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

Wu, Lo-Yu; Esporcatte, Louise Pellegrino Gomes; Li, Wenkai; Lin, Wei‐Cheng; Wu, Richard; White, Lynn Τ.; Salomão, Marcella Q.; Lopes, Bernardo; Ambrósio, Renato; Abass, Ahmed

doi:10.1016/j.heliyon.2022.e11699

Cited by 4 publications

(13 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Since it has long been thought that the BC of the OK lens is used to flatten the central cornea while the RC is used to steepen the mid-peripheral cornea to generate the defocus ring. 35,36 Therefore, what we find enriches the understanding of the function provided by BC and deepens the previous knowledge of the clamping effect generated by the reverse-geometry lens. 37 Meanwhile, the discovery of the stress feature at S2 indicated that it may be the breaking point between the two functions of BC to make central corneal flattening and mid-peripheral corneal steepening.…”

Section: Discussionsupporting

confidence: 66%

“…Hence, it raises the possibility that BC not only participates in central corneal flattening 34 but also contributes to mid‐peripheral corneal steepening. Since it has long been thought that the BC of the OK lens is used to flatten the central cornea while the RC is used to steepen the mid‐peripheral cornea to generate the defocus ring 35,36 . Therefore, what we find enriches the understanding of the function provided by BC and deepens the previous knowledge of the clamping effect generated by the reverse‐geometry lens 37 .…”

Section: Discussionmentioning

confidence: 55%

See 1 more Smart Citation

Biomechanical study of cornea response under orthokeratology lens therapy: A finite element analysis

Zhao

Zhai

Xiang

et al. 2023

Numer Methods Biomed Eng

View full text Add to dashboard Cite

Orthokeratology (OK) is becoming a mainstream modality for myopia correction and control, but its underlying mechanism is not yet fully understood. In this study, the biomechanical response of cornea under the OK lens was investigated to further understand the mechanism of OK therapy. Numerical models of the cornea and OK lens with different corneal refractive powers and myopia degrees were established to analyze features and differences of the spatial displacement and stress distribution in different areas of the anterior corneal surface by finite element method. Displacement distributions on the anterior cornea surface with refractive powers of 39.5, 43, 46 D, and myopia degrees of −1.0, −3.0, −6.0 D demonstrate similar deformation trends and nearly rotationally symmetrical attributes of different corneal parameters. Displacement of mid‐peripheral cornea was significantly high compared with that of the central and peripheral cornea, peaking at ~2.4 mm off the corneal apex. The stress increased with the increase in myopia degrees and was significantly large for the myopia degrees of −6.0 D at S1; the stress at S2 and S6 was low and stable and did not differ much at S3; the stress at S4 and S5, however, was extremely high. In summary, simulation result of orthokeratology can effectively evaluate the performance of OK lens and it properly associates with the differential map of the corneal topography. The base curve of the OK lens may also play a role in mid‐peripheral corneal steepening. The design around the OK lens' alignment curve needs to be optimized.

show abstract

Section: Discussionsupporting

confidence: 66%

Section: Discussionmentioning

confidence: 55%

Biomechanical study of cornea response under orthokeratology lens therapy: A finite element analysis

Zhao

Zhai

Xiang

et al. 2023

Numer Methods Biomed Eng

View full text Add to dashboard Cite

show abstract

“…10 The lens achieves corneal flattening by means of back central optic zone diameters (BOZD), which create an optical treatment zone (OTZ) on the cornea. 11 This process establishes a gap between the reverse curve of the lens and the front corneal surface, which is occupied by tears. As a consequence, a pressure gradient is generated, wherein positive pressure is exerted at the corneal centre and negative pressure is experienced in the surrounding areas.…”

Section: Introductionmentioning

confidence: 99%

“…Some reports suggest that the efficacy of Ortho-K treatment can be optimised by adjusting the lens parameters, especially considering pupil size and RDV status. 11,12,[15][16][17] However, currently there is no definitive method to measure the position of the pupil and defocus rings, and there is a lack of sufficient evidence regarding the correlation between their position and the magnitude of peripheral retinal defocus. Therefore, the main objective of this study was to examine the relationship between the cross-sectional area between the pupil and defocus rings and changes in RDV after wearing Ortho-K lenses for 3 or 6 months.…”

Section: Introductionmentioning

confidence: 99%

“…This reversible reduction has positioned Ortho‐K as a highly effective approach for managing myopia progression 10 . The lens achieves corneal flattening by means of back central optic zone diameters (BOZD), which create an optical treatment zone (OTZ) on the cornea 11 . This process establishes a gap between the reverse curve of the lens and the front corneal surface, which is occupied by tears.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Impact of pupil and defocus ring intersection area on retinal defocus

Guo,

Zhang,

Tong

et al. 2024

Ophthalmic Physiologic Optic

View full text Add to dashboard Cite

PurposeWith the rising prevalence of myopia, especially among the young, orthokeratology (Ortho‐K) stands out as a promising approach, not only to reduce myopia but also to control the progression of axial length (AL). This study examined how the intersection area between the pupil and defocus ring influenced retinal defocus and axial growth after Ortho‐K.MethodsA case–control study was conducted with 100 participants (100 eyes). Both AL and the refraction difference value (RDV), that is, the peripheral refractive error measured with respect to the central value after wearing Ortho‐K lenses, were determined. Subjects were categorised into two groups based on the size of the intersection area after 3 months of lens wear: Group A (<4.58 mm2) and Group B (≥4.58 mm2).ResultsGroup B demonstrated significantly lower changes in AL and RDV at 30–40° and 40–53° compared with Group A after 3 months of lens wear (all p < 0.05). After 6 months of lens wear, Group B showed significantly lower changes in AL and RDV in the 40–53° region compared with Group A (all p < 0.05). Correlation analysis revealed that as the intersection area increased, the changes in AL and RDV at 0–53°, 30–40° and 40–53° eccentricity decreased after both 3 and 6 months of lens wear (all p < 0.01).ConclusionsA larger intersection area between the pupil and defocus ring within a certain time period can cause a greater amount of myopic defocus at 30–53° from the fovea. The results suggest that a larger intersection area might lead to more effective control of axial growth.

show abstract

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

Wu,

Lin,

et al. 2024

Bioengineering

Self Cite

View full text Add to dashboard Cite

Purpose: 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. Methods: 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. Results: 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%. Conclusions: 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.

show abstract

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

Cited by 4 publications

References 28 publications

Biomechanical study of cornea response under orthokeratology lens therapy: A finite element analysis

Biomechanical study of cornea response under orthokeratology lens therapy: A finite element analysis

Impact of pupil and defocus ring intersection area on retinal defocus

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

Contact Info

Product

Resources

About