Corneal higher-order aberrations induced by overnight orthokeratology

BCLA CLEAR Presbyopia: Management with corneal techniques

Corneal techniques for enhancing near and intermediate vision to correct presbyopia include surgical and contact lens treatment modalities. Broad approaches used independently or in combination include correcting one eye for distant and the other for near or intermediate vision, (termed monovision or mini-monovision depending on the degree of anisometropia) and/or extending the eye's depth of focus [1]. This report reviews the evidence for the treatment profile, safety, and efficacy of the current range of corneal techniques for managing presbyopia. The visual needs and expectations of the patient, their ocular characteristics, and prior history of surgery are critical considerations for patient selection and preoperative evaluation. Contraindications to refractive surgery include unstable refraction, corneal abnormalities, inadequate corneal thickness for the proposed ablation depth, ocular and systemic co-morbidities, uncontrolled mental health issues and unrealistic patient expectations. Laser refractive options for monovision include surface/stromal ablation techniques and keratorefractive lenticule extraction. Alteration of spherical aberration and multifocal ablation profiles are the primary means for increasing ocular depth of focus, using surface and non-surface laser refractive techniques. Corneal inlays use either small aperture optics to increase depth of field or modify the anterior corneal curvature to induce corneal multifocality. In presbyopia correction by conductive keratoplasty, radiofrequency energy is applied to the mid-peripheral corneal stroma, leading to mid-peripheral corneal shrinkage and central corneal steepening. Hyperopic orthokeratology lens fitting can induce spherical aberration and correct some level of presbyopia. Postoperative management, and consideration of potential complications, varies according to technique applied and the time to restore corneal stability, but a minimum of 3 months of follow-up is recommended after corneal refractive procedures. Ongoing follow-up is important in orthokeratology and longer-term follow-up may be required in the event of late complications following corneal inlay surgery.

Changes in the Objective Vision Quality of Adolescents in a Mesopic Visual Environment After Wearing Orthokeratology Lenses: A Prospective Study

PURPOSE

This study aimed to investigate changes in objective vision quality in mesopic environments in teenagers with myopia after wearing orthokeratology (OK) lenses.

METHODS

This prospective clinical study included 45 patients (80 eyes) who received OK lenses at the First Affiliated Hospital of Jinan University from March 2021 to September 2021. An Optical Path Difference-Scan III refractive power/corneal analyzer was used to determine the corneal topographic parameters (corneal e, corneal Q, surface asymmetry index (SAI), and surface regularity index (SRI)), higher-order aberrations (HOAs), axial length (AL) change, lens decentration, induced astigmatism, target power, and Strehl ratio (SR) in a mesopic visual environment after wearing OK lenses for 6 months. In addition, corneal morphological parameters, HOAs, and SR were analyzed in a mesopic visual environment. Finally, we investigated the correlations among corneal morphology, HOAs, AL change, lens decentration, induced astigmatism, and SR.

RESULTS

The SAI value was significantly higher (P<0.01), and the corneal e was significantly lower (P<0.01), in a mesopic visual environment after wearing OK lenses for 1 week than baseline. A significant increase was observed in total HOAs and spherical aberrations, compared with before the OK lenses were worn (P<0.01). In addition, SR in the mesopic visual environment decreased significantly after wearing the lenses (P<0.01). No significant differences were observed (P>0.05) among the 1-week, 1-month, 3-month, and 6-month follow-up findings. After 6 months, AL and lens decentration did not differ significantly compared with before (P>0.05), whereas induced astigmatism significantly increased (P<0.05). Negative correlations were observed between corneal Q, SAI, SRI, HOAs, induced astigmatism, and SR, and positive correlations were found between corneal e, AL change, lens decentration, and SR, after wearing OK lenses.

KEY POINTS

• Wearing orthokeratology lenses significantly altered corneal morphology and HOAs in myopic teenagers within 1 week. • The changes that we observed in the eyes of adolescents with myopia after wearing orthokeratology lenses decreased vision quality in mesopic environments. • Strehl ratio is significantly correlated with multiple parameters, including HOAs, AL change, and lens decentration.

CONCLUSIONS

In teenagers with myopia wearing OK lenses, significant changes in vision quality and corneal morphology were observed, leading to increased aberrations and affecting optical imaging quality. Furthermore, SR is significantly correlated with multiple parameters, including HOAs, AL change, and lens decentration.

REGISTRATION NUMBER

This study is registered with the United States Clinical Trials Registry under registration number NCT04929119.

Analysis of Treatment Discontinuation in Orthokeratology: Studying Efficacy, Safety, and Patient Adherence Over Six Months

PURPOSE

This study aimed to evaluate the efficacy, safety, and participant compliance of orthokeratology treatment for the correction of myopic refractive errors over a six-month prospective study and to define the potential reasons for early treatment discontinuation.

METHODS

A total of 32 participants with low-to-moderate myopia were fitted with the spherical model of corneal refractive therapy (CRT) orthokeratology lenses (Paragon Vision Sciences) and followed over six months, with specific attention to alterations in refractive error, corneal topography, and epithelial thickness. Concurrently, participant feedback and reasons for any treatment discontinuation were documented.

RESULTS

Significant changes in refractive error and in corneal topography were observed, with approximately 50% of the refractive error being corrected on the first night of use and 100% by the first two weeks (P<0.001). Central epithelial thickness experienced substantial thinning, reducing to 15.65±4.49 μm (67.38%) (P<0.001) after 6 months of lens use. Six participants withdrew from this study for varied reasons, including unmet visual expectations and difficulty adhering to the lens-wearing regimen. Notably, the dropout group exhibited higher baseline low-order aberrations and less prolate corneas than those who persisted with the treatment (P<0.05).

CONCLUSION

Orthokeratology with CRT is efficacious and safe for the correction of low-to-moderate myopia in adults, but a portion of patients discontinue the treatment in the first 6 months of contact lens wear. Special care should be taken when recommending orthokeratology in patients with higher levels of myopia and corneas with less prolate shape, providing more realistic expectations and even changing to dual axis or more sophisticated designs.

Higher-Order Aberrations and Visual Performance in Myopic Children Treated With Aspheric Base Curve-Designed Orthokeratology

OBJECTIVES

To investigate the impact of aspheric base curve (BC)-designed orthokeratology (ortho-k) (AOK) lenses on higher-order aberrations (HOA) at different pupil diameters and visual performance.

METHODS

This prospective clinical study included subjects randomized to wear spherical BC-designed ortho-k (SOK) or AOK lenses. The Pediatric Refractive Error Profile (PREP) questionnaire was completed before and after 3 months of lens wear. The Strehl ratio (SR) and root mean square of ocular higher-order aberrations (HOAs), spherical aberration (SA), coma, and trefoil were measured under 4-mm, 5-mm, and 6-mm pupil diameters at baseline and 3-month visits. Corneal topography, uncorrected low-contrast (LC) visual acuity (VA), and high-contrast (HC) VA were measured at baseline and at 1 day, 1 week, 1 month, and 3 month follow-ups.

RESULTS

Sixty-five participants completed the study. After 3 months with the ortho-k lens, there were no significant differences in ocular HOA, SA, coma, or trefoil between the SOK group and AOK group at 4-mm, 5-mm, and 6-mm pupil diameters (all P>0.05), except for a significant increase in SA in the AOK group (P=0.01). Stratified analyses showed that the AOK group exhibited greater HOA and SA at 5-mm and 6-mm pupil diameters in the lower myopia subgroup and greater SA at 6 mm in the higher myopia subgroup (all P<0.05). There were no significant differences between the groups in SR, HC VA, LC VA, or PREP scores (all P>0.05).

CONCLUSION

Aspheric BC-designed ortho-k lenses produced a significantly greater SA than SOK lenses, with more significance at lower diopters, without sacrificing subjective visual performance.

The effect of back optic zone diameter on relative corneal refractive power distribution and corneal higher-order aberrations in orthokeratology

PURPOSE

To compare axial elongation, relative corneal refractive power (RCRP) distribution within the pupillary diameter, and corneal higher-order aberrations (HOAs) in myopic children wearing orthokeratology (ortho-k) lenses with different back optic zone diameters (BOZD).

METHODS

Children aged 8-11 years were fitted with 5.0 or 6.2 mm-BOZD ortho-k lenses (groups A and B, respectively). Axial length (AL) and corneal topography were measured at baseline and during the annual visit. RCRP and corneal HOAs were compared between the two groups after one-year treatment. Multivariate linear regression analysis was performed to determine the association between AL elongation and RCRP parameters, corneal HOAs, and other variables between the groups.

RESULTS

After one-year treatment, axial elongation was slower in group A than in group B, with a difference of 0.15 mm. Children in group A showed smaller treatment zone size, smaller 3/4X value (describing the distance from the apex RCRP profile rising to its three-quarter-peak level), greater RCRP sum value within the pupillary area, and higher increases in corneal total HOAs and horizontal coma (Z₃¹). AL elongation was significantly correlated with baseline age, baseline spherical equivalent refraction (SER), treatment zone size, and 3/4X value.

CONCLUSIONS

Ortho-k lenses designed with smaller BOZD increased myopia control efficacy, induced a steeper distribution of the RCRP profile within the pupillary diameter, and induced greater increases in corneal total HOAs and horizontal coma (Z₃¹). Lens-induced RCRP profile within pupillary diameter, rising to its three-quarter-peak level at a smaller distance, may show a better myopia control effect.

The effect of orthokeratology treatment zone decentration on myopia progression

Background

This study aimed to compare the changes in the axial length (AL) in myopic children that wear centered and decentered orthokeratology (Ortho-K).

Methods

This retrospective study included 217 subjects who were treated with an Ortho-K lens for >12 months. The subjects were divided into three groups based on the magnitude of the Ortho-K lens treatment zone decentration: mildly, moderately, and severely decentered groups. Distance and direction of treatment zone decentration were calculated using software that was developed in-house. The AL changes in different groups were compared.

Results

Based on the distance of the treatment zone decentration, 65 children (65 eyes) were included in the mildly decentered group, 114 children (114 eyes) in the moderately decentered group, and 38 children (38 eyes) in the severely decentered group. The mean decentration distance in the three groups was 0.35 ± 0.11 mm, 0.71 ± 0.13 mm, and 1.21 ± 0.22 mm, respectively. The mean AL increase in the three groups after 12 months of Ortho-K lens wear was 0.24 ± 0.21 mm, 0.23 ± 0.18 mm, and 0.19 ± 0.20 mm, respectively. There were no significant differences in AL changes among the three groups.

Conclusions

Ortho-K lens decentration is common in clinical practice. The AL change after Ortho-K lens wear was not significantly different in subjects with different magnitudes of Ortho-K lens decentration. Fitting the Ortho-K lens in the properly centered zone is recommended to ensure the safety of Ortho-K lens wear and to maintain visual quality.

The associations of accommodation and aberrations in myopia control with orthokeratology

Purpose

This study aimed to investigate the effect of orthokeratology (OK) on accommodative function and aberrations, to explore the correlations between them and determine what role they play in myopia control.

Methods

In this prospective case‐controlled study, 61 children were divided into an OK (n = 30) and a single‐vision spectacles (SVS) (n = 31) group. Accommodation and ocular wavefront aberrations in the OK group were measured at baseline and after 1, 3, 6, 9 and 12 months of OK wear, and again at 1 month after stopping OK (13^th month). The same procedure was performed in the SVS group at baseline and at 3, 6 and 12 months. Axial length (AL), accommodative lag area and aberrations including spherical aberration (SA), coma and total higher‐order aberrations (HOAs) were analysed.

Results

During OK wear, the accommodative lag area at each visit was lower than the baseline level (all p < 0.01); all aberrations at each visit were higher than pre‐treatment (all p < 0.001). After 1 month of OK treatment, changes in accommodative lag area and SA did not show significant correlation (p = 0.16), but after OK cessation these changes were correlated (p = 0.01). In the OK group, multivariate regression analysis showed changes in accommodative lag area were associated with AL progression in the first 6 months but not in the 1‐year analysis. For the SVS group, there were no significant changes in the accommodative lag area or any aberrations during the study period.

Conclusions

Increased HOAs and improved accommodative accuracy were observed during OK treatment, but began to regress after the cessation of OK. A significant positive correlation between improved accommodative accuracy and slowed axial elongation was only observed during the first 6 months of treatment.

Higher Order Aberrations following Scleral Buckling Surgery in Patients with Rhegmatogenous Retinal Detachment

We aim to evaluate magnitudes of higher order aberrations (HOAs) from 3rd–6th order after scleral buckling (SB) for rhegmatogenous retinal detachment (RRD). A retrospective cross-sectional study of 19 patients with RRD who received SB (six receiving encircling SB, thirteen receiving segmental SB) was conducted. A wavefront analysis for surveying HOAs and other ophthalmic parameters were collected. Data between operated and fellow eyes, and a subgroup analysis of operated eyes, were analyzed by the Mann–Whitney U test, while a generalized linear model was applied to evaluate the correlation of HOAs to best-corrected visual acuity (BCVA) and optical symptoms. BCVA in the operated eyes was significantly worse (LogMAR: 0.18 ± 0.23 versus 0.05 ± 0.07, p = 0.001). Tilt (0.32 ± 0.14 versus 0.13 ± 0.08, p = 0.004), defocus (1.78 ± 0.47 versus 1.05 ± 0.17, p = 0.019) and coma (0.43 ± 0.11 versus 0.27 ± 0.09, p = 0.016) were significantly increased after SB. All root mean square (RMS), including RMS-3, RMS-4 and total RMS, were higher in operated eyes (all p < 0.05). Regarding Zernike terms, a significant elevation of vertical coma in the operated eyes was found (p = 0.038). In addition, tilt (0.41 ± 0.10 versus 0.17 ± 0.12, p = 0.007), defocus (2.27 ± 0.58 versus 0.82 ± 0.39, p = 0.001) and coma (0.59 ± 0.17 versus 0.11 ± 0.10, p = 0.015) were higher in the segmental subgroup, whereas spherical aberration (SA) was higher in the encircling subgroup (0.22 ± 0.04 versus 0.40 ± 0.15, p = 0.024) and RMS-4 and total RMS were increased in the segmental subgroup (both p < 0.05). Besides, tilt was correlated to worse BCVA (p = 0.036), whereas all four HOAs were correlated to the presence of optical symptoms (all p < 0.05). In conclusion, SB may increase HOAs, which could be associated with unfavorable postoperative visual outcomes and subject symptoms.

Compression Factor and Visual Performance in Adults Treated With Orthokeratology

OBJECTIVES

To investigate the effect of compression factor on visual performance in orthokeratology (ortho-k).

METHODS

Myopic adults were fitted with ortho-k lenses with either a 0.75 diopter (D) or 1.75 D compression factor. Higher-order aberrations (HOAs), corneal topography, and responses to the National Eye Institute/Refractive Error Quality of Life Instrument-42 questionnaire were measured at baseline and 6-month and 12-month follow-up along with a satisfaction questionnaire. Subjective refraction, high-contrast, and low-contrast visual acuity were measured at baseline and 1-day, 1-week, 6-month, and 12-month follow-up.

RESULTS

Forty-four myopic (mean spherical equivalent refraction: -3.66±0.84 D) adults (median age 25 years) completed the 12-month follow-up. After ortho-k lens wear, levels of satisfaction of vision after waking were significantly higher than vision before sleep for both compression factors (both P<0.01). The increased compression factor (ICF) resulted in less myopia at the 1-week visit (P=0.04) and better high-contrast unaided visual acuity at the 1-day visit (P=0.03) compared with the conventional compression factor (CCF). No other significant differences were observed for the compression factor for treatment zone diameter, lens decentration, or any subjective measurements. Individual HOA terms , , , and were significantly higher in the CCF group (0.75 D) (all P<0.05). The HOA visual Strehl ratio decreased significantly after lens wear (P<0.001) but did not vary with the compression factor.

CONCLUSIONS

An ICF did not result in clinically significant differences in subjective refraction, visual acuity, unaided vision, or the total ocular HOA profile compared with a CCF (0.75 D) in myopic adults after long-term ortho-k lens wear.

Zone of Clear Single Binocular Vision in Myopic Orthokeratology

PURPOSE

To examine the zone of clear single binocular vision (ZCSBV) in myopic children and young adults after 12 months of orthokeratology (OK) wear, in comparison with single-vision soft contact lens (SCL) wear.

METHODS

Twelve children (8-16 years) and 8 adults (18-29 years) were assessed with a series of near-point binocular vision tests when myopia was corrected using single-vision SCLs and again after 1 and 12 months of OK wear, and axial length was measured. The ZCSBV was constructed for baseline SCL wear and after 12 months of OK wear.

RESULTS

After 1 month of OK wear, increased accommodative responses were noted in children (C) and adults (A) as increased binocular amplitude (C:P=0.03, A:P=0.04) and reduced accommodative lag (C:P=0.01, A:P=0.01). Divergence reserves improved after 1 month in both groups (P<0.04), and a near exophoric shift was evident at 12 months (C:P=0.01, A:P=0.04). All changes at 1 month maintained stability at 12 months. An increase in accommodation and vergence responses without reduction in range resulted in an expansion of the ZCSBV in both age groups. Axial length did not significantly change in either children (P=0.25) or adults (P=0.72).

CONCLUSION

In both pediatric and young adult myopes, the ZCSBV expands toward a more divergent, increased accommodation response in OK compared with SCL wear. This occurs without a corresponding loss of convergence or accommodation deactivation, indicating improved depth of focus. These findings are relevant to visual acceptance and possible mechanisms of OK's efficacy for myopia control.

Higher order aberrations and axial elongation in combined 0.01% atropine with orthokeratology for myopia control

PURPOSE

To compare the changes in higher order aberrations (HOA's) for photopic and mesopic pupil diameters in children undergoing orthokeratology treatment (OK) or combined 0.01% atropine with orthokeratology treatment (AOK), and their association with axial elongation.

METHODS

Children aged 6 to <11 years with 1.00-4.00 D of myopia were randomly assigned to each treatment group. Photopic and mesopic pupil diameters were quantified using automated pupillometry and HOA's were measured with a Hartmann-Shack aberrometer and Badal system to control for accommodation. HOA's were rescaled to photopic and mesopic pupil diameters and fitted with a 6^th order Zernike polynomial expansion. Axial length was measured using an optical biometer under cycloplegia.

RESULTS

Baseline and six-month data from 25 AOK and 28 OK participants were analysed. At the six-month visit, pupil diameter was larger in the AOK group under photopic conditions (3.70 ± 0.42 vs 3.12 ± 0.33 mm, p < 0.001), along with a range of HOA metrics [3^rd to 6^th order and higher order root mean square error values (HO RMS), all p ≤ 0.003] and individual Zernike terms (primary spherical aberration, and oblique quadrafoil, both p ≤ 0.03). Axial elongation was greater in the OK treatment group (0.05 ± 0.08 vs -0.01 ± 0.12 mm, p = 0.02). In the AOK group, axial elongation was correlated with the increase in photopic pupil diameter (r = -0.45, p = 0.02) and with several HOA metrics; however, these associations were not observed in the OK group.

CONCLUSION

AOK treatment resulted in increased photopic pupil size and HOA's, and significantly less axial elongation over a six-month period compared to OK treatment alone. The improved myopia control observed with combination 0.01% atropine and orthokeratology may be a result of an enhanced optical effect due to a larger photopic pupil size.

The Effect of Treatment Zone Decentration on Myopic Progression during Or-thokeratology

Purpose: To evaluate the relationship between magnitude of orthokeratology (OrthoK) treatment zone decentration and 2-year axial length (AL) elongation in myopic children.Methods: One-hundred and one Chinese children who wore OrthoK contact lenses for 2 years. The magnitude and direction of the OrthoK treatment zone center from the entrance pupil center were recorded after 3 and 24 months of lens wear along with AL measurement. Stepwise multiple linear regression analysis was performed to assess which factors significantly affected an increase in AL.Results: After 3 and 24 months of OrthoK treatment, the mean (± standard deviation [SD]) magnitude of the OrthoK treatment zone decentration was 0.64 ± 0.38 mm and 0.68 ± 0.32 mm, respectively. There were no significant differences between the two time points (P > .05). After 2 years of OrthoK contact lenses wear, the mean (± SD) AL growth was 0.36 ± 0.34 mm. The axial elongation was slightly correlated with baseline age of subjects (r = -0.073, P < .001), baseline spherical equivalent refractive error (r = -0.088, P < .001) and magnitude decentration of treatment zone (r = -0.190, P = .027).Conclusions: The decentration of OrthoK treatment zone stabilizes after 3 months of lens wear and slightly decreases AL growth.

Contrast sensitivity and visual acuity in subjects wearing multifocal contact lenses with high additions designed for myopia progression control

OBJECTIVES

To assess the visual performance of multifocal contact lenses (MFCLs) with high addition powers designed for myopia control.

METHODS

Twenty-four non-presbyopic adults (mean age 24 years, range 18-36 years) were fitted with soft MFCLs with add powers of +2.0 D (Add2) and +4.0 D (Add4) (RELAX, SwissLens) and single vision lenses (SVCL; Add0) in a counterbalanced order. In this double-masked study, half of the participants were randomly fitted with 3 mm-distance central zone MFCLs while the other half received 4.5 mm-distance central zone MFCLs. Visual acuity was measured at distance (3.0 m) and at near (0.4 m). Central and peripheral contrast sensitivity was evaluated at distance using the Gabor patch test. The area under the logarithmic contrast sensitivity function curve (ALCSF) was calculated and compared between the groups (i.e. different additions powers used).

RESULTS

Near and distance visual acuities were not affected by the lenses, neither Add2 nor Add4, when compared to Add0, however, CZ3 significantly reduced distance visual acuity with Add4 when compared to CZ4.5 (-0.08 logMAR vs. for CZ3 and -0.18 logMAR for CZ4.5, p = 0.013). MFCLs impaired central ALCSF only when Add2 was used (15.99 logCS for Add2 and 16.36 logCS for SVCLs, p = 0.021). Peripheral ALCSF was statistically lower for both addition powers of the MFCLs when compared to SVCLs (12.70 for Add2 and Add4, 13.73 for SVCLs, p = 0.009). The above effects were the same for both central zones used.

CONCLUSIONS

MFCLs with CZ3 diameter and high add power (Add4) slightly reduced distance visual acuity when compared to CZ4.5 but no reduction in this parameter was found with medium add power (Add2). Central contrast sensitivity was impaired only by MFCLs with the lower add power (Add2). Both add powers in the MFCLs reduced peripheral contrast sensitivity to a similar extent.

Correction of presbyopia: old problems with old (and new) solutions

We live in a three-dimensional world and the human eye can focus images from a wide range of distances by adjusting the power of the eye's lens (accommodation). Progressive senescent changes in the lens ultimately lead to a complete loss of this ability by about age 50, which then requires alternative strategies to generate high-quality retinal images for far and close viewing distances. This review paper highlights the biomimetic properties and underlying optical mechanisms of induced anisometropia, small apertures, dynamic lenses, and multi-optic lenses in ameliorating the visual consequences of presbyopia. Specifically, the advantages and consequences of non-liner neural summation leveraged in monovision treatments are reviewed. Additionally, the value of a small pupil is quantified, and the impact of pinhole pupil location and their effects on neural sensitivity are examined. Different strategies of generating multifocal optics are also examined, and specifically the interaction between ocular and contact or intraocular lens aberrations and their effect on resulting image quality are simulated. Interestingly, most of the novel strategies for aiding presbyopic and pseudophakic eyes (for example, monovision, multifocality, pinhole pupils) have emerged naturally via evolution in a range of species.

Accommodation response and spherical aberration during orthokeratology

PURPOSE

To evaluate the changes in the accommodative response and in the corneal and internal spherical aberration during 3 months of wear of orthokeratology lenses from the baseline.

METHODS

Fifty children aged 8 to 17 were recruited for a prospective study and were fitted with orthokeratology lenses. Refraction without cycloplegia, high and low uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), accommodation lag, horizontal near phoria without correction, corneal topography, corneal, and total wavefront aberration were performed at baseline, 1 day, 1 week, 1 month, and 3 months. Data were analyzed by Student's t test for related samples, repeated measures ANOVA test, and Pearson correlation test.

RESULTS

The spherical equivalent (SE) before and after 3 months was - 3.33 ± 1.60 D and - 0.30 ± 0.46 D, respectively. Accommodation lag was 0.53 ± 0.38 D and 0.20 ± 0.33 D at baseline and at 3 months, respectively. A moderate correlation between lag at the baseline and its change between baseline and the 3-month visit was found (P < 0.05; R = 0.748). The spherical aberration (SA) increased for anterior corneal and total measurement, being statistically significant for all visits (P < 0.05). The internal SA decreased: - 0.105 ± 0.006 at baseline and - 0.196 ± 0.203 at 1 week (P < 0.05). No difference between baseline and the follow-up visits in posterior corneal SA was found (P > 0.05) CONCLUSION: The negative SA of the lens increases during OK treatment compensated for the increase of the anterior corneal surface positive SA, in addition to increasing the accommodative response.

The influence of orthokeratology compression factor on ocular higher-order aberrations

BACKGROUND

To investigate the influence of compression factor upon changes in ocular higher-order aberrations (HOAs) in young myopic children undergoing orthokeratology treatment.

METHODS

Subjects aged between six and < 11 years, with low myopia (0.50-4.00 D inclusive), low astigmatism (≤ 1.25 D), and anisometropia (≤ 1.00 D), were randomly assigned to wear orthokeratology lenses of different compression factors in each eye (one eye 0.75 D and the fellow eye 1.75 D). HOAs were measured weekly over one month of lens wear. Wavefront analysis was conducted over a 5-mm pupil using a sixth order Zernike polynomial expansion. Linear mixed models were used to examine the individual Zernike co-efficients and specific root-mean-square (RMS) error (spherical, comatic, total HOAs) metrics and their changes between the two eyes during the study period.

RESULTS

Twenty-eight myopic (mean manifest spherical equivalent refraction: -2.10 ± 0.58 D) children (median [range] age: 9.3 [7.8-11.0] years) were analysed. Significant interocular differences in HOAs at baseline were observed for Z 6 - 6 and Z 6 - 4 only (both p < 0.05). During the lens wear period, eyes fitted with the increased compression factor showed greater changes in primary spherical aberration ( Z 4 0 , p = 0.04) and RMS values for spherical and total HOAs (both p < 0.01). Considering data from both eyes together, after adjusting for the paired nature of the data, some other Zernike terms ( Z 3 1 and Z 6 0 , both p < 0.01) and the RMS value of comatic aberrations (p < 0.001) significantly increased after one month of orthokeratology treatment. The increase in primary spherical aberration ( Z 4 0 ) was positively correlated with the reduction in spherical equivalent refractive error, but only in eyes fitted with the increased compression factor (r = 0.69, p < 0.001).

CONCLUSIONS

Increasing the orthokeratology compression factor by 1.00 D significantly altered some HOAs, particularly spherical aberration. Given the association between positive spherical aberration and eye growth in children, further research investigating the influence of orthokeratology compression factor on axial eye growth is warranted.

Vision-Specific Quality of Life: Laser-Assisted in situ Keratomileusis Versus Overnight Contact Lens Wear

OBJECTIVES

To compare the visual-related quality of life in myopic subjects with different refractive treatments such as continuous wear of silicone-hydrogel contact lenses (CL), corneal refractive therapy (CRT), and laser-assisted in situ keratomileusis (LASIK).

METHODS

The National Eye Institute Refractive Error Quality of Life Instrument (NEI RQL-42) questionnaire was administered to 96 subjects with a mean age of 30.0±7.9 years. There were 72 myopic subjects with a mean spherical equivalent of -2.74±0.98 D (-5.50 to -1.25 D). Subjects were corrected with LASIK (n=24), Paragon CRT orthokeratology lenses (n=24), and lotrafilcon A silicone-hydrogel CL under continuous wear (n=24). The NEI RQL-42 survey was used to compare differences between groups as well as with an emmetropic group (n=24).

RESULTS

After 1 year of treatment, significant differences were found among all groups in the subscales glare (P=0.017), symptoms (P=0.016), dependence on correction (P<0.001), and worry (P<0.001). The mean difference compared with emmetropes were -5.5% (P=0.063) for LASIK patients, -2.0% (P=0.212) for orthokeratology subjects, and +1.6% (P=0.934) for the silicone-hydrogel CL group.

CONCLUSIONS

Myopic subjects analyzed in this study reported better vision-related quality of life when they were corrected with continuous wear silicone-hydrogel lenses. The average score reached by CRT was similar to emmetropes, which showed the main disadvantage in worry subscale. The patients who underwent LASIK had the lowest valuation, highlighting the decreases in scores of diurnal fluctuations, glare, and especially in expectations and worry subscales, due to the first and second subscales, but especially to the false expectations created about treatment.

The Topographical Effect of Optical Zone Diameter in Orthokeratology Contact Lenses in High Myopes

Purpose

To evaluate the effect of the optical zone diameter (OZ) in orthokeratology contact lenses regarding the topographical profile in patients with high myopia (−4.00 D to −7.00 D) and to study its effect over the visual quality.

Materials and Methods

Twelve patients (18 eyes) were fitted with overnight orthokeratology (OrthoK) with a randomized 6 mm or 5 mm OZ lens worn for 2 weeks, followed by a 2-week washout period, between both designs. Keratometry (K) readings, optical zone treatment diameter (OZT), peripheral ring width (PRW), higher-order aberrations (HOA), high (HC) and low contrast (LC) visual acuity, and subjective vision and comfort were measured at baseline and after 2 weeks of OrthoK lens wear of each contact lens.

Results

No significant differences were found between any measurements for the same subject at both baselines (p value > 0.05). There was no difference between OZ lens designs found in refraction, subjective vision or comfort, and HC and LC visual acuity. Contrast sensitivity was decreased in the 5 mm OZ lens design compared with 6 mm OZ design (p-value < 0.05). 5 mm OZ design provoked a greater flattening, more powerful midperipheral ring and 4^th-order corneal and total spherical aberration than the 6 mm OZ design, being statistically significant after 7 days, for corneal aberration, and 15 days, for corneal and total, of wearing the lens (p-value < 0.05). The OZT obtained were 2.8 ± 0.2 mm and 3.1 ± 0.1 mm for 5 mm and 6 mm OZ design, respectively (p-value < 0.05). Regarding PRW, the 5 mm OZ design had a wider ring width in both the nasal and temporal zones (p-value < 0.05).

Conclusions

A smaller diameter optical zone (5 mm) in orthokeratology lenses produces a smaller treatment area and a larger and more powerful midperipheral ring, increasing the 4^th-order spherical aberration that affects only the contrast sensitivity but without differences in visual acuity and subjective vision compared with a larger OZ diameter (6 mm).

Changes and Diurnal Variation of Visual Quality after Orthokeratology in Myopic Children

Purpose

To assess the changes and the diurnal variation of visual quality after orthokeratology in myopic children.

Methods

Forty-four eyes of 22 subjects with a mean age of 10.55 ± 1.53 years (8 to 14 years) were enrolled in this prospective study. Their spherical equivalent ranged from -1.25 to -4.25 diopters (D) and astigmatism was less than 1.00 D. Parameters including corneal curvature, ocular objective scatter index (OSI), the modulation transfer function (MTF), root mean square of ocular and corneal wavefront aberrations, and contrast sensitivity function (CSF) were measured before and at two time points during the same day after 1 month of orthokeratology.

Results

After orthokeratology, uncorrected visual acuity (UCVA) and spherical equivalent were significantly improved from baseline (P < 0.001), and their diurnal variation was not significant (P=0.083, 0.568). OSI increased from 0.29 ± 0.15 to 0.65 ± 0.31 (P < 0.001). MTF decreased significantly (P < 0.01). Corneal curvature and ocular total aberration decreased (P < 0.001), while the ocular and corneal higher-order aberration increased significantly (P < 0.01). The CSF under photopic condition decreased at 3 cpd (P=0.006) and increased at 18 cpd (P=0.012). The diurnal variation of CSF at 18 cpd under mesopic and high glare conditions and at 12 cpd under photopic condition was significant (P=0.002, 0.01, 0.017).

Conclusions

Orthokeratology can effectively improve UCVA and high spatial frequency CSF by decreasing the low-order aberrations. However, MTF and CSF at low spatial frequency decreased because of the increase of intraocular scattering and high-order aberrations. Meanwhile, CSF at high spatial frequency fluctuates significantly at two times during the same day after 1 month orthokeratology.

Corneal epithelial and stromal thickness changes in myopic orthokeratology and their relationship with refractive change

Purpose

To investigate topographic changes in corneal epithelial thickness (CET) and stromal thickness following orthokeratology (OK) and to determine associated factors affecting refractive changes.

Methods

This study investigated the topographic changes in CET and stromal thickness in 60 myopic eyes that were fitted with OK lenses. CET and stromal thickness were obtained using spectral-domain optical coherence tomography (OCT) before and after OK lens wear. Changes in refractive error and corneal topography data were obtained. The correlation between refractive change and corneal thickness change, and various refractive, lens, and topographic parameters were analyzed using simple regression analysis.

Results

Mean refractive error changed by 1.75 ± 0.79 diopters (D). The mean CET of the center zone (2 mm in diameter), paracenter (2 to 5 mm annular ring: 1 to 2.5 mm from center), and mid-periphery (5 to 6 mm annular ring: 2.5 to 3 mm from center) changed by -8.4, -1.4, and +2.7 μm, respectively, after OK lens wear. There was an increase of 2.0, 3.3, and 3.9 μm, respectively, in the center, paracenter, and mid-periphery of the stroma. A larger refractive correction was associated with a flatter base curve of the lens, larger decrease in the central epithelium, and smaller treatment diameter in corneal topography.

Conclusion

OK lenses caused the central corneal epithelium to thin while the mid-peripheral epithelium and stroma became thicker. Refractive changes during OK are associated with changes in central epithelial thickness, while stromal changes did not contribute significantly.

Influence of overnight orthokeratology lens fitting decentration on corneal topography reshaping

Background

This retrospective study was designed to investigate the sole influence of orthokeratology (OK) lens fitting decentration on the Zernike coefficients of the reshaped anterior corneal surface.

Methods

This study comprised a review of 106 right eyes and measurements of corneal topography both before OK and at 1-month follow-up visit. A routine was designed to calculate local corneal surface astigmatism and assist the determination of OK lens fitting decentration from pupil center. The pupil-centered corneal Zernike coefficients of baseline (PCCB) and post-treatment (PCCP) were calculated. Meanwhile, the OK-lens-centered corneal Zernike coefficients of post-treatment (OCCP) were also calculated and considered as the presumptive ideal fitting group without decentration. Relationships between lens fitting decentration and the change of Zernike coefficients including (PCCP − PCCB) and (PCCP − OCCP) were analyzed.

Results

Patients with a mean age of 11 ± 2.36 years old had an average spherical equivalent refractive error of −3.52 ± 1.06 D before OK. One month after treatment, OK lens fitting decentration from pupil center was 0.68 ± 0.35 mm. RMS of 3rd-order (P < 0.05), RMS of 4th-order (P < 0.001) and RMS of total high order (P < 0.001) corneal Zernike coefficients were increased in PCCP by comparing with OCCP, which was solely caused by lens fitting decentration. Nevertheless, no significant difference was observed in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {C}_2^0 $$\end{document}C20 (P > 0.05). For the high order corneal Zernike coefficients in (PCCP – OCCP), radial distance of decentration was correlated with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {C}_3^{-1} $$\end{document}C3−1 (r = −0.296, P < 0.05), \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {C}_3^1 $$\end{document}C31 (r = −0.396, P < 0.001), and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {C}_4^0 $$\end{document}C40 (r = 0.449, P < 0.001), horizontal decentration was significantly correlated with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {C}_3^1 $$\end{document}C31 (r = 0.901, P < 0.001) and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {C}_5^1 $$\end{document}C51 (r = 0.340, P < 0.001), and vertical decentration was significantly correlated with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {C}_3^{-1} $$\end{document}C3−1 (r = 0.904, P < 0.001).

Conclusions

OK lens fitting decentration within 1.5 mm hardly influenced the change of corneal spherical power for myopia correction, but significantly induced additional corneal high order Zernike coefficients including \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {C}_3^{-1} $$\end{document}C3−1, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {C}_3^1 $$\end{document}C31, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {C}_4^0 $$\end{document}C40, and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {C}_5^1 $$\end{document}C51.

Repeatability of Monocular Acuity Testing in Adults with and without Down Syndrome

PURPOSE

Individuals with Down syndrome may experience greater difficulty reliably performing visual acuity (VA) tests because of intellectual disability and limitations in visual quality. This study evaluated the repeatability of acuity (Bailey-Lovie [BL] and HOTV) in subjects with and without Down syndrome.

METHODS

High-contrast VA was measured in both eyes of 30 subjects with Down syndrome (mean, 30 years; range, 18 to 50 years) and 24 control subjects without Down syndrome (mean, 29 years; range, 18 to 50 years). In the Down syndrome group, 23 subjects performed BL, and 7 subjects performed HOTV. All control subjects performed both BL and HOTV, but for HOTV analysis, only seven age-matched control subjects were included. For each eye, subjects performed VA three times on different charts (computer controlled, single-line display) until five total letters were missed on each chart. A repeated-measure ANOVA was used to compare the acuity measures between groups.

RESULTS

The average logMAR VA for subjects with Down syndrome was approximately six lines worse than the control subjects (BL: Down syndrome = right eye: 0.51 ± 0.16, left eye: 0.53 ± 0.18; control = right eye: -0.06 ± 0.06, left eye: -0.06 ± 0.08, P < .0001; HOTV: Down syndrome = right eye: 0.47 ± 0.19, left eye: 0.46 ± 0.16; control: right eye = -0.11 ± 0.09, left eye: -0.07 ± 0.07, P < .001). Bailey-Lovie VA repeatability (1.96 * Sw * √2) was 0.13 logMAR (6.5 letters) for Down syndrome and 0.09 logMAR (4.5 letters) for control subjects. HOTV VA repeatability was 0.16 logMAR (eight letters) for both Down syndrome and control subjects.

CONCLUSIONS

Despite poorer acuity in individuals with Down syndrome, repeatability of VA measurements was comparable to control subjects for both BL and HOTV techniques.

Evaluating internal and ocular residual astigmatism in Chinese myopic children

PURPOSE

To investigate the nature of internal astigmatism (IA) and ocular residual astigmatism (ORA) in Chinese myopic children and to identify factors that may influence IA and ORA.

METHODS

A total of 206 eyes of 206 myopic children (97 boys and 109 girls; 10.95 ± 2.2 years) were enrolled in this cross sectional study. Total ocular astigmatism (TOA), anterior corneal astigmatism (ACA), posterior corneal astigmatism (PCA) and total corneal astigmatism (TCA) were measured directly using either a Hartmann-Shack wavefront sensor or a Pentacam. IA and ORA were calculated by Fourier vector analyses (the definitions of IA and ORA are: IA = TOA - ACA - PCA, ORA = TOA - ACA). Spearman or Pearson correlation was adopted to detect multiple factors that may influence IA and ORA, which were then predicted by linear regressions. Modified compensation factors were applied to evaluate the inter-relationship between corneal astigmatism and ORA.

RESULTS

While the mean values of IA and ORA were -0.52 DC × 94.8° and -0.63 DC × 93.0°, respectively, the percentage of ORA power over 1.00 D was as high as 28.64%. Full or under-compensation of ACA by ORA predominated in the enrolled subjects. The mean ORA J₀ and J₄₅ were -0.311 ± 0.236 and -0.032 ± 0.156 D, respectively, negatively correlated with the corresponding ACA components (J₀: r = -0.276, J₄₅: r = -0.616, p < 0.001). While age was not correlated with either IA or ORA (p > 0.1), the power of IA or ORA was correlated inversely with the axial length (IA: r = -0.193, p = 0.005; ORA: r = -0.169, p = 0.015) and positively with the spherical equivalent refraction (IA r = 0.195, p = 0.005; ORA r = 0.213, p = 0.002) and power of corneal astigmatism (IA-ACA: r = 0.302, IA-TCA: r = 0.368, ORA-ACA: r = 0.334, ORA-TCA: r = 0.293). Girls had larger IA powers than boys (0.741 ± 0.345 D vs 0.651 ± 0.340, p = 0.036).

CONCLUSIONS

Full or under-compensation of ACA by ORA is common in Chinese myopic children, and the compensation efficiency may decrease with age. Among Chinese children with myopia, a larger ORA is more prevalent with less myopia and greater corneal astigmatism.

Effect of Pupil Size on Wavefront Refraction during Orthokeratology

PURPOSE

It has been hypothesized that central and peripheral refraction, in eyes treated with myopic overnight orthokeratology, might vary with changes in pupil diameter. The aim of this work was to evaluate the axial and peripheral refraction and optical quality after orthokeratology, using ray tracing software for different pupil sizes.

METHODS

Zemax-EE was used to generate a series of 29 semi-customized model eyes based on the corneal topography changes from 29 patients who had undergone myopic orthokeratology. Wavefront refraction in the central 80 degrees of the visual field was calculated using three different quality metrics criteria: Paraxial curvature matching, minimum root mean square error (minRMS), and the Through Focus Visual Strehl of the Modulation Transfer Function (VSMTF), for 3- and 6-mm pupil diameters.

RESULTS

The three metrics predicted significantly different values for foveal and peripheral refractions. Compared with the Paraxial criteria, the other two metrics predicted more myopic refractions on- and off-axis. Interestingly, the VSMTF predicts only a marginal myopic shift in the axial refraction as the pupil changes from 3 to 6 mm. For peripheral refraction, minRMS and VSMTF metric criteria predicted a higher exposure to peripheral defocus as the pupil increases from 3 to 6 mm.

CONCLUSIONS

The results suggest that the supposed effect of myopic control produced by ortho-k treatments might be dependent on pupil size. Although the foveal refractive error does not seem to change appreciably with the increase in pupil diameter (VSMTF criteria), the high levels of positive spherical aberration will lead to a degradation of lower spatial frequencies, that is more significant under low illumination levels.

Interaction between Corneal and Internal Ocular Aberrations Induced by Orthokeratology and Its Influential Factors

Purpose

To investigate the interaction between corneal, internal, and total wavefront aberrations (WAs) and their influential factors during orthokeratology (OK) treatment in Chinese adolescents.

Methods

Thirty teenagers (n = 30 eyes) were enrolled in the study; spherical equivalent refraction (SE), corneal curvature radius (CCR), central corneal thickness (CCT), WAs, and the difference in limbal transverse diameter and OK lens diameter (ΔLLD) were detected before and after one-month OK treatment. Every component of WAs was measured simultaneously by iTrace aberrometer. The influential factors of OK-induced WAs were analyzed.

Results

SE and CCT decreased while CCR increased significantly (P < 0.01). Higher-order aberrations (HOAs), Spherical aberrations (SAs), and coma increased significantly (P < 0.01). Corneal horizontal coma (Z3¹-C) and corneal spherical aberrations (Z4⁰-C) increased (P < 0.01). The HOAs, coma, SAs, Z3¹-C, Z3¹-T, Z4⁰-C, and Z4⁰-T were positively correlated with SE and CCR (P < 0.01). Z3⁻¹-C showed negative correlations with (ΔLLD) and positive correlations with SE (P < 0.05).

Conclusions

The increase in OK-induced HOAs is mainly attributed to Z3¹ and Z4⁰ of cornea. Z3⁻¹ in the internal component showed a compensative effect on the corneal vertical coma. The degree of myopic correction and increase in CCR may be the essential influential factors of the increase in Z3¹ and Z4⁰. The appropriate size of the OK lens may be helpful to decrease OK-induced vertical coma.

Corneal Aberrations, Contrast Sensitivity, and Light Distortion in Orthokeratology Patients: 1-Year Results

Purpose. To evaluate the corneal higher-order aberrations (HOA), contrast sensitivity function (CSF), and light distortion (LD) in patients undergoing orthokeratology (OK). Methods. Twenty healthy subjects (mean age: 21.40 ± 8 years) with mean spherical equivalent refractive error M = −2.19 ± 0.97 D were evaluated at 1 day, 1 month, and 1 year after starting OK treatment. Monocular LD, photopic monocular CSF, and corneal HOA for 6 mm pupil size were measured. Results. LD showed an increase after the first night (p < 0.05) and recovery to baseline after 1 month, remaining stable after 1 year (p > 0.05). Spherical-like, coma-like, and secondary astigmatism HOA RMS increased significantly (p ≤ 0.022) from baseline to 1-month visit, remaining unchanged over the follow-up. Contrast sensitivity for medium frequencies (3.0, 4.24, and 6.00 cpd) was significantly correlated with LD parameters at baseline (r ≤ −0.529, p < 0.001). However, after 1 year of treatment, this correlation was only statistically significant for 12 cpd spatial frequency (r ≤ −0.565, p < 0.001). Spherical-like RMS for 6 mm pupil size correlated with irregularity of the LD (r = −0.420, p < 0.05) at the 1-year visit. Conclusion. LD experienced by OK patients recovers after one month of treatment and remains stable in the long term while optical aberrations remain significantly higher than baseline.

Short-term changes in light distortion in orthokeratology subjects

Purpose. Quantifying adaptation to light distortion of subjects undergoing orthokeratology (OK) for myopia during the first month of treatment. Methods. Twenty-nine healthy volunteers (age: 22.34 ± 8.08 years) with mean spherical equivalent refractive error −2.10 ± 0.93D were evaluated at baseline and days 1, 7, 15, and 30 of OK treatment. Light distortion was determined using an experimental prototype. Corneal aberrations were derived from corneal topography for different pupil sizes. Contrast sensitivity function (CSF) was analyzed for frequencies of 1.50, 2.12, 3.00, 4.24, 6.00, 8.49, 12.00, 16.97, and 24.00 cpd under photopic conditions. Results. Average monocular values of all light distortion parameters measured increased significantly on day 1, returning to baseline after 1 week (P < 0.05 in all cases). Spherical-like aberration stabilized on day 7 for all pupil diameters, while coma-like for smaller pupils only. CSF was significantly reduced on day 1 for all spatial frequencies except for 1.5 cpd, returning to baseline afterwards. Significant correlation was found between light distortion and contrast sensitivity for middle and high frequencies (P < 0.05) after 15 days. Conclusion. Despite consistently increased levels of corneal aberrations, light distortion tends to return to baseline after one week of treatment, suggesting that neural adaptation is capable of overcoming optical quality degradation.

Multi-aspheric description of the myopic cornea after different refractive treatments and its correlation with corneal higher order aberrations

Background

To analyse the asphericity of the anterior corneal surface (ACS) for different diameters, and correlate those values with corneal higher order aberrations (cHOA) before and after myopic treatments with corneal refractive therapy (CRT) for orthokeratology and customized (CL) and standard laser (SL) assisted in situ keratomileusis (LASIK).

Setting

Clínica Oftalmológica NovoVisión, Madrid, Spain.

Methods

The right eyes of 81 patients (27 in each treatment group), with a mean age of 29.94 ± 7.5 years, were analysed. Corneal videokeratographic data were used to obtain corneal asphericity (Q) for different corneal diameters from 3 to 8 mm and cHOA root mean square (RMS) obtained from Zernike polynomials for a pupil diameter of 6 mm.

Results

There were statistically significant differences in asphericity values calculated at different corneal diameters for different refractive treatments and their changes. The difference between asphericity at 3 and 8 mm reference diameters showed statistically significant correlations with spherical-like cHOA that was also significantly increased after all procedures.

Conclusions

The shift in corneal asphericity and the differences among different treatment techniques are more evident for the smaller reference diameters. These differences can be much reduced or even masked for a peripheral reference point at 4 mm from centre, which is used by some corneal topographers.

Changes in refraction, ocular aberrations, and corneal structure after suspending rigid gas-permeable contact lens wear in keratoconus

PURPOSE

This study reports on changes in visual acuity, ocular higher-order aberrations, and refraction after suspending rigid gas-permeable lens wear for 1 week in 15 patients with moderate to severe keratoconus. Alterations in the anterior surface, central corneal powers and axes, and central corneal thickness were also explored.

METHODS

Scheimpflug photography and Hartmann-Shack aberrometry were performed at 2 visits, 7 days apart, after the patients had removed their habitual contact lenses. Subjective refraction and both high- and low-contrast logarithm of the minimum angle of resolution visual acuities were also recorded at both visits.

RESULTS

Reductions in both high-contrast visual acuity (P = 0.001) and low-contrast visual acuity (P = 0.002), along with an increase in third-order root mean square aberrations (P = 0.008), occurred after rigid gas-permeable lens wear was suspended in these patients with keratoconus. However, no significant changes in subjective refraction were found over the 1-week period (P ≥ 0.10). Significant correlations were observed between third-order coma root mean square aberrations and the measured high-contrast (r(p) ≥ 0.59; P ≤ 0.02) and low-contrast visual acuities (r(P) ≥ 0.61; P ≤ 0.015). In addition to increases in the anterior surface central corneal powers (P ≤ 0.02), a reduction in central corneal thickness also was found between the 2 visits (P = 0.00016).

CONCLUSIONS

Changes in the optical and structural parameters of the keratoconic cornea occur after suspending rigid gas-permeable contact lens wear. This information may be of interest to practitioners concerned with prescribing aberration-controlling soft contact lenses for such patients.

Wavefront analysis and Zernike polynomial decomposition for evaluation of corneal optical quality

Wavefront-guided excimer laser refractive surgery and new customized intraocular lens and contact lens designs are major clinical applications of corneal wavefront analysis. Other therapeutic applications include corneal disorders, conventional excimer laser refractive surgery, incisional techniques and cataract surgery, corneal transplantation, intrastromal corneal ring segment implantation, and crosslinking therapy. Basic data regarding corneal wavefront aberrations, such as distribution in the population and changes with aging, are essential for understanding the nature of each aberration and correcting it. Corneal aberrometry also improved our comprehension of the optical effects of the aforementioned topics while helping us assess the success of the procedures. Zernike polynomials are representations of the higher- and lower-order aberrations of the cornea, allowing a mathematical approach to their determination. Polynomials are used to model individual components of the wavefront in familiar terms. This article reviews the current knowledge of the wavefront aberrations of the human cornea and analyzes studies in the fields of anterior segment surgery and/or therapy, diseases, and optical quality in the context of this knowledge.

Quantitative evaluation of night vision and correlation of refractive and topographical parameters with glare after orthokeratology

PURPOSE

To evaluate night vision disturbance and investigate correlations between pre- and post-treatment parameters and glare scores in orthokeratology patients.

METHODS

Twenty-eight right eyes of 28 patients were enrolled in this study. Corneal topography and a night vision test (NVT) to evaluate the extent of glare were performed after orthokeratology. From the corneal topography, two indices [surface regularity index (SRI) and surface asymmetry index (SAI)] were calculated. Fourier analysis was performed on the topographic data from the central 6 mm, and data were decomposed into asymmetric and higher order components for analysis.

RESULTS

There was no correlation between the glare score and pre-treatment keratometric value, pre-treatment cylinder, post-treatment sphere, and post-treatment cylinder. However, there was a statistically significant correlation between pre-treatment sphere and glare score (Pearson correlation coefficient, r = -0.54, p < 0.01). SRI and SAI significantly correlated with glare score (SRI: r = 0.52, p < 0.01, SAI: r = 0.41, p < 0.05). Higher order and asymmetric components were also significantly correlated with glare score (asymmetry: r = 0.61, p < 0.01, higher order: r = 0.67, p < 0.001).

CONCLUSIONS

The glare score was significantly correlated with corneal irregularity, and appeared to be a beneficial parameter for assessment of night vision performance in patients receiving orthokeratology.

Effect of pupil size on corneal aberrations before and after standard laser in situ keratomileusis, custom laser in situ keratomileusis, and corneal refractive therapy

PURPOSE

To evaluate the effect of changing the pupil size on the corneal first-surface higher-order aberrations induced by different refractive treatments: standard laser in situ keratomileusis (LASIK), custom LASIK, and corneal refractive therapy.

DESIGN

Observational study.

METHODS

Eighty-one right eyes from patients with a mean age of 29.94 +/- 7.5 years, of which 50 were female (61.7%), were analyzed retrospectively at the Clínica Oftalmológica NovoVision, Madrid, Spain. Corneal videokeratographic data were used to obtain corneal first-surface higher-order aberrations for aperture diameters from 3 to 8 mm using the Vol-CT software (Sarver & Associates, Inc). Total root mean square (RMS) and RMS for third- to sixth-order Zernike polynomials as well as spherical-like, coma-like, secondary astigmatism, and spherical plus coma-like variables were calculated.

RESULTS

We verified an increase in the higher-order aberration total RMS after treatments of 0.014 +/- 0.025 microm, 0.019 +/- 0.027 microm, and 0.018 +/- 0.031 microm for standard LASIK, custom LASIK, and corneal refractive therapy, respectively, for 3-mm pupil diameter. For the 8-mm aperture diameter, changes in total RMS increased by a factor of 50 compared with the variation for the 3-mm diameter up to 0.744 +/- 0.731 microm, 0.493 +/- 0.794 microm, and 0.973 +/- 1.055 microm for standard LASIK, custom LASIK, and corneal refractive therapy, respectively.

CONCLUSIONS

The 3 techniques increase the wavefront aberrations of the cornea and change the relative contribution of coma-like and spherical-like aberrations. For a large aperture (> 5 mm), corneal refractive therapy induces more spherical-like aberrations than standard and custom LASIK. However, no clinically or statistically significant differences existed for narrower apertures. Standard and custom LASIK did not display statistically significant differences regarding higher-order aberrations.

Changes in higher order wavefront aberrations after contact lens corneal refractive therapy and LASIK surgery

PURPOSE

To compare ocular higher order aberrations induced by corneal refractive therapy (CRT, Paragon Vision) to those produced by LASIK for patients with comparable levels of myopia.

METHODS

A retrospective chart review of 11 patients who used CRT lenses and 12 patients who underwent LASIK for correction of low to moderate myopia was performed. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, and optical higher order aberrations were recorded before and 1 month after treatment for each patient.

RESULTS

The CRT group consisted of 11 patients (4 men, 7 women) with a mean age of 29.1+/-5.2 years (range: 23 to 40 years), and the LASIK group consisted of 12 patients (3 men, 9 women) with a mean age of 39.2+/-12.0 years (range: 23 to 60 years). Manifest refraction decreased statistically significantly from -2.81+/-1.05 diopters (D) at baseline to -0.77+/-0.64 D following CRT treatment at 1 month (P<.0001) and from -3.11+/-1.21 D at baseline to -0.43+/-0.27 D at 1 month after LASIK (P<.0001). Both CRT and LASIK exhibited no significant changes in total higher order aberrations for 4-mm pupils but induced statistically significant increases in total higher order aberrations for 6-mm pupils. Corneal refractive therapy and LASIK both exhibited statistically similar factors of change for total higher order aberrations and coma-like higher order aberrations for 6-mm pupils. Corneal refractive therapy demonstrated a statistically significant greater factor of increase in spherical-like higher order aberrations for 6-mm pupils (P=.01).

CONCLUSIONS

Contact lens corneal refractive therapy and LASIK can effectively correct myopia, but both increase higher order aberrations for 6-mm pupils to a similar degree. However, spherical-like aberrations were statistically significantly greater after CRT than after LASIK.

Influence of induced decentered orthokeratology lens on ocular higher-order wavefront aberrations and contrast sensitivity function

PURPOSE

To quantitatively evaluate the effect of overnight orthokeratology lenses intentionally left decentered after 3 months of wear and assess the influence on clinical outcomes such as ocular higher-order wavefront aberrations and contrast sensitivity function.

SETTING

Department of Ophthalmology, Tsukuba University Hospital, Ibaraki, Japan.

METHODS

This prospective study assessed refraction, visual acuity, corneal topography, wavefront aberration, and contrast sensitivity function before and 3 months after overnight orthokeratology treatment. Decentration of the treatment zone from the center of the entrance pupil was determined using computerized videokeratography (TMS-4) and data-analysis software (MatLab). The relationship between decentration and the clinical parameters was analyzed.

RESULTS

The mean age of the 23 patients (46 eyes) was 24.2 years+/-3.3 (SD) and the mean spherical equivalent refraction before treatment, -2.38+/-0.98 diopters. The mean magnitude of decentration (0.85+/-0.51 mm) was statistically significantly correlated with the amount of myopic correction (P<.05), increases in coma-like aberration (P<.01), increases in spherical-like aberration (P<.01), and reductions in contrast sensitivity function (P<.0001). Changes in contrast sensitivity function were also statistically significantly correlated with the amount of myopic correction (P<.05), changes in coma-like aberration (P<.01), and changes in spherical-like aberration (P<.01). Stepwise multiple regression analysis showed that the magnitude of decentration was the only explanatory variable related to contrast sensitivity function (P<.0001).

CONCLUSION

Decentered treatment of orthokeratology resulted in decreased contrast sensitivity after treatment, showing that centration of the procedure is crucial to good outcomes.