Refractive error and monochromatic aberrations in Singaporean children

Association of myopia and astigmatism with postoperative ocular high order aberration after small incision lenticule extraction

OBJECTIVE

To investigate the correlation between higher-order aberrations (HOA) after small incision lenticule extraction (SMILE) and the severity of myopia and astigmatism, along with the relevant factors. These findings will provide valuable insights for decreasing the occurrence of HOA after SMILE and enhancing visual quality.

METHODS

A total of 75 patients (150 eyes) with myopia and astigmatism who underwent SMILE were categorized into four groups based on the severity of myopia and astigmatism: Myopia Group 1 (Group M1, spherical diopter ranged from -1.00 D to -4.00 D), Myopia Group 2 (Group M2, spherical diopter ranged from -4.10 D to -10.00 D), Astigmatism Group 1 (Group A1, cylindrical diopter ranged from 0 D to -1.00 D), and Astigmatism Group 2 (Group A2, cylindrical diopter ranged from -1.10 D to -3.00 D). A comprehensive assessment was performed to examine the association between HOA and various relevant factors, including a detailed analysis of the subgroups.

RESULTS

Group M1 had significantly lower levels of total eye coma aberration (CA), corneal total HOA (tHOA), internal tHOA, and vertical CA ( Z 3 - 1 ) after SMILE than Group M2 (P < 0.05). Similarly, Group A1 had significantly lower levels of total eye tHOA, CA, trefoil aberration (TA), corneal tHOA, TA, and vertical TA ( Z 3 - 3 ) after SMILE than Group A2 (P < 0.05). Pearson correlation analysis indicated a statistically significant positive relationship between the severity of myopia/astigmatism and most HOA (P < 0.05). Subgroup evaluations demonstrated a notable increase in postoperative HOA associated with myopia and astigmatism in Groups M2 and A2 compared with the control group. Lenticule thickness, postoperative central corneal thickness (CCT), postoperative uncorrected distance visual acuity (UDVA), and postoperative corneal Km and Cyl were strongly correlated with most HOA. Age, eyes, and postoperative intraocular pressure (IOP) were only associated with specific HOA.

CONCLUSION

HOA positively correlated with the severity of myopia and astigmatism after SMILE. However, this relationship was not linear. HOA after SMILE was influenced by various factors, and additional specialized investigations are required to establish its clinical importance.

Higher order aberrations according to spherical, and astigmatic refractive errors in children

CLINICAL RELEVANCE

The results of this study present novel insights into the impact of spherical and astigmatic refractive errors on overall, corneal and internal aberrations and may provide a clear understanding of the emmetropisation process and the development of visual function.

BACKGROUND

This study aimed to assess the association between overall, corneal and internal higher-order aberrations and the spherical and astigmatic components (magnitude and angle) of refractive error in a large sample of children.

METHODS

A total of 311 children aged 7 - 8 years old were classified based on spherical equivalent refraction (myopic, emmetropic and hyperopic); magnitude of astigmatism (none, low and moderate); and angle of astigmatism (with-the-rule, against-the-rule and oblique). Refractive error and overall, corneal and internal higher-order aberrations were measured using the OPD-Scan III workstation.

RESULTS

Regarding spherical equivalent refraction, myopic eyes had greater root mean square (RMS) overall higher-order values, total spherical, tetrafoil and secondary astigmatism aberrations, and internal higher-order, total spherical and tetrafoil aberrations in comparison to emmetropic eyes. The magnitude of astigmatism was positively associated with all overall RMS aberrations and with internal higher order, coma, total coma, total spherical and tetrafoil aberrations. Eyes with with-the-rule astigmatism showed higher RMS values of coma and total coma compared to eyes with against-the-rule and oblique astigmatism.

CONCLUSIONS

Higher-order aberrations are dependent on the spherical as well as astigmatic components of refractive error. These findings enhance the current understanding of the emmetropisation process and visual function development.

Analysis of the relationship between lens morphology and aberrations in patients with myopia: a cross-sectional study

PURPOSE

To investigate the relationship between lens morphology and aberrations in patients with myopia.

METHODS

This cross-sectional study included 155 patients with myopia in their right eyes. Spherical power and cylindrical power were achieved by cycloplegic autorefraction. The eyes were divided into three groups for analysis based on their spherical equivalent (SE) values. The 4 mm and 6 mm ocular and internal aberrations were measured using the OPD-scan III. Lens parameters were measured using CASIA2, including lens thickness (LT), radius of anterior/posterior lens surface curvature (RAL/RPL), lens decentration (DEC), and lens tilt (TILT). The differences of lenticular parameters and aberration parameters among the three groups analyzed with ANOVA or Kruskal Wallis test. Pearson correlation or Spearman correlation analysis was performed to evaluate the relationships between the lens parameters and aberrations. A p value < 0.05 indicated statistical significance.

RESULTS

The difference in LT, RAL, DEC and TITL among the three groups was statistically significant (p < 0.05). And there were differences among differences in internal high-order aberrations, spherical aberration, and coma aberration(p < 0.05).Spherical power was positively correlated with LT and TITL (p < 0.05) and negatively correlated with DEC, RAL, and RPL (p < 0.05). Cylindrical power was positively correlated with LT (p < 0.05) and negatively correlated DEC (p < 0.05); The lenticular parameters (LT, RAL, DEC, and TILT) were mainly correlated with the ocular and internal spherical aberration. LT and DEC were correlated with ocular and internal higher-order aberrations and coma aberration.

CONCLUSION

DEC and LT were the main factors affecting aberrations in patients with myopia.

Higher order aberrations and visual function in a young Asian population of high myopes

Purpose

To examine the associations between higher order aberrations (HOAs), visual performance, demographics, and ocular characteristics in a young Asian population with high myopia.

Methods

This was a retrospective review of military pre-enlistees conducted between March 2014 to September 2018. Visual acuity and contrast sensitivity were tested under photopic, mesopic and simulated night conditions. Ocular, corneal and internal HOAs were measured with a Hartmann-Shack wavefront aberrometer (KR-1W, Topcon Co., Tokyo, Japan).

Results

522 eyes of 263 consecutive subjects with severe high myopia (defined as spherical equivalent refraction [SER] ≤ -10.00D) in at least one eye, and high myopia (SER ≤ -6.00D) in the fellow eye, [mean (SD) SER -11.85 (2.03D)] were analysed. The mean (SD) age of subjects was 18.5 (1.6) years. Chinese eyes had significantly greater internal total HOA root-mean-square (RMS) compared to Malay eyes [mean difference (SD) 0.0246 (0.007) μm, p < 0.001). More negative SER was associated with greater ocular total HOA (p = 0.038), primary coma (p = 0.003) and tetrafoil (p = 0.025) RMS, as well as more positive ocular (p = 0.003) and internal primary spherical aberration (p = 0.009). Greater ocular total HOAs was associated with reduced visual acuity in simulated night conditions and low contrast, decreased contrast sensitivity under mesopic and simulated night conditions (all p < 0.05).

Conclusions

Greater HOAs were associated with Chinese ethnicity and more negative SER in a young Asian population with high myopia. Greater HOAs were associated with poorer visual performance in low luminance and reduced contrast conditions.

Central and Peripheral Ocular High-Order Aberrations and Their Relationship with Accommodation and Refractive Error: A Review

High-order aberrations (HOAs) are optical defects that degrade the image quality. They change with factors such as pupil diameter, age, and accommodation. The changes in optical aberrations during accommodation are mainly due to lens shape and position changes. Primary spherical aberration (Z(4.0)) is closely related to accommodation and some studies suggested that it plays an important role in the control of accommodation. Furthermore, central and peripheral HOAs vary with refractive error and seem to influence eye growth and the onset and progression of myopia. The variations of central and peripheral HOAs during accommodation also appear to be different depending on the refractive error. Central and peripheral high-order aberrations are closely related to accommodation and influence the accuracy of the accommodative response and the progression of refractive errors, especially myopia.

Intraocular composition of higher order aberrations in non-myopic children

This study examined anterior corneal, internal ocular, and total ocular higher order aberrations (HOA's), and retinal image quality in a non-myopic, paediatric cohort. Anterior corneal aberrations were derived from corneal topography data captured using a Placido disk videokeratoscope (E300, Medmont International), and whole eye HOA's were measured using a Hartmann-Shack wavefront sensor (COAS-HD, Wavefront Sciences). The associations between HOA's and age, sex, refractive error, and axial length were explored using correlation analyses. Data for 84 children aged between 5 and 12 years (mean ± standard deviation spherical equivalent refraction (SER), +0.63 ± 0.35 D; range 0.00 to +1.75 D) were included, and an eighth order Zernike polynomial was fit for 4 and 6 mm pupil diameters for both the anterior corneal and total ocular HOA's, from which internal ocular HOA's were calculated via subtraction following alignment to a common reference axis (pupil centre). Internal ocular HOA's were of greater magnitude than previous studies of adolescents and adults, however partial internal "compensation" of HOA's was observed, which resulted in reduced levels of HOA's and excellent retinal image quality. Few significant associations were observed between HOA's and age, SER, and axial length (all correlations, p > 0.001), and there were minimal sex-based differences (all comparisons, p > 0.005). Coefficients for vertical coma ( C 3 - 1 and C 5 - 1 ) and spherical aberration ( C 4 0 and C 6 0 ), were most strongly associated with the visual Strehl ratio based on the optical transfer function (VSOTF), which indicated that the absolute magnitudes of these Zernike coefficients have the greatest impact on retinal image quality in this paediatric cohort. These findings provide an improved understanding of the optics and retinal image quality of children's eyes.

Photopic pupil size change in myopic orthokeratology and its influence on axial length elongation

AIM

To explore the photopic pupil size behavior in myopic children undergoing overnight orthokeratology (ortho-k) over 1-year period and its effects on the axial elongation.

METHODS

A total of 202 Chinese myopic children were enrolled in this prospective clinical trial. Ninety-five subjects in ortho-k group and eighty-eight subjects in spectacle group completed the 1-year study. Axial length (AL) was measured before enrollment and every 6mo after the start of ortho-k. The photopic pupil diameter (PPD) was determined using the Pentacam AXL and measured in an examination room with lighting of 300-310 Lx. Stepwise multiple linear regression analysis was used to identify variables contribution to axial elongation.

RESULTS

Compared with spectacle group, the average 1-year axial elongation was significantly slower in the ortho-k group (0.25±0.27 vs 0.44±0.23 mm, P<0.0001). In ortho-k group, PPDs significantly decreased from 4.21±0.62 mm to 3.94±0.53 mm after 1mo of lens wear (P=0.001, Bonferroni correction) and the change lasts for 3-month visit. No significantly change during the other follow-up visits was found (P>0.05, Bonferroni correction). The 4.81 mm PPD may be a possible cutoff point in the ortho-k group. Subjects with PPD below or equal to 4.81 mm tended to have smaller axial elongation compared to subjects with PPD above 4.81 mm after 1-year period (t=-3.09, P=0.003). In ortho-k group, univariate analyses indicated that those with older age, greater degree of myopia, longer AL, smaller baseline PPD (PPD_baseline) experienced a smaller change in AL. In multivariate analyses, older age, greater AL and smaller PPD_baseline were associated with smaller increases in AL. In spectacle group, PPD tended to be stable (P>0.05, Bonferroni correction) and did not affect axial growth.

CONCLUSION

PPDs experience significantly decreases at 1-month and 3-month ortho-k treatment. Children with smaller PPD tend to experience slower axial elongation and may benefit more from ortho-k.

Ocular aberrations in eyes with Primary Congenital Glaucoma

PURPOSE

To highlight the magnitude of ocular higher order aberrations (HOA) and lower order aberrations (LOA), including component contributions from corneal and internal planes in Primary Congenital Glaucoma (PCG) patients.

METHODS

Consecutive treated PCG patients co-operative for ocular examination and aberrometry, were enrolled over two years for this cross-sectional, comparative, single centre, unmasked study. Best corrected visual acuity, refraction, IOP, wavefront aberrometry and topography (iTrace) were performed and results were compared with unaffected fellow eyes of unilateral glaucoma patients as well as age and sex matched controls with no ocular anomalies other than treatable refractive error.

RESULTS

Both eyes of 32 consecutive PCG patients (17 unilateral, 15 bilateral) and 39 controls were enrolled. The median LogMAR corrected distance visual acuity of PCG eyes was 0.68 (IQR: 0.2 - 1.8). Total ocular (Root mean square (RMS) 1.7µm vs 0.3µm, p = 0.014), corneal (RMS 1.1µm vs 0.3µm, p = 0.004) and internal (RMS 1.1µm vs 0.2µm, p = 0.013) aberrations, as well as HOAs and LOAs at each plane were significantly higher in PCG eyes than in controls. Component HOAs from corneal and internal planes were positively correlated with each other (p < 0.001; rs: 0.7). Total aberrations were greater in the affected eyes of PCG compared to the rest. The predominant subtype of HOAs in PCG were coma and trefoil. PCG with corneal opacity/Haab's striae had significantly higher astigmatism than the affected eyes with clear corneae at corneal plane (p = 0.02). The aberrations were not statistically associated with the corneal diameter or refractive error in PCG eyes.

CONCLUSIONS

Significantly greater aberrations (Total, HOAs and LOAs, at corneal as well as internal plane) were seen among eyes affected with PCG. Though the exact impact of these aberrations on the final visual outcome is difficult to determine, these could play a pertinent role in compromising visual function, thus impacting the management of visual rehabilitation in these patients.

[Optical aberrations of the eyes with various degrees of myopia]

Purpose - to comparatively analyze the wavefront aberrations and biometric parameters of the eyes with various degrees of myopia.

MATERIAL AND METHODS

The study included 134 eyes of 67 patients with mild, moderate and high myopia aged 7-28 (mean age 19.3±1.5 years). The following biometric parameters were examined: anterior chamber depth (ACD), lens thickness (LT), axial length (AL), as well as corneal and total aberrations. The parameters were studied on the Galilei G6 system (Ziemer Ophthalmic Systems AG, Switzerland) and the OPD-Scan III aberrometer (Nidek, Japan). Spherical aberration (SA) was estimated as the sum of Z4+Z8+Z12.

RESULTS

As the refraction increased, the root mean square higher-order aberrations (RMS HOA) also increased significantly: from 0.24±0.02 μm in mild myopia to 0.45±0.03 μm in high myopia, and in eyes with AL of ≥27.0 mm - to 0.57±0.02 μm (p=0.01). An increase in vertical tilt, vertical coma and vertical trefoil were also observed. Total SA was positive and increased in eyes with moderate myopia compared to those with low myopia (from 0.02±0.01 μm to 0.06±0.02 μm, p=0.02), which coincided with changes in the internal optics of the eye: an increase in ACD and a decrease in LT. At the same time, no differences in corneal aberrations were observed among patients with low and moderate myopia. A significant decrease of SA occurred in high myopia (from 0.06 μm in low myopia to 0.015±0.02 μm in high myopia). The average value of SA was 0.005±0.01 μm in eyes with AL of ≥27.0 mm and appeared to be negative in 40% of cases. The average value of corneal SA was negative (-0.002±0.01μm) in eyes with AL of ≥27.0 mm. This group had predominantly patients with congenital myopia.

CONCLUSION

An increase of total positive SA in patients with moderate myopia compared to those with low myopia is associated with changes in the internal optics of the eye (ACD, LT). Significant increase of higher-order aberrations and decrease of SA with the transition to negative values was observed in patients with high axial myopia.

Functional integration of eye tissues and refractive eye development: Mechanisms and pathways

Refractive eye development is a tightly coordinated developmental process. The general layout of the eye and its various components are established during embryonic development, which involves a complex cross-tissue signaling. The eye then undergoes a refinement process during the postnatal emmetropization process, which relies heavily on the integration of environmental and genetic factors and is controlled by an elaborate genetic network. This genetic network encodes a multilayered signaling cascade, which converts visual stimuli into molecular signals that guide the postnatal growth of the eye. The signaling cascade underlying refractive eye development spans across all ocular tissues and comprises multiple signaling pathways. Notably, tissue-tissue interaction plays a key role in both embryonic eye development and postnatal eye emmetropization. Recent advances in eye biometry, physiological optics and systems genetics of refractive error have significantly advanced our understanding of the biological processes involved in refractive eye development and provided a framework for the development of new treatment options for myopia. In this review, we summarize the recent data on the mechanisms and signaling pathways underlying refractive eye development and discuss new evidence suggesting a wide-spread signal integration across different tissues and ocular components involved in visually guided eye growth.

Recent advances in measurement of monochromatic aberrations of human eyes

The field of aberrations of the human eye is moving rapidly, being driven by the desire to monitor and optimise vision following refractive surgery. It is important for ophthalmologists and optometrists to have an understanding of the magnitude of various aberrations and how these are likely to be affected by refractive surgery and other corrections. In this paper, I consider methods used to measure aberrations, the magnitude of aberrations in general populations and how these are affected by various factors (for example, age, refractive error, accommodation and refractive surgery) and how aberrations and their correction affect spatial visual performance.

Influence of refractive status and age on corneal higher-order aberration

This study aimed to investigate the influence of refractive status and age of patients on corneal higher-order aberrations (HOAs). Four hundred and twenty-six right eyes of 426 patients were enrolled in this study. The mean and standard deviation of patient age was 47.7 ± 22.1 years. Total HOAs, spherical-like aberration, coma-like aberration, Z^-1₃, Z¹₃, Z^-3₃, Z^-3₃ and spherical aberration (Z⁰₄) for 6-mm pupil were measured using anterior segment optical coherence tomography (AS-OCT). Subjects were classified into three groups according to the amount of spherical equivalent refractive error (SE): myopia (<-0.5 D), emmetropia (-0.5 to 0.5 D), and hyperopia (>0.5 D). The amount of corneal astigmatism was recorded. Relationship between corneal aberrations, refractive status, astigmatism, and age was analyzed. In total, total HOAs, spherical-like aberration and amount of Z^-3₃ and Z⁰₄ were significantly larger in the hyperopia group than in the myopia group. After adjustment for age, however, aberration components did not differ among the three refractive groups. In multiple regression analysis, age and corneal astigmatism showed significant correlation with aberrations, whereas amount of SE and refractive status did not. The current study indicated that age and amount of corneal astigmatism have significant influence on corneal HOAs, but refractive status (myopia, emmetropia, or hyperopia) is not associated with corneal HOAs.

Optical mechanisms regulating emmetropisation and refractive errors: evidence from animal models

Our current understanding of emmetropisation and myopia development has evolved from decades of work in various animal models, including chicks, non-human primates, tree shrews, guinea pigs, and mice. Extensive research on optical, biochemical, and environmental mechanisms contributing to refractive error development in animal models has provided insights into eye growth in humans. Importantly, animal models have taught us that eye growth is locally controlled within the eye, and can be influenced by the visual environment. This review will focus on information gained from animal studies regarding the role of optical mechanisms in guiding eye growth, and how these investigations have inspired studies in humans. We will first discuss how researchers came to understand that emmetropisation is guided by visual feedback, and how this can be manipulated by form-deprivation and lens-induced defocus to induce refractive errors in animal models. We will then discuss various aspects of accommodation that have been implicated in refractive error development, including accommodative microfluctuations and accommodative lag. Next, the impact of higher order aberrations and peripheral defocus will be discussed. Lastly, recent evidence suggesting that the spectral and temporal properties of light influence eye growth, and how this might be leveraged to treat myopia in children, will be presented. Taken together, these findings from animal models have significantly advanced our knowledge about the optical mechanisms contributing to eye growth in humans, and will continue to contribute to the development of novel and effective treatment options for slowing myopia progression in children.

Higher order aberrations, refractive error development and myopia control: a review

Evidence from animal and human studies suggests that ocular growth is influenced by visual experience. Reduced retinal image quality and imposed optical defocus result in predictable changes in axial eye growth. Higher order aberrations are optical imperfections of the eye that alter retinal image quality despite optimal correction of spherical defocus and astigmatism. Since higher order aberrations reduce retinal image quality and produce variations in optical vergence across the entrance pupil of the eye, they may provide optical signals that contribute to the regulation and modulation of eye growth and refractive error development. The magnitude and type of higher order aberrations vary with age, refractive error, and during near work and accommodation. Furthermore, distinctive changes in higher order aberrations occur with various myopia control treatments, including atropine, near addition spectacle lenses, orthokeratology and soft multifocal and dual-focus contact lenses. Several plausible mechanisms have been proposed by which higher order aberrations may influence axial eye growth, the development of refractive error, and the treatment effect of myopia control interventions. Future studies of higher order aberrations, particularly during childhood, accommodation, and treatment with myopia control interventions are required to further our understanding of their potential role in refractive error development and eye growth.

Peripheral Monochromatic Aberrations in Young Adult Caucasian and East Asian Eyes

SIGNIFICANCE

Myopia prevalence rates differ between racial groups. If the growth of the eye is sensitive to differences in optical input, the difference in spherical aberration between East Asian and Caucasian eyes found in this study may be important in understanding myopia development.

PURPOSE

The aim of this study was to determine differences in peripheral wavefront aberrations between two racial groups.

METHODS

Wavefront aberrations were measured using a COAS-HD aberrometer across the 42 × 32° central visual field on 37 right eyes of young adults (18 Caucasians, 19 East Asians; mean age 21.5 ± 2.4 years). The mean spherical equivalent refraction was -1.94 ± 1.63 diopters (D) with a range of -5.87 to +0.16 D. Effect of race and visual field position on refractions, individual Zernike aberration coefficients up to the fourth order, higher-order root-mean-square aberration, and total root-mean-square aberration were assessed by repeated-measures analysis of covariance.

RESULTS

Caucasians and East Asians had similar relative peripheral myopia across the visual field. All higher-order aberration coefficients were affected by visual field position. Race had no significant effect on any higher-order Zernike coefficient, but the difference in mean vertical coma coefficient (Equation is included in full-text article.)across the visual field (i.e., average of 38 field locations) approached significance, being less positive in Caucasians than in East Asians (P = .08). When correction was made for the Caucasian group being slightly less myopic than the East Asian group, spherical aberration coefficient (Equation is included in full-text article.)was less positive in Caucasians than in East Asians by 0.04 μm (P = .001). The rates of change of coma coefficients across the field were not affected by race.

CONCLUSIONS

Caucasians and East Asians had similar relative peripheral myopia, but with less positive spherical aberration coefficient in Caucasians than in East Asians. It remains to be determined whether aberrations have a role in the difference of myopia prevalence rates in different countries.

Wide-range adaptive optics visual simulator with a tunable lens

An adaptive optics visual simulator (AOVS) with an extended dioptric range was developed, allowing measuring and correcting aberrations in a majority of highly ametropic eyes. In the instrument, a tunable lens is used for defocus correction, while a liquid-crystal-on-silicon spatial light modulator is used for compensating or inducing any other aberration. The instrument incorporates a digital projector, which uses a micromirror array to display the stimuli. A motorized diaphragm enables operation for any physiological pupil size. A full description of the instrument and its calibration are provided, together with the results obtained in seven highly myopic subjects with refraction of -7.2±1.8  D (mean±SD). Refraction obtained with the instrument was compared to the standard refraction prescribed by trial lenses. When using the refraction obtained by the AOVS, the visual acuity (VA) exhibited an average increase of 0.21 (decimal scale). The visual impact of correcting high-order aberrations is presented in three subjects, whose VAs slightly improved with the correction. High myopes are able to benefit from the improved refraction assessment. The new instrument creates a possibility for a wide number of new experiments, especially for eyes exhibiting large refractive errors, where previous AO instruments failed to operate.

The Effect of Corneal Higher Order Aberrations on Postoperative Residual Astigmatism after Toric IOL Implantation

Background: To demonstrate the effect of preoperative higher order aberrations (HOAs) on postoperative residual astigmatism in toric intraocular lens (IOL) implantation. Methods: A retrospective, controlled, comparative study that involved patients who underwent toric IOL implantation. Patients were divided into two groups according to the difference between the estimated residual astigmatism and actual postoperative astigmatism [difference ≤0.5 diopters (D), Group A; difference >0.5 D, Group B]. Corneal astigmatisms with axis, and various aberration values were compared between the two groups. Results: Total RMS and HOA RMS values in Group B were significantly higher than those in Group A (p < .001, = 0.003). The vertical coma value, and its absolute value, in Group B were significantly higher than those in Group A (p < .001, = 0.002). The total RMS and absolute value of the vertical coma showed a positive linear correlation with the degree of residual postoperative astigmatism (R-square = 0.139, 0.131; p = .027, 0.036). Conclusions: If the residual astigmatism after insertion of the toric IOL was greater than expected, corneal aberrations, shown by total RMS and HOA RMS values before surgery, especially of the vertical coma, tended to be high.

IMI - Report on Experimental Models of Emmetropization and Myopia

The results of many studies in a variety of species have significantly advanced our understanding of the role of visual experience and the mechanisms of postnatal eye growth, and the development of myopia. This paper surveys and reviews the major contributions that experimental studies using animal models have made to our thinking about emmetropization and development of myopia. These studies established important concepts informing our knowledge of the visual regulation of eye growth and refractive development and have transformed treatment strategies for myopia. Several major findings have come from studies of experimental animal models. These include the eye's ability to detect the sign of retinal defocus and undergo compensatory growth, the local retinal control of eye growth, regulatory changes in choroidal thickness, and the identification of components in the biochemistry of eye growth leading to the characterization of signal cascades regulating eye growth and refractive state. Several of these findings provided the proofs of concepts that form the scientific basis of new and effective clinical treatments for controlling myopia progression in humans. Experimental animal models continue to provide new insights into the cellular and molecular mechanisms of eye growth control, including the identification of potential new targets for drug development and future treatments needed to stem the increasing prevalence of myopia and the vision-threatening conditions associated with this disease.

Profile of off-axis higher order aberrations and its variation with time among various refractive error groups

Peripheral higher order aberrations (HOA) of 646 children at 30° temporal, nasal and inferior visual field were measured under cycloplegia (5 mm pupil diameter) using a commercially available Shack-Hartmann aberrometer in the Sydney Myopia Study [age, 12.7 ± 0.4 years (mean ± standard deviation)] and five years later in the Sydney Adolescent Vascular and Eye Study. At baseline, 176 eyes were emmetropic, 95 were myopic and 375 were hyperopic. Coma, 3rd order and RMS of coma increased with eccentricity for all eyes and no difference was observed for 4th order and RMS of C(4,0) among refractive error groups. More positive C(4,0) was observed for hyperopic eyes at periphery. At follow up, 26% had 'myopic change' and 70% had 'no change' in refractive error. At follow-up, horizontal coma became more negative at nasal field and more positive at temporal field for all eyes. More positive C(4,0) for hyperopic eyes at baseline may indicate variation in optical characteristics of peripheral cornea and crystalline lens. An increase in horizontal coma with time, irrespective of refractive error change, may be attributed to variation in the shape factor of peripheral cornea and crystalline lens and/or misalignment of optical surfaces/components relative to the visual axis (angle kappa) as the eye grows in axial length.

Ocular higher-order aberrations and axial eye growth in young Hong Kong children

This retrospective longitudinal analysis aimed to investigate the association between ocular higher-order aberrations (HOAs) and axial eye growth in Hong Kong children. Measures of axial length and ocular HOAs under cycloplegia were obtained annually over a two-year period from 137 subjects aged 8.8 ± 1.4 years with mean spherical equivalent refraction of -2.04 ± 2.38 D. A significant negative association was observed between the RMS of total HOAs and axial eye growth (P = 0.03), after adjusting for other significant predictors of axial length including age, sex and refractive error. Similar negative associations with axial elongation were found for the RMS of spherical aberrations ([Formula: see text] and [Formula: see text] combined) (P = 0.037). Another linear mixed model also showed that greater levels of vertical trefoil [Formula: see text], primary spherical aberration [Formula: see text] and negative oblique trefoil [Formula: see text] were associated with slower axial elongation and longer axial length (all P < 0.05). These findings support the potential role of HOAs, image quality and a vision-dependent mechanism in childhood eye growth.

Real-Time Measurement of Ocular Wavefront Aberrations in Symptomatic Subjects

The purpose of this work was to study the real-time changes of the optical properties of the eye with accommodation in subjects with symptoms of accommodative disorders. From ocular aberrations, it is possible to compute several parameters like the response and lag of accommodation. The ocular aberrations were measured in 4 subjects, with different accommodative disorders, during several cycles of accommodation/disaccommodation and for different accommodative stimuli. The measurement was done continuously and in real time during different accommodative stimuli. It was possible to see the changes in accommodative response during the several stimuli of accommodation. Subjects with accommodative disorders showed different accommodative responses. The use of wavefront ocular aberrations can be a tool to diagnose accommodative disorders. In some subjects with complaints, this method showed irregularities even when the results of the usual clinical exams were normal.

Relationship between higher-order wavefront aberrations and natural progression of myopia in schoolchildren

This study investigated the relationship between higher-order aberrations (HOAs) and myopia progression as well as axial elongation in schoolchildren. We examined cycloplegic refraction, axial length, and wavefront aberrations prospectively in 71 myopic children. Changes in cycloplegic refraction and axial length during a 2-year study period were assessed, and their correlations with HOA components were analyzed. Sixty-four subjects ([mean ± SD] 9.2 ± 1.6 years) completed the 2-year examinations. Cycloplegic refraction was significantly changed after 2 years (P < 0.0001), and the average change (myopia progression) was -1.60 ± 1.04 D. Axial length also increased significantly (P < 0.0001), and the average increase (axial elongation) was 0.77 ± 0.40 mm. Myopia progression and axial elongation showed significant correlations with many components of corneal HOA (P < 0.0001 to P = 0.0270). Multivariate analysis showed that the total HOA of the cornea was the most relevant variable to myopia progression and axial elongation (P < 0.0001). Eyes with larger amounts of corneal HOAs showed less myopia progression and smaller axial elongation, suggesting that corneal HOAs play a role in the refractive and ocular developments in children.

Characteristics of higher-order aberrations and anterior segment tomography in patients with pathologic myopia

PURPOSE

To investigate prospectively the characteristics in the higher-order aberrations and anterior segment tomography in patients with pathologic myopia.

METHODS

One hundred and twelve consecutive highly myopic patients (mean age 43.4 ± 9.3 years, spherical equivalent of refractive error ≥8 D and an axial length ≥26.5 mm) were studied. Thirty-seven emmetropic individuals (mean age 37.0 ± 14.5 years, spherical equivalent of refractive error ≤ ±1 D) were analyzed as controls. The ocular and cornea higher-order aberrations were measured using a Hartmann-Shack wavefront sensor (KR-1W; Topcon Corporation, Tokyo, Japan). The crystalline lens rise, the angle-to-angle, and the white-to-white values were measured using anterior segment OCT (SS-1000; Tomey Corporation, Nagoya, Japan). The mean curvature of the anterior corneal surface, the thickness at the thinnest central corneal point, the location of the central corneal point, the corneal volume, the anterior chamber volume, and the anterior chamber depth were measured using the Pentacam HR (Oculus, Inc., Wetzlar, Germany).

RESULTS

The ocular total higher-order aberration for 4-mm pupil, the ocular spherical aberrations, and internal spherical aberration for 6-mm pupil were significantly higher in highly myopic eyes than in the emmetropic controls. The crystalline lens rise was significantly smaller in highly myopic eyes than in the emmetropic controls. The anterior chamber depth and the anterior chamber volume were significantly larger in highly myopic eyes than in the emmetropic controls.

CONCLUSION

Highly myopic eyes had higher-order aberrations than emmetropic eyes because of the increasing internal aberrations.

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.

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

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.

Higher-order aberrations and best-corrected visual acuity in Native American children with a high prevalence of astigmatism

PURPOSE

To determine whether higher-order aberrations (HOAs) in children from a highly astigmatic population differ from population norms and whether HOAs are associated with astigmatism and reduced best-corrected visual acuity.

METHODS

Subjects were 218 Tohono O'odham Native American children 5-9 years of age. Noncycloplegic HOA measurements were obtained with a handheld Shack-Hartmann sensor (SHS). Signed (z06s to z14s) and unsigned (z06u to z14u) wavefront aberration Zernike coefficients Z(3,-3) to Z(4,4) were rescaled for a 4 mm diameter pupil and compared to adult population norms. Cycloplegic refraction and best-corrected logMAR letter visual acuity (BCVA) were also measured. Regression analyses assessed the contribution of astigmatism (J0) and HOAs to BCVA.

RESULTS

The mean root-mean-square (RMS) HOA of 0.191 ± 0.072 μm was significantly greater than population norms (0.100 ± 0.044 μm). All unsigned HOA coefficients (z06u to z14u) and all signed coefficients except z09s, z10s, and z11s were significantly larger than population norms. Decreased BCVA was associated with astigmatism (J0) and spherical aberration (z12u) but not RMS coma, with the effect of J0 about 4 times as great as z12u.

CONCLUSIONS

Tohono O'odham children show elevated HOAs compared to population norms. Astigmatism and unsigned spherical aberration are associated with decreased acuity, but the effects of spherical aberration are minimal and not clinically significant.

Ocular Aberrations and Corneal Shape in Adults with and without Astigmatism

PURPOSE

To characterize and compare the corneal shapes and monochromatic aberrations in Chinese myopic adults with and without astigmatism.

METHODS

Forty-six Hong Kong Chinese aged 50 to 70 years with compound against-the-rule myopic astigmatism (n = 18) or simple myopia (n = 28) were recruited. Corneal shapes were measured by a Scheimpflug-based corneal topographer: the semimeridian corneal shape factors at the nasal, temporal, inferior, and superior corneal quadrants measured from the corneal apex to 3 mm midperiphery were analyzed. The ocular aberrations were measured by the COAS (Complete Ophthalmic Analysis System) Shack-Hartmann wavefront aberrometer; the corneal aberrations were computed using the corneal topographic map data measured by the Medmont E300 corneal topographer; and the internal aberrations were calculated from the ocular and corneal aberrations.

RESULTS

Compared with simple myopia, myopic astigmatism had more oblate nasal and temporal corneal shapes and showed significantly more negative Y trefoil and more positive vertical coma. The asymmetry in corneal shape along the vertical principal meridian (inferior - superior) was significantly associated with the Y trefoil and vertical coma of the cornea, suggesting that this regional asymmetry in corneal shape may contribute to the ocular aberrations.

CONCLUSIONS

The significant relationships found between astigmatism, corneal shapes, and monochromatic aberrations underscore the importance of taking corneal shape into account when correcting the optical defects in myopic Chinese adults with astigmatism.

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.

Progression of lower and higher-order aberrations: a longitudinal study

BACKGROUND

The aim of the present study was to investigate the effect of near-work on lower and higher-order aberrations, and its progression over a 9-month period during the school year.

METHODS

Data from 24 young-adult myopic eyes, and 24 non-myopic eyes were used in this investigation. The lower-order aberrations, coma, spherical aberration (SA), and total root mean square (RMS) of higher order aberrations (total HOA) were measured using an open-field iTrace aberrometer, at both the initial baseline evaluation, and then at the follow-up visits over a 9-month period. Pupil size of 4 mm was used for the aberration measurements.

RESULTS

The group mean (SD) of the subjects (mean age: 23.6 +/- 3.4 years) at the initial and follow-up visit was 0.47D (0.47D) and 0.31D (0.41D), in the non-myopes and -3.58D (2.08D) and -3.86D (2.14D) in the myopes, respectively. Significant increases in myopic refraction were observed. The group mean (SD) total HOA at the initial and final visit was 0.12 (0.08) and 0.11 (0.06) microns, in the non-myopes, and 0.15 (0.08) and 0.15 (0.08) microns, in the myopes, respectively. The group mean RMS of the coma at the initial and final visit was 0.06 (0.04) and 0.07 (0.05), in the non-myopes, and 0.08 (0.06) and 0.09 (0.06) microns, in the myopes, respectively. The group mean SA of the subjects at the initial and last visit was 0.04 (0.04) and 0.03 (0.03), in the non-myopes, and 0.04 (0.04) and 0.04 (0.04) microns, in the myopes, respectively.

CONCLUSIONS

There was a significant difference in myopic refraction, over the 9-month assessment period. However, no significant difference in total HOA, SA, and coma between the initial and follow-up visits in both the myopes and the non-myopes was observed.

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.

Influence of cycloplegia with topical cyclopentolate on higher-order aberrations in myopic children

PURPOSE

To investigate the influence of cycloplegia with topical cyclopentolate on wavefront aberrations in myopic children.

DESIGN

This is a prospective, comparative study.

METHODS

Twenty-eight myopic children with a mean age of 7.25 ± 2.55 were enrolled in this study. We evaluated refraction and wavefront aberrations before and after cycloplegia with 1% cyclopentolate hydrochloride. Ocular and corneal aberrations were simultaneously measured and compared with each other. Individual Zernike components were also analyzed up to the sixth order. All these parameters were compared before and after cycloplegia.

RESULTS

Ocular higher-order aberrations (HOAs) significantly increased after cycloplegia (P=0.012 for spherical-like and P=0.015 for total HOAs). Corneal HOAs did not change after cycloplegia. When corneal and ocular HOAs were compared, the ocular HOAs were significantly smaller than the corneal HOAs in spherical-like aberrations (P<0.001) and total HOAs (P=0.006). As for individual Zernike components, ocular aberration generally showed smaller or equivalent values in comparison with corneal aberration. In addition, each Zernike component showed a large standard deviation.

CONCLUSIONS

Internal optics compensates for corneal HOAs in myopic children, and paralysis of tonic accommodation with cyclopentolate considerably affects ocular HOAs. However, inter-individual variation in each Zernike component is quite large in myopic children.

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.

Diurnal variations in ocular aberrations of human eyes

PURPOSE

To investigate the diurnal variations in ocular wavefront aberrations over two consecutive days in young adult subjects.

MATERIALS AND METHODS

Measurements of both lower-order (sphero-cylindrical refractive powers) and higher-order (third and fourth-order aberration terms) ocular aberrations were collected for 30 young adult subjects at 10 different times over two consecutive days using a Hartmann-Shack aberrometer. Seventeen subjects were myopic and 13 were emmetropic. Five sets of measurements were collected each day at approximately 3 hourly intervals, with the first measurement taken at ∼9 am and the final measurement at ∼9 pm.

RESULTS

Spherical equivalent refraction (p = 0.029) and spherical aberration (p = 0.043) were both found to undergo significant diurnal variation over the two measurement days. The spherical equivalent was typically found to be at a maximum (i.e. most hyperopic) at the morning measurement, with a small myopic shift of 0.37 ± 0.15 D observed over the course of the day. The mean spherical aberration of all subjects (0.038 ± 0.048 μm) was found to be positive during the day and gradually became more negative into the evening, with a mean amplitude of change of 0.036 ± 0.02 μm. None of the other considered sphero-cylindrical refractive power components or higher-order aberrations exhibited significant diurnal variation over the two days of the experiment (p > 0.05). Except for the lower-order astigmatism at 90/180 degree (p = 0.040), there were no significant differences between myopes and emmetropes in the magnitude and timing of the observed diurnal variations (p > 0.05).

CONCLUSIONS

Significant diurnal variations in spherical equivalent and spherical aberration were consistently observed over two consecutive days of measurement. Research and clinical applications requiring precise refractive error and wavefront measurements should take these diurnal changes into account when interpreting wavefront data.

The effect of simulated normal and amblyopic higher-order aberrations on visual performance

PURPOSE

To study the effect of simulated amblyopic and normal higher-order aberrations on visual performance of normal eyes.

METHODS

To assess visual function, an adaptive optics visual simulator was used to compensate volunteers' ocular aberrations and simulate the wavefront aberration patterns found in healthy and amblyopic eyes in 7 healthy individuals. Visual acuity for high (100%), medium (50%), and low (10%) contrast and contrast sensitivity at 10, 20, and 25 cycles per degree (cpd) were measured after simulation of both pattern aberrations. The modulation transfer function and the point spread function were computed based on the aberration data. All measures were taken for 3 and 5.5 mm pupil sizes.

RESULTS

No statistically significant differences in visual acuity and contrast sensitivity were found between both groups for any analyzed contrast level, spatial frequency, and pupil size values. Mean logMAR visual acuity for a 3 mm pupil was -0.11 ± 0.04 for 100% contrast levels, -0.06 ± 0.06 for 50%, and 0.17 ± 0.07 for 10%. For a 5.5 mm pupil, the values were -0.06 ± 0.04 (100%), 0.00 ± 0.05 (50%), and 0.21 ± 0.06 (10%). Mean contrast sensitivity for a 3 mm pupil was 1.9 ± 0.2 for 10 cpd, 1.2 ± 0.15 for 20 cpd, and 0.9 ± 0.1 for 25 cpd. For a 5.5 mm pupil, contrast sensitivity was 1.4 ± 0.2 (10 cpd), 0.9 ± 0.2 (20 cpd), and 0.6 ± 0.2 (25 cpd). MTFs and PSFs were comparable in the two groups for both pupils.

CONCLUSIONS

The higher-order aberrations seen in idiopathic amblyopic eyes alone do not appear to contribute to the decreased visual function.

Population spherical aberration: associations with ametropia, age, corneal curvature, and image quality

PURPOSE

The aim of this analysis was to determine the total ocular wavefront aberration values of a large phakic population of physiologically normal, ametropic eyes, gathered under the same clinical protocol using the same diagnostic wavefront sensor.

MATERIALS AND METHODS

Studies were conducted at multiple sites in Asia, North America, Europe, and Australia. A Bausch + Lomb Zywave II Wavefront Aberrometer (Rochester, NY, USA) was used to measure the lower and higher order aberrations of each eye. Data analysis was conducted using linear regression analysis to determine the relationship between total spherical aberration, ametropia, age, corneal curvature, and image quality.

RESULTS

Linear regression analysis showed no correlation (r = 0.0207, P = 0.4874) between degree of ametropia and the amount of spherical aberration. There was also no correlation when the population was stratified into myopic and hyperopic refractive groups (r m = 0.0529, P m = 0.0804 and r h = 0.1572, P h = 0.2754). There was a statistically significant and weak positive correlation (r = 0.1962, P < 0.001) between age and the amount of spherical aberration measured in the eye; spherical aberration became more positive with increasing age. Also, there was a statistically significant and moderately positive correlation (r = 0.3611, P < 0.001) with steepness of corneal curvature; spherical aberration became more positive with increasing power of the anterior corneal surface. Assessment of image quality using optical design software (Zemax™, Bellevue, WA < USA) showed that there was an overall benefit in correcting the average spherical aberration of this population.

CONCLUSION

Analysis of this dataset provides insights into the inherent spherical aberration of a typical phakic, pre-presbyopic, population and provides the ability to determine what drives the spherical aberration of the eye, as well as what potential benefit a person could gain by compensating for that average spherical aberration.

Relationship between ocular wavefront aberrations and refractive error in Chinese school children

BACKGROUND

The relationship between ocular wavefront aberrations and refractive error in children's eyes remains controversial. The purpose of this study is to re-examine this relationship in Chinese school children under natural distance accommodation.

METHODS

Ocular wavefront aberrations were measured in 86 Chinese children with spherical equivalent refraction (SER) between +0.5 D and -6.0 D and astigmatism less than -1.00 D. Wavefront aberrations were calculated using an objective method based on the Hartmann-Shack principle. Refractive error was obtained using a phoropter after cycloplegia. Subjects were categorised into three groups based on the mean SER: emmetropia (SER from -0.50 D to +0.50 D), mild myopia (SER greater than -0.50 D to -3.00 D) and moderate myopia (SER greater than -3.00 D to -6.00 D). Of the 86 participants, 22 were emmetropic, 43 were mildly myopic and 21 were moderately myopic. The root mean square (RMS) values of higher-order aberrations, Zernike coefficients (third-, fourth- and fifth-order aberrations) and R(j) (the ratio of third-, fourth- or fifth-order aberrations to total higher-order aberrations) were compared across the three refractive groups.

RESULTS

No significant correlations were found between the RMS values of total higher-order aberrations, third-order aberrations, fourth-order aberrations, fifth-order aberrations, spherical aberration or coma and SER. No significant differences in the RMS values of total higher-order aberrations or R(j) were observed among the groups. The difference in fifth-order aberrations was statistically significant among the groups (p = 0.022); no other differences in higher-order aberration were found. Aside from C (3,1), no other differences were observed for Zernike coefficients.

CONCLUSION

Ocular wavefront aberrations are similar among Chinese school children with different refractive errors under natural accommodation for a distance target. There is no evidence that myopes have a different amount of ocular higher-order aberrations than emmetropes.

Ocular higher-order aberrations and mesopic pupil size in individuals screened for refractive surgery

AIM

To study the distribution of ocular higher-order aberrations(HOAs) and mesopic pupil size in individuals screened for refractive surgery.

METHODS

Ocular HOAs and mesopic pupil size were studied in 2 458 eyes of 1 240 patients with myopia, myopic astigmatism and compound myopic astigmatism and 215 eyes of 110 patients with hyperopia, hyperopic astigmatism and compound hyperopic astigmatism using the Zywave aberrometer (Busch& Lomb). All patients had correctable refractive errors without a history of refractive surgery or underlying diseases. Root-mean-square values of HOAs, total spherical aberration, total coma and mesopic pupil size were analyzed. Ocular HOAs were measured across a ≥ 6.0 mm pupil, and pupil size measurements were performed under the mesopic condition.

RESULTS

The mean values of HOAs, total spherical aberration and total coma in the myopic group were 0.369µm, ±0.233, 0.133± 0.112µm and 0.330±0.188µm, respectively. In the hyperopic group the mean values of HOAs, total spherical aberration and total coma were 0.418µm ±0.214, 0.202±0.209µm and 0.343±0.201µm, respectively. Hyperopes showed greater total HOAs (P<0.01) and total spherical aberration (P<0.01) compared to myopes. In age-matched analysis, only the amount of total spherical aberration was higher in the hyperopic group (P=0.05). Mesopic pupil size in the myopic group was larger (P≤0.05).

CONCLUSION

The results suggested that significant levels of HOAs were found in both groups which are important for planning refractive surgeries on Iranians. There were significantly higher levels of total spherical aberration in hyperopes compared to myopes. Mesopic pupil size was larger in myopic group.

Total ocular, anterior corneal and lenticular higher order aberrations in hyperopic, myopic and emmetropic eyes

Total ocular higher order aberrations and corneal topography of myopic, emmetropic and hyperopic eyes of 675 adolescents (16.9 ± 0.7 years) were measured after cycloplegia using COAS aberrometer and Medmont videokeratoscope. Corneal higher order aberrations were computed from the corneal topography maps and lenticular (internal) higher order aberrations derived by subtraction of corneal aberrations from total ocular aberrations. Aberrations were measured for a pupil diameter of 5mm. Multivariate analysis of variance followed by multiple regression analysis found significant difference in the fourth order aberrations (SA RMS, primary spherical aberration coefficient) between the refractive error groups. Hyperopic eyes (+0.083 ± 0.05 μm) had more positive total ocular primary spherical aberration compared to emmetropic (+0.036 ± 0.04 μm) and myopic eyes (low myopia=+0.038 ± 0.05 μm, moderate myopia=+0.026 ± 0.06 μm) (p<0.05). No difference was observed for the anterior corneal spherical aberration. Significantly less negative lenticular spherical aberration was observed for the hyperopic eyes (-0.038 ± 0.05 μm) than myopic (low myopia=-0.088 ± 0.04 μm, moderate myopia=-0.095 ± 0.05 μm) and emmetropic eyes (-0.081 ± 0.04 μm) (p<0.05). These findings suggest the existence of differences in the characteristics of the crystalline lens (asphericity, curvature and gradient refractive index) of hyperopic eyes versus other eyes.

The effects of spherical aberration on static accommodative responses in emmetropes and myopes

PURPOSE

To compare the effects of spherical aberration (SA) on accommodative responses between emmetropes (EMs), stable myopes (SMs), and progressing myopes (PMs).

METHODS

The accommodative responses (AR) induced by negative lenses from 0 to -5 D in 1 D steps were measured with a Complete Ophthalmic Analysis System (COAS) for 10 emmetropes (EMs), 13 stable myopes (SMs), and 9 progressing myopes (PMs). Three types of AR were calculated from wavefront aberration data based on ocular foci within a paraxial area, natural pupil area, and a 3.5 mm-diameter annular pupil area. The accommodative stimulus response curves (ASRCs) were compared between the three groups and between the three AR conditions.

RESULTS

The difference in the slope of ASRC was significant between the three AR conditions (p < 0.0001) but it was not significant between the three refractive groups. In each group, the slope of ASRC for the accommodative response measured within the paraxial area of the pupil (paraxial AR) was significantly steeper than that measured for the natural pupil (total AR) and also for that estimated for the 3.5 mm-diameter annular pupil (p < 0.01). The difference in the y-intercept of ASRC between the three AR conditions was also significant (p = 0.02) but not between the three refractive groups. The y-intercept of ASRC for paraxial AR was more positive than that for total AR in SMs (p < 0.01) and in PMs (p < 0.05); the y-intercept of ASRC for the 3.5 mm peripheral AR was more positive than that for total AR in SMs (p < 0.05).

CONCLUSIONS

The spherical aberration of the eye has a significant effect on the slope of ASRC and is less in PMs than in EMs and SMs.