Long-term Changes in Corneal Morphology Induced by Overnight Orthokeratology

Redistribution of Epithelium and Stroma and Their Relationship With Corneal Curvature After 1-Month Cessation of Overnight Orthokeratology

OBJECTIVES

To investigate the changes in the thickness of epithelium and stroma and their relationship with corneal curvature following the cessation of overnight orthokeratology for a period of 1 month.

METHODS

This prospective study consecutively included 20 juveniles (20 right eyes) who had undergone overnight orthokeratology for a minimum of one year and were willing to discontinue the treatment. The study measured and compared epithelial and corneal curvature using optical coherence tomography and Medmont topographer at the first day of cessation and 1 month after cessation. In addition, changes in uncorrected visual acuity and refractive error before and after the cessation of the treatment were analyzed.

RESULTS

The study found a significant increase in the thickness of the epithelium in the central 2-mm area after the cessation of the treatment (t = -4.807, P <0.001). Moreover, the stroma in the paracentral area (2-5 mm) and peripheral area (5-6 mm) showed a general thinning trend ( P =0.016, P =0.016). Regarding the correlation analysis, the change in central epithelial thickness (ΔCET) was significantly correlated with the change in paracentral corneal curvature (ΔPCCC) (r=0.610, P =0.007) and the change in peripheral corneal curvature (ΔPCC) (r=0.597, P =0.009). Similarly, the change in central stromal thickness (ΔCST) was significantly correlated with the change in central corneal curvature (ΔCCC) (r=0.500, P =0.035), ΔPCCC (r=0.700, P =0.001), and ΔPCC (r=0.635, P =0.005).

CONCLUSIONS

The study found that the corneal remodeling induced by orthokeratology was reversible after the cessation of the treatment. Specifically, changes in the epithelium were found to be more prominent in the central area, while changes in the stroma were more pronounced in the paracentral and peripheral areas. In addition, the study established a significant correlation between central corneal remodeling and changes in curvature.

In vivo assessment of human corneal epithelial cells in orthokeratology lens wearers: A pilot study

SIGNIFICANCE

Central corneal epithelial thinning associated with midperipheral epithelial thickening has been reported as the main factor contributing to the effectiveness of orthokeratology (ortho-k) in myopia control. Yet, the cellular mechanism governing the regional change in refractive power remains elusive.

PURPOSE

This study aimed to evaluate the correlation between the regional change in corneal epithelial thickness and cell density in ortho-k wearers.

METHODS

A new human prototype of a polarization-dependent optical coherence microscope was developed to enable noncontact and noninvasive in vivo imaging of corneal epithelial cells in ortho-k wearers with and without their ortho-k lens. The epithelial thickness and cell density were evaluated at the central and midperipheral corneal locations in four ortho-k wearers and four spectacle wearers serving as controls.

RESULTS

Polarization-dependent optical coherence microscope achieved in vivo volumetric imaging of all epithelial cell types in ortho-k wearers with and without their lens over a field of view of 0.5 × 0.5 mm 2 with an isotropic resolution of ~2.2 mm. The central epithelial thinning and midperipheral epithelial thickening were consistent across all ortho-k wearers. However, the inconsistency in their regional epithelial cell density highlighted a great variability in individual response to ortho-k treatment. There was no strong correlation between epithelial thickness and cell density, especially at the midperipheral cornea, in ortho-k participants.

CONCLUSIONS

This study constitutes our first step toward uncovering the cellular mechanism underlying the effectiveness of ortho-k in myopia control. Future studies will focus on the longitudinal evaluation of epithelial cells before and during ortho-k treatment to identify factors governing individual response to ortho-k treatment and ultimately inform the dynamics of epithelial cells taking place during the ortho-k treatment.

Systematic Review of Myopia Progression after Cessation of Optical Interventions for Myopia Control

Despite high discontinuation rates for myopia optical interventions, limited attention has been given to the potential rebound effects post-discontinuation. This systematic review aims to assess the extent of the rebound effects following the cessation of common clinical optical myopia-control interventions in children. A comprehensive search of PubMed, Embase, Cochrane CENTRAL, and ClinicalTrials.gov was conducted from inception to October 2023. The rebound effects, defined as changes in the axial length or spherical equivalent during and after treatment cessation, were categorized into four levels. These studies encompassed 703 participants and spanned from 2019 to 2023, with durations of treatment and cessation ranging from 6 months to 3.5 years and from 2 weeks to 5 years, respectively. This review, encompassing 14 studies, revealed a predominant strong rebound effect in orthokeratology (8 studies), a weak rebound effect in multifocal soft contact lenses (4 studies), and a variable rebound effect in peripheral-plus spectacle lenses (2 studies). Notably, with the increasing cessation duration, the rebound effects diminished, potentially linked to the reversal of choroidal thickening and the disappearance of peripheral myopic defocus. In conclusion, a temporal trend of rebound effects exists in all three myopia optical interventions, possibly contributing to their myopia control mechanisms.

Short-term Changes in Epithelial and Optical Redistribution Induced by Different Orthokeratology Designs

OBJECTIVES

This study aimed to investigate corneal epithelial and topographic changes caused by two commercial myopia orthokeratology (ortho-k) designs.

METHODS

Twenty-six subjects fitted with vision shape treatment (VST) lenses and 30 subjects fitted with corneal reshaping therapy (CRT) lenses were reviewed 1 day, 1 week, and 1 month after lens initiation. A spectral-domain optical coherence tomography system was used to create epithelial maps that were in turn used to determine the average epithelial thickness of each zone and the diameter of treatment zone. By measuring the topographic tangential differential map, the treatment zone diameter and the power and width of the high convex zone (HCZ) were obtained. All epithelial thicknesses and topographic corneal variations recorded were analyzed.

RESULTS

At the central zone, the epithelial thickness changes (△ET) decreased significantly after 1 day of ortho-k in two groups. At 2- to 9-mm peripheral zone, ortho-k increased △ET until 1 week in the VST group, whereas it kept increasing in the CRT group after 1 week. At 1 month, the central △ET is -9.51±2.38 mm in the VST group, which was comparable to -8.72±3.43 mm in the CRT group. The nasal HCZ power and the △ET of nasal and inferior nasal were significantly larger in the CRT group. A positive correlation was found between the HCZ power and △ET generated by VST-type lenses inferiorly and temporally. For the CRT group, a positive correlation was found between inferior HCZ power and △ET.

CONCLUSIONS

At the early stage of ortho-k, epithelial thickness and topography change quickly and simultaneously. Epithelial changes were in line with corneal topography reshaping. Epithelial and optical remodelling were affected by different lens types.

The alterations in ocular biometric parameters following short-term discontinuation of long-term orthokeratology and prior to subsequent lens fitting: a preliminary study

PURPOSE

To investigate the alterations in biometric parameters among Chinese adolescents over an extended period of wearing orthokeratology lenses, as well as the subsequent changes after a one-month cessation of lens usage prior to the secondary lens fitting.

METHODS

Twenty-four myopic patients aged 7-14 were enrolled in this 37-month prospective observational study. Ocular biometric parameters were measured in the study. Ocular biometric parameters were assessed, and the utilization of Generalized Estimating Equations (GEE) was employed in the analysis to address the correlation between the two eyes of each participant.

RESULTS

The axial length (AL) increased by 0.55 mm after 36 months of lens wearing and further increased to 0.62 mm at the 37-month follow-up compared to the initial measurement. The differences in AL elongation per month between the 37-month time point and the 12-, 24-, and 36-month marks of lens wearing were found to be statistically significant (p12-month = 0.001; p24-month = 0.003; p36-month = 0.001). Following the cessation of lens wear for 1 month, there was no significant complete recovery observed in the flat and steep keratometry values. However, the intraocular pressure and anterior chamber depth returned to their baseline levels.

CONCLUSIONS

The AL elongation undergoes alterations during temporary discontinuation of lenses, with the flat and steep keratometry measurements remaining significantly flatter compared to the baseline. However, the intraocular pressure and anterior chamber depth return to their initial levels after one month of lens cessation.

Orthokeratology in adults and effect on quality of life

OBJECTIVE

To determine changes in various ocular parameters of adults wearing orthokeratology (ortho-k) lenses and their levels of satisfaction and quality of life (QoL) after commencing treatment.

METHODS

Adults aged 18-38 years, with mild to moderate myopia and astigmatism < 1.50D, were wearing ortho-k lenses for one year. Data collection, which included history taking, refraction, axial length (AL), corneal topography, corneal biomechanics, and biomicroscopy examination, was performed at baseline and every 6 months during the study period. The level of satisfaction with the treatment and QoL was determined via questionnaires.

RESULTS

Forty-four subjects completed the study. AL was shortened significantly at the 12-month visit: AL -0.03 (-0.45 to 0.13) mm compared to baseline (p < 0.05). A significant number of subjects in both groups presented with overall and central corneal staining, but the majority were mild (Grade 1). Central endothelial cell density was reduced by 40/mm² (loss rate 1.4 %) (p < 0.05). High scores were obtained in the satisfaction questionnaire, with no significant differences between visits. At the 12-month visit, NEI-RQL-42 total score, dependence on correction, activity limitation, appearance, and satisfaction with the treatment all significantly increased compared to baseline values.

CONCLUSIONS

Results suggest that ortho-k can be an effective and safe myopia correction technique for adults with low to moderate myopia, improving daytime vision without serious adverse events. Satisfaction with ortho-k lens wear was high, particularly those who were dependent on vision correction and found spectacles or contact lenses limiting specific activities or cosmetically undesirable.

Modeling and Prediction of the Immediate and Short-Term Effect of Myopic Orthokeratology

PURPOSE

To characterize the clinical changes occurring in the initial phase of the orthokeratology (OK) treatment for myopia correction, developing a model of prediction of the refractive changes in such phase.

METHODS

Prospective study enrolling 64 eyes of 32 patients (range, 20-40 years) undergoing myopic OK treatment with the reverse geometry contact lens CRT (Paragon Vision Science). Changes in uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), refraction, corneal topography, ocular aberrations, and corneal epithelial thickness were evaluated during the first hour of OK lens wear and after 1 week of OK treatment. Multiple linear regression analysis was used to obtain a model to predict the short-term refractive effect of OK.

RESULTS

The UCVA improved at each visit, reaching normal visual acuity values after a week (P<0.001) of OK treatment, which was consistent with the significant spherical equivalent (SE) reduction and central flattening (P<0.001). Multiple linear regression analysis revealed that one night change in refraction (ΔR×1N) could be predicted according to the following expression (P<0.001, R2=0.686): ΔR×1N=1.042+0.028×Age+1.014×BCET (baseline central epithelium thickness)-0.752×BKm (baseline mean keratometry)-1.405×BSE (baseline SE)+1.032×ΔR×1 h (change in SE after 1 hr of OK lens use). Similarly, a statistically relevant linear relationship was obtained for predicting the refractive change after 1 week (ΔR×1W) of OK use (P<0.001, R2=0.928): ΔR×1W=3.470-1.046×BSE-1.552×BBCVA (baseline BCVA)-0.391×BKm+0.450×ΔR×1 h.

CONCLUSIONS

The immediate and short-term refractive effects of myopic OK with the reverse geometry contact lens CRT can be predicted with enough accuracy from baseline and first trial visits data.

[Effect of conventional and orthokeratological hard contact lenses on anatomical and functional characteristics of the cornea]

Contact lenses are widely used for correction of myopia due to their accessibility, effectiveness and relative safety.

PURPOSE

This study evaluated the potential effects of conventional hard contact lenses (HCL) and orthokeratological contact lenses (OKL) on anatomical and functional condition of the cornea in myopia correction.

MATERIAL AND METHODS

The study included 80 patients (159 eyes) with low, moderate and high myopia. Group 1 consisted of 40 patients (79 eyes) who used conventional HCL; group 2 included 40 patients (80 eyes) who used OKL. All patients underwent topographic keratometry, corneal pachymetry mapping (Pentacam, Oculus, Germany; Visante OCT, Carl Zeiss, Germany), high-order aberrometry (OPD Scan, Nidek, Japan), confocal microscopy (Confoscan 4, Nidek, Japan), evaluation of corneal biomechanical properties (ORA, Reichert Technologies, USA) and corneal light scattering (Pentacam, Oculus, Germany). Examinations were taken before the treatment started and after 8-12 months of contact lens wear.

RESULTS

Group 1 showed corneal thickness increase in all zones (by 0.9-1.1%), no significant changes in corneal refraction, and increase in corneal hysteresis and corneal resistance factor. OKL wear led to a significant flattening of anterior surface of the cornea and steepening of its paracentral area, decrease in central corneal thickness (by 2.8%) and increase in mid-peripheral thickness (by 2.2%). No significant changes in posterior corneal surface were observed in the study patients. More significant increase in higher-order aberrations and the degree of light scattering was observed in group 2, while changes in subepithelial nerve plexus and stromal structure were more significant in group 1.

CONCLUSION

Long-term OKL wear shows more significant morphological and functional corneal changes compared to RGP lens.

Corneal endothelial cell density and its correlation with birth weight, anthropometric parameters, and ocular biometric parameters in Chinese school children

Background

To describe the distribution of corneal endothelial cell density (ECD), and to explore its correlation with birth weight (BW), anthropometric parameters, and ocular biometric parameters in Chinese school children.

Methods

In the population-based cross-sectional Nanjing Eye Study, children were measured for anthropometric information, for ECD by the noncontact specular microscope and for ocular biometric parameters by the optic low-coherent reflectometer. Data from right eyes were analyzed to illustrate the distribution of ECD and for determining correlated factors with ECD using univariate and multiple linear regression analysis. Comparisons among three different BW groups were performed using a one-way ANOVA analysis followed by the Bonferroni correction for pairwise comparisons.

Results

Of 1171 children, the mean (± standard deviation) ECD was 2875.34 ± 195.00 cells/mm². In the Multiple Linear Regression analysis, BW, gender and central corneal thickness were significantly associated with ECD. The ECD increased by 36.16 cells/mm² with BW increasing by 1 kg (P = 0.001) and increased by 0.44 cells/mm² for every additional 1 mm in central corneal thickness (P = 0.01). The ECD of girls was 54.41 cells/mm² higher than boys (P < 0.001). Children born with low BW presented significantly lower ECD than those born with normal BW (P < 0.05) and high BW (P < 0.05). Age and axial length were not significantly associated with ECD (P = 0.06 and P = 0.21, respectively).

Conclusions

In Chinese school children aged 82 to 94 months, the ECD is positively correlated with BW and central corneal thickness, in which BW is a newly identified associated factor. It is like that gender plays an important role in ECD distribution while girls have relatively greater ECD than boys.

Post-Ortho-K Corneal Epithelium Changes in Myopic Eyes

The study is aimed at evaluating corneal epithelial thickness changes associated with overnight orthokeratology (ortho-K). In this retrospective study, epithelial thickness was measured using optical coherence tomography (OCT) before and after 1 day, 1 week, 1 month, and 3 months ortho-K nightly lens wear. Compared with pre-orthokeratology measurements, central (2 mm) corneal epithelium thickness was significantly reduced at 1 day, 1 week, 1 month, and 3 months with ortho-K (P < 0.05). Paracentral (2 mm~5 mm annular ring) epithelial thickness was also significantly reduced at superior temporal, inferior temporal, temporal, and inferior locations after ortho-K (P < 0.05), while midperipheral (5 mm~6 mm annular ring) epithelial thickness was greater post- than pre-ortho-K at superior, superior temporal, inferior temporal, inferior, and inferior nasal locations (P < 0.05). In other zones, superior, superior nasal, nasal, and inferior nasal in paracentral annular ring and temporal and superior nasal in midperipheral ring, epithelial thickness underwent no significant change. Ortho-K lens wear caused the central corneal epitheliums to thin. The temporal half zones become thinner in paracentral zones and thicker in midperipheral zones.

Changes in corneal densitometry after long-term orthokeratology for myopia and short-term discontinuation

Purpose

To quantify changes in corneal densitometry after long-term orthokeratology treatment in myopic children and to analyze the reversibility one month after discontinuation.

Methods

Seventy-four myopic subjects aged 8–16 years, who wore orthokeratology lenses for two years, were divided into relatively steep- (lens movement within 1.0–1.5 mm, thirty-six participants) and flat-fitting groups (lens movement within 1.5–2.0 mm, thirty-eight participants). Based on refractive errors, they were divided into low and moderate myopia groups (thirty-seven participants in each group). Corneal densitometry was performed using Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) at each follow-up timepoint. Repeated-measures analysis of variance was used to compare the parameters before and after orthokeratology.

Results

The corneal densitometry values over the 0–10 mm diameter area increased from 12.84±1.38 grayscale units (GSU) at baseline to 13.59±1.42 GSU after three-month orthokeratology (P = .001) and reached 14.92±1.45 GSU at two years (P < .001). An increase in densitometry began at one month (P = .001) over the 0–2 mm annulus compared with that at three months over the 2–6 mm and 6–10 mm zones (P = .002,.014). The densitometry values significantly increased at three months in the relatively steep-fitting group (P = .003) and at one year in the relatively flat-fitting group (P = .001). After discontinuation of orthokeratology for one month, the values showed no significant decrease.

Conclusions

Long-term orthokeratology treatment causes a small but statistically significant increase in corneal densitometry values. During the first year, the onset of these changes was related to the fitting mode. Corneal densitometry values showed no significant reduction after one-month discontinuation.

Change in Corneal Power Distribution in Orthokeratology: A Predictor for the Change in Axial Length

Purpose

To investigate the correlation between the change in spatial corneal power distribution and axial length (AL) elongation during orthokeratology (Ortho-k) treatment using mathematical methods.

Methods

Seventy-six subjects aged from eight to 13 years were fitted with Paragon CRT ortho-k lenses. Manifest refraction and corneal topography were checked at baseline and one day, one week, two weeks, one month, three months, six months, nine months, and one year after lens wear. AL was measured at baseline and the six-month and one-year follow-up visits. Relative corneal refractive power change (RCRPC) was calculated by a polynomial function and a monomial function. Factors including age, baseline spherical equivalent refractive error (SER), power exponent and RCRPC were tested against one-year AL growth in a stepwise multiple linear regression model.

Results

A total of 67 subjects completed the one-year study, with nine dropouts. The SER significantly reduced after the first month of lens wear (P < 0.001). AL significantly changed over time (P = 0.0003) with the annual growth being 0.32 ± 0.18 mm. Power exponent and RCRPC were stable throughout the follow-up visits (all P > 0.05). Change of AL was significantly correlated with baseline age (standardized β = −0.292, P < 0.001) and power exponent (standardized β = 0.691, P < 0.001), but not with the other factors being analyzed. The regression equation using baseline age (X₁) and power exponent (X₂) as functions for 1-year AL change (Y) was Y = 0.438-0.034X₁ + 0.309X₂, with R² being 0.752.

Conclusions

The asphericity of the treatment zone may affect axial elongation in children undergoing ortho-k therapy.

Translational Relevance

Because the ortho-k lens design may affect myopia control effect in children undergoing ortho-k therapy, future ortho-k lenses should consider applying these designs to obtain a better myopia control effect in children.

Nasal-temporal asymmetric changes in retinal peripheral refractive error in myopic adolescents induced by overnight orthokeratology lenses

Objective

To observe the changes in peripheral refraction in myopic adolescents after overnight orthokeratology and its influencing factors.

Methods

This was a prospective study among young myopic adolescents aged 8-14 years (n = 21). The peripheral refraction of the subjects was measured at 5, 10, 15, 20, 25, and 30° from the nasal and temporal side to the central fixation by WAM-5500 Open-field refractometer. The axial length, baseline spherical equivalent refraction, and other parameters were measured. The data were measured at baseline and 1, 3, and 12 months after wearing orthokeratology lenses.

Results

The relative peripheral refraction at the nasal and temporal side from central to 30° eccentricity revealed relative hyperopic defocus in all subjects at baseline measurement. One month after wearing the orthokeratology lenses, the relative peripheral refraction changed to myopic defocus, the nasal-temporal relative peripheral refraction was asymmetric, and the observed difference was statistically significant. Positive correlations were found between the change amount of nasal relative peripheral refraction and baseline spherical equivalent refraction, the baseline nasal relative peripheral refraction was higher than that on the temporal side, and after orthokeratology, the value of nasal relative peripheral refraction was lower than that on the temporal side. The changes at 30° on both sides were correlated to the axial elongation (r_Nasal = 0.565, r_Temporal = 0.526, p < 0.05).

Conclusion

This study demonstrated that after orthokeratology, relative peripheral hyperopia in the myopic patients turned into relative peripheral myopia, and the nasal-temporal asymmetry changed significantly after orthokeratology, which was correlated with the baseline refractive state.

A new approach for quantifying epithelial and stromal thickness changes after orthokeratology contact lens wear

The aim of the study was to develop an automatic segmentation approach to optical coherence tomography (OCT) images and to investigate the changes in epithelial and stromal thickness profile and radius of curvature after the use of orthokeratology (Ortho-K) contact lenses. A total of 45 right eyes from 52 participants were monitored before, and after one month of, uninterrupted overnight Ortho-K lens wear. The tomography of their right eyes was obtained using optical OCT and rotating Scheimpflug imaging (OCULUS Pentacam). A custom-built MATLAB code for automatic segmentation of corneal OCT images was created and used to assess changes in epithelial thickness, stromal thickness, corneal and stromal profiles and radii of curvature before, and after one month of, uninterrupted overnight wear of Ortho-K lenses. In the central area (0-2 mm diameter), the epithelium thinned by 12.8 ± 6.0 µm (23.8% on average, p < 0.01) after one month of Ortho-K lens wear. In the paracentral area (2-5 mm diameter), the epithelium thinned nasally and temporally (by 2.4 ± 5.9 µm, 4.5% on average, p = 0.031). The stroma thickness increased in the central area (by 4.8 ± 16.1 µm, p = 0.005). The radius of curvature of the central corneal anterior surface increased by 0.24 ± 0.26 mm (3.1%, p < 0.01) along the horizontal meridian and by 0.34 ± 0.18 mm (4.2%, p < 0.01) along the vertical meridian. There were no significant changes in the anterior and posterior stromal radius of curvature. This study introduced a new method to automatically detect the anterior corneal surface, the epithelial posterior surface and the posterior corneal surface in OCT scans. Overnight wear of Ortho-K lenses caused thinning of the central corneal epithelium. The anterior corneal surface became flattered while the anterior and posterior surfaces of the stroma did not undergo significant changes. The results are consistent with the changes reported in previous studies. The reduction in myopic refractive error caused by Ortho-K lens wear was mainly due to changes in corneal epithelium thickness profile.

Integrating Clinical Data and Tear Proteomics to Assess Efficacy, Ocular Surface Status, and Biomarker Response After Orthokeratology Lens Wear

Purpose

This study evaluated the efficacy and ocular surface status of Breath-O Correct, novel orthokeratology (OK) lenses, worn overnight for 3 months. Lens-induced changes in the tear proteome were evaluated.

Methods

Thirty-one subjects, aged 19 to 26 years with refractive error from -1.00 to -5.00 D, were randomly assigned 1:1 to the treatment or control group. Refraction, visual acuity, corneal integrity, biomechanics and endothelial health, ocular surface changes, and subjective symptoms were assessed at the baseline, one-month, and three-month visits. The tear proteome was characterized over time using sequential window acquisition of all theoretical ion spectra mass spectrometry.

Results

Lenses improved uncorrected visual acuity and reduced spherical powers with similar efficacy to other OK lenses. Significant reductions (P < 0.05) in corneal hysteresis (11.12 ± 1.12 to 10.38 ± 1.36 mm Hg) and corneal resistance factor (11.06 ± 1.32 to 9.90 ± 1.45 mm Hg) were observed in the treatment group after one month of lens wear, whereas other assessed factors remained unchanged. Thirteen and eight differentially expressed proteins were found after one month and three months of lens wear, respectively. Two proteins (proline-rich protein 27 and immunoglobulin V regions) were differentially expressed at both visits.

Conclusions

Over a three-month period, Breath-O Correct lenses were overall safe, well tolerated, efficacious in refractive power reduction, and comparable with other OK lenses. Furthermore, their use caused only minor noninflammatory protein expression changes in the tear proteome.

Translational Relevance

This study investigated the safety of orthokeratology contact lenses on the ocular surface in molecular aspects and standard clinical parameters.

Corneal thickness changes in myopic children during and after short-term orthokeratology lens wear

PURPOSE

To evaluate thickness changes in the central and mid-peripheral cornea (CCT and mPCT), corneal epithelium (CET and mPET) and stroma (CST and mPST) of myopic children during and after short-term orthokeratology (ortho-k) lens wear, with conventional (CCF, 0.75 D) and increased compression factors (ICF, 1.75 D).

METHODS

This was a self-controlled case series study. Subjects wore a CCF lens in one eye and an ICF lens in the other. Anterior segment optical coherence tomography images were captured weekly for 1 month during lens wear and for 2 weeks after discontinuing lens wear. CCT and CET (central 3-mm cornea) and mPCT and mPET (within a 4-6 mm diameter annulus) were measured. Stromal thickness (ST) was determined by subtracting epithelium thickness (ET) from corneal thickness (CT). The repeatability of the analytical software was also investigated on age-matched spectacle-wearing subjects (n = 98).

RESULTS

Excluding three outliers (>3 S.D.s), the coefficient of repeatability and intraclass correlation coefficients of 98 spectacle-wearing subjects ranged from 2.63 to 4.64 μm and from 0.90 to 0.99, respectively. For the weekly-change study, CCT and CET in both eyes were significantly thinner after lens wear (p < 0.001) and CET thinning in the ICF eyes were significantly higher (p < 0.02). CCT changes were mainly contributed by CET. CST, mPCT, mPET and mPST changes were not significant (p > 0.20) in either eye. CT (all sublayers) rebounded to baseline values 2 weeks after discontinuing lens wear (0.99 > p > 0.12).

CONCLUSIONS

Significant reductions in CT and ET, but not ST, were observed within 1 month of ortho-k lens wear. Wearing ICF lenses resulted in a higher reduction in CET. Corneal thickness changes were reversible after discontinuing lens wear.

CLEAR - Effect of contact lens materials and designs on the anatomy and physiology of the eye

This paper outlines changes to the ocular surface caused by contact lenses and their degree of clinical significance. Substantial research and development to improve oxygen permeability of rigid and soft contact lenses has meant that in many countries the issues caused by hypoxia to the ocular surface have largely been negated. The ability of contact lenses to change the axial growth characteristics of the globe is being utilised to help reduce the myopia pandemic and several studies and meta-analyses have shown that wearing orthokeratology lenses or soft multifocal contact lenses can reduce axial length growth (and hence myopia). However, effects on blinking, ptosis, the function of Meibomian glands, fluorescein and lissamine green staining of the conjunctiva and cornea, production of lid-parallel conjunctival folds and lid wiper epitheliopathy have received less research attention. Contact lens wear produces a subclinical inflammatory response manifested by increases in the number of dendritiform cells in the conjunctiva, cornea and limbus. Papillary conjunctivitis is also a complication of all types of contact lenses. Changes to wear schedule (daily disposable from overnight wear) or lens materials (hydrogel from SiHy) can reduce papillary conjunctivitis, but the effect of such changes on dendritic cell migration needs further study. These changes may be associated with decreased comfort but confirmatory studies are needed. Contact lenses can affect the sensitivity of the ocular surface to mechanical stimulation, but whether these changes affect comfort requires further investigation. In conclusion, there have been changes to lens materials, design and wear schedules over the past 20+ years that have improved their safety and seen the development of lenses that can reduce the myopia development. However, several changes to the ocular surface still occur and warrant further research effort in order to optimise the lens wearing experience.

Corneal Total and Epithelial Thickness Measured by Sonogage Ultrasound Pachometry and High-resolution Optical Coherence Tomography

SIGNIFICANCE

This research questions the validity of using the Sonogage ultrasound (US) pachometer to measure corneal epithelial thickness and coincidentally provides confirmation for the conventional view of the mechanism of orthokeratology (OK) based on central epithelial thinning.

PURPOSE

The Sonogage (Corneo-Gage Plus 1) pachometer uses A-scan US to measure total corneal thickness. It is claimed that this instrument can also measure corneal epithelial thickness. We sought to validate this claim by comparing total and epithelial thickness measurements with the Sonogage with those obtained with high-resolution optical coherence tomography (OCT).

METHODS

Fourteen non-contact lens wearers and 14 subjects who had worn Paragon CRT OK lenses overnight for greater than 1 month were recruited. Three OCT and five US measurements were taken in one eye of each subject. Depending on normality of data, paired t tests or Wilcoxon tests were used to compare total and epithelial thicknesses measured with the Sonogage pachometer and the Tomey Casia OCT. Pearson or Spearman correlation analyses were used to examine relationships between measurements obtained with the two instruments.

RESULTS

There was a significant difference in total corneal thickness measurements between the two instruments. Although a significant correlation was found (r = 0.916, P < .001), the Sonogage consistently measured greater total corneal thickness than did the OCT (+19.5 ± 9.2 μm; P < .001). Epithelial thickness using the Sonogage showed little variation (range, 46.4 to 50.0 μm), whereas epithelial thickness using the OCT ranged from 30.7 to 54.7 μm. There was no significant correlation between epithelial thicknesses obtained with the two instruments (r = -0.135, P = .49). Epithelial thickness measured by OCT was significantly thinner in OK wearers (35.8 ± 2.8 μm) than in nonlens wearers (46.7 ± 4.5 μm, P < .001).

CONCLUSIONS

The Sonogage is not able to measure epithelial thickness in vivo, returning essentially identical measurements over a range of epithelial thicknesses. Optical coherence tomography measurements confirm the conventional view of the mechanism of OK based on central epithelial thinning.

Full-field displacement measurement of corneoscleral shells by combining multi-camera speckle interferometry with 3D shape reconstruction

Changes in the biomechanical properties of the connective tissue of the eye occur with age and underlie the development of several ocular diseases, such as glaucoma, myopia, and keratoconus. The biomechanical dynamics of ocular connective tissue are measured by ex vivo inflation testing, in which intraocular pressure (IOP) is varied and optical methods are used to produce maps of corneal and scleral displacement. Current optical methods are limited by acquisition rate, occlusions, poor spatial resolution, and insufficient 3D mapping. We developed an interferometric optical method integrates four-camera electronic speckle pattern interferometry (ESPI) and a novel three-dimensional (3D) shape reconstruction process to measure shape and full-field mechanical deformations of corneal and scleral shells during ex vivo inflation testing. Each camera provides accurate measurements of the laser beam phase related to deformations of the specimen surface; a multi-view stereovision method generates the shape of the specimen and a functional form that links every pixel of a given camera to 3D points on the specimen's visible surface. In this way, dynamic deformations of the specimen are localized, with quantification of the time-dependent 3D displacements of the specimen at nanometric accuracy. The ESPI-3D system is suitable for analyzing scleral deformation and morphological changes caused by time-varying IOP.

Association between long-term orthokeratology responses and corneal biomechanics

Myopia is very prevalent worldwide, especially among Asian populations. Orthokeratology is a proven intervention to reduce myopia progression. The current study investigated association between baseline corneal biomechanics and orthokeratology responses, and changes of corneal biomechanics from long-term orthokeratology. We fitted 59 adult subjects having myopia between −4.00D to −5.00D with overnight orthokeratology. Corneal biomechanics was measured through dynamic bidirectional corneal applanation (in terms of corneal hysteresis, CH and corneal resistance factor, CRF) and corneal indentation (in terms of corneal stiffness, S and tangent modulus, E). Subjects with poor orthokeratology responses had lower E (mean 0.474 MPa) than subjects with good orthokeratology responses (mean 0.536 MPa). Successful orthokeratology for 6 months resulted in reducing CH (reduced by 5.8%) and CRF (reduced by 8.7%). Corneal stiffness was stable, but E showed an increasing trend. Among subjects with successful orthokeratology, a higher baseline S resulted in greater myopia reduction (Pearson correlation coefficient, r = 0.381, p = 0.02).

Current State and Future Trends: A Citation Network Analysis of the Orthokeratology Field

Introduction

Citation network analysis is a powerful tool that allows for a visual and objective representation of the past, present, and potential future directions of a research field. The objective of this study is using citation analysis network to analyse the evolution of knowledge in the field of orthokeratology.

Materials and Methods

The database used in this citation networks analysis study was Scopus. The descriptor used was “orthokeratology” limited to three fields: title, keywords, and/or abstract, analysing the five most cited authors. Only articles cited at least twenty times were used. The computer software used was UCINET with two types of analysis, qualitative and quantitative.

Results

27 nodes have been included according to the search and inclusion criteria. In qualitative analysis, based on illustrate results, the relationships among nodes and their positions and connections show how the study of Cho et al. in 2005 is clearly positioned as a central cutoff point in the network. Quantitative analysis reveals the normalized value of the sample and shows how the study of Cho et al. in 2005 presents the highest percentage of input connections.

Conclusions

This study shows the state of the flow of information in the orthokeratology field by providing links in bibliographic citations from a qualitative and quantitative point of view.

Modified Posterior Scleral Reinforcement as a Treatment for High Myopia in Children and Its Therapeutic Effect

Purpose

To investigate the safety and therapeutic effect of a modified posterior scleral reinforcement (PSR) in treating high myopia.

Methods

A total of 85 highly myopic eyes in 47 children (6.3±3.6 years of age, range from 3 years to 15 years) who underwent this modified PSR were included in this study. Axial length, refractive error, best-corrected visual acuity (BCVA), macular scans, and adverse events were recorded before the operation (as a baseline) and in postoperative reviews taken yearly for 5 years.

Results

This was a 5-year research: 50% of the children (20 children, 40 eyes) participated in the 6-month review, 41% of the children (17 children, 33 eyes) participated in the 1-year review, 26% of the children (11 children, 21 eyes) participated in the 2-year review, 16% of the children (7 children, 13 eyes) participated in the 3-year review, 13% of the children (5.3 children, 11 eyes) participated in the 4-year review, and 8% of the children (3.3 children, 7 eyes) participated in the 5-year review. Compared with the baseline, axial elongation was significantly changed (P<0.05) over the 5-year period in all of the children: 6-month (P=0.003), 1-year (P=0), 2-year (P=0), 3-year (P=0), 4-year (P=0), and 5-year (P=0). The axial length was extended. No significant difference was found in refractive error between measurements taken at baseline and at the 5-year postoperative visit in all of the children: 6-month (P=0.51), 1-year (P=0.50), 2-year (P=0.46), 3-year (P=0.56), 4-year (P=0.30), and 5-year (P=0.16). There were significant differences in BCVA between measurements taken at baseline and at the postoperative 5-year visit in all the children: 6-month (P=0), 1-year (P=0), 2-year (P=0), 3-year (P=0), 4-year (P=0), and 5-year (P=0). BCVA improved in 71 eyes (83.52%), remained stable in 14 eyes (16.47%), and declined in none of the children. No serious adverse events occurred before the operation and during the 5-year follow-up period.

Conclusion

This modified PSR could be a therapeutic treatment for high myopia.

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).

Short-Term Effects of Overnight Orthokeratology on Corneal Sensitivity in Chinese Children and Adolescents

Purpose

To assess the effects of the 3-month period of orthokeratology (OK) treatment on corneal sensitivity in Chinese children and adolescents.

Methods

Thirty subjects wore overnight OK lenses in both eyes for 3 months and were assessed at baseline, 1 day, 1 week, 1 month, and 3 months after the treatment. Changes in corneal sensitivity were measured by the Cochet–Bonnet (COBO) esthesiometer at the corneal apex and approximately 2 mm from the temporal limbus. Changes in refraction and corneal topography were also measured.

Results

Central corneal sensitivity suffered a significant reduction within the first month of the OK treatment period but returned to the baseline level at three months (F = 3.009, P=0.039), while no statistically significant difference occurred in temporal sensitivity (F = 2.462, P=0.074). The baseline of central corneal sensitivity correlated with age (r = −0.369, P=0.045). A marked change in refraction (uncorrected visual acuity, P < 0.001; spherical equivalent, P < 0.001) and corneal topographical condition (mean keratometry reading, P < 0.001; eccentricity value, P < 0.001; Surface Regularity Index, P < 0.001) occurred, but none of these measurements were correlated with corneal sensitivity.

Conclusions

A 3-month period OK treatment causes a reduction in central corneal sensitivity in Chinese children and adolescents but with a final recovery to the baseline level, which might be because neuronal adaptation occurred earlier in children and adolescents than in adults.

Comparison Between Viscous Teardrops and Saline Solution to Fill Orthokeratology Contact Lenses Before Overnight Wear

OBJECTIVE

To compare, in terms of efficacy, the differences between the use of saline solution and a viscous artificial tear to fill the lens during the first month of orthokeratology wear.

METHODS

A pilot, double-masked, crossed, randomized, and prospective study was conducted. In this study, 20 subjects (14 males and 6 females) with a mean age of 16.29±6.22 years (range, 10-26) were fitted with orthokeratology contact lenses. For the study, nonpreserved 0.9% NaCl commercial saline solution (Avizor, Madrid, Spain) and nonpreserved artificial teardrops with 0.3% of hyaluronic acid (Ocudry 0.3%; Avizor, Madrid, Spain) were used. Corneal staining, tear break up time (TBUT), topography, refraction, visual acuity, and subjective comfort and vision with the visual analog scale (score from 0 to 10, being 10 better comfort and vision) were evaluated at 1 day, 1 week, and 1 month of contact lens wear.

RESULTS

The corneal staining was statistically greater in the saline group than in the Ocudry group for the first day and during 1 week of wear (P<0.05). Comfort was found to be statistically better, with Ocudry 0.3% than saline solution, being 7.17±1.94 and 6.37±1.63, for the first day, and 8.78±0.43 and 8.15±0.62 for the day 28, respectively (P<0.05). However, no differences were found for subjective vision scores, TBUT, spherical equivalent, best-corrected visual acuity and uncorrected visual acuity, and mean keratometry between groups for any visit (P>0.05).

CONCLUSION

Viscous artificial tears improve the subjective comfort of patients and reduce the corneal staining, compared with saline solution during the orthokeratology lenses fitting process. However, no differences between solutions for the treatment efficacy, in vision and corneal topography, were found.

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.

Long-Term Changes in Straylight Induced by Overnight Orthokeratology: An Objective Measure Using the Double-Pass System

Purpose: To map the time course of changes in intraocular straylight of the human eye 1 year after initial lens wearing for orthokeratology treatment using the objective double-pass technique. Materials and Methods: A total of 35 subjects (19 males and 16 females) completed the study. The mean age was 11.46 ± 2.33 years (range, 8-16 years). All subjects were fitted with spherical four-zone orthokeratology lenses following the procedures recommended by the lens manufacturer. The subjects were required to wear the lens for at least eight consecutive hours at night. After lens removal during the daytime, objective scattering index (OSI) was evaluated using the double-pass technique (OQAS-II, Visiometrics, Terrassa, Spain) prior to lens dispatch (baseline), followed by evaluations at 1 week, 1 month, 6 months, and 12 months after the initial lens wearing. Longitudinal changes were fitted to a model containing both an impairing and recovery component, and the results were based on an extrapolation between the visits. Results: OSI rose quickly following lens wearing, reaching its highest level (double that of baseline values) by approximately 1.47 months. However, the recovery phase was slow and modest. One year after the initial lens wearing, OSI exhibited a 20% recovery from the peak level, but remained 63% higher than the baseline level. Conclusions: Intraocular straylight immediately increased flowing lens wearing, and this change reaches maximal level around 1 month after lens wearing. Slow but significant recoveries of optical quality subsequently followed.

Short-Term Effects of Overnight Orthokeratology on Corneal Sub-basal Nerve Plexus Morphology and Corneal Sensitivity

OBJECTIVE

To assess the effects of a short period of orthokeratology (OK) on corneal sub-basal nerve plexus (SBNP) morphology and corneal sensitivity.

METHODS

Measurements were made in 56 right eyes of 56 subjects with low-to-moderate myopia who wore 2 OK lens designs (Group CRT: HDS 100 Paragon CRT, n=35; Group SF: Seefree; n=21) for a period of 1 month and in 15 right eyes of noncontact lens wearers as controls. The variables determined in each participant were corneal sensitivity using a Cochet-Bonnet esthesiometer and 12 SBNP variables determined on laser scanning confocal microscopy images using 3 different software packages. Correlation between SBNP architecture and corneal sensitivity was also examined.

RESULTS

Few changes were observed over the 1-month period in the variables examined in the OK treatment and control groups. However, significant reductions were detected over time in the number of nerves in the central cornea in the groups CRT (P=0.029) and SF (P=0.043) and in central corneal sensitivity in CRT (P=0.047) along with significant increases in central and midperipheral corneal Langerhans cell counts in SF (P=0.001 and 0.048, respectively).

CONCLUSIONS

This study provides useful data to better understand the anatomical changes induced by OK in corneal SBNP. The different response observed to the 2 OK lens designs requires further investigation.

Posterior cornea and thickness changes after scleral lens wear in keratoconus patients

PURPOSE

To evaluate the changes in the corneal thickness, anterior chamber depth and posterior corneal curvature and aberrations after scleral lens wear in keratoconus patients with and without intrastromal corneal ring segments (ICRS).

METHODS

Twenty-six keratoconus subjects (36.95 ± 8.95 years) were evaluated after 8 h of scleral lens wear. The subjects were divided into two groups: those with ICRS (ICRS group) and without ICRS (KC group). The study variables evaluated before and immediately after scleral lens wear included corneal thickness evaluated in different quadrants, posterior corneal curvature at 2, 4, 6 and 8 mm of corneal diameter, posterior corneal aberrations for 4, 6 and 8 mm of pupil size and anterior chamber depth.

RESULTS

There was a statistically significant corneal thinning (p < 0.05) in the inferior region of the KC group and in the superior region of the ICRS group. No change (p > 0.05) in the anterior chamber depth was found. The KC group showed a steepening (p < 0.05) in the temporal quadrant and a flattening that mainly affected to the superior-nasal quadrant. The ICRS group showed a steepening (p < 0.05) that mainly affected to the superior-nasal quadrant. Regarding posterior corneal aberrations, only changes (p < 0.05) in Z4 for 8 mm and Z8 for 4 mm were found in the KC group.

CONCLUSIONS

Short-term scleral lens wear showed a thinning of the cornea and changes in the posterior corneal curvature affects different regions in keratoconus patients with and without ICRS.

Does a two-year period of orthokeratology lead to changes in the endothelial morphology of children?

PURPOSE

To compare changes in endothelial morphology in the central and superior cornea in subjects wearing single-vision spectacles and orthokeratology lenses over two years.

METHODS

Endothelial images of the two locations of 99 subjects (6-12 years) from completed myopia control studies were analysed. Endothelial cell density (ECD), coefficient of variation in cell size (CV), and hexagonality (HEX) before and two years after treatment were compared between the two groups of subjects.

RESULTS

Baseline ECD and CV in the central cornea were slightly lower than those in the superior cornea, but no significant difference in HEX was found in the two corneal locations. After two years, reduction in ECD and increase in CV were only significant in the central cornea, but not in the superior cornea. Reduction in HEX was significant in both corneal locations. Subjects receiving orthokeratology had smaller reduction in ECD in the central cornea compared to the controls (orthokeratology: 56±94 cells/mm²; control: 98±91 cells/mm², p=0.024), otherwise, there were no significant differences in the changes in endothelial morphology in the two corneal locations between the two groups of subjects.

CONCLUSIONS

The current study confirmed that there were differences in endothelial morphology of central and superior cornea of Chinese children aged 6-12 years. The morphological response to normal ageing differed between the two corneal locations as reduction in cell density and polymegathism were found only in the central cornea whilst pleomorphism was found in both locations. Orthokeratology lens wear had minimal effect on the developmental changes in endothelial morphology.

Repeatability and Reproducibility of Quantitative Corneal Shape Analysis after Orthokeratology Treatment Using Image-Pro Plus Software

Purpose. To evaluate the repeatability and reproducibility of quantitative analysis of the morphological corneal changes after orthokeratology treatment using “Image-Pro Plus 6.0” software (IPP). Methods. Three sets of measurements were obtained: two sets by examiner 1 with 5 days apart and one set by examiner 2 on the same day. Parameters of the eccentric distance, eccentric angle, area, and roundness of the corneal treatment zone were measured using IPP. The intraclass correlation coefficient (ICC) and repetitive coefficient (COR) were used to calculate the repeatability and reproducibility of these three sets of measurements. Results. ICC analysis suggested “excellent” reliability of more than 0.885 for all variables, and COR values were less than 10% for all variables within the same examiner. ICC analysis suggested “excellent” reliability for all variables of more than 0.90, and COR values were less than 10% for all variables between different examiners. All extreme values of the eccentric distance and area of the treatment zone pointed to the same material number in three sets of measurements. Conclusions. IPP could be used to acquire the exact data of the characteristic morphological corneal changes after orthokeratology treatment with good repeatability and reproducibility. This trial is registered with trial registration number: ChiCTR-IPR-14005505.

Consistency of Corneal Sublayer Thickness Measurements using Fourier-Domain Optical Coherence Tomography after Phacoemulsification

Purpose

To assess the reliability of corneal epithelial thickness (CET), nonepithelial central corneal thickness (NECCT), and central corneal thickness (CCT) measurements using Cirrus high-definition optical coherence tomography (HD-OCT) in patients who did and did not undergo cataract surgery.

Methods

Forty patients who underwent uneventful phacoemulsification and 40 healthy participants were recruited to evaluate the intraobserver repeatability and interobserver reproducibility of CET, NECCT, and CCT measurements using Cirrus HD-OCT. To analyze repeatability, one examiner obtained 5 consecutive scans in each participant; for interobserver reproducibility, another examiner randomly obtained another scan. Within-subject standard deviation, coefficient of variation (CV), limits of agreement, and intraclass correlation coefficient (ICC) data were obtained.

Results

For intraobserver repeatability, the intrasession CV (CVw) and ICC values of the CET in the operated and nonoperated groups were 3.7% and 0.80 and 3.8% and 0.73, respectively; for NECCT, 0.7% and 0.98 and 0.8% and 0.97; and for CCT, 0.6% and 0.99 and 0.7% and 0.98. For interobserver reproducibility, the CVw and ICC values for the CET in the operated and nonoperated groups were 2.6% and 0.82 and 2.3% and 0.62, respectively; for NECCT, 0.7% and 0.98 and 0.5% and 0.98; and for CCT, 0.5% and 0.99 and 0.4% and 0.99.

Conclusions

The corneal sublayer thickness can be measured reliably using Cirrus HD-OCT in patients who underwent cataract surgery and elderly participants; however, the CET consistency is poorer than the NECCT. Corneal epithelial thickness modifications exceeding 4% reflect true thickness changes instead of random error variations using HD-OCT.

An efficient intelligent analysis system for confocal corneal endothelium images

A confocal microscope provides a sequence of images of the corneal layers and structures at different depths from which medical clinicians can extract clinical information on the state of health of the patient's cornea. A hybrid model based on snake and particle swarm optimisation (S-PSO) is proposed in this paper to analyse the confocal endothelium images. The proposed system is able to pre-process images (including quality enhancement and noise reduction), detect cells, measure cell densities and identify abnormalities in the analysed data sets. Three normal corneal data sets acquired using a confocal microscope, and three abnormal confocal endothelium images associated with diseases have been investigated in the proposed system. Promising results are presented and the performance of this system is compared with manual and two morphological based approaches. The average differences between the manual and the automatic cell densities calculated using S-PSO and two other morphological based approaches is 5%, 7% and 13% respectively. The developed system will be deployable as a clinical tool to underpin the expertise of ophthalmologists in analysing confocal corneal images.

Corneal power change is predictive of myopia progression in orthokeratology

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

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.