Ortho-k Contact Research Articles

Can AI Predict the Magnitude and Direction of Ortho-K Contact Lens Decentration to Limit Induced HOAs and Astigmatism?

Background: The aim is to investigate induced higher-order aberrations (HOA)s and astigmatism as a result of non-toric ortho-k lens decentration and utilise artificial intelligence (AI) to predict its magnitude and direction. Methods: Medmont E300 Video topographer was used to scan 249 corneas before and after ortho-k wear. Custom-built MATLAB codes extracted topography data and determined lens decentration from the boundary and midpoint of the central flattened treatment zone (TZ). An evaluation was carried out by conducting Zernike polynomial fittings via a computer-coded digital signal processing procedure. Finally, an AI-based machine learning neural network algorithm was developed to predict the direction and magnitude of TZ decentration. Results: Analysis of the first 21 Zernike polynomial coefficients indicate that the four low-order and four higher-order aberration terms were changed significantly by ortho-k wear. While baseline astigmatism was not correlated with lens decentration (R = 0.09), post-ortho-k astigmatism was moderately correlated with decentration (R = 0.38) and the difference in astigmatism (R = 0.3). Decentration was classified into three groups: ≤0.50 mm, reduced astigmatism by -0.9 ± 1 D; 0.5~1 mm, increased astigmatism by 0.8 ± 0.1 D; >1 mm, increased astigmatism by 2.7 ± 1.6 D and over 50% of lenses were decentred >0.5 mm. For lenses decentred >1 mm, 29.8% of right and 42.7% of left lenses decentred temporal-inferiorly and 13.7% of right and 9.4% of left lenses decentred temporal-superiorly. AI-based prediction successfully identified the decentration direction with accuracies of 70.2% for right and 71.8% for left lenses and predicted the magnitude of decentration with root-mean-square (RMS) of 0.31 mm and 0.25 mm for right and left eyes, respectively. Conclusions: Ortho-k lens decentration is common when fitting non-toric ortho-k lenses, resulting in induced HOAs and astigmatism, with the magnitude being related to the amount of decentration. AI-based algorithms can effectively predict decentration, potentially allowing for better control over ortho-k fitting and, thus, preferred clinical outcomes.

FEA-Based Stress-Strain Barometers as Forecasters for Corneal Refractive Power Change in Orthokeratology.

To improve the effectivity of patient-specific finite element analysis (FEA) to predict refractive power change (RPC) in rigid Ortho-K contact lens fitting. Novel eyelid boundary detection is introduced to the FEA model to better model the effects of the lid on lens performance, and stress and strain outcomes are investigated to identify the most effective FEA components to use in modelling. The current study utilises fully anonymised records of 249 eyes, 132 right eyes, and 117 left eyes from subjects aged 14.1 ± 4.0 years on average (range 9 to 38 years), which were selected for secondary analysis processing. A set of custom-built MATLAB codes was built to automate the process from reading Medmont E300 height and distance files to processing and displaying FEA stress and strain outcomes. Measurements from before and after contact lens wear were handled to obtain the corneal surface change in shape and power. Tangential refractive power maps were constructed from which changes in refractive power pre- and post-Ortho-K wear were determined as the refractive power change (RPC). A total of 249 patient-specific FEA with innovative eyelid boundary detection and 3D construction analyses were automatically built and run for every anterior eye and lens combination while the lens was located in its clinically detected position. Maps of four stress components: contact pressure, Mises stress, pressure, and maximum principal stress were created in addition to maximum principal logarithmic strain maps. Stress and strain components were compared to the clinical RPC maps using the two-dimensional (2D) normalised cross-correlation and structural similarity (SSIM) index measure. On the one hand, the maximum principal logarithmic strain recorded the highest moderate 2D cross-correlation area of 8.6 ± 10.3%, and contact pressure recorded the lowest area of 6.6 ± 9%. Mises stress recorded the second highest moderate 2D cross-correlation area with 8.3 ± 10.4%. On the other hand, when the SSIM index was used to compare the areas that were most similar to the clinical RPC, maximum principal stress was the most similar, with an average strong similarity percentage area of 26.5 ± 3.3%, and contact pressure was the least strong similarity area of 10.3 ± 7.3%. Regarding the moderate similarity areas, all components were recorded at around 34.4% similarity area except the contact pressure, which was down to 32.7 ± 5.8%. FEA is an increasingly effective tool in being able to predict the refractive outcome of Ortho-K treatment. Its accuracy depends on identifying which clinical and modelling metrics contribute to the most accurate prediction of RPC with minimal ocular complications. In terms of clinical metrics, age, Intra-ocular pressure (IOP), central corneal thickness (CCT), surface topography, lens decentration and the 3D eyelid effect are all important for effective modelling. In terms of FEA components, maximum principal stress was found to be the best FEA barometer that can be used to predict the performance of Ortho-K lenses. In contrast, contact pressure provided the worst stress performance. In terms of strain, the maximum principal logarithmic strain was an effective strain barometer.

Investigation of the relationship between contact lens design parameters and refractive changes in Ortho-K

PurposeTo investigate the relationship between Ortho-K contact lens design parameters and refractive power change of the eye through a parametric mathematical representation. MethodsThe current study utilises fully anonymized records of 249 eyes, 132 right eyes, and 117 left eyes from subjects aged 14.1 ± 4.0 years on average (range 9–38 years) which were selected for secondary analysis processing. The data were split into 3 groups (G1 up to 35 days wear, from 10 to 35 days, G2 up to 99 days wear, more than 35–99 days & G3 more than 100 days wear) according to the length of time, in days, that the lenses were worn. Corneal shape was measured before and after contact lens wear using the Medmont E300 topographer, from which height and distance files were read by a custom-built MATLAB code to construct the corneal anterior surface independently. Changes in refractive power pre and post-Ortho-K wear were determined using constructed tangential refractive power maps from which both centrally flattened and annular steepened zones were automatically bounded, hence used to determine the refractive power change. ResultsOn average, flat Sim-K and steep Sim-K were reduced after Ortho-K lens wear by 1.6 ± 1.3 D and 1.3 ± 1.4 D respectively. The radius of the base curve was correlated with the mean central flattened zone power change strongly in G1 (R = 0.7, p < 0.001) and moderately in G2 (R = 0.4) and G3 (R = 0.4, p < 0.001). Hence, a strong correlation with the base curve was recorded in group G1 and moderate in G2 and G3. The reverse curve was very strongly correlated to the mean central flattened zone power change in G1 (R = 0.8, p < 0.001) and strongly correlated with G2 (R = 0.6, p < 0.001) and G3 (R = 0.7, p < 0.001). The reverse curve was also strongly correlated with the mean annular steepened zone power change among all groups G1, G2, and G3 (R = 0.7, R = 0.6 and R = 0.6) respectively (p < 0.001). ConclusionsAlthough the central corneal refractive power change was strongly correlated to the Ortho-K lens base curve, it characterized only 50% of the target power change. However, the annular steepened zone refractive power change appears to be a clearer predictor of target power change, as there appears to be a one-to-one inverse relationship with the target refractive power correction. Differences between these results and the literature may be a result of the topography software smoothing effect.

Evaluation of children in the Netherlands fitted with custom made ortho-k contact lenses

Purpose: Studies on Ortho-K (OK) lenses for myopia management have demonstrated efficacy on children in controlled studies. However, performance and wearer acceptance in a real-world practice environment is also important. A retrospective chart review was conducted to evaluate myopia progression in children who were fitted with OK for myopia correction.

Role of Short Term Open Eye OrthoK Lens Wear in Inducing Myopia Control Changes in Eyes With Moderate Myopia

Purpose: To assess peripheral refraction, corneal, and visual acuity changes after open eye use of orthokeratology (OrthoK) contact lenses. Methodology: OrthoK contact lenses were worn on separate occasions for half an hour and 2 hours in open eye condition. The peripheral refraction (PR) changes were assessed monocularly up to 30° nasally and temporally in the horizontal visual field using the open field autorefractometer. Average corneal power (ACP), central corneal thickness (CCT), and visual acuity (VA) was recorded using corneal topographer, specular microscope, and LogMAR chart respectively. Results: Mean baseline PR at 25° and beyond both nasally and temporally was -0.54 ± 1.68D (mean ± SD) which increased to mean -1.29 ± 1.43D (p < 0.01) post half an hour of lens wear and further increased to mean -1.62 ± 1.53D (p < 0.01) after 2 hours lens wear. The mean baseline ACP was 43.45 ± 1.34D that reduced to mean 43.11 ± 1.37D (p < 0.01) after half an hour of lens wear and a further reduction to mean 42.73 ± 1.34D (p < 0.01) 2 hours post lens wear. Mean CCT changes after half an hour lens wear were not significant but it reduced by mean 14.92 ± 4.68 µm (p < 0.01) 2 hours post lens wear as compared to baseline. The unaided VA improved from mean 0.85 + 0.37 log at baseline to mean 0.49 + 0.35 log (p < 0.01) after half an hour of lens wear and mean 0.39 + 0.35 log (p < 0.01) after 2 hours of OrthoK lens wear. Conclusion: Rapid corneal and peripheral refraction shifts are seen after half an hour of open-eye wear of the OrthoK lens with a gradual rise in impact for 2 hours of lens wear.

Role of Short Term Open Eye Orthok Lens Wear in Inducing Myopia Control Changes in Eyes with Moderate Myopia

Purpose: To assess peripheral refraction, corneal, and visual acuity changes after open eye use of orthokeratology (OrthoK) contact lenses. Methodology: OrthoK contact lenses were worn on separate occasions for half an hour and 2 hours in open eye condition. The peripheral refraction (PR) changes were assessed monocularly up to 30° nasally and temporally in the horizontal visual field using the open field autorefractometer. Average corneal power (ACP), central corneal thickness (CCT), and visual acuity (VA) was recorded using corneal topographer, specular microscope, and LogMAR chart respectively. Results: Mean baseline PR at 25° and beyond both nasally and temporally was -0.54 ± 1.68D (mean ± SD) which increased to mean -1.29 ± 1.43D (p &lt; 0.01) post half an hour of lens wear and further increased to mean -1.62 ± 1.53D (p &lt; 0.01) after 2 hours lens wear. The mean baseline ACP was 43.45 ± 1.34D that reduced to mean 43.11 ± 1.37D (p &lt; 0.01) after half an hour of lens wear and a further reduction to mean 42.73 ± 1.34D (p &lt; 0.01) 2 hours post lens wear. Mean CCT changes after half an hour lens wear were not significant but it reduced by mean 14.92 ± 4.68 µm (p &lt; 0.01) 2 hours post lens wear as compared to baseline. The unaided VA improved from mean 0.85 + 0.37 log at baseline to mean 0.49 + 0.35 log (p &lt; 0.01) after half an hour of lens wear and mean 0.39 + 0.35 log (p &lt; 0.01) after 2 hours of OrthoK lens wear. Conclusion: Rapid corneal and peripheral refraction shifts are seen after half an hour of open-eye wear of the OrthoK lens with a gradual rise in impact for 2 hours of lens wear.

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

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

Peripheral refraction changes post short-term OrthoK contact lens wear

Peripheral refraction changes post short-term OrthoK contact lens wear

Effects of Myopic Orthokeratology on Visual Performance and Optical Quality.

To analyze the changes in visual performance and optical quality after orthokeratology (ortho-k) treatment and its correlation with the magnitude of lens decentration and the diameter of treatment zone (TxZ). A prospective study was conducted in 27 eyes of 27 patients wearing ortho-k contact lens. Area under log contrast sensitivity function (AULCSF), modulation transfer function cutoff values (MTFcutoff), Strehl ratio (SR), and objective scattering index (OSI) were measured and compared before and 1 month after ortho-k lens treatment. Refractive sphere, astigmatism, and diameter and decentration of TxZ were tested against the change in AULCSF, MTFcutoff, SR, and OSI after ortho-k treatment in stepwise multiple linear regression models. Objective scattering index significantly increased and AULCSF, MTFcutoff, and SR significantly decreased after ortho-k lens wear (all P<0.001). The mean TxZ diameter was 3.61±0.26 mm, and the mean magnitude of TxZ decentration was 0.60±0.16 mm. The amount of lens decentration significantly correlated with the change in AULCSF and MTFcutoff (P=0.027 and P=0.005, respectively). The diameter of TxZ significantly correlated with the change in MTFcutoff and SR (P=0.005 and P=0.024, respectively). Visual and optical quality decreases after ortho-k treatment, which can be alleviated by a larger TxZ diameter and a smaller lens decentration.

Changes of meibomian gland function and the stability of tear film after long-term wearing orthokeratolog

Objective This study was to observe the meibomian gland scores, the miss rate of meibomian, break-up time of tear film (BUT) changes after long-term wearing orthokeratolog, and to evaluate orthokeratolog impact on meibomian gland function and the stability of the tear film. Methods A prospective case-controlled study was performed.Fifty patients 98 eyes with myopia were enrolled.According to the myopia correction mode, the patients were divided into control group (24 cases) and experimental group (overnight orthokeratolog treatment) group (26 cases). All subjects were underwent the examinations sequentially as follows: evaluation of ocular surface disease symptoms using the Ocular Surface Disease Index(OSDI), lid margin and ocular surface examination by slit lamp microscrope, infrared meibomian photography and BUT.All measurements were repeated at 3 months, 6 months, 24-months follow-up visit.All patients signed informed consent before examination. Results After wearing orthok-contact lens for 24 months, the meibomian gland score was 4.54±1.10 and 2.29±0.75 in the experimental group and control group, respectively, the difference was statistically significant (P 0.05). Conclusions Long-term wearing orthokeratolog has negetive effects on meibomian gland function and the stability of the tear film. Key words: Myopia; Orthokeratolog; Meibomian gland; Meibomian gland scores; Miss rate of meibomian; Break-up time of tear film

Prediction of Orthokeratology Lens Decentration with Corneal Elevation

Lens decentration is common and unavoidable to some extent during ortho-k treatment. By using a simplified method, we are able to predict the magnitude and direction of ortho-k lens decentration, which provides useful insights in screening for ideal ortho-k candidates and to make a quick decision when decentration happens. The aim of this study was to investigate the influence of corneal elevation asymmetry on ortho-k lens decentration. Thirty-six eyes of 36 subjects were fitted with four-curve reverse geometry ortho-k contact lenses. Corneal topography was collected before and 1 month after ortho-k lens wear. The difference in corneal elevation at the 8-mm chord of the respective two principal meridians of corneal astigmatism was calculated. Vector analyses were performed on these differences to calculate the magnitude and direction of a vector (corneal asymmetry vector). The relationship between the angle and magnitude of corneal asymmetry vector and lens decentration was analyzed. Baseline refractive sphere and cylinder for the 36 tested eyes were -2.84 ± 1.04 diopters (D) (range, -4.75 to -1.00 D) and -0.21 ± 0.28 D (range, -1.00 to 0 D), respectively. The mean magnitude of lens decentration was 0.72 ± 0.26 mm (0 to 1.34 mm). For overall displacement, inferotemporal decentration was the most common as observed in 24 eyes (67%). The mean angle of the corneal asymmetry vector (202 ± 39 degrees) was significantly correlated to the mean angle of lens decentration (200 ± 39 degrees) (r = 0.76, P < .001). The magnitude of corneal asymmetry vector significantly contributed to the magnitude of lens decentration (standardized β = 0.448, P = .002) whereas the other tested variables did not affect lens decentration (all P > .05). Lens decentration is a common phenomenon in ortho-k that mostly happens toward the inferotemporal quadrant of the cornea. The magnitude and direction of lens decentration are predetermined by paracentral corneal asymmetry.

The role of outdoor activity in myopia prevention

Myopia, also known as nearsightedness, is the most common vision disorder among children and young adults. In the last several decades, the prevalence of myopia has surged in East Asia. In some industrialized regions it has already reached an epidemic level (1,2). A smaller increase in the prevalence has also been observed in Western countries (2,3). The cost of visual aids or corrections put a great financial burden on individuals, families and the health care system. Myopia is not just an optical inconvenience. Early onset myopia is often accompanied with fast progression and very likely it will end up with high myopia (higher than 6.00 D myopia). High myopia poses a higher risk for developing glaucoma, retinal detachments and other vision threatening conditions. As our understanding of myopia was and is still poor, the research and development of an effective and safe tool in controlling myopia has been moving forward slowly. The current options for slowing down myopia progression include applying pharmaceutical agents such as atropine, wearing corrections with special optical design including bifocal spectacles, dual-focal contact lenses, and orthokeratology (ortho-K) (4). The most effective treatment up-to-date is 1% atropine, with well-established clinically relevant efficacy. However, the side-effect of long-term use and rebound effect after discontinuation of atropine were major concerns. Recently published results from a study conducted in Singapore clearly showed that atropine at a much lower dosage 0.01% could slow down myopia progression in children though its treatment size was smaller compared to the higher dosage levels: 1.0%, 0.5% and 0.1% (5). In addition, their results indicated that the group with 0.01% atropine had little rebound after cessation of the treatment while the other groups progressed much faster than the control group. More investigations on this promising strategy are still ongoing. Another promising option is ortho-K contact lenses. The benefit of wearing ortho-K in retarding axial elongation has been confirmed by randomized clinical trials (RCTs) (6). Prescribing contact lenses in very young children is still non-conventional due to hygiene and safety concerns. Other optical correction methods include multifocal and bifocal spectacles. Multifocal/bifocal spectacle provides minimal myopia control effect: statistically significant but without clinical significance (4). Finally, none of these intervention methods had been studied for a long period of time (>5 years) and thus their long-term effect is unknown. Unlike studies on retarding myopia progression, publications on myopia prevention methods are rarely seen in literature.

Observation and nursing strategy of side effects for children wearing Ortho-K contact lens

Objective To summarize the observation and nursing strategy of side effects for children wearing Ortho-K contact lens in order to improve the effects of treatment and reduce side effects. Methods A total of 1 066 myopic children wearing Ortho-K CL, who could recheck on time in Beijing Children′s Hospital from May 2013 to June 2014 were included. The reason of dyed cornea, dislocation, and discomfortable were analyzed, and corresponding nursing and healthy propaganda were performed. Results Among 1 066 children, 350 children (32.8%) wearing Ortho-K CL had epithelial dyed cornea after 6 months, and most of them appeared 1 month after wearing the lens. It would disappear after the treatment by levofloxacin eye drops, sodium hyaluronate eye drops and recombinant bovine basic fibroblast growth factor gel, stopping using the Ortho-K contact lens and providing healthy progaganda after 1 week. A total of 170 children (16%) wearing Ortho-K CL had dislocation, in which 2 children slipped into conjunctival sac and it was taken out under guidance of nurse by parents. A total of 128 children (12%) suffered from diplopia after wearing the lens, and 234 children(22%) wearing Ortho-K CL had discomfortable feeling. No children had irreversible impairment and ocular infection. Conclusions According to the reason of side effects, appropriate nursing strategy and healthy propaganda can improve the success rate of Ortho-K contact lens, prolong their service time, contribute treatment effectiveness, and reduce its side effects. Key words: Children; Ortho-K contact lens; Side effects; Nursing

The long-term clinical effects of orthokeratology in high myopia children

To investigate the long-term clinical effects of orthokeratology (ortho-k) in high myopia children with 5 years of follow-ups. Prospective study. We chose 30 high myopia patients to wear ortho-k contact lenses (CLs) for controlling or delaying myopia progression from 2003. Among them, there were 10 boys and 20 girls whose average age was (15 ± 2) years, spherical diopters were (-7.34 ± 0.91) D, corneal astigmatism diopters were (-1.06 ± 0.62) D, uncorrected visual acuity was LogMAR 0.89 ± 0.29, corneal flattened curvature was (43.54 ± 1.16) D, and axial length was (26.38 ± 0.94) mm. All patients, with informed consent before fitting of ortho-k CLs, had conventional refraction and ocular tests. We compared the values of spherical diopters, visual acuity, corneal flattened curvature and axial length before and 6 months, 1 year, 2 years, 3 years, 4 years and 5 years after wearing CLs, respectively. The results were analyzed by SPSS 16.0 software. During the five years of observation periods, all patients' visual acuity and corneal flattened curvature were different from the pre-fitting (P < 0.05). Compared to the pre-fitting, the naked visual acuity was some degree improved, it was LogMAR 0.45 ± 0.31, 0.49 ± 0.32, 0.43 ± 0.30, 0.47 ± 0.31, 0.58 ± 0.35, 0.53 ± 0.27, respectively. F = 10.725, P = 0.000. Corneal flatten curvature was tend to be flatter, such was 41.14 ± 1.54, 41.75 ± 1.88, 41.54 ± 2.10, 41.73 ± 1.89, 41.94 ± 1.61, 40.70 ± 1.67. F = 10.161, P = 0.000 (All P < 0.05). The spherical diopters during the first two years after wearing ortho-k CLs were significantly reduced, compared with the previous values (it was -5.23 ± 1.81, -5.59 ± 2.75, -6.29 ± 2.12, -6.63 ± 2.31, -6.83 ± 2.33, -7.01 ± 1.81, respectively, F = 4.929, P = 0.000), and kept stable in the long-term observation. The axial length checked at 5 years was slightly elongated (it was 26.41 ± 0.90, 26.68 ± 0.93, 26.69 ± 1.06, 26.75 ± 0.94, 26.81 ± 1.04, 27.04 ± 1.01. F = 1.831, P = 0.094). The axial elongation was retarded by using ortho-k CLs in high myopia children. All patients were not subjected to severe complications which may lead to quitting the enrollments. Orthokeratology used in controlling or delaying high myopia progression is definitely outstanding in 5 years observations. Standard lens wearing and regular lens check improve safety of lens use in high myopia.

Effects of wearing long-term Ortho-K contact lens on corneal thickness and corneal endothelium

The current study evaluated the response of the cornea to more than 3 years of Ortho-K CL wearing by investigating the changes of corneal thickness and corneal endothelium. One hundred and thirty-two subjects were fitted with Ortho-K CL (Dk 100), which were worn overnight or daily for more than 3 years. Central and para-peripheral corneal thickness and corneal endothelium were measured before and during this period by using A scan pachymeter and non contact specular microscope. There were no significant changes in corneal thickness (P < 0.05) and corneal endothelial polymegathism and pleomorphism could not be found after long-term wearing of Ortho-K CL (overnight or daily wear). This study shows that high Dk Ortho-K CL used for scientific reshaping treatment only induces mild corneal response. Therefore, the Ortho-K CL can be worn safely for long-term control of myopia.

A study of the central and peripheral refractive power of the cornea with orthokeratology treatment

The central and peripheral refracting power of the cornea after orthokeratology treatment was studied by a cross-sectional method. Three Asian subject groups were recruited. Group 1 consisted of 31 normal non-contact lens wearers, group 2 consisted of 14 subjects who wore orthoK contact lenses for 10–20 months, and group 3 consisted of 14 subjects who wore orthoK contact lenses for more than 20 months. Our results showed that the corneal refracting power (central 3.3 mm) in both of the groups with orthoK contact lens treatment did not differ significantly from the average cornea. The group that wore orthoK lenses for more than 20 months had a flatter temporal peripheral cornea than did the normal group at approximately 2.95 mm from the corneal apex. Because the temporal cornea is steeper than the nasal cornea in normal eyes, a relatively flatter temporal cornea in the orthoK group produces a more symmetrical peripheral cornea.