Hartmann-Shack Wavefront Aberrometer Research Articles

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

PurposeTo examine the associations between higher order aberrations (HOAs), visual performance, demographics, and ocular characteristics in a young Asian population with high myopia. MethodsThis 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). Results522 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). ConclusionsGreater 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.

Higher order aberrations and retinal image quality during short-term accommodation in children

Changes in higher order aberrations (HOA’s) and retinal image quality during accommodation have not previously been examined in children. This study measured ocular HOA’s in ninety non-myopic, school-aged children during short-term accommodation tasks at 0, 3, 6, and 9 D demands presented via a Badal optometer mounted to a Hartmann-Shack wavefront aberrometer (COAS-HD, Wavefront Sciences). Eighty-four participants who exhibited active accommodation were included in the analyses. An eighth order Zernike polynomial was fit across a 2.3 mm, 4 mm, and natural pupil diameter to evaluate changes in refractive power vectors (M, J180, and J45), accommodation errors (lags and leads), HOA root mean square (RMS) variables, individual Zernike coefficients, and the visual Strehl ratio based on the optical transfer function (VSOTF). All HOA RMS variables changed significantly with accommodation, with the greatest change observed for the 9 D demand. Of the individual Zernike coefficients, primary (C40) and secondary spherical aberration (C60) exhibited the greatest magnitude of change, becoming negative and positive with increasing accommodation, respectively. The VSOTF changed significantly with greater accommodation for both the 4 mm and natural pupil size, becoming significantly worse for the 9 D demand. HOA’s increase and retinal image quality decreases significantly during higher levels of accommodation in children, similar to adults. These findings provide a greater understanding of the optical properties of children’s eyes and insights into possible mechanisms for the association between accommodation, near work, and refractive error development.

Insufficient accommodation during binocular near viewing in eyes with intermittent exotropia.

To investigate the changes in spherical equivalent and pupil response during near viewing in patients with intermittent exotropia (IXT) who have complaints of blurred vision or asthenopia from near viewing in daily life using a novel binocular wavefront aberrometer. A cross-sectional study. Ten IXT patients and ten healthy subjects wearing full-correction lenses at far sight (5 m) were instructed to fixate on a near target at 67 cm, which was then moved to 40 cm three times. Serial changes in the spherical equivalent (SE) refractive error (SE) were measured during this task using a laboratory-made open-field binocular Hartmann-Shack wavefront aberrometer and compared between patients and healthy subjects. In the IXT patients, regression analysis was performed between ∆SE and exodeviation angles, as measured by an alternate prism and cover test. Pupil-diameter and pupil-constriction ratios were also compared between patients and healthy subjects, and the correlation of constriction ratio with ∆SE was calculated for both groups. Compared to healthy subjects, IXT patients demonstrated significantly lower ∆SE of convergence (mean ± SD, 0.91 ± 0.26 D vs. 1.15 ± 0.19 D; P < 0.05) and divergence (0.93 ± 0.28 D vs. 1.16 ± 0.20 D; P < 0.05). Angle of exotropia was negatively correlated with ∆SE during far-sight and near-sight convergence and divergence (P < 0.05). Pupil-constriction ratio was also reduced in patients compared to healthy subjects (6.67% ± 3.31% vs. 11.9% ± 5.96%; P<0.05). Pupil-constriction ratio was positively correlated with ∆SE during convergence in both groups (P < 0.05). Insufficient accommodation and pupil constriction during near viewing were observed in patients with IXT who had complaints of blurred vision or asthenopia from near viewing. These conditions might contribute to symptoms, such as fatigue, eye strain and impaired visual performance.

Nonlinear refractive index of electric field aligned gold nanorods suspended in index matching oil measured with a Hartmann-Shack wavefront aberrometer.

The capability to dynamically control the nonlinear refractive index of plasmonic suspensions may enable innovative nonlinear sensing and signaling nanotechnologies. Here, we experimentally determine the effective nonlinear refractive index for gold nanorods suspended in an index matching oil aligned using electric fields, demonstrating an approach to modulate the nonlinear optical properties of the suspension. The nonlinear optical experiments were carried out using a Hartmann-Shack wavefront aberrometer in a collimated beam configuration with a high repetition rate femtosecond laser. The suspensions were probed at 800 nm, overlapping with the long-axis absorption peak of the nanorods. We find that the effective nonlinear refractive index of the gold nanorods suspension depends linearly on the orientational order parameter, S, which can be understood by a thermally induced nonlinear response. We also show the magnitude of the nonlinear response can be varied by ∼ 60%.

Evaluation of the SVOne Handheld Autorefractor in a Pediatric Population

The SVOne is a portable, Hartmann-Shack wavefront aberrometer, which can be attached to a smartphone to determine the refractive error of the eye objectively. Previous results have shown the device to provide measurements equivalent to those of standard clinical techniques in young, healthy adults. The aim of the present study was to compare the findings of the SVOne with retinoscopy, subjective refraction, and two commercially available autorefractors (Retinomax-3 and WAM-5500) in a pediatric population. The refractive error of the right eye was assessed both without and with cycloplegia in 40 visually normal children between 5 and 17 years of age (mean age = 11.3 years) using the five techniques described above. Further, to assess repeatability of the instruments, the entire procedure was repeated in a subgroup of five subjects. All data were analyzed in terms of power vectors (M, J0, and J45). No significant difference was observed between the mean values of M (spherical equivalent) for the different techniques. Retinoscopy showed the best agreement with subjective refraction, both without and with cycloplegia, followed by the open-field WAM-5500. The most repeatable procedures, when measured without and with cycloplegia, were the WAM-5500 and retinoscopy, respectively. Measurements with the SVOne showed a decline in repeatability under cycloplegia. The results indicate that the SVOne provides measurements of refractive error in a normal, pediatric population that are not significantly different from other subjective and objective procedures. Accurate alignment along the visual axis, especially when measuring through a dilated pupil, is critical. This instrument is valuable for vision screenings, for examinations taking place outside the clinical office, and a starting point for the refractive assessment.

Correlations between Corneal and Internal Wavefront Aberrations through Zernike Coefficients Analysis

Objectives: To examine corneal aberrations are offset by internal aberrations more closely, the Zernike coefficients of corneal aberrations and internal aberrations were compared and analyzed. Methods/Statistical Analysis: Measurements of higher-order aberrations were performed with KR-9000 PW (Topcon Corp., Japan), a Hartmann-Shack Wavefront aberrometer. The coefficients from the 2nd to 4th expressions on Zernike Polynomials were analyzed for cornea and internal optics within 6mm measurement zone. 342 healthy eyes of 171 young adults who have never received eye surgery and do not wear contact lenses were selected as subjects of this study. Findings: There were significant negative correlations among all Zernike coefficients of corneal and internal aberrations. In Z31(r=-0.887, p=0.00), Z4-4(r=-0.698, p=0.00), and Z44(r=-0.688, p=0.00), there were high correlations between corneal and internal aberrations. On the other hand, the correlation coefficients of Z20 and Z22 that belonged to lower-order aberration were very weak at -0.129 and -0.136 respectively, having almost no correlation. Improvements/Applications: Since some signs of their Zernike coefficients are different, it is considered necessary to analyze not the both eyes but a single eye to identify the accurate RMS values of each Zernike coefficients and not only the correlations.

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.

A modified Hartmann–Shack aberrometer for measuring stray light in the anterior segment of the human eye

To examine the use of a modified Hartmann-Shack wave front aberrometer (WASCA; Carl Zeiss Meditec AG, Germany) to measure objective stray light caused by forward light scatter from the anterior segment of the human eye. HELIOS Klinikum Erfurt/Institute of Biomedical Engineering and Informatics, Ilmenau University of Technology, Germany. Scatter parameters, including the Michelson contrast and cross-sectional area at half height (CAHM) were examined in Hartmann-Shack images from ten subjects with a cataract in one eye and an intraocular lens (IOL) in the other. The parameters were compared between each eye. Light scatter was then measured in 40 healthy subjects (age range, 23-75 years) with spherical ametropia ranging from -0.25 to 0.25 diopters. The subjects were divided into three age groups; 23-35, 36-50, and 51-75 years. Light scatter was also measured using four alternative methods. CAHM and contrast were significantly different between the eyes with the cataract and the IOL (P = 0.007 and P = 0.004, respectively). CAHM (r = 0.557, P < 0.001) and contrast (r = -0.467, P < 0.001) were both significantly correlated with age. There were significant differences in CAHM and contrast between the age groups. The modified wave front aberrometer can be used to measure stray light, although its diagnostic sensitivity in individual patients must be improved.

Serial measurements of accommodation by open-field Hartmann–Shack wavefront aberrometer in eyes with accommodative spasm

To investigate the serial changes of accommodation and spherical aberration in eyes with accommodative spasm. Four patients with accommodative spasm and ten healthy subjects were studied. The ocular refractive power (spherical equivalent) and spherical aberration were measured serially with an open-field, binocular Hartmann-Shack wavefront aberrometer. Patients and subjects wore full-correction lenses and were instructed to fixate a target set at 50 cm from the eye. The time-average of the refractive power, spherical aberration, and fluctuations of accommodation analyzed by the fast Fourier transform (FFT) of the two groups were compared. The average ± standard deviation refractive power in the patients was significantly more negative than that in the healthy subject (-3.12 ± 1.06 vs. -1.49 ± 0.17 D). The integrated intensity of the FFT from 1 to 4 Hz was significantly higher in the patients than in the healthy subjects. The spherical aberration in patients was more negative than that in the healthy subjects (-0.033 ± 0.048 μm vs. 0.002 ± 0.027 μm). Eyes with accommodative spasm are characterized by a lead of accommodation with greater fluctuations and negative spherical aberrations. Excessive accommodation can be measured objectively in such eyes with a binocular wavefront aberrometer without cycloplegics.

Wavefront-guided refractive surgery results of training-surgeons

To assess clinical outcomes and changes on higher-order aberrations (HOA) after wavefront-guided laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) for correction of myopia and myopic astigmatism performed by training-surgeons. One hundred and seventy patients had customized LASIK (207 eyes) and PRK (103 eyes) performed by surgeons in-training using the LADARVision 4000 (Alcon, Fort Worth, TX). Preoperative and 1, 3, 6 and 12 months postoperative data of spherical equivalent (SE), best spectacle-corrected visual acuity (BSCVA) and uncorrected visual acuity (UCVA) were analysed. Wavefront changes were determined using the LADARWave Hartmann-Shack wavefront aberrometer and the pupil size was scaled for 6.5 mm. The mean SE in the LASIK group was -3.04 ±1.07 D and in the PRK group was -1.60 ± 0.59 D. At 1-year follow-up, (80.6%) (LASIK) and (66.7%) (PRK) were within ± 0.50 D of the intended refraction. The UCVA was 20/20 or better in (58.1%) (LASIK) and (66.7%) (PRK) of the operated eyes. A statistically significant positive correlation was found between achieved versus attempted refractive correction in both groups: LASIK (r=0.975, P<0.0005) and PRK (r=0.943, P<0.005). The higher-order aberrations (HO) RMS and coma did not changed significantly in the PRK group between preoperative and 1-year follow-up. In the LASIK group the HO RMS and coma changed between preoperative and 1-month postoperative but remained statistically unchanged during 1-year follow-up. The spherical aberration showed statistically significant changes in both groups. Wavefront-guided LASIK and photorefractive keratectomy performed by training-surgeons were found to be similarly effective, predictable and stable.

Intensity Analysis of Hartmann-Shack Images in Cataractous, Keratoconic, and Normal Eyes to Investigate Light Scattering

A clinical investigation of novel methods for evaluating light scattering using a Hartmann-Shack aberrometer. Aberrometry was performed on normal eyes (n=7; patient age, 26.7+/-2.5 years, mean+/-SD), eyes with keratoconus (n=22; patient age, 26.1+/-8.1 years), and eyes with cataract (n=17; patient age, 56.5+/-16.9 years) using a Hartmann-Shack wavefront aberrometer. We introduced two methods: (1) a contrast method, in which we calculated the inverse of contrast of the local images around 12 spots in a Hartmann-Shack image, and (2) a difference of point spread function (PSF) method, in which we analyzed the difference between the width of the PSF computed with aberration information and the width of the measured PSF, which contains both aberration and light scattering information. The inverse contrast in cataractous eyes (5.04+/-3.06 inverse contrast units) was significantly larger than that in normal eyes (1.57+/-0.56) or keratoconic eyes (1.83+/-0.79). The difference of PSF in cataractous eyes (81.8+/-65.2 microm) was also significantly larger than that in normal eyes (9.3+/-4.3 microm) or keratoconic eyes (30.0+/-20.1 microm). The inverse contrast and the difference in the PSF were highly correlated (r=0.89, P<0.0001). The two methods introduced here successfully distinguished cataractous eyes from normal and keratoconic eyes. After the results were analyzed by a discriminant analysis, the separation of the three categories proved to be excellent.

Influence of wavefront aberration and corneal subepithelial haze on low-contrast visual acuity after photorefractive keratectomy

To assess low-contrast visual acuity (LCVA) after photorefractive keratectomy in relation to ocular higher-order wavefront aberration and corneal subepithelial haze. Prospective, cross-sectional analysis. Photorefractive keratectomy was performed in 51 eyes of 27 subjects with myopic refractive error of -2.0 to -10.5 diopters. Ocular higher-order wavefront aberrations for a 4-mm pupil were measured using Topcon Hartmann-Shack wavefront aberrometer, and the extent of corneal subepithelial haze was quantified with Nidek TSPC-3 hazemeter before and 1 month after photorefractive keratectomy. Low-contrast visual acuity was recorded with Vector Vision CSV-1000LanC10% chart. Total higher-order, third-order (coma-like), and fourth-order (spherical-like) aberrations of the eye were determined. The influence of wavefront aberration and corneal subepithelial haze on LCVA was analyzed. Total higher-order, third-order, and fourth-order aberrations significantly increased by surgery (P < .001, Wilcoxon signed rank test). Photorefractive keratectomy induced a significant increase in corneal haze (P < .01), but no case presented severe corneal haze (grade 3 or greater by Fantes grading). By surgery, LCVA was reduced significantly (P < .001). The logarithm of the minimal angle of resolution LCVA showed a significant correlation with total higher-order aberration (Spearman rank correlation coefficient, r(s) = 0.642, P < .0001). Both third-order (r(s) = 0.618, P < .0001) and fourth-order aberrations (r(s) = 0.552, P < .0001) also significantly correlated with logarithm of the minimal angle of resolution LCVA. There was no correlation between the degree of corneal haze and logarithm of the minimal angle of resolution LCVA (r(s) = 0.094, P = .523). In eyes with mild to moderate corneal haze after photorefractive keratectomy, deterioration of LCVA is mainly attributable to increases in wavefront aberration, and not to corneal haze.

Age-related changes in corneal and ocular higher-order wavefront aberrations

PurposeTo investigate age-related changes in ocular and corneal higher-order wavefront aberrations and elucidate relative contributions of the cornea and the lens in the age-related changes. DesignObservational case series. MethodsCorneal and ocular higher-order wavefront aberrations in the central 6 mm diameter were measured with videokeratography and the Hartmann-Shack wavefront aberrometer in 75 normal eyes of 75 patients with a mean age of 43.5 ± 11.7 years (range, 18–69 years). Higher-order wavefront aberrations were calculated with Zernike polynomials up to sixth order. From the Zernike coefficients, we calculated root mean square (RMS) of coma and spherical aberration. To examine age-related changes of the polarity of spherical aberration, the changes of the Zernike coefficient Z40 was also investigated. ResultsBoth corneal (r = .307, P = .007) and ocular (r = .334, P = .0033) coma RMS showed positive correlations with age. There was a positive correlation between corneal and ocular coma RMS (r = .468, P < .0001). The RMS of corneal spherical aberration did not change with aging (r = .153, P = .1895), whereas the RMS of ocular spherical aberration had a positive correlation with aging (r = .308, P = .0068). ConclusionsThese results suggest that the ocular coma increases with age, mainly because of the increase in the corneal coma, and the ocular spherical aberration increases with age, mainly because of the increase in the spherical aberration in the internal optics.

Wavefront analysis in eyes with accommodative spasm

Purpose To investigate changes of spherical aberration in eyes with accommodative spasm. Design Case reports. Methods Four eyes of two patients with accommodative spasm were studied. Ocular spherical aberration was measured with a Hartmann-Shack wavefront aberrometer for the central 4-mm zone. Results The root mean square values of spherical aberration were negative (−0.086 ± 0.026 μm root mean square). However, when the spasm of accommodation was cured or treated with a cycloplegic agent, the value shifted toward positivity (0.025 ± 0.004 μm root mean square). Conclusions Excessive accommodative tone is manifested objectively by negative spherical aberration in eyes with accommodative spasm.

Changes of ocular aberration with accommodation

Purpose To study the effect of accommodation on ocular aberrations. Design Observational case series. Methods The ocular aberrations in 33 eyes of 33 young adults were measured with a Hartmann–Shack wavefront aberrometer before and during 3 diopters of accommodation. Results The root mean square values of wavefront error did not change for a 4-mm and a 6-mm zone; however, spherical aberration changed significantly toward negativity for both the 4-mm zone ( P < .001) and 6-mm zone ( P = .022). Conclusions During accommodation, the significant change in spherical aberration occurs without a change of image quality. Therefore, for customized aberration, it may not be advantageous to eliminate the physiologic spherical aberration for far vision.