia in children is associated with hyperopic relative peripheral defocus. I do not believe that the study supports this conclusion. While the central refraction difference between the two groups was not significantly different, this may be because of the small number in their progressing group; the initial mean refraction for the progressing group was about 1.4 D more myopic than that of the non-progressing group, and this is expected to give more hyperopic relative peripheral defocus [2–4]. The similar axial length between the groups means little without information about the gender distribution, because males have about 0.5 mm longer axial lengths than females of similar refractions and age [5–7]; also, again, there may have been insufficient children in this group to show a real difference.

Peripheral optical quality and myopia progression in children

To investigate the peripheral optical quality and its relationship with axial elongation, myopic progression in Japanese children. Twenty-nine Japanese children, ages 10 to 12 years old, with baseline refraction from +0.75 D to -5.5 D, were included and followed for 9 months. The central and peripheral point spread functions (PSFs; 0°, 10°, 20°, 30° nasally) were obtained at 0.25 D steps around ±2.5 D of best-focus PSF (BF-PSF) using double-pass PSF system. Modulation transfer function (MTF) area of the BF-PSF was calculated from BF-PSF to represent the peripheral optical quality. Relative peripheral defocus (RPD), the refraction of anterior/posterior focal lines, MTF area, and their correlations with myopia progression were analyzed. The average refractive change in 9 months was -0.5 ± 0.8 D. The change in axial length was significantly positively correlated with the amount of myopic progression (P = 0.0058) and RPD (P = 0.0007, 0.0036 and 0.0040, at 10°, 20°, 30° respectively) at the initial visit, but did not correlate with the peripheral MTF area. Myopic progression of more than 0.5 D with axial elongation was observed in seven children (MP group). The RPDs at 20° and 30° in the MP group were significantly more hyperopic than in the non-MP group (P = 0.002 and 0.007), whereas there was no significant difference in axial length, and central and peripheral MTF area between the MP and non-MP groups. MP group had more hyperopic focal lines compared with non-MP group at 20° and 30°. These results suggest that the progression of axial myopia in children is associated with hyperopic RPD and refraction of focal lines, not with peripheral optical quality.

Wide two-dimensional field laser ray-tracing aberrometer

There is an increasing interest in measuring the peripheral optical quality of the eye. Optical aberrations have been studied extensively in the center of the visual field due to the development of Hartmann-Shack wavefront sensor. However, experimental data of the peripheral field of view are still scarce, partly due to the fact that this evaluation presents various challenges. Here, we propose a novel device based on the laser ray-tracing (LRT) aberrometer, which is well suited for measuring the off-axis aberrations. The proposed instrument is able to measure a wide (±40°) 2D visual field and is based on three main design principles: spiral-shaped sampling of the visual field, real-time detection of the eye's entrance pupil, and automatic shaping and delivering of the ray bundle that optimally samples the eye pupil. We present experimental data obtained on 11 healthy subjects and a novel analysis based on a 2D quadratic model of the aberrations as a function of visual field and azimuth. The obtained results are consistent with previous findings.

Fast scanning peripheral wave-front sensor for the human eye

We designed and built a fast scanning peripheral Hartmann-Shack (HS) wave-front sensor to measure the off-axis wave-front aberrations in the human eye. The new instrument is capable of measuring the optical quality over the central 80° horizontal visual field in 1.8 seconds with an angular resolution of 1°. The subject has an open field of view without any moving elements in the line-of-sight and the head is kept in place by a head-chin rest. The same efficiency, reliability and measurement quality as the current static HS sensor were found but with much higher acquisition speed and comfort for the patients. This instrument has the potential to facilitate and improve future research on the peripheral optical quality of the eye in large groups of subjects.

Symmetries in peripheral ocular aberrations

A mirror symmetry in the aberrations between the left and right eyes has previously been found foveally, but while a similar symmetry for the peripheral visual field is likely, it has not been investigated. Nevertheless, the peripheral optical quality is often evaluated in only one eye, because it is more time efficient than analyzing the whole visual field of both eyes. This study investigates the correctness of such an approach by measuring the peripheral wavefront aberrations in both eyes of 22 subjects out to ±40° horizontally. The largest aberrations (defocus, astigmatism, and coma) were found to be significantly correlated between the left and right eyes when comparing the same temporal or nasal angle. The slope of the regression line was close to ±1 (within 0.05) for these aberrations, with a negative slope for the horizontally odd aberrations, i.e. the left and right eyes are mirror symmetric. These findings justify that the average result, sampled in one of the two eyes of many subjects, can be generalized to the other eye as well.

Designing contact lenses for a wide field of view via ocular wavefront tomography

Purpose Correcting the off-axis wavefront aberration is potentially important for peripheral vision, for diagnostic imaging of the retina, and for influencing refractive development. A new technique called ocular wavefront tomography (OWT) was adapted to optimize the design of contact lenses to improve the eye's peripheral optical quality. Methods OWT is a technique for customizing a multi-surface model eye to mimic the off-axis wavefront aberrations for an individual eye. This technique was adapted for contact lens design by establishing clear design goals for the eye + contact lens system. To demonstrate the method we optimized the shape of an aspheric and bifocal contact lens to correct a wide angle model eye with −2D foveal myopia. Two strategies for correction reflected alternative design goals: 1) to fully correct central vision while also improving optical quality peripherally to enhance vision and retinal imaging, or 2) fully correct central vision while introducing a degree of peripheral myopia relative to central vision in order to slow myopia progression. Results The OWT technique successfully produced aspheric and bifocal contact lens designs over a wide field of view. In addition to correcting foveal vision, the optimized contact lens designs either 1) improved the retinal image quality across the visual field (< 45°) significantly to obtain a visual performance and retinal imaging benefit or 2) produced the desired level of myopia in the peripheral field to obtain a refractive development benefit. Conclusion The OWT technique is a validated tool to optimize contact lens design over a wide field.

Peripheral optical errors and their change with accommodation differ between emmetropic and myopic eyes

The progression of myopia is thought to be controlled by the retinal image quality, but its triggering factors are not yet well known. The differences between the peripheral optics in emmetropic and myopic eyes might explain why some eyes become myopic. The present study further investigates peripheral optical quality and how it is affected by accommodation. The refraction and aberrations of the right eyes of five emmetropes and five myopes were measured using a laboratory Hartmann-Shack wave front sensor, specially designed for peripheral measurements with an open field of view. The off-axis optical quality was assessed in steps of 10 degrees out to +/-40 degrees horizontally and +/-20 degrees vertically for two different states of accommodation (targets at 0.5 D and 4.0 D). As expected, the emmetropes had a higher relative peripheral myopia, that is, more positive c(2)(0) coefficient, than the myopes. The new results of this study are that this well-known difference was found to be asymmetric over the visual field and that it increased with accommodation. This increase was because the relative peripheral defocus profile of the myopes did not show a consistent change between far and near vision, whereas the emmetropes became relatively more myopic in the periphery with accommodation. These findings may indicate a difference between emmetropic and myopic eyes that could be an important clue to understand myopia progression.

Corneal model

Purpose To describe the optical region of the cornea with as few parameters as possible and to compare this approach to commonly used mathematical models for the cornea. Setting University eye hospital, Mainz, Germany. Methods Corneal surface is approximated by a simple model (SM) that is defined by 2 perpendicular vertex radii, their angle to the horizontal, and a unique numerical eccentricity. These parameters, together with a parameter quantifying the decentration of the recording, are obtained in a consistent fit of corneal topographic data. The SM is compared to Zernike polynomial approximations of the 4th (Z4 model) and 8th (Z8 model) radial orders. Residual refraction errors for these approximations are calculated by numerical ray tracing, allowing a comparison of the different approaches. The statistical evaluation was carried out in 100 healthy eyes. Results The model approximation accuracy for the SM was at least as high as the reproducibility of the topographic measurements. For small optical zones up to 4.0 mm in diameter, the SM was on average more accurate than the Z4 model. Conclusions The parameters of the SM, which are closely related to conventional parameters of the cornea, provided a highly accurate basis for following refractive interventions (customized corneal or cataract surgery). Zernike polynomials tend to improve peripheral optical quality at the expense of the central quality. Except in cases of technical optics, this is an unwanted effect in the human eye.

HAND NEUTRALIZATION OF APHAKIC-RANGE CORNEAL CONTACT LENSES; A PRACTICAL METHOD OF DISCOVERING SURFACING AND POWER BLEMISHES IN THE PERIPHERY OF THE REFRACTING LENTICULAR ZONE.

Unexplained visual acuity loss or a complaint of intermittent blurred vision experienced by the contact lens corrected aphakic may all too frequently be caused by surfacing imperfections in the front surface optical zone of these high-plus corneal lenses. The lensometer is a highly inadequate instrument for the optics of a corneal contact lens; yet it is usually the only instrument used for this purpose. The can be used to check the back-surface optics of a corneal lens; yet it is rarely used to check anything but the radius of the central 3 or 4 mm of the rear surface of the lens. The radiuscope is almost never used to check the peripheral optical portions of the front surface. It can be particularly revealing and useful in front surface checking of the periphery of the lenticular zone of the high-plus corneal lens. After suspecting flaws in peripheral optical quality