Anterior and posterior corneal elevation after orthokeratology and standard and customized LASIK surgery

Efficacy of the DRL orthokeratology lens in slowing axial elongation in French children

Background

This study aims to assess and compare the impact of Orthokeratology Double Reservoir Lens (DRL) versus Single Vision Lenses (SVL) on axial elongation and anterior chamber biometric parameters in myopic children over a 6- and 12-month treatment period in France.

Methods

A retrospective study involving 48 patients aged 7 to 17 years, who underwent either orthokeratology treatment or single-vision spectacle correction, was conducted. Changes in refractive error, axial length, and anterior chamber depth were examined.

Results

Twenty-five patients comprised the Orthokeratology (OK) group, while twenty-three were in the control group (single-vision spectacle group). Significant increases in mean axial length were observed over time in both the control (0.12 ± 0.13 mm and 0.20 ± 0.17 mm after 6 and 12 months, respectively; F (2,28.9) = 27.68, p < 0.001) and OK groups (0.02 ± 0.07 mm and 0.06 ± 0.13 mm after 6 and 12 months, respectively; F (2,29.1) = 5.30, p = 0.023). No statistically significant differences in axial length were found between male and female children (p > 0.620). Age-specific analysis revealed no significant axial elongation after 12 months in the 14-17 years group in the OK group. Anterior biometric data analysis at 6 and 12 months showed statistical significance only for the DRL group.

Conclusion

Orthokeratology resulted in an 86 and 70% reduction in axial elongation after 6 and 12 months of lens wear, respectively, compared to the single-vision spectacles group. Myopia progression was more pronounced in younger children, underscoring the importance of initiating myopia control strategies at early ages.

Comparison of Corneal Power Difference Maps with Achieved Myopic Correction Using Scheimpflug Tomography After LASIK, PRK, and SMILE

Purpose

To compare corneal power difference maps (∆maps) obtained from the Pentacam in patients with 1 year follow-up after LASIK, PRK, and SMILE with further stratification to low, moderate, and high myopia.

Patients and methods

This retrospective study was comprised of patients who had preoperative and 1-year postoperative power maps that were obtained-front sagittal (SagF), refractive power (RP), true net power (TNP), and total corneal refractive power (TCRP)-for evaluation. Measurements were recorded and compared at the 4mm, 5mm and 6mm pupil and apex zones. Comparisons were made between each specific power ∆map and the surgically induced refractive change (SIRC). Further analysis of the ∆maps was performed based on degree of myopia (high, moderate, and low). Correlation and agreement were also assessed with regression and limits of agreement (LoA).

Results

There were 172 eyes in the LASIK group, 187 eyes in the PRK group, and 46 eyes in the SMILE group. In the LASIK group, TNP ∆map at 5mm pupil zone had the least absolute mean difference with SIRC (0.007 ± 0.42D). In the PRK group, TNP ∆map at 5mm apex zone was most accurate compared to SIRC (0.066 ± 0.45D). In the SMILE group, TCRP ∆map at 4mm apex zone had the closest absolute value when compared to SIRC (0.011 ± 0.50D). There was good correlation and agreement for all three surgery groups, LASIK: r = 0.975, LoA -0.83D to +0.83D, PRK: r = 0.96, LoA -0.83D and +0.95D, and SMILE: r = 0.922, LoA -0.97 D to +0.99D.

Conclusion

TNP ∆maps most accurately measured corneal power in the LASIK and PRK groups while TCRP ∆maps were most accurate in the SMILE group. The degree of myopia may change which ∆map is most accurate.

Posterior corneal elevation changes during 12 month of overnight orthokeratology

Aims

the aim of this study to investigate the elevation changes in posterior corneal surface after 12 months of orthokeratology (ortho-k) treatment.

Methods

In this retrospective chart review, medical records of 37 Chinese children who wore ortho-k lenses over 12 months were reviewed. The data of only right eye were analyzed. Variables including the flat and steep keratometry of anterior and posterior corneal principal meridians, central corneal thickness (CCT), posterior thinnest elevation of cornea (PTE), posterior central elevation of cornea (PCE) and posterior mean elevation of cornea (PME) were measured by Pentacam. Variables including anterior chamber depth (ACD), lens thickness (CLT) and ocular axis length (AL) were measured by optical biometry. All variables differences between baseline and 12 months after ortho-k treatment were assessed by statistical analyses.

Results

The average age of all subjects was 10.70 ± 1.75 years (range 8-15 years old). The baseline spherical equivalent (SE) was -3.26 ± 1.52 D (-0.50D to -5.00D). Both flat and steep keratometry of anterior corneal surface and CCT were significantly decreased after 12 month follow up during ortho-k treatment (both P < 0.000). Both flat and steep keratometry of posterior corneal surface were not significantly different after 12 month follow up compared with that of baseline (P = 0.426, 0.134 respectively). PCE, PTE and PME were not significantly changed over 12 months of ortho-k treatment (P = 0.051, 0.952 and 0.197 respectively). The ACD was significantly decreased in 12 month follow up during ortho-k treatment (P = 0.001). The CLT and the AL were significantly increased during this period (both P < 0.000).

Conclusion

Although the anterior corneal surface was significantly changed by ortho-k lens, the posterior corneal surface did not show any changes during 12 months follow up. Simultaneously, The ACD, CLT and AL were significantly changed during this period.

Axial length growth difference between eyes after monocular laser refractive surgery: eight patients who underwent myopic laser ablation for both eyes at intervals of several years

Background

Myopia is a global public health issue. Controlling myopia progression is a primary focus of myopia studies today. Peripheral retinal myopic defocus is considered the mechanism for reduced myopia progression in orthokeratology studies. The topographic change in the front corneal surface after laser refractive surgery and orthokeratology procedures may appear similar. The purpose of this study was to explore the role of myopic laser ablation on axial length (AL) growth.

Methods

Myopic patients who underwent monocular excimer laser refractive surgery first in one eye and then in another eye several years later because of myopia occurrence or myopia progression were recruited. The axial length elongation and refraction (spherical equivalent) between the two eyes were observed and compared.

Results

A total of 8 myopic patients were enrolled in the study. The AL increased from 24.52 ± 0.96 mm to 24.68 ± 1.03 mm but without significance (T = 1.49, P > 0.05) in the ablated eyes. The AL increased significantly from 23.73 ± 0.91 mm to 24.26 ± 0.95 mm in the nonablated eyes (T = 6.76, P < 0.001). The AL elongation of the ablated eyes with 0.16 ± 0.30 mm growth was significantly lower than that of the nonablated eyes with 0.53 ± 0.32 mm growth (T = 8.98, P < 0.001). The spherical equivalent (SE) increased significantly in the ablated eyes (− 0.59 ± 0.21 (D), T = 6.36, P < 0.001) and in the nonablated eyes (− 0.97 ± 0.55 (D), T = 4.91, P < 0.01), and the difference between the two eyes was significant (T = 3.05, P < 0.05).

Conclusions

The inhibitory effect of myopic laser ablation on AL elongation reported in the limited case studies argues for animal research on its efficacy as a new intervention for myopia progression.

Spotlight on the Corneal Back Surface Astigmatism: A Review

Recent evidence indicates that the corneal back surface astigmatism (CBSA) contributes to the refractive state of the eye in cataract surgery, especially with the implantation of toric intraocular lenses. But this has been met with some scepticism. A review of key studies performed over the past three decades shows that the mean CBSA power ranges from 0.18(±0.16)D to 1.04(±0.20)D. The clinical assessment of CBSA is problematic. There is poor agreement between the current automated systems for assessment of CBSA and it is assumed that these systems directly measure the CBSA. But CBSA cannot be measured directly in vivo. A historical review of methods used to quantify the curvature of the posterior corneal surface reveals that CBSA estimated by current systems is based on values for corneal front surface astigmatism, corneal refractive index, central corneal thickness, corneal thickness at peripheral locations and the exact distance between the corneal apex and each one of these peripheral locations. Doubts and errors in these values, coupled with the precise details of the algorithm incorporated to estimate CBSA, are the likely sources of the lack of agreement between current systems. These systematic errors cloud the assessment of CBSA. Mean CBSA may be low, but it varies from case to case. There is a clear need for a realistic, practical procedure for clinicians to independently calibrate systems for estimating CBSA. This would help to reduce uncertainty and the discrepancies between instruments designed to measure the same parameter.

Should Overnight Orthokeratology Patients Wear Their Lenses During Their Afternoon Nap?

PURPOSE

The purpose of this study was to evaluate changes in visual acuity, corneal curvature, elevation, pachymetry, and objective quality of vision of experienced orthokeratology patients using their contact lenses during a simulated 30-min afternoon nap.

METHOD

Twelve patients aged 30.8±8.3 years were recruited for the study, with a history of overnight orthokeratology of 27.4±23.0 months. Patients were instructed to close their eyes for 30 min while wearing their contact lenses or without lenses. Anterior corneal curvature, elevation, and corneal pachymetry were assessed with the Pentacam Scheimpflug System at 17 predefined corneal locations, and the HD Analyzer (Terrassa, Spain) was used to measure objective quality of vision. Measurements were conducted before eye closure (baseline), immediately after eye opening/lens removal (M1), and 30 min later (M2).

RESULTS

No statistically significant differences were found in anterior corneal curvature and elevation between baseline values and M1 or M2, with and without contact lenses. Corneal swelling at M1 was greater without contact lenses (change in central corneal thickness of 2.3%±3.1%, P=0.001) than with contact lenses (1.7%±1.3%, P<0.001). Recovery at M2 was slower when lenses were worn. A statistically significant improvement in objective quality of vision and visual acuity was found only when patients napped with their lenses.

CONCLUSIONS

Even if no significant changes were found in corneal curvature and elevation, patients of overnight orthokeratology may benefit from using their contact lenses during their afternoon nap in terms of objective quality of vision and visual acuity.

Orthokeratology and Low-Intensity Laser Therapy for Slowing the Progression of Myopia in Children

Orthokeratology (OK) is widely used to slow the progression of myopia. Low-level laser therapy (LLLT) provides sufficient low energy to change the cellular function. This research is aimed at verifying the hypothesis that LLLT treatment could control myopia progression and comparing the abilities of OK lenses and LLLT to control the refractive error of myopia. Eighty-one children (81 eyes) who wore OK lenses, 74 children (74 eyes) who underwent LLLT treatment, and 74 children (74 eyes) who wore single-vision distance spectacles for 6 months were included. Changes in axial length (AL) were 0.23 ± 0.06 mm for children wearing spectacles, 0.06 ± 0.15 mm for children wearing OK lens, and -0.06 ± 0.15 mm for children treated with LLLT for 6 months. Changes in subfoveal choroidal thickness (SFChT) observed at the 6-month examination were -16.84 ± 7.85 μm, 14.98 ± 22.50 μm, and 35.30 ± 31.75 μm for the control group, OK group, and LLLT group, respectively. Increases in AL at 1 month and 6 months were significantly associated with age at LLLT treatment. Changes in AL were significantly correlated with the baseline spherical equivalent refraction (SER) and baseline AL in the OK and LLLT groups. Increases in SFChT at 1 month and 6 months were positively associated with age at enrolment for children wearing OK lens. At 6 months, axial elongation had decelerated in OK lens-wearers and LLLT-treated children. Slightly better myopia control was observed with LLLT treatment than with overnight OK lens-wearing. Evaluations of age, SER, and AL can enhance screening for high-risk myopia, improve the myopia prognosis, and help determine suitable control methods yielding the most benefits.

Impact of ablation ratio on 5-year postoperative posterior corneal stability after refractive surgery: SMILE and FS-LASIK

BACKGROUND

To investigate the impact of the ablation ratio on 5-year postoperative posterior corneal stability in myopic eyes after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery.

METHODS

A prospective, nonrandomized, cohort study: 80 eyes of 43 patients underwent SMILE surgery and 63 eyes of 32 patients underwent FS-LASIK surgery at the EYE & ENT Hospital, Fudan University. Ablation ratio was defined as lenticule thickness (SMILE cases) or ablation depth (FS-LASIK cases) divided by central corneal thickness (CCT). Posterior corneal elevation changes were recorded as posterior central elevation (PCE), posterior corneal surface at thinnest point (PTE) and posterior corneal mean elevation (PME). Patients were followed up at 6-month and 5-year interval to investigate the impact of the ablation ratio on posterior corneal elevation after SMILE and FS-LASIK surgery.

RESULTS

PCE dropped at the 6-month follow-up for both SMILE (decreased by -1.11 ± 2.93 μm, P < 0.05) and FS-LASIK groups (decreased by -0.46 ± 3.72 μm, P < 0.05). PTE also dropped in SMILE (reduced by -2.04 ± 3.02 μm, P < 0.05) and FS-LASIK group (reduced by -1.28 ± 4.21 μm, P < 0.05) at the 6-month follow-up. Stable PCE (elevation change: SMILE -0.28 ± 4.03 μm; FS-LASIK 0.79 ± 4.13 μm, P > 0.05) and PTE (elevation change: SMILE -0.08 ± 4.28 μm; FS-LASIK 1.42 ± 3.85 μm, P > 0.05) for both groups were recorded at the 5-year follow-up compared to the 6-month visit. Ablation ratio was strongly correlated with 5-year postoperative PCE (β = 2.68 ± 1.05, P < 0.01) and PTE (β = 2.35 ± 1.17, P < 0.05). Cut-off value for 5-year postoperative raised PCE and PTE was 27.3 and 27.1%, respectively.

CONCLUSIONS

Ablation ratio was strongly correlated with postoperative posterior corneal elevation in a 5-year follow-up in both SMILE and FS-LASIK groups. PCE and PTE underwent slight backward displacement 6-month postoperatively and remain stable at the 5-year follow-up. Threshold of the ablation ratio for resisting forward displacement of posterior corneal surface was 27.3 and 27.1% for SMILE and FS-LASIK groups, respectively.

Retinal Response of Low Myopes during Orthokeratology Treatment

The aim of this study was to evaluate the changes in retinal activity during orthokeratology (OK) treatment in 20 myopic eyes. Pattern electroretinography (PERG) and visual evoked potential (VEP) were assessed with the RETI-port/scan21 (Roland Consult, Wiesbaden, Germany). Measurements were taken at baseline (BL) and 1 night (1N), 15 nights (15N), 30 nights (30N), and 60 nights (60N) of OK lens wear. Repeated measures analysis of variance (ANOVA) and the Friedman test were used. Twenty eyes (23.20 ± 3.46 years, 70% female) with visual acuity ≤ 0.00 logMAR in post-treatment showed that despite a slight increase in retinal and cortical response amplitude, observed with both PERG and VEP, respectively, immediately after the initial treatment, these differences found were not statistically significant during the 60 days of OK treatment, despite a statistically significant increase in N95 response with PERG. This shows that retinal and cortical visual-related electrical activity is maintained or slightly increased during OK treatment.

Comparison of four different orthokeratology lenses in controlling myopia progression

PURPOSE

To compare axial length (AL) elongation in myopic children with four Orthokeratology (OrthoK) lenses and spectacles.

METHODS

The medical records of 266 patients (532 eyes) who were fitted with OrthoK lenses or spectacles (control group) were reviewed. Data collection included baseline age, gender, baseline objective sphere and cylinder, baseline flat and steep corneal meridian power, corneal asphericity coefficient (Q value), AL at baseline and after 1-year, and 2-years of OrthoK or spectacle wear analyzed using analysis of repeated measures data ANOVA. Stepwise linear regressions between the changes in AL after 2 years relative to baseline parameters were calculated for the OrthoK and control groups separately.

RESULTS

The baseline subject parameters for each of the four OrthoK lenses were not statistically different. Statistically significant differences between time points were found between 12- and 24- months (all P < 0.05). AL growth was slower in all OrthoK groups than in the control group (all P < 0.05). AL grew 0.081±0.034 mm per year slightly less than average with Essence compared to the Mouldway OrthoK group (P = 0.019). The coefficient of regression weakly expressed between the increases in AL over 2-years study period and baseline spherical equivalent refraction was 0.065 in Essence, 0.079 in Euclid and 0.087 in Mouldway. The coefficient of regression was also weakly between age and the increases AL over 2-years study period and baseline age in all groups.

CONCLUSION

Different OrthoK lenses differ minimally in slowing axial elongation effectively in myopic children during 2-years lens wear.

Influence of Overnight Orthokeratology Lens Treatment Zone Decentration on Myopia Progression

Purpose

To investigate the effect of OK lens treatment zone decentration on myopia control.

Methods

We retrospectively selected 30 OK lens wearers who met the following conditions in our hospital from more than 1300 cases: wearing lens in both eyes and only one eye was off-center while the other one was centric for more than 12 months. During the period of follow-up, the UCVA of each eye was better than 0.1 of logMAR and there were no obvious tropia, Kappa angle, and complications such as glare and diplopia.

Result

Among 30 cases, 15 are males and 15 are females, with an average age of 9.3 ± 1.51Y. There were no significant differences in equivalent spherical lens, astigmatism, e value, flat K, steep K, astigmatism, lens diameter, and toric between the two groups (p > 0.05). The average distance of decentration was 0.73 ± 0.25 mm. Axis growth per year in was 0.20 ± 0.24 mm the OK-lens-decentered group and 0.29 ± 0.20 mm in the OK-lens-centric group, which shows significant difference between them (p < 0.05). According to the direction of decentration, 30 decentered eyes were divided into temporal group (20 eyes) and other direction group (10 eyes). The efficiency of myopia control (the growth of AL per year in OK-lens-decentered eye/the growth of AL per year in the contralateral OK-lens-centric eye) was 0.69 ± 0.50 in the temporal decentration group and 0.75 ± 0.52 in the other direction group, showing no significant difference between them (p > 0.05). There was no significant correlation between the efficiency of myopia control and the degree of decentration among temporal decentration group (p > 0.05).

Conclusion

This self-control study without much interference factors shows that the decentration of OK lens can delay the development of myopia more effectively than being centric when uncorrected visual acuity was acceptable without obvious corneal complications, glare, or ghosting.

Refractive, biometric and corneal topographic parameter changes during 12 months of orthokeratology

BACKGROUND

The aim of this study was to monitor refractive, topographic and biometric changes in Singaporean myopic children fitted with orthokeratology over a period of 12 months.

METHODS

Data from 62 myopic eyes from an Asian population corrected with orthokeratology were retrospectively collected from an optometric clinic in Singapore. Anterior segment parameters were analysed with a Pentacam. Axial length was measured using the IOLMaster and refraction was assessed by subjective examination before the treatment and after one night, one week, and one, three, six and 12 months. A logistic regression model was built to evaluate the probability of slower (< 0.10 mm/year) or faster eye growth (≥ 0.10 mm/year).

RESULTS

Subjects had a mean age of 12.2 ± 3.9 years (range 5-19 years), and 71 per cent were female. Baseline myopia was -3.95 ± 1.59 D (range -1.50 and -8.75 D). Statistically significant differences were found after 12 months of treatment for refractive error, parameters of the central anterior corneal surface (curvature and elevation) and central corneal thickness. Topographic and thickness changes stabilised after one week of treatment. During 12 months of orthokeratology treatment there was a significant increase of axial length (difference = 0.11 ± 0.18 mm, p < 0.001) while refraction remained stable. Changes in axial length of subjects above 11 years were not statistically significantly independent of the baseline myopia, and in subjects with baseline myopia greater than 4.00 D. Logistic regression showed that each additional year of age and each additional dioptre of baseline myopia decreased the probability of faster axial elongation (odds ratio [OR] = 1.23, 2.19 95% CI; OR = 1.08, 3.47 95% CI, respectively).

CONCLUSION

Corneal parameters in orthokeratology treatment were stable after one week, particularly for myopes under 4.00 D. Axial length did not change significantly in children older than 11 years of age or in subjects with myopia above 4.00 D undergoing orthokeratology treatment.

IMI - Clinical Myopia Control Trials and Instrumentation Report

The evidence-basis based on existing myopia control trials along with the supporting academic literature were reviewed; this informed recommendations on the outcomes suggested from clinical trials aimed at slowing myopia progression to show the effectiveness of treatments and the impact on patients. These outcomes were classified as primary (refractive error and/or axial length), secondary (patient reported outcomes and treatment compliance), and exploratory (peripheral refraction, accommodative changes, ocular alignment, pupil size, outdoor activity/lighting levels, anterior and posterior segment imaging, and tissue biomechanics). The currently available instrumentation, which the literature has shown to best achieve the primary and secondary outcomes, was reviewed and critiqued. Issues relating to study design and patient selection were also identified. These findings and consensus from the International Myopia Institute members led to final recommendations to inform future instrumentation development and to guide clinical trial protocols.

One-year effect of wearing orthokeratology lenses on the visual quality of juvenile myopia: a retrospective study

Objective

To study the one-year effect of wearing orthokeratology (OK) lenses on the visual quality of juvenile myopia.

Methods

The right eyes of 36 juvenile myopias were retrospectively studied in this work. Q-value, e-value, corneal curvature, strehl ratio (SR), modulation transfer function (MTF) and wavefront aberration (WA) were compared before and at 1, 3 and 12 months after wearing OK lenses. The SR, MTF and WA of cornea, internal optic and ocular were analyzed separately. The spherical and cylinder diopter, vision acuity, compensating factor (CF) and compensative rate (CF%) were compared before and at 12 months after wearing OK lenses.

Results

(1) The vision of LogMAR increased and the corneal curvature decreased significantly after wearing OK lenses. There was no significant difference for the e-value before and after wearing OK lenses. The Q-value increased at 1 month but decreased at 3 and 12 months remarkably. (2) The ocular and internal optic SR and MTF increased significantly at 1 month and then remained stable. The MTF in different spacial frequencies increased after wearing OK lenses. There was no significant difference for the corneal SR before and after wearing OK lenses, and the corneal MTF decreased significantly after wearing OK lenses. (3) For the ocular, the total higher order aberration (HOA), spherical, coma and trefoil aberrations increased, and the total aberration, total lower order aberration (LOA) and defocus aberration decreased obviously except astigmatism. The corneal aberrations increased significantly after wearing OK lenses except astigmatism. For the internal optic, the total aberration, total LOA and defocus aberration decreased, and the total HOA, coma and trefoil aberration increased significantly except the astigmatism and spherical aberrations. (4) The CF and CF% of total aberration, total LOA, total HOA and coma aberrations increased, and those of astigmatism and spherical decreased at 12 months.

Conclusions

Orthokeratology is effective in correcting the refractive error and improving the vision quality of juvenile myopia over the one-year follow-up period.

Corneal morphology and visual outcomes in LASIK patients after orthokeratology: A pilot study

A STATEMENT OF SIGNIFICANCE

For the first time, this study shows that corneas that previous undergone orthokeratology treatment do not respond differently to LASIK compared with previous soft contact lens wear experience.

PURPOSE

To evaluate and compare the corneal morphology and visual outcomes of long-term soft and orthokeratology (OK) contact lens fitting in wearers undergoing corneal refractive surgery (LASIK) for myopia correction.

METHODS

Sixteen (16) myopic patients wearing hydrophilic soft contact lens (SCL, n = 8 subjects, control group) and OK (n = 8 subjects, OK group) lenses who undergone LASIK were retrospectively evaluated. Preoperative fitting of contact lenses and one year postoperative were studied using Pentacam (Oculus, Inc. GmbH, Wetzlar, Germany). Corneal pachymetry and volume, corneal topography, anterior and posterior surface elevation data and the anterior surface aberrometry of the cornea were recorded and used for fitting.

RESULTS

Age, refractive error and topographic parameters before LASIK did not showed statistically significant differences between the two study groups. LASIK post-treatment results showed identical changes in both control and OK groups and did not show significant differences in all the parameters evaluated. The changes on corneal parameters and HOA due to refractive surgery intervention were not different between Control and OK group (p > 0.050).

CONCLUSIONS

Corneal changes due to OK treatment are reversible after its discontinuation. The present study gives an overview of how OK does not impair future LASIK surgery for the correction of myopia and does not influence the success/results of such intervention. These findings suggest that OK CL wear does not change corneal biomechanics and does not compromise a possible LASIK refractive surgery. Although this is a pilot study and there is a need of evaluate this results/changes in future studies.

Effects of Orthokeratology on Choroidal Thickness and Axial Length

PURPOSE

To investigate the effect of orthokeratology (ortho-k) treatment on choroidal thickness and its relationship with axial length change.

METHODS

Seventy-seven myopic subjects aged between 7 and 17 years were treated with ortho-k lenses (n = 39) or single-vision spectacle lenses (SVL, n = 38). Choroidal thickness and axial length measurements were taken at baseline and repeated 1 week and 3 weeks after lens wear for the ortho-k group and at 3 weeks for the SVL group. Parafoveal choroidal thickness was assessed using optical coherence tomography and segmented into nine regions according to the Early Treatment Diabetic Retinopathy Study (ETDRS) within a 6 × 6 mm circular zone centered on the fovea. Axial length was measured using partial coherence interferometry. The changes in subfoveal choroidal thickness were compared to the changes in axial length in both study groups.

RESULTS

The change in axial length was significantly correlated with the change in choroidal thickness in both groups at 3 weeks (ortho-k, r = -0.351, p = 0.028 vs. SVL, r = -0.408, p = 0.011). Parafoveal choroidal thickness increased after 3 weeks of lens wear in the ortho-k group (mean, 21.8 ± 25.2 μm) but did not change in the SVL group (mean, 0.1 ± 19.7 μm). Choroidal thickness significantly varied across the posterior retinal regions (F = 82.14, p < 0.001), with the temporal regions being thickest and nasal regions being thinnest. After 3 weeks of ortho-k treatment, the magnitude of change (range, 14.1-27.6 μm) in choroidal thickness of the nine ETDRS regions was proportional to the baseline choroidal thickness in those regions (r = 0.88, p = 0.002). Axial length did not significantly change over time (F = 0.001, p = 0.975) and did not differ between the two treatment modalities (F = 0.305, p = 0.582).

CONCLUSIONS

Choroidal thickness increases after short-term ortho-k treatment. Regional choroidal thickening after ortho-k treatment may be attributable to the altered retinal defocus profile associated with ortho-k lens wear.

The analysis of corneal asphericity (Q value) and its related factors of 1,683 Chinese eyes older than 30 years

Purpose

To determine corneal Q value and its related factors in Chinese subjects older than 30 years.

Design

Cross sectional study.

Methods

1,683 participants (1,683 eyes) from the Handan Eye Study were involved, including 955 female and 728 male with average age of 53.64 years old (range from 30 to 107 years). The corneal Q values of anterior and posterior surfaces were measured at 3.0, 5.0 and 7.0mm aperture diameters using Bausch & Lomb Orbscan IIz (software version 3.12). Age, gender and refractive power were recorded.

Results

The average Q values of the anterior surface at 3.0, 5.0 and 7.0mm aperture diameters were -0.28±0.18, -0.28±0.18, and -0.29±0.18, respectively. The average Q value of the anterior surface at the 5.0mm aperture diameter was negatively correlated with age (B = -0.003, p<0.01) and the refractive power (B = -0.013, p = 0.016). The average Q values of the posterior surface at 3.0, 5.0, and 7.0mm were -0.26±0.216, -0.26±0.214, and -0.26±0.215, respectively. The average Q value of the posterior surface at the 5.0mm aperture diameter was positively correlated with age (B = 0.002, p = 0.036) and the refractive power (B = 0.016, p = 0.043).

Conclusion

The corneal Q value of the elderly Chinese subjects is different from that of previously reported European and American subjects, and the Q value appears to be correlated with age and refractive power.

Pachymetry map of corneal epithelium in children wearing orthokeratology contact lenses

PURPOSE

To study the pachymetry map of the corneal epithelium in children wearing orthokeratology lenses automatically generated by a Fourier-domain optical coherence tomography.

MATERIALS AND METHOD

The study was conducted on 60 children who had been fitted with myopic orthokeratology lenses. Patients were divided into two groups according to the duration of OK lens treatment (group 1: ≤14 days, n = 28; group 2: >14 days, n = 32). The control group consisted of 44 children. An FD-OCT device with a pachymetry module was used to map the central 6-mm corneal epithelial thickness. An epithelial thickness map was automatically generated and divided into three zones: central 2 mm, paracentral 2 to 5 mm (P1) and mid-peripheral 5 to 6 mm (P2). The average epithelial thickness of central (C), the temporal (T1), nasal (N1), superior (S1) and inferior (I1) sectors of P1, and the temporal (T2), nasal (N2), superior (S2) and inferior (I2) sectors of P2 were recorded and compared. The minimum and maximum points of epithelial thickness across the map were also recorded. Munnerlyn's formula was used to model the expected change in refractive error based on Δ(Max-Min) (Δ(Max-Min) = (Max-Min)study-(Max-Min) mean of control).

RESULTS

The central epithelial thickness was significantly different between individual groups and a significant difference from the control (Group 0) was seen in each treatment group. Both the epithelial thickness measurements of T1 and I1 were thinnest in Group 1. Both the epithelial thickness measurements of S2 and I2 were thickest in Group 2. The difference between maximum and minimum thickness was significantly different between groups with the largest effect in Group 2. The refractive changes predicted by Munnerlyn's formula were less than the actual refractive changes measured in both study groups.

CONCLUSIONS

The epithelial thickness map automatically generated by FD-OCT can provide regional information about corneal epithelium thickness following overnight wearing of OK lenses.

Anterior segment changes produced in response to long-term overnight orthokeratology

PURPOSE

To evaluate the effect of overnight orthokeratology (OK) on anterior chamber depth (ACD), posterior radius of corneal curvature (PRCC) and axial length (AL) over one year.

METHODS

In this prospective longitudinal study, measurements were made in 34 right eyes of 34 subjects at baseline, 15 days, 1 and 12 months after starting OK treatment. ACD and PRCC measurements were obtained using a Pentacam system and AL was measured using an IOL-Master. ACD and PRCC were measured along the horizontal and vertical meridians at 1 mm intervals. These measurements were expressed as the distance from the center in the nasal (N), temporal (T), superior (S) and inferior (I) directions.

RESULTS

A significant reduction in ACD was observed in both meridians during treatment. PRCC flattened significantly in the (T) direction after 15 d (1 mm, p < 0.05), at the corneal center after 15 d (p < 0.01), in the (T) direction after 1 month (1 mm, p < 0.05), in the (S) direction after 12 months (1 mm p < 0.05), in the (N) direction after 12 months (1 mm p < 0.05), in the (N) and (T) directions after 12 months (3 mm, p < 0.05) and in the (T) direction after 12 months (4 mm p < 0.05), at the corneal center after 12 months (p < 0.01). AL was significantly reduced during treatment (p < 0.05).

CONCLUSIONS

A long period of OK reduces ACD and AL and changes PRCC.