Changes In Ocular Aberrations Research Articles

Comparison of changes in ocular aberrations with accommodation and accommodative facility

Aims/Purpose: This study aimed to analyse whether a relationship exists between subjectively measured monocular Accommodative Facility (AF), the magnitude of the revolution‐symmetric Zernike coefficients C20, C40 and C60, and the objectively measured Accommodative Response (AR).Methods: A total of 66 eyes, from 33 healthy young volunteers (26 women and 10 men) with a mean age of 25.12 ± 3.40 years (range age 20–30) participated in this study. Three measurements were made for each eye with the aberrometer Hartmann‐Shack (IRX3, Imagine Eyes, Orsay, France). The stimulus vergence was increased from 0 to 5 D (near vision) in steps of 0.5 D. The AR for each Zernike coefficient was calculated as the difference between the value at 5 D and the value at 0 D, for 4.0 mm pupil size. Monocular assessment of AF was assessed monocularly and conducted at 40 cm ± 2.00 D flippers. Statistical analysis was performed to determine a relationship between the Zernike coefficients, AR and AF. The coefficient of determination (R‐squared) was calculated to measure the proportional amount of variance.Results: The results showed that the highest values of R‐squared were obtained for the C20 coefficient measured at 5D of accommodation (R2 = 0.196, p < 0.01). Lower values were obtained for C40 and C60. The R‐squared values decreased from 0D (R2 = 0.097, p = 0.10) to 5D (R2 = 0.044, p = 0.60) for C40. However, there was an increase in R‐squared values from 0D (R2 = 0.0081, p = 0.47) to 5D (R2 = 0.058, p = 0.05) for C60.Conclusions: No clear trends were found when comparing the Zernike coefficients C20, C40 and C60, analysed in three stages of accommodative demand compared with the accommodative facility measured.The Zernikes coefficients analysed do not explain the differences in AF in this sample of young adult healthy eyes. However, there was found a trend that deserves further investigation.

Parafoveal and Perifoveal Accommodation Response to Defocus Changes Induced by a Tunable Lens

The accommodative response of the human eye is predominantly driven by foveal vision, but reacts also to off-foveal stimuli. Here, we report on monocular accommodation measurements using parafoveal and perifoveal annular stimuli centered around the fovea and extending up to 8° radial eccentricity for young emmetropic and myopic subjects. The stimuli were presented through a sequence of random defocus step changes induced by a pupil-conjugated tunable lens. A Hartmann–Shack wavefront sensor with an infrared beacon was used to measure real-time changes in ocular aberrations up to and including the fourth radial order across a 3 mm pupil at 20 Hz. Our findings show a significant reduction in accommodative response with increased radial eccentricity.

Optical changes and association with axial elongation in children wearing orthokeratology lenses of different back optic zone diameter

PurposeTo compare changes in ocular aberrations in children wearing orthokeratology (ortho-k) lenses with a back optic zone diameter (BOZD) of 6 mm (6-MM group) or 5 mm (5-MM group) and their associations with axial elongation (AE) over two years.MethodsSeventy Chinese children, aged 6 to < 11 years, with myopia between − 4.00 to − 0.75 D, were randomly allocated to 5-MM and 6-MM groups. Ocular aberrations were measured, rescaled to a 4-mm pupil, and fitted with a 6th order Zernike expansion. Measurements, including axial length, were taken prior to commencing ortho-k treatment and then every six months over two years.ResultsAfter two years, the 5-MM group displayed a smaller horizontal treatment zone (TZ) diameter (by 1.14 ± 0.11 mm, P < 0.001) and less AE (by 0.22 ± 0.07 mm, P = 0.002) compared with the 6-MM group. A greater increase in total root mean square (RMS) of higher-order aberrations (HOAs), primary spherical aberration (SA) ({mathrm{C}}_{4}^{0}), and coma were also observed in the 5-MM group at all follow-up visits. The horizontal TZ diameter was significantly associated with changes in RMS HOAs, SA (RMS, primary and secondary SA), and RMS coma. After controlling for baseline parameters, RMS HOAs, RMS SA, RMS coma, and primary ({mathrm{C}}_{4}^{0}) and secondary ({mathrm{C}}_{6}^{0}) SA were significantly associated with AE.ConclusionsOrtho-k lenses with a smaller BOZD created a smaller horizontal TZ diameter and a significant increase in total HOAs, total SA, total coma, and primary SA and a decrease in secondary SA. Of these ocular aberrations, total HOAs, total SA, and primary SA were negatively correlated with AE over two years.Trial registration: ClinicalTrial.gov, NCT03191942. Registered 19 June 2017, https://clinicaltrials.gov/ct2/show/NCT03191942.

Age-Related Changes in Ocular Aberrations and the Yamagata Study (Funagata).

Human vision quality is influenced by ocular aberrations, including astigmatism and higher-order aberrations (HOAs), in combination with other optical factors. In this study, we introduce the results and perceptions of previous studies investigating these aberrations. We also introduce our results obtained as part of the Yamagata Study (Funagata), a population-based epidemiologic study. To investigate the astigmatic change with age, researchers have used the power vector analysis, allowing incorporation of the magnitude and axis of astigmatism into statistical analyses. It was found that the axes of refractive astigmatism shift from with-the-rule toward against-the-rule with aging. It was demonstrated that the change in corneal curvature causes this shift. It was further reported that HOA increase is associated with deterioration of visual function. Some authors described that HOA increases with age in adults and that aging disrupts compensation between corneal and internal aberrations. Our study confirmed these results after considering possible confounding factors. HOA decreased from childhood to early adulthood and then increased with age, as modeled by a second-order polynomial regression. It is possible that the reduction in HOA is involved in emmetropization. In addition to age, HOA is known to be influenced by several factors, including pupil diameter, accommodation, and pupil shift. Although HOA increases with aging, the increase may be compensated by decreasing the pupil diameter. Better understanding of the causes of optical alterations with aging will improve the maintenance of vision quality.

Retinal image quality during accommodation

We asked if retinal image quality is maximum during accommodation, or sub-optimal due to accommodative error, when subjects perform an acuity task. Subjects viewed a monochromatic (552nm), high-contrast letter target placed at various viewing distances. Wavefront aberrations of the accommodating eye were measured near the endpoint of an acuity staircase paradigm. Refractive state, defined as the optimum target vergence for maximising retinal image quality, was computed by through-focus wavefront analysis to find the power of the virtual correcting lens that maximizes visual Strehl ratio. Despite changes in ocular aberrations and pupil size during binocular viewing, retinal image quality and visual acuity typically remain high for all target vergences. When accommodative errors lead to sub-optimal retinal image quality, acuity and measured image quality both decline. However, the effect of accommodation errors of on visual acuity are mitigated by pupillary constriction associated with accommodation and binocular convergence and also to binocular summation of dissimilar retinal image blur. Under monocular viewing conditions some subjects displayed significant accommodative lag that reduced visual performance, an effect that was exacerbated by pharmacological dilation of the pupil. Spurious measurement of accommodative error can be avoided when the image quality metric used to determine refractive state is compatible with the focusing criteria used by the visual system to control accommodation. Real focusing errors of the accommodating eye do not necessarily produce a reliably measurable loss of image quality or clinically significant loss of visual performance, probably because of increased depth-of-focus due to pupil constriction. When retinal image quality is close to maximum achievable (given the eye's higher-order aberrations), acuity is also near maximum. A combination of accommodative lag, reduced image quality, and reduced visual function may be a useful sign for diagnosing functionally-significant accommodative errors indicating the need for therapeutic intervention.

Changes in Accommodation and Ocular Aberration With Simultaneous Vision Multifocal Contact Lenses

The aim of this study was to evaluate ocular aberration changes through different simultaneous vision multifocal contact lenses (CLs). Eighteen young-adult subjects with a mean age of 29.8±2.11 years took part. Changes in accommodative response, spherical aberration (C(4)(0)), horizontal coma (C(3)(1)), vertical coma (C(3)(-1)), and root mean square (RMS) of higher-order aberrations (HOAs, third to sixth orders) were evaluated. Measurements were obtained with a distance-single vision CL and 2 aspheric multifocal CLs of simultaneous focus center-near design (PureVision Low Add and PureVision High Add) for 2 accommodative stimuli (-2.50 and -4.00 D). All measurements were performed monocularly with a Hartmann-Shack aberrometer (IRX-3; Imagine Eyes, Orsay, France). No statistically significant differences were found in accommodative responses to -2.50- and -4.00-D stimuli between the single vision CL and the 2 multifocal CLs. Spherical aberration was found to decrease and become more negative with accommodation for both stimuli with all three CLs. Horizontal coma decreased significantly with accommodation (-2.5- and -4.00-D stimuli) for the distance-single vision CLs (P=0.002 and P=0.003). No differences were found in vertical coma Zernike coefficients. The RMS of HOAs was found to decrease only with the single vision CLs for both stimuli (P<0.01). Data obtained in this study suggest that in young subjects, the multifocal CLs studied do not induce large changes in accommodative response compared with the distance-single vision CLs. Spherical aberration reduced significantly with accommodation.

The influence of downward gaze and accommodation on ocular aberrations over time

A Shack-Hartmann wavefront sensor was modified to allow measurement of ocular aberrations in downward gaze with binocular fixation. Subjects first performed a control task prior to four different trials involving a distance task or a near task (accommodative demand of 2.5 D) performed in primary and downward gaze (25°). Immediately after beginning and then again 5 and 10 min after the commencement of each trial, ocular aberrations were measured. To observe the recovery in ocular aberrations following each test condition, subjects again viewed a distance target in primary gaze and aberration measurements were taken at 0, 5, and 10 min. During the distance task, small but significant changes in refractive power and higher order aberrations were observed in downward gaze compared to primary gaze. The changes in ocular aberrations that occurred in downward gaze recovered almost immediately after shifting gaze from downward back to primary gaze. During the accommodation tasks, there was a significant influence of gaze for changes in primary spherical aberration C(4, 0) [p=0.004] and secondary spherical aberration C(6, 0) [p=0.02]. There was also a significant gaze by time interaction (p=0.04) for changes in C(6, 0). These findings show that ocular aberrations change from primary to downward gaze, particularly during accommodation.

Wavefront-Optimized Ablation Versus Topography-Guided Customized Ablation in Myopic LASIK: Comparative Study of Higher Order Aberrations

To compare the outcomes of wavefront-optimized ablation and topography-guided ablation in fellow eyes of patients undergoing laser in situ keratomileusis (LASIK) for myopia. This prospective study included 84 patients who underwent LASIK in both eyes: wavefront-optimized ablation in one eye (group I) and topography-guided ablation in the fellow eye (group II). The Moria2 microkeratome with a 110 single-use head (Moria, Antony, France) was used to create a superior hinged flap and the Allegretto Wave Excimer Laser (Alcon/Wavelight Light Laser Technologie GmbH, Erlangen, Germany) for photoablation. The Allegretto wave analyzer was used to measure the ocular aberrations before and 6 months after LASIK. Refractive visual outcomes and ocular aberration changes were compared between the two treatment modalities. Six months postoperatively, the mean uncorrected visual acuity of group II was statistically better than that of group I (P = .02). Seventy percent of group I and 83% of group II achieved a postoperative spherical equivalent refraction of ±0.5 diopters. The postoperative total root-mean-square of higher order aberrations (HOAs) of group II was smaller than that of group I, but the difference was not statistically significant (P = .51). There was a decrease in most of the individual terms of HOAs in group II, but it was only statistically significant in Z(3) (-1) (P = .04). The reverse occurred in group I, where most of the individual terms of HOAs increased, but it was not statistically significant. Significant improvement was only noted in Z(5) (3) (P = .05) and Z(5) (5) (P = .04). Both wavefront-optimized ablation and topography-guided ablation provided good refractive results, but the latter induced fewer HOAs.

Time Course of Changes in Ocular Aberrations After Instillation of Carteolol Long-Acting Solution and Timolol Gel-Forming Solution

To investigate the influence of 2% carteolol long-acting solution (long-acting carteolol) and 0.5% timolol gel-forming solution (timolol gel) on ocular wavefront aberrations. Ocular aberrations were assessed in the right eye of 24 healthy volunteers at baseline and at 2, 5, 10, and 15 min after instillation of long-acting carteolol, timolol gel or physiological saline using the Hartmann-Shack aberrometer. Ten serial measurements were taken over 10 s at each time point, and the root mean square (RMS) of second-, third-, fourth-, and total higher-order aberrations were calculated. The stability index and fluctuation index were also determined. Second-order aberrations did not change significantly after instillation of study eye-drops. Higher-order aberrations increased significantly after instillation of long-acting carteolol and timolol gel. Timolol gel induced significantly larger changes than long-acting carteolol in third-order RMS at 2 min (P = 0.001), fourth-order RMS at 2 (P < 0.001) and 5 (P = 0.013) min, and total higher-order RMS at 2 (P < 0.001) and 5 (P = 0.016) min after instillation, but not at 10 and 15 min after administration. Fluctuation index increased significantly after instillation of each eye-drop (P < 0.001), with significantly larger increases after timolol gel than long-acting carteolol at 2 min (P = 0.005) and 5 min (P = 0.011). No significant changes were observed in stability index. Both topical β blockers with a once-daily dosing regimen temporarily deteriorate optical quality of the eye by increasing higher-order aberrations, and the increases are much larger after instillation of timolol gel than long-acting carteolol.

Changes of ocular aberrations with gaze

The dependence of the ocular aberrations on gaze has been studied in three eyes using a fast-acquisition, Hartmann-Shack wavefront sensor. Although there were some trends in the change of some aberration terms with gaze, the changes of most Zernike coefficients were smaller than their variability at each individual gaze position, due to the combined effects of microfluctuations of accommodation, eye movements, tear film dynamics, and measurement noise. For our particular experimental dataset, the confidence level at which the null hypothesis (i.e. that the aberrations do not change significantly with gaze) can be rejected is very low. Further advances in the study of the dependence of eye aberrations with gaze will require a tighter control of the sources of aberration variability at each individual gaze position.

Age-Related changes in ocular aberrations with accommodation

This study investigates the changes in aberrations with monocular accommodation as a function of age. Second-order and higher order wavefront aberrations and pupil size were measured as a function of accommodation demand over the range of 0-4 D in the right eyes of 47 normal subjects with ages between 17 and 56 years. Higher order ocular Zernike aberrations were analyzed for the natural pupil size in terms of their equivalent defocus and were also determined for fixed pupil diameters of 4.5 mm in the unaccommodated eyes and 2.5 mm in the accommodating eyes. With relaxed accommodation (0 D accommodation stimulus), the major change with age was in the value of C4(0), which increased in positive value over the age range studied, although the total higher order RMS wavefront aberration did not increase. When the data were analyzed for natural pupils, spherical aberration was again found to change systematically in the positive direction with age. The equivalent defocus of total higher order RMS error for natural pupils showed no significant correlation with age (p > .05). With active accommodation, spherical aberration was found to decrease and become negative as the accommodative response increased in the younger subjects (<40 years). Near-zero spherical aberration was found at accommodation levels of about 0.50 D in the youngest subjects (<20 years) and at around 2-3 D in subjects between 20 and 39 years. In the older subjects (>40 years), the spherical aberration showed only small changes, some of which were positive, within the limited amplitude of accommodation available. Other higher order aberrations and the RMS of higher order aberrations did not appear to change systematically with accommodation, except in the oldest subjects. The change with age in the relationship between aberration and accommodation is interpreted in terms of the changing gradients of refractive index and surface curvatures of the crystalline lens.

The effect of ocular aberrations on steady-state errors of accommodative response

It is well accepted that the accommodation system is characterized by steady-state errors in focus. The purpose of this study was to correlate these errors with changes in ocular wavefront aberration and corresponding image quality when accommodating. A wavefront analyzing system, the Complete Ophthalmic Analysis System (COAS), was used in conjunction with a Badal optometer to allow continuous recording of the aberration structure of the eye for a range of accommodative demands (up to 8 D). Fifty consecutive recordings from seven subjects were taken. Monocular accommodative response was calculated as (i) the equivalent refraction minimizing wavefront error and (ii) the defocus needed to optimize the modulation transfer function at high spatial frequencies. Previously reported changes in ocular aberrations with accommodation (e.g., the shift of spherical aberration to negative values) were confirmed. Increased accommodation errors for near targets (lags) were evident for all subjects, although their magnitude showed a significant intersubject variability. It is concluded that the one-to-one stimulus/response slope in accommodation function should not always be considered as ideal, because higher order aberrations, especially changes of spherical aberration, may influence the actual accommodative demand. Fluctuations may serve to preserve image quality when errors of accommodation are moderate, by temporarily searching for the best focus.

Changes in ocular aberrations after instillation of artificial tears in dry-eye patients

Purpose: To study the effect of artificial tear instillation on ocular aberrations in dry-eye patients. Setting: Research, Development and Innovation Department, Instituto Oftalmológico de Alicante, Alicante, Spain. Methods: Ocular aberrations (total, spherical-like, and coma-like) were measured with a Hartmann-Shack aberrometer before and after artificial tear instillation (immediately and 10 minutes later) in 15 eyes of 15 dry-eye patients. Results: Optical aberrations showed a statistically significant reduction after artificial tear instillation ( P<.01). Total aberrations decreased on average by a factor of 2 to 3 times immediately after instillation; the reduction was maintained after 10 minutes ( P>.01). Conclusions: After artificial tear instillation, the reduction in optical aberrations associated with an increasingly irregular tear film may cause an improvement in the optical quality of dry eyes. Wavefront analysis facilitates the evaluation of improvement in optical quality after artificial tear instillation in patients with dry eye.

The effect of corneal flap on optical aberrations

Purpose To evaluate the changes in ocular aberrations induced by corneal flap creation. Design Prospective interventional nonrandomized clinical trial. Methods This study included 15 patients who were scheduled for laser in situ keratomileusis. A nasal hinge flap was created, using the Nidek MK-2000 microkeratome and then replaced without performing laser ablation. The ocular aberrations were measured before and after flap creation using the Nidek Optical Path Difference Scanning System ARK-10000. Results The root mean square wavefront errors of the higher-order optical aberrations (third-, fourth-, fifth-, and sixth-order aberrations) were not significantly altered at 1 week postsurgery compared with the preoperative values ( P > .35). Conclusions Creating a corneal flap with the Nidek MK-2000 microkeratome did not induce changes in higher-order optical aberrations as measured with the Nidek Optical Path Difference Scanning System ARK-10000 during the early postoperative period.

Spatially variant changes in lens power during ocular accommodation in a rhesus monkey eye.

This study investigated the changes in ocular aberrations that occur over the entire lens equatorial diameter during accommodation in iridectomized rhesus monkey eyes to understand the nature of accommodative lenticular deformation. Accommodation was centrally stimulated to a range of different response amplitudes (0 D to approximately 11 D), and ocular aberrations were measured with a Shack-Hartmann wavefront sensor in both eyes of one previously iridectomized 10-year-old rhesus monkey. At the highest amplitude in the two eyes, aberrations were analyzed over entrance pupil diameters ranging from 3 to 8 mm in steps of 1 mm. Root mean square error of the total measured aberrations, excluding defocus, increased systematically with increasing accommodation from about 1 to 3.5 microns. Spherical aberration became systematically more negative, and vertical coma increased significantly in magnitude with accommodation. There was a strong accommodative change in power near the center of the lens and little change in power at the periphery. At the highest accommodative state, decreasing the analyzed entrance pupil diameter from 8 to 3 mm considerably reduced the wavefront error. The greater increase in optical power near the central region of the lens, combined with an accommodative pupillary miosis, would serve to maximize accommodative refractive change while maintaining acceptable image quality.

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.

Changes in ocular aberrations during accommodation in rhesus monkeys

Changes in ocular aberrations during accommodation in rhesus monkeys

Are optical aberrations during accommodation a significant problem for refractive surgery?

To study the limits to a perfect ideal customized wavefront correction due to the change of aberrations during accommodation. METHODS. We measured the dynamic changes of ocular aberrations during accommodation in normal eyes with a real-time Hartmann-Shack wavefront sensor. Those results were used in computer simulations to predict the benefit of a perfect customized correction. Due to the continuous changes of the aberrations over time, an ideal perfect static correction will not provide stable aberration-free optics. For example, when the eye accommodates to near objects, due to the changing aberrations, the eye will become aberrated again. An alternative correction using the aberration pattern for a slightly accommodated condition could provide a better-correction in a larger accommodative range, although at the cost of non-perfect correction for far vision. Due to the dynamic nature of ocular optics, a static perfect correction, for instance performed in customized refractive surgery, would not remain perfect for every condition occurring during normal accommodation.

Are changes in ocular aberrations with age a significant problem for refractive surgery?

We discuss current knowledge about the change of aberrations with aging, cataract surgery, and laser in situ keratomileusis (LASIK) for myopia. Based on this evidence, we speculate about the long-term expectations for postoperative LASIK eyes in terms of aberrations. Standard myopic LASIK surgery produces a significant increase in aberrations, particularly corneal spherical aberration, which changes to positive values. Aberrations increase with age, and in particular, the spherical aberration of the crystalline lens shifts toward positive values. Therefore, no compensatory effect is expected to occur with age after standard myopic LASIK, but rather the unusually high amount of aberrations in postoperative LASIK patients is expected to worsen with age. The amount of aberrations in patients after cataract surgery with implantation of standard intraocular lenses (IOLs) is higher than in normal young subjects. If an ideal customized ablation (not inducing aberrations and reducing naturally existing aberrations) is ever possible, the perfect correction will not last (due to the change of aberrations with age), and aberrations of the crystalline lens corrected on the cornea are likely to reappear after conventional cataract surgery. Potential benefits of customized IOLs for cataract surgery and improved optics in older patients are discussed.