Monochromatic aberrations of the human eye in a large population

Adaptive optics full-field optical coherence tomography

We describe a simple and compact full-field optical coherence tomography (FFOCT) setup coupled to a transmissive liquid crystal spatial light modulator (LCSLM) to induce or correct aberrations. To reduce the system complexity, strict pupil conjugation was abandoned because low-order aberrations are often dominant. We experimentally confirmed a recent theoretical and experimental demonstration that the image resolution was almost insensitive to aberrations that mostly induce a reduction of the signal level. As a consequence, an image-based algorithm was applied for the optimization process by using the FFOCT image intensity as the metric. Aberration corrections were demonstrated with both an USAF resolution target and biological samples for LCSLM-induced and sample-induced wavefront distortions.

Objective functional visual outcomes of cataract surgery in patients with good preoperative visual acuity

PurposeTo explore the objective functional visual outcomes of cataract surgery in patients with good preoperative visual acuity.MethodsWe enrolled 130 cataract patients whose best-corrected visual acuity (BCVA) was 20/40 or better preoperatively. Objective visual functions were evaluated with a KR-1W analyzer before and at 1 month after cataract surgery.ResultsThe nuclear (N), cortical (C), and N+C groups had very high preoperative ocular and internal total high-order aberrations (HOAs), coma, and abnormal spherical aberrations. At 1 month after cataract surgery, in addition to the remarkable increase of both uncorrected visual acuity and BCVA, both ocular and internal HOAs in the three groups decreased significantly after cataract surgery (all P<0.05). Point spread function and modulation transfer functions were also improved significantly in these patients (all P<0.05).ConclusionsThe objective functional vision of patients with 20/40 or better preoperative BCVA improved significantly after cataract surgery. This finding shows that the arbitrary threshold of BCVA worse than 20/40 in China cannot always be used to determine who will benefit from cataract surgery.

Soft multifocal simultaneous image contact lenses: a review

Soft multifocal simultaneous image contact lenses have boomed in recent years due to the growing number of presbyopic patients demanding visual solutions, allowing them to maintain their current standard of living. The concept of 'simultaneous image' is based on blur interpretation and/or blur tolerance of superimposed multiple images on the retina formed by various powers of a contact lens. This is the basis for a specific type of multifocal contact lens developed for the compensation of presbyopia. Manufacturers have released a great variety of soft simultaneous image lens designs to meet different patient needs but their fitting is still unsatisfactory in some cases. Some presbyopes discontinue wearing contact lenses due to some limitations in visual quality and comfort that can be overcome with an appropriate contact lens selection based on a comprehensive pre-fitting evaluation. This paper aims to review the different types of soft multifocal contact lenses that are currently available for presbyopic correction and to define the steps and factors crucial for their fitting, such as pupil, aberrations, accommodation and centring. A discussion about useful tools to achieve a customised fitting leading to a successful outcome, such as the defocus curve, power profile and questionnaires, is performed.

Corneal Higher-Order Aberrations after Phacoemulsification: A Comparison of 3 Different Incision Sizes

Purpose

To analyze the impact of different incision sizes for phacoemulsification on corneal higher-order aberrations (HOA).

Methods

Patients seeking cataract surgery were randomly assigned to one of the following groups: 1.4 mm with biaxial microincision phacoemulsification (25 eyes), 1.8 mm with coaxial phacoemulsification (27 eyes), and 2.2 mm with coaxial phacoemulsification (62 eyes). Inclusion criteria were a minimum age of 18 years and uncomplicated cataract. Exclusion criteria were history of ocular trauma or intraocular surgery, any sign of inflammation or infection, pseudoexfoliation syndrome, glaucoma, optic atrophy, diabetic retinopathy, lens dislocation, cataracta intumescens, cataracta matura, and corneal diseases. Patients underwent phacoemulsification with implantation of an intraocular lens. Aberrometry was performed using an iTrace aberrometer with a pupil scan size of 5.0 mm preoperatively and at postoperative follow-up visits after 1 month. The paired sample t test and analysis of covariance were used for statistical analysis.

Results

Ninety patients (114 eyes) were enrolled (mean age 73.7 ± 8.9 years). In all groups, an increase of total HOAs could be measured. The strongest increase was seen in the 2.2 mm group (mean difference 0.031 [95% confidence interval (CI) 0.006-0.056], p = 0.014) and in the 1.4 mm group (mean difference 0.035 [95% CI -0.007 to 0078], p = 0.097). No important difference was found in the 1.8 mm group.

Conclusions

The 2.2 mm and the 1.4 mm incisions seem to have a higher impact on corneal HOAs in comparison to the 1.8 mm incision.

Influence factors of estimation errors for total corneal astigmatism using keratometric astigmatism in patients before cataract surgery

PURPOSE

To evaluate the influence factors of the estimation errors for total corneal astigmatism using keratometric astigmatism in patients preparing for cataract surgery.

SETTING

EYE and ENT Hospital of Fudan University, Shanghai, China.

DESIGN

Prospective observational study.

METHODS

Eyes of patients preparing for cataract surgery were measured with Pentacam Scheimpflug imaging device. Keratometric astigmatism was obtained using the anterior corneal surface measurement and the keratometric index (1.3375) while neglecting the posterior corneal surface measurement. The Scheimpflug-measured total corneal astigmatism was derived by vector analysis of the astigmatism on both corneal surfaces.

RESULTS

The study comprised 374 eyes of 374 patients 45 to 84 years old. The mean absolute error in magnitude and mean absolute error in angle comparing keratometric astigmatism with Scheimpflug-derived astigmatism was 0.18 ± 0.14 diopter (D) and 7.7 ± 11.0 degrees, respectively. The mean magnitude of the error vector was 0.24 ± 0.14 D. The error in magnitude was significantly larger in eyes with against-the-rule anterior astigmatism, while error in angle was larger in eyes with with-the-rule and oblique anterior astigmatism. Multiple regressions showed that 4 predictors (difference in anterior-posterior astigmatism axis, magnitude of posterior astigmatism, magnitude of keratometric astigmatism, and axial length [AL]) were significantly associated with the absolute error in magnitude. Predictors including the difference in the anterior-posterior astigmatism axis, magnitude of posterior astigmatism, magnitude of keratometric astigmatism, and age were significantly associated with the absolute error in angle and magnitude of the error vector.

CONCLUSIONS

Neglecting posterior corneal astigmatism yielded significant estimation errors in total corneal astigmatism in patients preparing for cataract surgery. Estimation errors were significantly influenced by the difference in the anterior -posterior astigmatism axis, magnitude of posterior astigmatism, keratometric astigmatism, AL, and age.

FINANCIAL DISCLOSURE

None of the authors has any conflicts of interest to disclose.

Temporal multiplexing with adaptive optics for simultaneous vision

We present and test a methodology for generating simultaneous vision with a deformable mirror that changed shape at 50 Hz between two vergences: 0 D (far vision) and -2.5 D (near vision). Different bifocal designs, including toric and combinations of spherical aberration, were simulated and assessed objectively. We found that typical corneal aberrations of a 60-year-old subject changes the shape of objective through-focus curves of a perfect bifocal lens. This methodology can be used to investigate subjective visual performance for different multifocal contact or intraocular lens designs.

Bilateral symmetry in vision and influence of ocular surgical procedures on binocular vision: A topical review

We analyze the role of bilateral symmetry in enhancing binocular visual ability in human eyes, and further explore how efficiently bilateral symmetry is preserved in different ocular surgical procedures. The inclusion criterion for this review was strict relevance to the clinical questions under research. Enantiomorphism has been reported in lower order aberrations, higher order aberrations and cone directionality. When contrast differs in the two eyes, binocular acuity is better than monocular acuity of the eye that receives higher contrast. Anisometropia has an uncommon occurrence in large populations. Anisometropia seen in infancy and childhood is transitory and of little consequence for the visual acuity. Binocular summation of contrast signals declines with age, independent of inter-ocular differences. The symmetric associations between the right and left eye could be explained by the symmetry in pupil offset and visual axis which is always nasal in both eyes. Binocular summation mitigates poor visual performance under low luminance conditions and strong inter-ocular disparity detrimentally affects binocular summation. Considerable symmetry of response exists in fellow eyes of patients undergoing myopic PRK and LASIK, however the method to determine whether or not symmetry is maintained consist of comparing individual terms in a variety of ad hoc ways both before and after the refractive surgery, ignoring the fact that retinal image quality for any individual is based on the sum of all terms. The analysis of bilateral symmetry should be related to the patients' binocular vision status. The role of aberrations in monocular and binocular vision needs further investigation.

Correlation of higher order aberrations and components of astigmatism in myopic refractive surgery candidates

Purpose

To evaluate the correlation between refractive, corneal, and residual astigmatism and higher order aberrations (HOA) in refractive surgery candidates.

Methods

Three hundred and seventy-five eyes of 188 patients aged 28.2 ± 6.24 years with a predominance of females (62.7%) were enrolled in this study. Refraction, topography (Orbscan IIz, Bausch & Lomb, Rochester, NY, USA), and aberrometry (Zywave, Bausch & Lomb, Rochester, NY, USA) were performed to determine refractive and corneal astigmatism and HOA for all participants. Ocular residual astigmatism was calculated using vector analysis.

Results

The mean spherical equivalent was −3.59 ± 1.95 D and the mean refractive astigmatism was −1.97 ± 1.3 D. The mean HOA was 0.38 ± 0.15 μm in all cases, which increased with spherical equivalent (p < 0.05). There was a positive significant correlation between both corneal and refractive astigmatism and HOA (p < 0.05), but there was no significant correlation between residual astigmatism and HOA (p = 0.122).

Conclusion

The results of the study showed significant correlations between corneal and refractive astigmatisms and HOA.

Optical differentiation wavefront sensing with binary pixelated transmission filters

Sensors measuring the spatial phase of optical waves are widely used in optics. The optical differentiation wavefront sensor (ODWS) reconstructs the wavefront of an optical wave from wavefront slope measurements obtained by inducing linear field-transmission gradients in the far-field. Its dynamic range and sensitivity can be adjusted simply by changing the gradient slope. We numerically and experimentally demonstrate the possibility of implementing the spatially varying transmission gradient using distributions of small pixels that are either transparent or opaque. Binary pixelated filters are achromatic and can be fabricated with high accuracy at relatively low cost using commercial lithography techniques. We study the impact of the noise resulting from pixelation and binarization of the far-field filter for various test wavefronts and sensor parameters. The induced wavefront error is approximately inversely proportional to the pixel size. For an ODWS with dynamic range of 100 rad/mm over a 1-cm pupil, the error is smaller than λ/15 for a wide range of test wavefronts when using 2.5-μm pixels. We experimentally demonstrate the accuracy and consistency of a first-generation ODWS based on binary pixelated filters.

Multi-modal adaptive optics system including fundus photography and optical coherence tomography for the clinical setting

We present a new compact multi-modal imaging prototype that combines an adaptive optics (AO) fundus camera with AO-optical coherence tomography (OCT) in a single instrument. The prototype allows acquiring AO fundus images with a field of view of 4°x4° and with a frame rate of 10fps. The exposure time of a single image is 10 ms. The short exposure time results in nearly motion artifact-free high resolution images of the retina. The AO-OCT mode allows acquiring volumetric data of the retina at 200kHz A-scan rate with a transverse resolution of ~4 µm and an axial resolution of ~5 µm. OCT imaging is acquired within a field of view of 2°x2° located at the central part of the AO fundus image. Recording of OCT volume data takes 0.8 seconds. The performance of the new system is tested in healthy volunteers and patients with retinal diseases.

Higher order aberrations of the eye: Part two

This article is the second in a series of two articles, which provides a discussion of the factors that may possibly contribute to variable results when wavefront aberrations of the human eye are measured. Some of the factors discussed in this article are the influences that refractive errors (specifically myopia and astigmatism), pupil diameter, accommodation of the crystalline lens, age, mydiatric drops and the integrity of the tear film may have on these wavefront measurements. The first article in the series explained the general principles of higher order aberrations (HOAs), as well as HOAs of importance in the eye and the measuring apparatus used to measure HOAs of the eye.Keywords: wavefront aberrations; aberrometry

Higher order aberrations of the eye: Part one

This article is the first in a series of two articles that provide a comprehensive literature review of higher order aberrations (HOAs) of the eye. The present article mainly explains the general principles of such HOAs as well as HOAs of importance, and the measuring apparatus used to measure HOAs of the eye. The second article in the series discusses factors contributing to variable results in measurements of HOAs of the eye.Keywords: Higher order aberrations; wavefront aberrations; aberrometer

Pattern of astigmatism in a clinical setting in Maldives

BACKGROUND

Patterns of refractive errors have never been reported in Maldives. This study aims to dissect astigmatism and provide a general view in context of this island country.

METHODS

A clinic based cross sectional study was designed with 277 patients, aged ≥3.5 years and with a primary astigmatism of ≥-1.00 diopters (D). They underwent complete eye examination and a vector analysis was done.

RESULTS

Mean age was 28.58 (SD 19.15) years. Astigmatic magnitude depended on age (p<0.05) but not on gender (p>0.05). Severity of visual impairment after refractive correction was very less, with only 2.2% having visual acuity ≤6/60. Mean spherical, spherical equivalent and astigmatic refraction were -1.35 (SD 2.94 D), -2.40 (SD 3.04) and -2.12 (SD 1.11 D), respectively. Between fellow eyes, refractive and corneal astigmatism highly correlated (0.83 and 0.73). Fifty eyes (18.1%) had an astigmatic error of ≥-3.00 D which peaked in the second and third decades of life (p<0.0001) and was corneal in origin (p<0.0001). Internal J45 and J0 tended to be more negative with increasing age, showing a trend toward against the rule astigmatism. Correlation between corneal and refractive J0 and J45 were 0.88 and 0.62 (p<0.0001). With the rule astigmatism was more common followed by against the rule and oblique.

CONCLUSION

In conclusion, this study inferred that among patients with relatively higher magnitude of astigmatism attending to the clinics in Maldives, younger patients are affected more, which could possibly link to the environment, genetics and nutrition. The probable association between nutrition and astigmatism needs to be investigated to fill the gap in literature.

Simplifying numerical ray tracing for two-dimensional non circularly symmetric models of the human eye

Ray tracing is a powerful technique to understand the light behavior through an intricate optical system such as that of a human eye. The prediction of visual acuity can be achieved through characteristics of an optical system such as the geometrical point spread function. In general, its precision depends on the number of discrete rays and the accurate surface representation of each eye's components. Recently, a method that simplifies calculation of the geometrical point spread function has been proposed for circularly symmetric systems [Appl. Opt.53, 4784 (2014)]. An extension of this method to 2D noncircularly symmetric systems is proposed. In this method, a two-dimensional ray tracing procedure for an arbitrary number of surfaces and arbitrary surface shapes has been developed where surfaces, rays, and refractive indices are all represented in functional forms being approximated by Chebyshev polynomials. The Liou and Brennan anatomically accurate eye model has been adapted and used for evaluating the method. Further, real measurements of the anterior corneal surface of normal, astigmatic, and keratoconic eyes were substituted for the first surface in the model. The results have shown that performing ray tracing, utilizing the two-dimensional Chebyshev function approximation, is possible for noncircularly symmetric models, and that such calculation can be performed with a newly created Chebfun toolbox.

Evaluation of patient visual comfort and repeatability of refractive values in non-presbyopic healthy eyes

AIM

To evaluate the intra-operator repeatability in healthy subjects using the WAM-5500 auto-kerato/refractometer and the iTrace aberrometer, to compare the refractive values and the subjective refraction obtained with both devices and to determine which of these three spherocylindrical corrections allows the subject to achieve the best visual comfort.

METHODS

Forty-two non-presbyopic healthy eyes of 42 subjects were enrolled in this prospective study. Refractive values were compared, evaluating the repeatability, the relationship between the methods and the best visual comfort obtained.

RESULTS

Sphere, cylinder and axis results showed good intraclass correlation coefficients (ICC); the highest ICC was obtained using the spherical refraction with the autorefractometer and the aberrometer, achieving levels of 0.999 and 0.998, respectively. The power vector (PV) was calculated for each refraction method, and the results indicated that there were no statistically significant differences between them (P>0.05). Direct comparison of PV measurements using the three methods showed that aberrometer refraction gave the highest values, followed by the subjective values; the autorefractometer gave the lowest values. The subjective method correction was most frequently chosen as the first selection. Equal values were found for the autorefractometer and the aberrometer as the second selection.

CONCLUSION

The iTrace aberrometer and the WAM-5500 auto-kerato/refractometer showed high levels of repeatability in healthy eyes. Refractive corrections with the aberrometer, the autorefractometer and subjective methods presented similar results, but spherocylindrical subjective correction was the most frequently selected option. These technologies can be used as complements in refractive evaluation, but they should not replace subjective refraction.

From corneal shape to ocular wavefront in eyes with aspheric IOLs: the feasibility of IOL customisation

PURPOSE

To determine if it is possible to predict the ocular wavefront aberrations of eyes with an aspheric IOL from the corneal shape and other readily available eye characteristics. A reliable prediction is a prerequisite for future IOL customisation.

METHODS

Sixty pseudophakic eyes with aspheric IOLs of 60 patients were included. The corneal shape and the ocular wavefront aberrations were measured postoperatively with a Scheimpflug camera and an aberrometer, respectively. The elevation data of the anterior corneal surface were fitted by Zernike polynomials. Linear regression models for the Zernike coefficients describing the ocular wavefront aberrations up till the fourth order were determined, with as independent variables the Zernike coefficients describing the corneal shape, the eye (right/left), IOL power, and axial length.

RESULTS

Linear regression equations with an explained variance (adjusted R-square) above 0.50 were found for five Zernike aberration terms: defocus (z(2,0); adjusted R-square 0.90), the astigmatism terms (0.81 for oblique astigmatism [z(2,-2)] and 0.88 for regular astigmatism [z(2,2)]), vertical coma (z(3,-1); 0.52), and spherical aberration (z(4,0); 0.71).

CONCLUSION

The defocus, astigmatism, vertical coma, and spherical aberration terms of the ocular wavefront are strongly associated with the corneal shape in pseudophakic eyes and may thus be predicted from the corneal shape and other eye characteristics.

Comparison of higher order aberrations in patients with various refractive errors

OBJECTIVE

To compare the mean root mean square (RMS) of total higher order aberrations (HOAs), coma and spherical aberrations in individuals with myopia, hypermetropia and myopic astigmatism.

METHODS

This prospective analytical study was conducted at Armed Forces Institute of Ophthalmology, Rawalpindi, Pakistan from Jan 2014 to Dec 2014. Two hundred eyes of 121 patients with age ranging from 18-40 years were included in the study. Patients were divided into 4 group namely Low myopia, High myopia, Astigmatism and Hypermetropia on the basis of refractive error. Included were the patients who had refractive error more than ± 0.5D and best corrected visual acuity (BCVA) of 0.00 or better. Patients who had history of surgery and / or eye disease were excluded from the study. Visual acuity (VA), Spherical equivalent (SE) of refractive error, RMS value of total HOAs, coma and spherical aberrations were evaluated. HOAs were measured with aberrometer (Wavelight analyzer version 1073) at 6 mm pupil size.

RESULTS

Age of the patients ranged from 18 years to 40 years with mean age of 29.10±10.6 years. Seventy one (35.5%) were males and 129 (64.5%) were female. Mean RMS value of HOAs, coma and spherical aberrations was calculated in all four groups. RMS of total HOAs and spherical aberrations in hypermetropia was 0.96±0.96 and 0.30±0.42 respectively and it was higher than other three groups.

CONCLUSIONS

In overall comparison the mean RMS of total HOAs and spherical aberrations was significantly increased in hypermetropia group and there was a statistically significant negative correlation of SE of hypermetropia with RMS of total HOAs and spherical aberration.

High-speed adaptive optics for imaging of the living human eye

The discovery of high frequency temporal fluctuation of human ocular wave aberration dictates the necessity of high speed adaptive optics (AO) correction for high resolution retinal imaging. We present a high speed AO system for an experimental adaptive optics scanning laser ophthalmoscope (AOSLO). We developed a custom high speed Shack-Hartmann wavefront sensor and maximized the wavefront detection speed based upon a trade-off among the wavefront spatial sampling density, the dynamic range, and the measurement sensitivity. We examined the temporal dynamic property of the ocular wavefront under the AOSLO imaging condition and improved the dual-thread AO control strategy. The high speed AO can be operated with a closed-loop frequency up to 110 Hz. Experiment results demonstrated that the high speed AO system can provide improved compensation for the wave aberration up to 30 Hz in the living human eye.

Verification of the lack of correlation between age and longitudinal chromatic aberrations of the human eye from the visible to the infrared

Several researchers studied the longitudinal chromatic aberration (LCA) of the human eye and observed that it does not change due to age. We measured the LCA of 45 subjects' normal right eyes at three distinct wavelengths (561, 690, and 840 nm) using a Hartmann-Shack wavefront aberrometer (HSWA) while consecutively switching between three light sources for wavefront sensing. We confirmed that the LCA of the human eye does not change due to age between 22 and 57 years.

Contrast sensitivity function after correcting residual wavefront aberrations during RGP lens wear

PURPOSE

To investigate the effect on the contrast sensitivity function (CSF) of correcting the residual wavefront aberrations in myopic and keratoconic subjects wearing rigid gas permeable (RGP) contact lenses.

METHODS

Seventeen eyes of 16 myopic subjects and 20 eyes of 19 keratoconic subjects were included in this study. All eyes were habitually corrected with RGP lenses. The residual aberrations of the RGP lens-wearing eyes were compensated by an adaptive optics (AO) system. The contrast sensitivities were measured through a 4-mm artificial pupil at spatial frequencies of 2, 4, 8, 16, and 32 cycles per degree (cpd) during RGP lens wear for the myopic and keratoconic groups, respectively. The CSF measurements were repeated with and without AO correction. Comparisons of contrast sensitivity at all spatial frequencies with and without AO correction were performed respectively for the myopic and keratoconic groups during RGP lens wear.

RESULTS

In the myopic RGP lens-wearing group, the differences in contrast sensitivity at each spatial frequency, with and without AO correction, were not significant (all p values > 0.05). In the keratoconic RGP lens-wearing group, the contrast sensitivities at all spatial frequencies with AO correction were higher than those without AO correction, but differences only at the low (2 cpd) and intermediate (4, 8, and 16 cpd) spatial frequencies were significant (p = 0.039, 0.005, 0.001, and 0.007).

CONCLUSIONS

The residual aberrations significantly reduced the contrast sensitivities at low and intermediate spatial frequencies for keratoconic RGP lens-wearing eyes but did not have any effect on the CSF for the myopic RGP lens-wearing eyes. Developing techniques that could more completely correct the wavefront aberrations may improve visual performance in keratoconus.

Clinical applications of wavefront refraction

Purpose

To determine normative reference ranges for higher-order wavefront error (HO-WFE), compare these values with those in common ocular pathologies, and evaluate treatments.

Methods

A review of 17 major studies on HO-WFE was made, involving data for a total of 31,605 subjects. The upper limit of the 95% confidence interval (CI) for HO-WFE was calculated from the most comprehensive of these studies using normal healthy patients aged 20 to 80 years. There were no studies identified using the natural pupil size for subjects, and for this reason, the HO-WFE was tabulated for pupil diameters of 3 to 7 mm. Effects of keratoconus, pterygium, cataract, and dry eye on HO-WFE were reviewed and treatment efficacy was considered.

Results

The calculated upper limit of the 95% CI for HO-WFE in a healthy normal 35-year-old patient with a mesopic pupil diameter of 6 mm would be 0.471 μm (471 nm) root-mean-square or less. Although the normal HO-WFE increases with age for a given pupil size, it is not yet completely clear how the concurrent influence of age-related pupillary miosis affects these findings. Abnormal ocular conditions such as keratoconus can induce a large HO-WFE, often in excess of 3.0 μm, particularly attributed to coma. For pterygium or cortical cataract, a combination of coma and trefoil was more commonly induced. Nuclear cataract can induce a negative spherical HO-WFE, usually in excess of 1.0 μm.

Conclusions

The upper limit of the 95% CI for HO-WFE root-mean-square is about 0.5 μm with normal physiological pupil sizes. With ocular pathologies, HO-WFE can be in excess of 1.0 μm, although many devices and therapeutic and surgical treatments are reported to be highly effective at minimizing HO-WFE. More accurate normative reference ranges for HO-WFE will require future studies using the subjects’ natural pupil size.

Ocular higher-order aberrations in a school children population

PURPOSE

The primary objective of the study was to explore the statistics of ocular higher-order aberrations in a population of primary and secondary school children.

METHODS

A sample of 557 children aged 10-15 years were selected from two primary and two secondary schools in Heraklion, Greece. Children were classified by age in three subgroups: group I (10.7±0.5 years), group II (12.4±0.5 years) and group III (14.5±0.5 years). Ocular aberrations were measured using a wavefront aberrometer (COAS, AMO Wavefront Sciences, USA) at mesopic light levels (illuminance at cornea was 4lux). Wavefront analysis was achieved for a 5mm pupil. Statistical analysis was carried out for the right eye only.

RESULTS

The average coefficient of most high-order aberrations did not differ from zero with the exception of vertical (0.076μm) and horizontal (0.018μm) coma, oblique trefoil (-0.055μm) and spherical aberration (0.018μm). The most prominent change between the three groups was observed for the spherical aberration, which increased from 0.007μm (SE 0.005) in group I to 0.011μm (SE 0.004) in group II and 0.030μm (SE 0.004) in group III. Significant differences were also found for the oblique astigmatism and the third-order coma aberrations.

CONCLUSIONS

Differences in the low levels of ocular spherical aberration in young children possibly reflect differences in lenticular spherical aberration and relate to the gradient refractive index of the lens. The evaluation of spherical aberration at certain stages of eye growth may help to better understand the underlying mechanisms of myopia development.

Tilt after-effect from high spatial-frequency patterns in the amblyopic eye of adults with anisometropic amblyopia

With abnormal visual cortical development, amblyopia is generally associated with high spatial frequency deficits in spatial vision. In this study, we aim to answer a critical question: How much high spatial frequency information is available to the amblyopic visual system? We measured the tilt after-effect following adaption to perceptually resolvable and unresolvable sinewave gratings, and showed that gratings with spatial frequency up to 1.5 times the cutoff frequency in grating orientation identification can still produce significant tilt after-effects in adults with amblyopia. Our results suggest that neural connections in the amblyopic visual cortex, at least in V1, may have profoundly developed to represent high spatial frequency information. The demonstration of extant neural connections for high spatial frequencies may have important implications for the development of training protocols for amblyopia treatment. Our paradigm may also serve as a non-invasive probe to diagnose the status of neural connections in other visual deficits.

In vivo imaging of human photoreceptor mosaic with wavefront sensorless adaptive optics optical coherence tomography

Wavefront sensorless adaptive optics optical coherence tomography (WSAO-OCT) is a novel imaging technique for in vivo high-resolution depth-resolved imaging that mitigates some of the challenges encountered with the use of sensor-based adaptive optics designs. This technique replaces the Hartmann Shack wavefront sensor used to measure aberrations with a depth-resolved image-driven optimization algorithm, with the metric based on the OCT volumes acquired in real-time. The custom-built ultrahigh-speed GPU processing platform and fast modal optimization algorithm presented in this paper was essential in enabling real-time, in vivo imaging of human retinas with wavefront sensorless AO correction. WSAO-OCT is especially advantageous for developing a clinical high-resolution retinal imaging system as it enables the use of a compact, low-cost and robust lens-based adaptive optics design. In this report, we describe our WSAO-OCT system for imaging the human photoreceptor mosaic in vivo. We validated our system performance by imaging the retina at several eccentricities, and demonstrated the improvement in photoreceptor visibility with WSAO compensation.

Single neural code for blur in subjects with different interocular optical blur orientation

The ability of the visual system to compensate for differences in blur orientation between eyes is not well understood. We measured the orientation of the internal blur code in both eyes of the same subject monocularly by presenting pairs of images blurred with real ocular point spread functions (PSFs) of similar blur magnitude but varying in orientations. Subjects assigned a level of confidence to their selection of the best perceived image in each pair. Using a classification-images-inspired paradigm and applying a reverse correlation technique, a classification map was obtained from the weighted averages of the PSFs, representing the internal blur code. Positive and negative neural PSFs were obtained from the classification map, representing the neural blur for best and worse perceived blur, respectively. The neural PSF was found to be highly correlated in both eyes, even for eyes with different ocular PSF orientations (rPos = 0.95; rNeg = 0.99; p < 0.001). We found that in subjects with similar and with different ocular PSF orientations between eyes, the orientation of the positive neural PSF was closer to the orientation of the ocular PSF of the eye with the better optical quality (average difference was ∼10°), while the orientation of the positive and negative neural PSFs tended to be orthogonal. These results suggest a single internal code for blur with orientation driven by the orientation of the optical blur of the eye with better optical quality.

Super-Resolution Scanning Laser Microscopy Based on Virtually Structured Detection

Light microscopy plays a key role in biological studies and medical diagnosis. The spatial resolution of conventional optical microscopes is limited to approximately half the wavelength of the illumination light as a result of the diffraction limit. Several approaches-including confocal microscopy, stimulated emission depletion microscopy, stochastic optical reconstruction microscopy, photoactivated localization microscopy, and structured illumination microscopy-have been established to achieve super-resolution imaging. However, none of these methods is suitable for the super-resolution ophthalmoscopy of retinal structures because of laser safety issues and inevitable eye movements. We recently experimentally validated virtually structured detection (VSD) as an alternative strategy to extend the diffraction limit. Without the complexity of structured illumination, VSD provides an easy, low-cost, and phase artifact-free strategy to achieve super-resolution in scanning laser microscopy. In this article we summarize the basic principles of the VSD method, review our demonstrated single-point and line-scan super-resolution systems, and discuss both technical challenges and the potential of VSD-based instrumentation for super-resolution ophthalmoscopy of the retina.

A pilot study on total, corneal, and internal aberrations in insulin-dependent and non-insulin-dependent diabetes mellitus patients

PURPOSE

To explore the distribution of total, corneal, and internal higher-order aberrations (HOAs) in both insulin-dependent (IDDM) and non-insulin-dependent (NIDDM) diabetic patients.

METHODS

Pilot study including seven patients with IDDM (14 eyes) and 11 patients with NIDDM (22 eyes). Ocular HOAs were examined using ray tracing aberrometry (i-Trace, Tracey Technologies Corp., Houston, TX) and the measurements of anterior segment using Scheimpflug imaging (Pentacam, Oculus Inc. Germany).

RESULTS

Total HOAs was slightly higher in IDDM (0.634 ± 0.228 μm, 95% IC ± 0.131) than in NIDDM patients (0.527 ± 0.245 μm, 95% IC ± 0.108) (p = 0.267). The greatest contributor for total ocular HOAs was internal vertical coma (Z3 (- 1)) for both diabetic groups. In NIDDM, age and central corneal thickness (CCT) were correlated with total HOAs (p < 0.001, p = 0.0180 respectively); however, anterior chamber volume (ACV) was inversely correlated with total HOAs (p = 0.019). In IDDM, total HOAs were correlated with posterior asphericity (Q) (p = 0.002) and inversely correlated with ageing (p = 0.013).

CONCLUSIONS

Diabetic patients showed high values of total and internal vertical coma (Z3 (- 1)). There might be a role for optical quality measurements in monitoring changes due to DM.

Critical band masking reveals the effects of optical distortions on the channel mediating letter identification

There is evidence that letter identification is mediated by only a narrow band of spatial frequencies and that the center frequency of the neural channel thought to underlie this selectivity is related to the size of the letters. When letters are spatially filtered (at a fixed size) the channel tuning characteristics change according to the properties of the spatial filter (Majaj et al., 2002). Optical aberrations in the eye act to spatially filter the image formed on the retina-their effect is generally to attenuate high frequencies more than low frequencies but often in a non-monotonic way. We might expect the change in the spatial frequency spectrum caused by the aberration to predict the shift in channel tuning observed for aberrated letters. We show that this is not the case. We used critical-band masking to estimate channel-tuning in the presence of three types of aberration-defocus, coma and secondary astigmatism. We found that the maximum masking was shifted to lower frequencies in the presence of an aberration and that this result was not simply predicted by the spatial-frequency-dependent degradation in image quality, assessed via metrics that have previously been shown to correlate well with performance loss in the presence of an aberration. We show that if image quality effects are taken into account (using visual Strehl metrics), the neural channel required to model the data is shifted to lower frequencies compared to the control (no-aberration) condition. Additionally, we show that when spurious resolution (caused by π phase shifts in the optical transfer function) in the image is masked, the channel tuning properties for aberrated letters are affected, suggesting that there may be interference between visual channels. Even in the presence of simulated aberrations, whose properties change from trial-to-trial, observers exhibit flexibility in selecting the spatial frequencies that support letter identification.

Eigencorneas: application of principal component analysis to corneal topography

PURPOSE

To determine the minimum number of orthonormal basis functions needed to accurately represent the great majority of corneal topographies from a normal population.

METHODS

Principal Component Analysis was applied to the elevation topographies of the anterior and posterior corneal surfaces and central thickness of 368 eyes of 184 healthy subjects. PCA was applied directly to the input elevation data points and after fitting them to Zernike polynomials (up to 8th order, 8 mm diameter). The anterior and posterior surfaces, as well as right eye and left eye data, were analysed both separately and jointly. A threshold based on the amount of explained variance (99%) was applied to determine the minimum number of basis functions (eigencorneas) or degrees of freedom (DoF) in the population.

RESULTS

The eigenvectors directly obtained from elevation data resemble Zernike polynomials. The separate principal component analysis on the Zernike coefficients of anterior and posterior surfaces yielded 5 and 9 DoF, respectively. An additional reduction to 11 DoF (instead of 15 DoF) was achieved when performing a joint PCA that included both surfaces as well as central thickness. Finally, a further reduction was obtained by pooling right and left eye data together, to only 18 DoF.

CONCLUSIONS

The combination of Zernike fit and Principal Component Analysis yields a strong reduction of dimensionality of elevation topography data, to only 19 independent parameters (18 DoF plus population average), which indicates a high degree of correlation existing between anterior and posterior surfaces, and between eyes. The resulting eigencorneas are especially well suited for practical applications, as they are uncorrelated and orthonormal linear combinations of Zernike polynomials.

Clinical features of subepithelial layer irregularities of cornea

PURPOSE

To illustrate surgical outcomes of subepithelial irregularities that were identified incidentally during laser refractive surgery.

MATERIALS AND METHODS

The study group consisted of 406 patients who underwent 787 surface ablation refractive surgeries. Ophthalmologic evaluations were performed before each procedure and at 1, 3 and 6 months post-operatively. Subepithelial irregularities were evaluated by analyzing still photographs captured from video recordings. Sizes and locations were determined by a calibrated scale located at the major axis of the tracking system's reticle.

RESULTS

Subepithelial irregularities were identified in 27 eyes during 787 surface ablation refractive surgeries. Most of the subepithelial irregularities did not show any abnormalities in the wavefront aberrometer. However, one case with diameter greater than 1.00 mm and one case of clustered multiple subepithelial irregularities with moderate size were corresponded significant coma (Z31) and increased higher order aberration (HOA) in the HOA gradient map.

CONCLUSIONS

Corneal subepithelial irregularities may be related to problems that include significantly increased localized HOA and remaining permanent subepithelial opacity. Subepithelial irregularity should be considered even if the surface of the cornea is intact and there are no specific findings measured by corneal topography.

Asymmetric wavefront aberrations and pupillary shapes induced by electrical stimulation of ciliary nerve in cats measured with compact wavefront aberrometer

To investigate the changes in the wavefront aberrations and pupillary shape in response to electrical stimulation of the branches of the ciliary nerves in cats. Seven eyes of seven cats were studied under general anesthesia. Trains of monophasic pulses (current, 0.1 to 1.0 mA; duration, 0.5 ms/phase; frequency, 5 to 40 Hz) were applied to the lateral or medial branch of the short ciliary nerve near the posterior pole of the eye. A pair of electrodes was hooked onto one or both branch of the short ciliary nerve. The electrodes were placed about 5 mm from the scleral surface. The wavefront aberrations were recorded continuously for 2 seconds before, 8 seconds during, and for 20 seconds after the electrical stimulation. The pupillary images were simultaneously recorded during the stimulation period. Both the wavefront aberrations and the pupillary images were obtained 10 times/sec with a custom-built wavefront aberrometer. The maximum accommodative amplitude was 1.19 diopters (D) produced by electrical stimulation of the short ciliary nerves. The latency of the accommodative changes was very short, and the accommodative level gradually increased up to 4 seconds and reached a plateau. When only one branch of the ciliary nerve was stimulated, the pupil dilated asymmetrically, and the oblique astigmatism and one of the asymmetrical wavefront terms was also altered. Our results showed that the wavefront aberrations and pupillary dilations can be measured simultaneously and serially with a compact wavefront aberrometer. The asymmetric pupil dilation and asymmetric changes of the wavefront aberrations suggest that each branch of the ciliary nerve innervates specific segments of the ciliary muscle and dilator muscle of the pupil.

Binocular open-view instrument to measure aberrations and pupillary dynamics

We have designed and built a binocular Hartmann-Shack wave-front sensor using a single microlens array and camera for real-time aberration measurement of both eyes in an open-view configuration. Furthermore, the use of a long wavelength (1050 nm) laser diode makes the illumination source completely invisible, so that measurements can be unobtrusively performed while the subject stares at the visual world under realistic conditions. The setup provides a large dynamic range and simultaneous measurements of convergence, pupil size, accommodation, and aberrations. The open-view design not only offers the possibility of measuring the subject's ocular optics under natural conditions but also allows coupling the device with other existing vision testing instruments and setups, which increases its potential to become a powerful tool for different visual optics studies.

Influence of simple myopic against-the-rule and with-the-rule astigmatism on visual acuity in eyes with monofocal intraocular lenses

PURPOSE

To analyze the influence of simple myopic against-the-rule (ATR) and with-the-rule (WTR) astigmatism on uncorrected distance visual acuity (UDVA) in eyes after monofocal intraocular lens (IOL) implantation.

METHODS

Patients with a postoperative spherical refractive error within ±0.5 diopter (D) and a negative cylindrical refractive error ≥0.5 D were enrolled and divided into two groups: ATR or WTR astigmatism. Age, pupil size, spherical equivalent refractive error, spherical refractive error, cylindrical refractive power, UDVA, corrected distance visual acuity (CDVA) and ocular wavefront aberrations were compared between groups. Correlations between UDVA and other parameters were also examined within groups.

RESULTS

Twenty-five eyes (25 patients) with ATR astigmatism and 18 eyes (18 patients) with WTR astigmatism were evaluated. The logMAR UDVA was 0.30 ± 0.22 (mean ± SD) in the ATR group and 0.11 ± 0.15 in the WTR group, showing a significant difference between groups (P < 0.01). There were no significant differences in other parameters between groups. The UDVA was significantly correlated with spherical equivalent refractive error (r = -0.51, P < 0.01) and cylindrical refractive power (r = -0.48, P = 0.01) in the ATR group, but not in the WTR group. No other parameters were significantly correlated with UDVA in either group.

CONCLUSION

After monofocal IOL implantation, UDVA in eyes with simple myopic ATR astigmatism was worse than in eyes with simple myopic WTR astigmatism. Additionally, UDVA was significantly influenced by cylindrical refractive power in eyes with ATR astigmatism, but not in eyes with WTR astigmatism.

Wavefront aberration statistics in normal eye populations: are they well described by the Kolmogorov model?

This Letter studies the statistics of wavefront aberrations in a sample of eyes with normal vision. Methods relying on the statistics of the measured wavefront slopes are used, not including the aberration estimation stage. Power-law aberration models, an extension of the Kolmogorov one, are rejected by χ2-tests performed on fits to the slope structure function data. This is due to the large weight of defocus and astigmatism variations in normal eyes. Models of only second-order changes are not ruled out. The results are compared with previous works in the area.

Ocular monochromatic aberrations in a rural Chinese adult population

PURPOSE

To investigate the distribution of monochromatic aberrations in a rural Chinese adult population and the possible effect of aberrations on the development of refractive error.

METHODS

A total of 404 Chinese adults who grew up in rural Yongnian County, Handan City, Northern China, were included. Monochromatic aberrations of left eyes were measured using iTrace Dynamic Laser Refraction at 5.0-mm pupil size without cycloplegia.

RESULTS

Mean age of all participants was 49.9 ± 10.5 years (range, 31 to 86 years). Mean spherical equivalent was 0.22 ± 1.14 diopters (D) (range, -7.06 to +3.62 D). With age, the refraction demonstrated a significant hyperopic shift (r = 0.25, p < 0.01). Oblique trefoil (C3), vertical coma (C3), horizontal coma (C3), and spherical aberration (SA) (C4) significantly differed from zero (-0.065 ± 0.133 μm, -0.043 ± 0.161 μm, +0.070 ± 0.115 μm, and +0.058 ± 0.082 μm, respectively). Total root mean square values of higher-order aberrations (HOAs) were 0.296 ± 0.147 μm, with predominant ones of coma (0.180 ± 0.115 μm), trefoil (0.151 ± 0.116 μm), and SA (0.081 ± 0.060 μm). Root mean square values of total HOAs, coma, trefoil, SA, and third- to seventh-order aberrations significantly increased with age (p < 0.01). Total HOAs, SA, coma, and trefoil were not significantly different between hyperopic, emmetropic, and myopic eyes after adjusting for age (p = 0.26, 0.15, 0.24, and 0.28, respectively). Zernike coefficient of SA showed a significant difference between hyperopic (0.076 ± 0.086), emmetropic (0.056 ± 0.079), and myopic (0.028 ± 0.088) eyes (p = 0.00).

CONCLUSIONS

Ocular refraction in rural Chinese adults showed significantly hyperopic shift with age. Magnitudes of HOAs in rural Chinese adults were similar to that of other populations and significantly increased with age but showed no differences in myopic, emmetropic, and hyperopic adults. The existence of HOAs is not, in itself, sufficient to account for the myopia epidemic in China.

Immature visual neural system in children reflected by contrast sensitivity with adaptive optics correction

This study aimed to explore the neural development status of the visual system of children (around 8 years old) using contrast sensitivity. We achieved this by eliminating the influence of higher order aberrations (HOAs) with adaptive optics correction. We measured HOAs, modulation transfer functions (MTFs) and contrast sensitivity functions (CSFs) of six children and five adults with both corrected and uncorrected HOAs. We found that when HOAs were corrected, children and adults both showed improvements in MTF and CSF. However, the CSF of children was still lower than the adult level, indicating the difference in contrast sensitivity between groups cannot be explained by differences in optical factors. Further study showed that the difference between the groups also could not be explained by differences in non-visual factors. With these results we concluded that the neural systems underlying vision in children of around 8 years old are still immature in contrast sensitivity.

Changes in ocular monochromatic higher-order aberrations in the aging eye

PURPOSE

To characterize corneal, internal, and total ocular monochromatic higher-order aberration (MHOA) changes that occur in the aging eye.

METHODS

Prospective observational case series including 300 eyes of 167 patients (mean age = 63.8 years) attending the ophthalmology service at University Hospital Ayr, Scotland. Corneal, internal, and total ocular aberrations were measured over a 6-mm dilated pupil. Zernike coefficients were obtained to the sixth order. Changes in MHOA between age groups and inter-eye correlations between right and left eyes were analyzed.

RESULTS

A significant inter-eye correlation was found for refractive mean spherical equivalent and cylinder. A significant inter-eye correlation for the whole eye, corneal, and internal MHOA was found (p < 0.001). Right eye analysis found a significant positive correlation between age and the root mean square of whole eye MHOA (p = 0.012), with an increase from 0.517 μm in the fifth decade to 0.824 μm in the ninth. Total internal MHOA increased from 0.411 to 0.704 μm. A significant positive correlation was found between age and internal fourth- (p = 0.007), fifth- (p = 0.029), and sixth-order (p = 0.025) root mean square aberrations. There were no significant age-related changes in corneal MHOA or corneal spherical aberration. Overall mean (SD) corneal SA was 0.203 (0.082) μm.

CONCLUSIONS

A strong correlation between the right and left eyes exists for MHOA. Whole eye MHOA increases with age. Such changes can be attributed to age-related changes in the internal optical quality of the eye. Such normative data are useful to the cataract surgeon when considering the use of an aspherical IOL to counteract corneal-induced SA during cataract surgery.

Compressed wavefront sensing

We report on an algorithm for fast wavefront sensing that incorporates sparse representation for the first time in practice. The partial derivatives of optical wavefronts were sampled sparsely with a Shack-Hartman wavefront sensor (SHWFS) by randomly subsampling the original SHWFS data to as little as 5%. Reconstruction was performed by a sparse representation algorithm that utilized the Zernike basis. We name this method sparse Zernike (SPARZER). Experiments on real and simulated data attest to the accuracy of the proposed techniques as compared to traditional sampling and reconstruction methods. We have made the corresponding dataset and software freely available online. Compressed wavefront sensing offers the potential to increase the speed of wavefront acquisition and to defray the cost of SHWFS devices.

Comparison of monochromatic aberrations in young adults with different visual acuity and refractive errors

PURPOSE

To compare the monochromatic aberrations in a large cohort of 20-year-old Australians with differing levels of visual acuity and explore the relationship between these aberrations and refractive error.

SETTING

Lions Eye Institute, Perth, Western Australia, Australia.

DESIGN

Cross-sectional analysis of a population-based cohort.

METHODS

Monochromatic aberrations were measured using a Zywave II wavefront aberrometer with natural pupils in a dark room. The logMAR corrected distance visual acuity (CDVA) was measured monocularly under normal illumination. Cycloplegic autorefraction was also performed.

RESULTS

The study enrolled 2039 eyes of 1040 participants. Data from 1007 right eyes were analyzed. The median CDVA and spherical equivalent were -0.06 logMAR (interquartile range [IQR], -0.10 to 0.00) and +0.25 diopters (D) (IQR, -0.38 to 0.63), respectively. The median 6.0 mm higher-order aberration (HOA) was 0.58 μm (IQR, 0.44 to 0.79). Coma-like aberrations and 3rd-, 4th-, and 5th-order HOAs were significantly different between subjects with a CDVA of -0.10 logMAR or better and those with a CDVA worse than -0.10 logMAR. Fourth-order aberrations Z(4,-4) (P=.024) and Z(4,-2) (P=.029) and 2nd-order aberration Z(2,0) (P<.001) differed significantly between myopic eyes, emmetropic eyes, and hyperopic eyes. Subjects with higher myopia had slightly higher total HOAs.

CONCLUSIONS

The HOAs in this population were marginally higher than previously reported values. The findings confirm there is a difference in monochromatic aberrations between different vision and refractive groups. Results in this study will benefit decision-making processes in the clinical setting.

Impact of pupil transmission apodization on presbyopic through-focus visual performance with spherical aberration

PURPOSE

To investigate the impact on through-focus retinal image quality and visual performance of apodizing the pupil's transmission function in combination with extended depth of focus presbyopic corrections, such as spherical aberration (SA).

METHODS

Through-focus retinal image quality was determined theoretically for various magnitudes of pupil transmission apodization and Zernike primary SA (-0.5 to +0.5 μm) for a 4-mm pupil. The impact of pupil transmission apodization was also assessed psychophysically with a vision simulator equipped with a liquid crystal spatial light modulator for controlling pupil transmission. Through-focus visual acuity (VA) was measured with and without apodization in three cyclopleged subjects from distance to near with monochromatic light (550 nm) under two multifocal aberration conditions. Phase plates induced +0.2 and -0.2 μm of SA over a 4-mm artificial pupil. A baseline condition of zero SA was also included for comparison.

RESULTS

The theoretical investigation showed that pupil transmission apodization significantly improved distance image quality in the presence of positive and negative SA. Retinal image quality at all target vergences for negative SA conditions was improved by apodization. Pupil transmission apodization improved through-focus VA by 0.1 to 0.2 logMAR at intermediate and near object distances for the zero and negative SA conditions. In the positive SA condition, apodization degraded VA by approximately 0.1 logMAR at intermediate object distances.

CONCLUSIONS

Pupil transmission apodization had a significant impact on though-focus visual performance. Pupil transmission apodization affects through-focus retinal image quality by diminishing the relative contribution to the retinal image from the peripheral region of the wavefront aberration. Through-focus visual performance in presbyopic eyes with negative SA was improved due to pupil transmission apodization.