A pilot study on the corneal biomechanical changes in short-term orthokeratology

Orthokeratology effect on the corneoscleral profile: Beyond the bull's eye

PURPOSE

To assess the impact of 3 months of orthokeratology (ortho-k) contact lenses (CLs) for myopia correction on the corneoscleral profile, as changes in scleral geometry could serve as indirect evidence of alteration in the corneal biomechanical properties.

METHODS

Twenty subjects (40 eyes) were recruited to wear ortho-k lenses overnight; however, after discontinuation (two CL fractures, one under-correction and two non-serious adverse events), 16 subjects (31 eyes) finished a 3-month follow-up. Corneoscleral topographies were acquired using the Eye Surface Profiler (ESP) system before and after 3 months of lens wear. Steep (SimKs) and flat (SimKf) simulated keratometry and scleral sagittal height measurements for 13-, 14- and 15-mm chord lengths were automatically calculated by the ESP software. Additionally, sagittal height and slope were calculated in polar format from 21 radii (0-10 mm from the corneal apex) at 12 angles (0-330°). Linear mixed models were fitted to determine the differences between visits.

RESULTS

SimKs and SimKf were increased significantly (p ≤ 0.02). The sagittal height in polar format increased significantly (p = 0.046) at a radius of 2.5 mm for 150°, 180°, 210° and 240° orientations and at a radius of 3.0 mm for 210°. Additionally, the slope in polar format significantly decreased (p ≤ 0.04) at radii ranges of 0.0-0.5, 0.5-1.0 and 1.0-1.5 mm for multiple angles and at a radii range of 5.0-5.5 mm for 90°. It also increased significantly (p ≤ 0.045) at a radii range of 1.5-2.0 mm for 30° and at radii ranges of 2.0-2.5, 2.5-3.0 and 3.0-3.5 mm for multiple angles. No significant changes were found for any parameter measured from the scleral area.

CONCLUSIONS

Three months of overnight ortho-k lens wear changed the central and mid-peripheral corneal geometry as expected, maintaining the peripheral cornea and the surrounding sclera stability.

The corneal biomechanical differences after wearing orthokeratology lenses and multifocal soft lenses in children: A self-control study

BACKGROUND

To compare the changes in corneal biomechanics after orthokeratology (OK) lens and Defocus Incorporated Soft Contact (DISC) lens treatment.

METHODS

Of 28 myopic children were recruited, with one eye wearing OK lens and the other eye wearing DISC lens for one year, and the data after discontinued for 4 weeks were also collected. Major outcomes were corneal biomechanics and axial length (AL) elongation.

RESULTS

Throughout the follow-up period, the DISC group had longer the first applanation (A1) time, larger A1 deformation amplitude, A1 deflection length (A1 DLL), and A1 deflection amplitude than the OK group. AL elongation was less in the OK group at each visit (all P < 0.05) but faster in the OK group than in the DISC group after discontinuation (P = 0.006). Moreover, AL elongation was related to baseline A1 time, A1 velocity and whole eye movement max in the DISC group, and in the OK group, was related to the baseline the second applanation (A2) DLL, A2 delta arc length and stiffness parameter A1 (all P < 0.05).

CONCLUSIONS

The cornea was more deformable after wearing DISC lens than OK lens, and corneal biomechanical parameters were associated with AL elongation. Eyes showed less AL elongation during OK lens treatment while faster AL elongation after discontinuation than DISC lens. The baseline corneal biomechanics may help to predict AL elongation in myopic control strategies.

Evaluation of changes in corneal biomechanics after orthokeratology using Corvis ST

PURPOSE

To investigate the alterations in corneal biomechanical metrics induced by orthokeratology (ortho-k) using Corvis ST and to determine the factors influencing these changes.

METHOD

A prospective observational study was conducted to analyze various Corvis ST parameters in 32 children with low to moderate myopia who successfully underwent ortho-k lens fitting. Corneal biomechanical measurements via Corvis ST were acquired at six distinct time points: baseline (pre) and 2 h (pos2h), 6 h (pos6h), and 10 h (pos10h) following the removal of the first overnight wear ortho-k, one week (pos1w) and one month (pos1m) subsequent to the initiation of ortho-k.

RESULT

Significant differences were observed in Corvis ST Biomechanical parameters DAR2, IIR, CBI, and cCBI post ortho-k intervention. The integration of covariates (CCT, SimK, and bIOP) mitigated the differences in DAR2, IIR, and cCBI, but not in CBI. Initially, the stiffness parameter at first applanation, SP-A1, did not demonstrate significant variations, but after adjusting for covariates, noticeable differences over time were observed. The Stress-Strain Indeces, SSIv1 and SSIv2, did not manifest considerable changes over time, irrespective of the adjustment for covariates. No significant disparities were identified among different ortho-k lens brands.

CONCLUSION

Corneal biomechanics remained consistent throughout the one-month period of ortho-k lens wear. The observed changes in Corvis ST parameters subsequent ortho-k are primarily attributable to alterations in corneal pachymetry and morphology, rather than actual alterations in corneal biomechanics. The stability of corneal biomechanics post ortho-k treatment suggests the safety of this approach for adolescents from a corneal biomechanics perspective.

A Corneal Biomechanical Study Measured with a Scheimpflug Dynamic Analyser in Soft Contact Lens Wearers

The aim of this study was to evaluate the biomechanical changes in the cornea after wearing soft contact lenses (CLs) in healthy myopic patients measured with a Corvis ST® (CST, Oculus Optikgeräte GmbH, Wetzlar, Germany) analyser. This prospective, cross-sectional, single-centre study was performed on twenty-two Caucasian patients aged between 19 and 24 years (20.64 ± 1.21 years) range. Five device-specific biomechanical parameters, the central corneal thickness (CCT), and biomechanically corrected intraocular pressure (bIOP) were measured prior to fitting and one month after CL wear. Differences between the means of the deflection amplitude ratio (DA Ratio) and the standard deviation of the DA Ratio (SD DA Ratio) pre- and post-CL wear were found to be significant (p value = 0.002 in both cases). Significant differences were found between pre- and post-CL wear values in CCT (p value = 0.013). For all other biomechanical measures, no significant differences were observed before and after treatment. A significant association was found between changes in bIOP and classification according to changes in Int. Radius (p value = 0.047) and SSI (p value = 0.026) standard deviations. The corneal biomechanical indices provided by CST demonstrate that the fitting of soft CLs is a safe optical compensation method for the stability of corneal stiffness. No significant differences were found pre- and post-CL wear in the assessment of bIOP.

Short- and mid-term changes in CORVIS ST parameters in successful, adult orthokeratology patients

CLINICAL RELEVANCE

The changes in various biomechanical and tomographic characteristics of the cornea associated with orthokeratology may allow us to identify potential mid- and long-term structural alterations, resulting in a better understanding of the governing mechanisms of this procedure and in its optimisation.

BACKGROUND

The study aimed at describing short and mid-term changes in CORVIS ST® parameters and indices in orthokeratology (ortho-k), and their diurnal variations.

METHODS

A prospective observational study was designed in which several CORVIS ST® parameters of 75 new adult participants successfully fitted with overnight ortho-k Seefree® (Conóptica - Hecht Contactlinsen) contact lenses were explored. Measurements were conducted in baseline (BL) conditions and in the morning and evening at the one-night (1 NM/1NT), one-week (1WM/1 WT) and 3-month (3 MM/3MT) follow-up visits.

RESULTS

Statistically significant differences were found in DARatio_2 mm, IntRad, ARTh, CBI and TBI following overnight ortho-k, when compared with BL values, with most values reaching stability at 1WM or reverting to BL values at 3 MM. The ARTh and CBI parameters showed some of the most significant temporal variations (both p < 0.001), probably reflecting the encountered differences in central corneal thickness between BL and 1WM (p = 0.010) and between BL and 3 MM (p = 0.016). In general, corneal rigidity was higher in the morning at all follow-up visits, and decreased during the day. No statistically significant changes in adjusted intraocular pressure values were found.

CONCLUSION

Ortho-k in adults may be considered a safe procedure in terms of short and mid-term changes in CORVIS ST® parameters. The observed alterations in most of the parameters provided by the Corvis ST® probably responded to the well-described changes in corneal pachymetry and tomography, rather than to actual alterations in corneal rigidity.

The relationship between corneal biomechanical parameters and treatment outcomes of orthokeratology lenses

Background

To evaluate changes in corneal biomechanical properties after long-term orthokeratology (OK) treatment and the factors affecting treatment outcomes.

Methods

Twenty-four myopic teenagers who wore OK lenses for more than 1 year were included. Twenty-three individuals of the same age and with the same spherical equivalent wearing single-vision spectacles (SVS) were enrolled as controls. After routine eye examinations, corneal biomechanical properties and axial length were measured. Parameters were compared between groups.

Results

Less axial elongation (AE) occurred in the OK group (P = 0.021). The OK group experienced a statistically significant decrease in the A1 deformation amplitude (P = 0.02), whole eye movement maximum (P = 0.026), and Ambrósio’s relational thickness to the horizontal profile (ARTh) (P < 0.001), and a statistically significant increase in the pachyslope (P < 0.001) and Corvis biomechanical index (P < 0.001). Smaller ARTh and a larger highest concavity deflection area resulted in a better refractive state. The inhibitory effect of AE was better for older patients with smaller ARTh.

Conclusions

Long-term OK treatment slowed myopia progression by reshaping the cornea. Smaller ARTh after OK lens wear indicated a better refractive state and slower AE and could predict OK lens treatment outcomes.

Practice of orthokeratology in Algeria: a retrospective study

PURPOSE

To report the practice of orthokeratology (OK) in Algeria and to investigate the visual outcomes, safety and subjective responses with this technique in myopes.

METHODS

A retrospective chart review of 48 participants using OK lenses since January 2010 were included in the study. Lenses were selected and fitted according to the manufacturer's recommendations using their respective software and the number of lenses required for a successful fit was recorded. Visual acuity (VA) in logMAR units and biomicroscopic findings were recorded for each visit. Subjective ratings was determined with analogue rating scale was filled in by the investigator, the participants were divided into Group 1 (> 4.00D) and Group 2 (< 3.75D) myopic groups for analysis.

RESULTS

First lens fitting success rate of 64.58%. There was also a significant difference between the BCVA at baseline and VA at Day 1 (P < 0.05), and no significant difference at Day 7, Day 30 and the final visit (P = 0.51, P = 0.93, P = 0.62, respectively), for Group 2. There was a significant difference between the BCVA at baseline and VA at Day 1, 7, 30 and the final visit (P < 0.05), for Group 1. the patients of the second group were happier but the results from the survey were not statistically significant (P = 0.10), no serious complication was reported.

CONCLUSION

the technique was efficient and safe as we didn't have any serious complication, with a high success rate for first lens fitting.

Repeatability of corneal biomechanics waveform signal parameters derived from Ocular Response Analyzer in children

PURPOSE

To investigate the repeatability of waveform signal parameters, measured with the Ocular Response Analyzer (ORA), in children.

METHODS

Two sets of ORA measurements, with a 10-min break between them, were performed on children, aged six to <11 years old, either wearing single-vision spectacles (SVS) or orthokeratology (ortho-k) lenses. Intraclass correlation coefficients (ICCs) were used to assess agreements between two sets of measurements (37 waveform signal parameters). Bland-Altman (BA) plots were used to further analyse waveform signal parameters which had ICC 95 % confidence interval (95 % CI) between 0.50 to >0.90 (regarded as moderate to excellent agreement).

RESULTS

A total of 30 participants [15 SVS, 15 ortho-k (3.6 ± 2.4 months)] completed the study. Since no significant between-group differences were detected in demographic data (p > 0.28) and all waveform signal parameters (p > 0.05), data from the two groups of participants were pooled for the analysis of repeatability. Six parameters, h2, h21, p1area, p1area1, p2area, and p2area1, achieved ICCs (95 % CI) of 0.82-0.85 (0.61-0.93). The mean (SD) of these six parameters were 372 (91), 248 (61), 4077 (854), 1762 (399), 2359 (670), and 1020 (300), respectively. Bland-Altman plots and 95 % limits of agreement (95 % LoA) showed considerable agreement for all six parameters, the mean difference (95 % LoA) were -3 (-101 to 94), -2 (-67.56-62.70), 111 (-723 to 946), 102 (-334 to 539), 25 (-718 to 768), and -3 (-350 to 343), respectively.

CONCLUSIONS

Six waveform signal parameters (h2, h21, p1area, p1area1, p2area, and p2area1), which represent or are related to the areas under the waveform at the peaks in the signal, had moderate to excellent agreement in children. Results of the current study provides fundamental information for further studies on the potential clinical application of these waveform signal parameters in children.

Effects of corneal crosslinking on corneal shape stabilization after orthokeratology

Orthokeratology (Ortho-K) works to reshape cornea and is the only non-surgical way to enable vision without corrective aids. However, its effect is only temporary, and successful stabilization requires ongoing Ortho-K wear to maintain the reshaping effect. Corneal crosslinking (CXL) is a commonly-used technique in clinical practice to stabilize corneal shape in keratoconic eyes. However, whether or not CXL can stabilize corneal shape after Ortho-K in normal cornea has not been reported. Therefore, this proof-of-concept study using 2 rhesus monkeys aimed to determine the efficacy of the combined procedure. One monkey wore Ortho-K bilaterally for 24 hours, and the other from 6 pm to 8 am for 7 days. The left eyes of both monkeys underwent CXL after Ortho-K while the contralateral eye served as control. Results showed a gradual regression of corneal shape in all eyes with or without CXL. However, eyes underwent CXL regressed more slowly than the control eyes. The control eyes and the CXL treatment eye in the 7-day Ortho-K monkey regressed completely at last, while the CXL treatment eye in the 24 h Ortho-K monkey maintained a corneal flattening of −1.48 D 27 days after procedure. These findings suggest CXL can slow the regression of Ortho-K for a short duration, but cannot sustain its effect according to the current protocol.

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).

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.

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.

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.

The relationship between corneal biomechanics and anterior segment parameters in the early stage of orthokeratology: A pilot study

To investigate the relationship between corneal biomechanics and anterior segment parameters in the early stage of overnight orthokeratology.Twenty-three eyes from 23 subjects were involved in the study. Corneal biomechanics, including corneal hysteresis (CH) and corneal resistance factor (CRF), and parameters of the anterior segment, including corneal curvature, central corneal thickness (CCT), and corneal sublayers' thickness, were measured at baseline and day 1 and 7 after wearing orthokeratology lens. One-way analysis of variance with repeated measures was used to compare the longitudinal changes and partial least squares linear regression was used to explore the relationship between corneal biomechanics and anterior segment parameters.At baseline, CH and CRF were positively correlated with CCT (r = 0.244, P = .008 for CH; r = 0.249, P < .001 for CRF), central stroma thickness (CST) (r = 0.241, P = .008 for CH; r = 0.244, P = .002 for CRF) and central Bowman layer thickness (CBT) (r = 0.138, P = .039 for CH; r = 0.171, P = .006 for CRF). Both CH and CRF significantly decreased from day 1 after orthokeratology. The corneal curvature and the epithelium thickness also significantly decreased, while the stromal layer thickened significantly from day 1 after orthokeratology. There was no correlation between the changes of corneal biomechanics and anterior segment parameters at day 1 and 7 after orthokeratology.While corneal biomechanics were positively correlated with CCT, CST, and CBT, the changes of CH and CRF were not correlated with the changes of corneal curvature, CCT, and corneal sublayers' thickness in the early stage of orthokeratology in our study.

Corneal Biomechanical Findings in Contact Lens Induced Corneal Warpage

Purpose. To evaluate the difference in biomechanical properties between contact lens induced corneal warpage and normal and keratoconic eyes. Method. Prospective observational case control study, where 94 eyes of 47 warpage suspicious and 46 eyes of 23 keratoconic patients were included. Warpage suspected cases were followed until a definite diagnosis was made (warpage, normal, or keratoconus). Results. 44 eyes of 22 patients had contact lens related corneal warpage. 46 eyes of 23 people were diagnosed as nonwarpage normal eyes. 46 eyes of 23 known keratoconus patients were included for comparison. The mean age of the participants was 23.8 ± 3.8 years, and 66.2% of the subjects were female. The demographic and refractive data were not different between warpage and normal groups but were different in the keratoconus group. The biomechanical properties (corneal hysteresis or CH and corneal resistance factor or CRF) were different with the highest value in the warpage group followed by normal and keratoconus groups. CRF was 10.08 ± 1.75, 9.23 ± 1.22, and 7.38 ± 2.14 and CH was 10.21 ± 1.57, 9.59 ± 1.21, and 8.69 ± 2.34 in the warpage, normal, and keratoconus groups, respectively. Conclusion. Corneal biomechanics may be different in people who develop contact lens induced warpage.

Corneal biomechanics: a review

Biomechanics is often defined as 'mechanics applied to biology'. Due to the variety and complexity of the behaviour of biological structures and materials, biomechanics is better defined as the development, extension and application of mechanics for a better understanding of physiology and physiopathology and consequently for a better diagnosis and treatment of disease and injury. Different methods for the characterisation of corneal biomechanics are reviewed in detail, including those that are currently commercially available (Ocular Response Analyzer and CorVis ST). The clinical applicability of the parameters provided by these devices are discussed, especially in the fields of glaucoma, detection of ectatic disorders and orthokeratology. Likewise, other methods are also reviewed, such as Brillouin microscopy or dynamic optical coherence tomography and others with potential application to clinical practice but not validated for in vivo measurements, such as ultrasonic elastography. Advantages and disadvantages of all these techniques are described. Finally, the concept of biomechanical modelling is revised as well as the requirements for developing biomechanical models, with special emphasis on finite element modelling.

Corneal biomechanical properties in different ocular conditions and new measurement techniques

Several refractive and therapeutic treatments as well as several ocular or systemic diseases might induce changes in the mechanical resistance of the cornea. Furthermore, intraocular pressure measurement, one of the most used clinical tools, is also highly dependent on this characteristic. Corneal biomechanical properties can be measured now in the clinical setting with different instruments. In the present work, we review the potential role of the biomechanical properties of the cornea in different fields of ophthalmology and visual science in light of the definitions of the fundamental properties of matter and the results obtained from the different instruments available. The body of literature published so far provides an insight into how the corneal mechanical properties change in different sight-threatening ocular conditions and after different surgical procedures. The future in this field is very promising with several new technologies being applied to the analysis of the corneal biomechanical properties.

Straylight and contrast sensitivity after corneal refractive therapy

PURPOSE

To compare intraocular straylight and contrast sensitivity determined before corneal refractive therapy and after 15 days and 1 month of treatment.

METHODS

A single-center, prospective, and longitudinal study was performed in 30 subjects undergoing corneal refractive therapy. In each subject, high-contrast visual acuity (HCVA), low-contrast visual acuity (LCVA), straylight, and contrast sensitivity were determined at baseline and after 15 days and 1 month after the treatment. Straylight was measured using the van den Berg straylight meter (third generation). Contrast sensitivity was determined under both photopic and mesopic conditions using the VCTS 6500 instrument (Vision Contrast Test System). EDTRS charts (logMAR units) were used to measure HCVA and LCVA.

RESULTS

Straylight (mean ± standard deviation) significantly fell from baseline (0.94 ± 0.14) to the values recorded at 1 month (0.85 ± 0.11, p = 0.009). Photopic contrast sensitivity remained stable yet mesopic contrast sensitivity measured at high spatial frequencies was significantly reduced. No correlations between intraocular straylight and contrast sensitivity, HCVA, or LCVA were observed 15 days and 1 month after corneal refractive therapy.

CONCLUSIONS

Our findings suggest improved intraocular straylight readings 1 month after starting the treatment, although the changes observed in straylight could not be related to changes in mesopic and photopic contrast sensitivity or HCVA and LCVA. Mesopic contrast sensitivity was more affected by the treatment intervention than photopic contrast sensitivity.

Short-term effects of overnight orthokeratology on corneal cell morphology and corneal thickness

PURPOSE

To examine the morphological and biometric corneal changes produced over periods of 15 days and 1 month after overnight orthokeratology (OK).

METHODS

Prospective, single-center, longitudinal trial. Twenty-seven right eyes of 27 subjects (group 1) with low to moderate myopia wore OK lenses for 1 month. Ten right eyes of 10 subjects (group 2) with emmetropia to low myopia who did not wear any type of contact lens served as controls. Corneal morphometric measurements were obtained in vivo using a confocal microscope to examine the central and midperipheral cornea. Thickness measurements in the peripheral cornea were obtained by optical coherence tomography. Changes in visual acuity, refractive error, and corneal topography were also analyzed.

RESULTS

No significant changes in either endothelial cell or stromal cell density were observed after 1 month of OK. Basal epithelial cells were, however, significantly reduced (P < 0.01), and epithelial wing and superficial cells showed enhanced visibility (P < 0.05). Superficial cells increased in height and width, the width increase after 1 month being significant (P < 0.01). Epithelial thickness was significantly reduced in the central cornea and 2 mm around the center. Corneal pachymetry increased significantly in the band from 5 to 10 mm from the corneal apex (P < 0.01).

CONCLUSIONS

OK lenses for myopia induce significant structural and optical changes particularly in the central epithelium after 15 days or 1 month of wear. The central corneal epithelium responds to OK wear by undergoing significant epithelial cell shape and size alterations with no effects, however, on the cells of the corneal endothelium or the corneal stroma. Peripheral corneal thickness increased with respect to baseline values. These findings suggest that the corneal epithelium is the principal structure affected by the mechanical forces exerted by the OK lenses.