Orthokeratology Research Articles

Objective optical quality after orthokeratology

To determine the changes of objective optical quality after orthokeratology. Prospective, self-controlled study. Optical quality, including objective scatter index (OSI), modulation transfer function (MTF) cutoff frequency, contrast visual acuity (CVA) and objective tear film quality, was assessed with the OQAS II instrument before and 1 week, 1 month, and 3 months after orthokeratology. Parameters of corneal astigmatism and e value from topography were also assessed. The data was analyzed using one-way ANOVA. Cylinder refraction was (-0.39 ± 0.39)D, (-0.65 ± 0.57)D, (-0.79 ± 0.56)D, and (-0.81 ± 0.53) D, respectively, at the four timepoints, and there was a statistically significant difference between before and after therapy (P < 0.05). Uncorrected visual acuity was 3.97 ± 0.51, 4.95 ± 0.12, 5.00 ± 0.06, and 5.00 ± 0.05, respectively. The e value was 0.37 ± 0.24, -0.23 ± 0.42, -0.29 ± 0.39, and -0.30 ± 0.37, respectively. The negative values after therapy were significantly different from the value before therapy (P < 0.01). The corneal astigmatism in 3 mm diameter was (1.27 ± 0.75) D, (1.06 ± 0.69) D, (1.11 ± 0.68) D , and (1.15 ± 0.67) D, respectively. There was no significant difference in astigmatism between before and after therapy (P ≥ 0.05). After therapy, the OSI increased from 0.59 ± 0.47 before therapy to 0.99 ± 0.66 at 1 week, 1.47 ± 1.17 at 1 month, and 1.49 ± 1.03 at 3 months. The difference between pre- and post-therapy OSI values was statistically significant (P < 0.05). The MTF cutoff frequency decreased from (36.6 ± 12.0) cpd before therapy to (34.2 ± 8.9) cpd at 1 week, (27.9 ± 12.6) cpd at 1 month, and (27.7 ± 11.6) cpd at 3 months after therapy. The difference in MTF cutoff frequency between before and 1 month after therapy was statistically significant (P < 0.05). The 100% CVA, 20% CVA, and 9% CVA all declined after therapy, but there was no statistically significant difference between before and after therapy. The OSI of tear film quality was 1.27 ± 1.12, 2.09 ± 1.67, 2.07 ± 1.12, and 2.10 ± 1.33, respectively, and the difference was statistically significant between before and after therapy (P < 0.05). After 3 months of orthokeratology, the corneal central astigmatism remained, and the e value became negative, while OSI increased, and MTF cutoff frequency and tear film quality declined. The alteration was more and more obvious along with the therapy within 1 month, and was not significant within the following month. After short-term corneal reshaping, the ocular optical quality declined in some degree, but the loss was acceptable.

Orthokeratology for the high myopia and high astigmatism is worth watching

The prevalence of high myopia in teenagers is rising. Due to both genetic factors and environmental factors, most of myopia occurs in early age with rapid progress, and the prevention and control are very difficult. Orthokeratology is considered as one of the most effective ways of controlling myopia for children. It is proved effective through many years of clinical studies not only for low to moderate myopia, but also for high myopia with astigmatism. However, professional knowledge is lacking domestically. This paper introduces the local and overseas research results in recent years, and discusses the necessity and feasibility of high diopter orthokeratology correction, implementation methods and requirements, and safety and effectiveness evaluation standards for reference.

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.

Accommodative changes produced in response to overnight orthokeratology.

To evaluate short-term (3 months) and long-term (3 years) accommodative changes produced by overnight orthokeratology (OK). A prospective, longitudinal study on young adult subjects with low to moderate myopia was carried out. A total of 93 patients took part in the study. Out of these, 72 were enrolled into the short-term follow-up: 21 were on a control group, 26 on a Paragon CRT contact lenses group, and 25 on a Seefree contact lenses group. The other 21 patients were old CRT wearers on long-term follow-up. Accommodative function was assessed by means of negative and positive relative accommodation (NRA / PRA), monocular accommodative amplitude (MAA), accommodative lag, and monocular accommodative facility (MAF). These values were compared among the three short-term groups at the follow-up visit. The long- and short-term follow-up data was compared among the CRT groups. Subjective accommodative results did not suffer any statistically significant changes in any of the accommodative tests for any of the short-term groups when compared to baseline. There were no statistically significant differences between the three short-term groups at the follow-up visit. When comparing the short- and long-term groups, only the NRA showed a significant difference (p = 0.0006) among all the accommodation tests. OK does not induce changes in the ocular accommodative function for either short-term or long-term periods.

Influence of orthokeratology lenses on the state of accommodative function in children with myopia

Оптимальна оптична корекція – один із засобів, що позитивно впливає на стан акомодаційного апарату міопічного ока. З метою оцінки стану акомодаційної функції ока вивчили резерви абсолютної акомодації, запас відносної акомодації і положення найближчої точки ясного зору в 50 пацієнтів (100 очей) із міопією слабкого ступеня, які отримують курс терапії рефракції ортокератологічними лінзами Paragon CRT протягом року. Встановили, що застосування ортокератологічних лінз у пацієнтів із міопією призводить до підвищення резервів акомодації в 3,8 раза, збільшення запасу відносної акомодації у 2,8 раза, найближчої точки ясного зору – на 2,4 см. Це свідчить про позитивний вплив на акомодаційні можливості міопічного ока і є засобом профілактики прогресування міопії.

Corneal Reshaping and Wavefront Aberrations During Overnight Orthokeratology

To investigate changes of corneal thickness at the vertical and horizontal meridians and of wavefront aberrations (WA) over a 30-day period of overnight myopia orthokeratology (OK) lens wear. Sixteen subjects (11 women, 5 men, 26.3±3.2 years) were enrolled and fitted for OK lenses. Long scan depth optical coherence tomography was used to measure corneal thickness profiles at both horizontal and vertical meridians at baseline and on days 1, 7, and 30 days. Corneal and ocular WA of a 6-mm pupil were measured and the root-mean-square (RMS) of the astigmatism, coma, spherical aberration (SA), and total higher-order aberrations (HOAs) were determined. During the 30-day period, the central cornea thinned in the horizontal and vertical meridians, whereas corneal thickening occurred in the temporal, nasal, and inferior mid-peripheries. In contrast, the cornea thinned in the mid-peripheral superior. There were significant increases in RMS for astigmatism, SA, coma, and positive horizontal coma during the study period. After OK, there were significant positive correlations between the midperipheral-central thickness change difference and the changes in corneal and ocular RMS of total HOAs and SA (r range: 0.281 to 0.492, P<0.05). Only the change of corneal coma RMS was correlated with midperipheral-central thickness change difference (r=0.270, P<0.05). The change in corneal horizontal coma was correlated with the temporal-nasal thickness change difference (r=-0.289, P<0.05). Overnight OK caused unique changes in corneal thickness profiles at the vertical and horizontal meridians and increased corneal and ocular HOAs related to corneal reshaping.

Corneal Power Change Is Predictive of Myopia Progression in Orthokeratology

This study aims to investigate the relationship between corneal refractive power change along three axes (nasal, temporal, and inferior) after orthokeratology (OK) treatment and 2-year axial growth in children. Thirty-two Chinese children aged from 9 to 14 were fitted with OK. When corneal reshaping process following OK treatment was completed and stabilized, the 3-month topographic outputs were taken as the post-OK data. Corneal refractive powers along the nasal, temporal, and inferior axes were collected over an 8-mm-diameter ring in 1-mm steps using the sagittal power map. The maximum power change along each axis was selected and divided into two subcategories, level 1 and level 2, depending on whether the value was below or above the average. Axial length (AL) was measured every 6 months during a 24-month period. The relationship between the maximum power changes and 2-year axial elongation were analyzed. Twenty-seven subjects completed the 24-month study. After OK treatment, statistically significant steepening (p < 0.05) was observed at the nasal 2 mm and 3 mm; temporal 3 mm; and inferior 2 mm, 3 mm, and 4 mm locations compared with the apical center. AL increased significantly throughout the 24-month observation period (p < 0.001). Changes in corneal refractive power significantly affected axial elongation (nasal, p = 0.001; temporal, p = 0.011; inferior, p = 0.001). Two-year axial elongation in patients with larger corneal power changes (level 2) was reduced by 54% to 69% compared with those with smaller corneal power changes (level 1). Maximum power changes along the three axes were negatively correlated (p < 0.05) with 2-year axial growth. Subjects with larger magnitude of corneal relative peripheral power change along specific axes after OK treatment experienced slower axial elongation by the end of 24 months. This effect might be mediated by the induction of greater amount of relative myopic defocus on the peripheral retina. Our study lends weight to potential OK lens designs for myopia control in children.

Overnight orthokeratology is comparable with atropine in controlling myopia

BackgroundMany efforts have been invested in slowing progression of myopia. Among the methods, atropine administration and orthokeratology (OK) are most widely used. This study analyzed the efficacy of atropine and OK lens in controlling myopia progression and elongation of axial length.MethodsThis retrospective study included 105 patients (210 eyes) who wore OK lenses and 105 patients (210 eyes) who applied 0.125% atropine every night during the 3 following period. Student t-test, linear regression analysis, repeated measure ANOVA, and Pearson’s correlation coefficient were used for statistical analysis.ResultsThe change in axial length per year was 0.28 ± 0.08 mm, 0.30 ± 0.09 mm, and 0.27 ± 0.10 mm in the OK lens group, and 0.38 ± 0.09 mm, 0.37 ± 0.12 mm, and 0.36 ± 0.08 mm in the atropine group for years 1, 2, and 3, respectively. Linear regression analysis revealed an increase in myopia of 0.28 D and 0.34 D per year, and an increase in axial length of 0.28 mm and 0.37 mm per year in the OK lens and atropine groups, respectively. Repeated measure ANOVA showed significant differences in myopia (p = 0.001) and axial length (p < 0.001) between the atropine and OK lens groups; in astigmatism, there was no significant difference in these parameters (p = 0.320). Comparison of increases in axial length in relation to baseline myopia showed significant correlations both in the OK lens group (Pearson’s correlation coefficient, r = 0.259; p < 0.001) and atropine group (r = 0.169; p = 0.014). High myopia patients benefited more from both OK lenses and atropine than did low myopia patients. The correlation of baseline myopia and myopia progression was stronger in the OK lens group then in the atropine group.ConclusionsOK lens is a useful method for controlling myopia progression even in high myopia patients.

Short-Term Changes in Ocular Biometry and Refraction After Discontinuation of Long-Term Orthokeratology

To assess refractive and biometric changes 1 week after discontinuation of lens wear in subjects who had been wearing orthokeratology (OK) contact lenses for 2 years. Twenty-nine subjects aged 6 to 12 years and with myopia of -0.75 to -4.00 diopters (D) and astigmatism of ≤1.00 D participated in the study. Measurements of axial length and anterior chamber depth (Zeiss IOLMaster), corneal power and shape, and cycloplegic refraction were taken 1 week after discontinuation and compared with those at baseline and after 24 months of lens wear. A hyperopic shift was found at 24 months relative to baseline in spherical equivalent refractive error (+1.86±1.01 D), followed by a myopic shift at 1 week relative to 24 months (-1.93±0.92 D) (both P<0.001). Longer axial lengths were found at 24 months and 1 week in comparison to baseline (0.47±0.18 and 0.51±0.18 mm, respectively) (both P<0.001). The increase in axial length at 1 week relative to 24 months was statistically significant (0.04±0.06 mm; P=0.006). Anterior chamber depth did not change significantly over time (P=0.31). Significant differences were found between 24 months and 1 week relative to baseline and between 1-week and 24-month visits in mean corneal power (-1.68±0.80, -0.44±0.32, and 1.23±0.70 D, respectively) (all P≤0.001). Refractive change at 1 week in comparison to 24 months strongly correlated with changes in corneal power (r=-0.88; P<0.001) but not with axial length changes (r=-0.09; P=0.66). Corneal shape changed significantly between the baseline and 1-week visits (0.15±0.10 D; P<0.001). Corneal shape changed from a prolate to a more oblate corneal shape at the 24-month and 1-week visits in comparison to baseline (both P≤0.02) but did not change significantly between 24 months and 1 week (P=0.06). The effects of long-term OK on ocular biometry and refraction are still present after 1-week discontinuation of lens wear. Refractive change after discontinuation of long-term OK is primarily attributed to the recovery of corneal shape and not to an increase in the axial length.

The impact of amplitude of accommodation on controlling the development of myopia in orthokeratology

To evaluate the impact of amplitude of accommodation on controlling the development of myopia in orthokeratology. Forty-nine children aged 7 to 14 years were enrolled in this prospective clinical study.Orthokeratology was performed to correct the refractive errors of these children after measurement of refraction, corneal topography, amplitude of accommodation and axial length. Axial length (AL) and amplitude of accommodation was measured after treatment. The average amplitude of accommodation was calculated and was used as the cutting point for dividing the cohort into "amplitude of accommodation above average" vs. "amplitude of accommodation below average". Data were analyzed by paired t-test, independent t-test, repeated measures-ANOVAs and Pearson correlation analysis. The AL before and after 1- year and 2-year treatment was (24.98 ± 0.75) mm, (25.13 ± 0.74) mm and (25.32 ± 0.78) mm, respectively. AL increased significantly throughout the observed 24-month period (F = 75.848, P < 0.001) . Amplitude of accommodation increased from (13.68 ± 2.65) D to (16.12 ± 2.41) D in 2 years (t = -6.461, P < 0.001) and amplitude of accommodation significantly affected axial growth (F = 7.395, P = 0.009) . The axial growth of subjects with below average amplitude of accommodation and those with above average amplitude of accommodation was (0.23 ± 0.25) and (0.44 ± 0.30) mm, indicating a statistically difference(t = -2.719, P = 0.009). AL change in subjects with below average amplitude of accommodation was 55.81% that of the subjects with above average amplitude of accommodation. Baseline amplitude of accommodation was positively correlated to axial growth at 24-month visit (r = 0.502, P < 0.001). Linear regression analysis was used between baseline amplitude of accommodation and 2-year axial growth: Axial growth = 0.055· Baseline amplitude of accommodation-0.409(F = 15.806, P < 0.001). The change of amplitude of accommodation for subjects with below average amplitude of accommodation and those with above average amplitude of accommodation after 2-year was (4.04 ± 2.16) D and (0.91 ± 2.15) D, indicating statistically difference (t = 5.084, P < 0.001). Myopic control effect would be more beneficial to lower amplitude of accommodation children than that to higher amplitude of accommodation children in orthokeratology. The enhancement of accommodation provides some basis for slowing myopia progression with orthokeratology.

Corneal thickness and endothelial observation for youth myopia patients fitted with ortho-k lens for seven years

To observe the changes of the corneal thickness and endothelial cell for youth myopia patients fitted with long-term orthokeratology (Ortho-K, OK). Retrospective case series study. During 2000 to 2005, 30 patients with OK lens wearing more than seven years in the Bei Yi Optometry & Ophthalmology Center had been chose in this study, and all the right eye of each person was selected for retrospective case statistics (30 eyes). the measure instruments, including A scan pachymeter and endothelium microscope, were used to the long-term continuous supervise, which involved the central and para-peripheral corneal thickness, corneal endothelium and corneal conjunctival complications rate. Then the 30 patients were divided into two groups: the moderate-low myopia group is less than -4.00 D with 12 patients (24 eyes), and the high myopia group is more than -5.00 D with 10 patients (20 eyes). And the difference between two groups was involved in this research. The one-way analysis of variance was used to compare before, after six months, after one year, after three years, after five years and after seven years OK lens wearing for the patients. And the variance analysis was used to compare between moderate-low and high myopia groups. Corneal thickness analysis during these seven years: the average central corneal thickness before and after seven-years wearing are (549.45 ± 33.72) and (538.97 ± 34.28) µm, respectively, and the central corneal thickness had no significant changes (F = 1.749, P = 0.076); The corneal thickness of nasal, superior, temporal and inferior also had no significant changes (P > 0.05). The average corneal endothelial cell densities before and after seven-years wearing are (3188.53 ± 272.25) and (3186.64 ± 278.69) num/mm(2), respectively, and the corneal endothelial cell density had no significant changes during seven years wearing (F = 2.204, P = 0.088). The average hexagonal cell ratio before and after seven-years wearing are 66.18% ± 6.42% and 64.65% ± 8.03%, respectively, and the hexagonal cell ratio had no significant changes during seven-years wearing (F = 2.097, P = 0.085). The average cell area and coefficient of variation also had no significant change during seven-years wearing (F = 2.143, 2.114; P > 0.05). There was also no statistics significance between moderate-low and high myopia of the endothelial cell and the corneal thickness change with long-term OK lens wearing. The slight corneal conjunctival complication was occurred during seven-year wearing, such as corneal fluorescence stain (less than 7%), and no serious complication was happened during seven-year wearing. In generally, it is safety for youth with long-term scientific and standardized wearing high Dk material orthokeratology contact lens.

The security evaluation of corneal endothelium in the children wearing orthokeratology contact lens for longterm

Background Wearing of orthokeratology contact lens can slow down the development of myopia,especially in childhood.However,if wearing orthokeratology contact lens for long-term affect the corneal health is worthy of consideration.Objective This study was to evaluate the security of wearing orthokeratology contact lens in children.Methods A retrospective case-observational study was adopted.One hundred and fifty eyes of 76 myopic children aged 8-15 years were enrolled in Shanghai Tenth People's Hospital during December,2009 to December,2011.Orthokeratology contact lens were worn at night for 8-10 hours daily.Area of corneal endothelial cells,density of corneal endothelial cells,coefficient of variation of corneal endothelial cells and percentage of hexagonal cells were measured before wearing and 3,6,12,24 months after wearing.Repeated measurement of single factor analysis of variance was used to evaluate the changes of corneal endothelial cells after wearing of orthokeratology contact lens.Results No significant differences were found in the area of corneal endothelial cells and density of corneal endothelial cells among the different time points (F =11.34,P＞0.05 ; F =7.16,P＞0.05).A significant difference was seen in the coefficient of variation of corneal endothelial cells at various time points in the children(F=12.70,P=0.02),and the coefficient of variation of corneal endothelial cells was 0.36±0.02 24 months after wearing lens,which was higher than 0.28 ±0.05 before wearing lens (P＜0.05).In addition,the percentage of hexagonal cells in different time points was significantly different (F=13.40,P =0.04),and the percentages of hexagonal cells at 12 hours and 24 months after wearing lens were (62±12)％ and (60±14)％ respectively,which was significantly lower than (69±12)％ before wearing lens (P＜0.05).Conclusions Wearing of orthokeratology contact lens for over one year leads to the decrease of percentage of hexagonal cells and increase of coefficient of variation of corneal endothelial cells. Key words: Ametropy/myopia ; Childhood ; Orthokeratology contact lens ; Corneal endothelial cells ; Security

Can Manipulation of Orthokeratology Lens Parameters Modify Peripheral Refraction?

To investigate changes in peripheral refraction, corneal topography, and aberrations induced by changes in orthokeratology (OK) lens parameters in myopes. Subjects were fitted with standard OK lenses that were worn overnight for 2 weeks. Peripheral refraction, corneal topography, and corneal surface aberrations were measured at baseline and after 14 nights of OK lens wear. Subsequent to a 2-week washout period, subjects were refitted with another set of lenses where one eye was randomly assigned to wear an OK lens with a smaller optic zone diameter (OZD) and the other eye with a steeper peripheral tangent. Measurements were taken again at a second baseline and after 14 days of overnight wear of the second OK lens set. Standard OK lenses with a 6-mm OZD and 1/4 peripheral tangent caused significant changes in both peripheral refraction and corneal topography. Significant hyperopic shift occurred in the central visual field (VF) while a myopic shift was found at 35 degrees in the nasal VF. OK induced significant reductions in corneal power at all positions along the horizontal corneal chord except at 2.4 mm nasal where there was no significant change and at 2.8 mm nasal where there was an increase in corneal refractive power. A positive shift in spherical aberration was induced for all investigated lens designs except for the 1/2 tangent design when calculated over a 4-mm pupil. Reducing OZD and steepening the peripheral tangent did not cause significant changes in peripheral refraction or corneal topography profiles across the horizontal meridian. OK lenses caused significant changes in peripheral refraction, corneal topography, and corneal surface aberrations. Modifying OZD and peripheral tangent made no significant difference to the peripheral refraction or corneal topography profile. Attempting to customize refraction and topography changes through manipulation of OK lens parameters appears to be a difficult task.

Subjective Satisfaction in Long-term Orthokeratology Patients

To evaluate the subjective satisfaction in visual stability, night vision complains, and light distortion phenomena, and also the number of hours and days per week of lens wear, in patients with myopia undergoing orthokeratology (OK) treatment for at least 1 year. A visual analog scale (VAS) questionnaire containing 18 items was administered to 44 patients, 29 women and 15 men (mean age, 24.39 ± 9.11 years), with a baseline spherical equivalent refractive error of -2.40 ± 0.94 diopters and astigmatism up to -0.5 diopters. Average treatment period by the time of data collection was 19 ± 7 months. Patients rated their satisfaction with the correction, with complaints of visual distortion being graded on a scale of 0 to 10, where 0 indicated no discomfort at all. More than 50% of patients skipped lens wear at least 1 night per week. The most common wearing pattern was 6-8 hours a day for 72.7% with 54.5% of patients wearing lenses every 2-3 nights only. Subjective vision scores after lens removal was 9.1 ± 1.1 after having worn the lenses and 8.1 ± 1.4 after skipping lens wear for 1 night. Subjective vision scores before lens insertion at the end of the day was 6.9 ± 2.0 and 5.8 ± 2.4, respectively. The number of hours until noticeable blur reduced with increased level of baseline myopia (r = 0.396; P < 0.001). Orthokeratology patients show an irregular wearing pattern after 1 year of treatment that has significant effects on the subjective visual performance over the next day of skipping lens wear. Light distortion under low-light conditions seems to be a transient complication of the treatment and most of the patients report an improvement after the first weeks of treatment.

Long-term changes in straylight induced by corneal refractive therapy: A pilot study

To assess long-term intraocular straylight changes induced by corneal refractive therapy (CRT) and to determine whether these changes persist after cessation of CRT lens wear. A single-center, prospective, longitudinal study was performed in 22 subjects (group 1) undergoing overnight corneal refractive therapy for 1 year. Ten right eyes of 10 subjects (group 2) with emmetropia served as controls. In each subject, high contrast visual acuity (HCVA), manifest refraction and intraocular straylight were determined at several time points during treatment and 1 month after discontinuing treatment. Straylight was measured using the van den Berg straylight meter (third generation). EDTRS charts (logMAR units) were used to assess HCVA. For both groups, only data for the right eyes were analyzed. Straylight (mean ± standard deviation) significantly fell from baseline (0.98 ± 0.13) to values recorded after 1 month (0.88 ± 0.13, p=0.011), 3 months (0.88 ± 0.13, p=0.004), 6 months (0.88 ± 0.13, p=0.000) and 12 months (0.76 ± 0.12, p=0.003) of treatment. One month after discontinuing CRT lens wear, straylight was still significantly lower than baseline (0.89 ± 0.13, p=0.003). No correlations were observed between intraocular straylight and HCVA. Good refractive outcomes and reductions in straylight were observed in response to corneal refractive therapy for myopia. The reduction in straylight observed after discontinuing CRT warrents further investigation.

Short-Term Effects of Overnight Orthokeratology on Corneal Epithelial Permeability and Biomechanical Properties

To investigate the effects of 30 nights of overnight orthokeratology (OOK) on corneal epithelial permeability (Pdc) and corneal biomechanical properties. BE Retainer and Paragon CRT lenses were used. Visits were scheduled approximately 4 hours after awakening at baseline and after 1, 5, 10, 14, and 30 days of treatment. Pdc was measured at baseline and at day 30, whereas corneal biomechanical properties and visual acuities (VAs) were measured at all visits. Thirty-nine neophytes and soft contact lens wearers completed the study. There was no difference in Pdc between baseline (ln[Pdc] [95% confidence interval (CI)] = -2.65 [-2.80 to -2.50]) and day 30 (ln[Pdc][CI] = -2.68 [-2.85 to -2.50]) (P = 0.88). Corneal hysteresis (CH) and corneal resistance factor (CRF) reduced significantly from baseline (CH [CI] = 10.89 [10.59-11.19] mm Hg and CRF [CI] = 10.35 [9.99-10.72] mm Hg) to day 30 (CH [CI] = 10.59 [10.31-10.87] mm Hg and CRF [CI] = 9.58 [9.26-9.89] mm Hg) (P = 0.001 for CH and P < 0.001 for CRF). Posttreatment VA did not reach baseline targets, and the difference was worse with low-contrast letters. Asian individuals (n = 18) had significantly worse VA than non-Asian individuals (n = 21) under most conditions through day 5, and the difference extended through day 14 with low-contrast letters under mesopic conditions. The percentage of participants who achieved 20/20 uncorrected was 17% Asian and 40% non-Asian individuals after day 1 and reached 69% Asian and 83% non-Asian individuals at day 30. Thirty nights of OOK did not alter Pdc when measured 4 hours after awakening. OOK caused CH and CRF to decrease, but the changes were not clinically significant compared with diseased and postsurgical cases. Asian individuals, who had lower baseline CH in this study, responded slower to OOK based on early uncorrected VA and overrefraction measurements.

Ocular Changes after Simulated Ejection Following Orthokeratology

Purposes: To determine the stability of subjects' visual acuity, refraction, corneal topography, pachymetry, anterior chamber depth, and intraocular pressure following overnight orthokeratology when subjected to vertical acceleration at six times the force of gravity (+6 Gz) in a simulated ejection system on the ground. Methods: The subjects were 10 healthy male flight surgeons, aged 25-26 years (mean 25.3), who had undergone overnight orthokeratology for two weeks before controlled rapid-sequence ejection at +6 Gz. Their visual acuity, refraction, and corneal parameters, including corneal curvature, corneal thickness, anterior chamber depth, and intraocular pressure, were recorded before, immediately after, and 20 min after the +6 Gz ejection. We compared the study group findings with those of a control group of 20 subjects who had not undergone orthokeratology but were exposed to the same ejection procedure. Results: The measurements of visual acuity, refraction, and Orbscan topographic parameters, including the anterior and posterior corneal curvatures, central corneal thickness, and intraocular pressure, made before, immediately after, and 20 min after ejection did not differ significantly between the pre- and post ejection values on paired t tests. The only significant difference in the orthokeratology group was in the anterior chamber depth, which was 2.978 mm before ejection and 3.01mm 20 min after ejection (p ＜ 0.05). Conclusion: The visual acuity, refraction, and corneal topographic changes in patients after orthokeratology are stable under rapid vertical ejection at six times the force of gravity. An increase in anterior chamber depth was the only significant change after ejection in the orthokeratology group.

Corneal Versus Ocular Aberrations After Overnight Orthokeratology

To investigate relationships between changes to corneal and ocular aberrations induced by orthokeratology (OK) and their influence on visual function. Eighteen subjects (aged 20 to 23 years) were fitted with OK lenses (BE Enterprises Pty Ltd, Australia), manufactured in Boston XO material (Bausch & Lomb Boston, Wilmington, MA), and worn overnight for seven nights. Corneal and ocular aberrations were simultaneously captured (Discovery, Innovative Visual Systems, Elmhurst, IL), and contrast sensitivity function was measured on days 1 and 7, within 2 and 8 hours after lens removal on waking. Data from the eye achieving the higher myopic correction were analyzed for changes over time. There was a significant refractive effect at all visits. Orthokeratology induced an increase in corneal and ocular root mean square higher order aberrations (HOAs) and a positive shift in spherical aberration (SA) on day 1, with further increases by day 7. Increases in root mean square coma became significant by day 7. Changes to corneal and ocular SA were similar on day 1; however, by day 7, there was a greater increase in corneal than ocular SA, indicating a change in internal SA. Orthokeratology led to an overall decrease in contrast sensitivity function, which was isolated to spatial frequency changes on day 1 at 1 cycle per degree and on day 7 at 1 and 8 cycles per degree. A greater positive shift in corneal compared with ocular SA on day 7 suggests a negative shift in internal SA, which would be consistent with an increased accommodative response. Lack of any difference on day 1 indicates that this may be an ocular adaptation response toward neutralizing induced positive SA, rather than a direct effect of SA changes on the accommodation mechanism.

Recovery Evaluation of Induced Changes in Higher Order Aberrations From the Anterior Surface of the Cornea for Different Pupil Sizes After Cessation of Corneal Refractive Therapy

To assess corneal aberration changes induced by corneal refractive therapy (CRT) for different pupil sizes and to examine the recovery after cessation of contact lens wear. A single-center, prospective, and longitudinal study was performed. Thirty-four subjects who underwent CRT for 1 year were included. High-contrast corrected distance visual acuity (CDVA), manifest refraction, and corneal topography were determined during the treatment and 1 month after the discontinuation of the treatment. Corneal aberrations were calculated using the Vol-CT 6.89 software. Corneal spherical aberration, Z(4,0), and root mean square values (RMS) for coma-like, trefoil, tetrafoil, and higher order aberrations (HOAs) were estimated for different pupil sizes (3-, 4-, 5-, 6-, and 7-mm diameters). Early Treatment Diabetic Retinopathy Study charts were used to measure CDVA. The CRT treatment induced a statistically significant increase of all aberrations studied for all pupil diameters. RMS values for coma-like, trefoil, and tetrafoil aberrations and HOAs after cessation of contact lens wear were not statistically significantly different for any of the different pupil diameters studied at baseline. However, Z(4,0) significantly increased from baseline to 1 month after discontinuation of the CRT lens wear for 5-, 6-, and 7-mm diameter pupils. Our results suggest that CRT is a treatment completely reversible at 1 month after cessation of contact lens wear in terms of CDVA, refractive error, and RMS of coma-like aberrations and HOAs for all pupil sizes. However, for spherical aberration, 1 month is not enough to recover to the baseline level.

Refractive Changes From Hyperopic Orthokeratology Monovision in Presbyopes

To investigate the time course of refractive and corneal topographic changes in overnight hyperopic orthokeratology (OK) for emmetropic presbyopes. Sixteen adult emmetropic presbyopic subjects were fitted with rigid hyperopic OK lenses (BE Enterprises, Brisbane, Australia/Capricornia, Slacks Creek, Australia) targeted to correct +2.00 D, in one eye only. The fellow eye acted as a non-lens-wearing control. Thirteen subjects completed the study. Lenses were worn overnight for a 7-day period, and changes in subjective refraction and corneal topography were measured in the morning on lens removal (A.M.) and 8 hr after lens removal (P.M.). There were statistically significant changes from baseline in all variables at all visits in lens-wearing eyes. Hyperopic OK caused a -1.00 (0.33) D shift in best vision sphere refraction at Day1 A.M., and -1.11 (0.61) D, at Day7 A.M., with -0.91 D of best vision sphere change from baseline still apparent by Day7 P.M. (mean [SD]). This led to an improvement in monocular near visual acuity (VA) from Jaeger 10.8 (2.4) at baseline to Jaeger 4.6 (2.5) at Day1 A.M., Jaeger 3.2 (2.3) at Day7 A.M., and Jaeger 3.9 (3.0) at Day7 P.M. Binocular distance VA did not change from baseline. The central cornea steepened, and the mid-peripheral nasal cornea flattened at lens removal after one night of wear. There was no significant difference in central corneal steepening between A.M. visits, but there was longer retention of effect by Day7 P.M. Nasal paracentral corneal flattening also showed a greater effect and longer retention of effect by Day7. Hyperopic OK induced central corneal steepening and paracentral corneal flattening, which led to a monovision myopic shift in refraction that was sufficient to provide functional correction of near vision. Lack of change in binocular distance VA indicates that hyperopic OK offers a viable option for providing monovision correction in emmetropic presbyopia.