Translation model for CW chord to angle Alpha derived from a Monte-Carlo simulation based on raytracing.
<h4>Background</h4>The Chang-Waring chord is provided by many ophthalmic instruments, but proper interpretation of this chord for use in centring refractive procedures at the cornea is not fully understood. The purpose of this study is to develop a strategy for translating the Chang-Wari...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Public Library of Science (PLoS)
2022-01-01
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| Series: | PLoS ONE |
| Online Access: | https://doi.org/10.1371/journal.pone.0267028 |
| _version_ | 1811329191841366016 |
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| author | Achim Langenbucher Nóra Szentmáry Alan Cayless Johannes Weisensee Jascha Wendelstein Peter Hoffmann |
| author_facet | Achim Langenbucher Nóra Szentmáry Alan Cayless Johannes Weisensee Jascha Wendelstein Peter Hoffmann |
| author_sort | Achim Langenbucher |
| collection | DOAJ |
| description | <h4>Background</h4>The Chang-Waring chord is provided by many ophthalmic instruments, but proper interpretation of this chord for use in centring refractive procedures at the cornea is not fully understood. The purpose of this study is to develop a strategy for translating the Chang-Waring chord (position of pupil centre relative to the Purkinje reflex PI) into angle Alpha using raytracing techniques.<h4>Methods</h4>The retrospective analysis was based on a large dataset of 8959 measurements of 8959 eyes from 1 clinical centre, using the Casia2 anterior segment tomographer. An optical model based on: corneal front and back surface radius Ra and Rp, asphericities Qa and Qp, corneal thickness CCT, anterior chamber depth ACD, and pupil centre position (X-Y position: PupX and PupY), was defined for each measurement. Using raytracing rays with an incident angle IX and IY the CW chord (CWX and CWY) was calculated. Using these data, a multivariable linear model was built up in terms of a Monte-Carlo simulation for a simple translation of incident ray angle to CW chord.<h4>Results</h4>Raytracing allows for calculation of the CW chord CWX/CWY from biometric measures and the incident ray angle IX/IY. In our dataset mean values of CWX = 0.32±0.30 mm and CWY = -0.10±0.26 mm were derived for a mean incident ray angle (angle Alpha) of IX = -5.02±1.77° and IY = 0.01±1.47°. The raytracing results could be modelled with a linear multivariable model, and the effect sizes for the prediction model for CWX are identified as Ra, Qa, Rp, CCT, ACD, PupX, PupY, IX, and for CWY they are Ra, Rp, PupY, and IY.<h4>Conclusion</h4>Today the CW chord can be directly measured with any biometer, topographer or tomographer. If biometric measures of Ra, Qa, Rp, CCT, ACD, PupX, PupY are available in addition to the CW chord components CWX and CWY, a prediction of angle Alpha is possible using a simple matrix operation. |
| first_indexed | 2024-04-13T15:39:27Z |
| format | Article |
| id | doaj.art-33a2f1d910ae4b90b58a5f616a758481 |
| institution | Directory Open Access Journal |
| issn | 1932-6203 |
| language | English |
| last_indexed | 2024-04-13T15:39:27Z |
| publishDate | 2022-01-01 |
| publisher | Public Library of Science (PLoS) |
| record_format | Article |
| series | PLoS ONE |
| spelling | doaj.art-33a2f1d910ae4b90b58a5f616a7584812022-12-22T02:41:11ZengPublic Library of Science (PLoS)PLoS ONE1932-62032022-01-01175e026702810.1371/journal.pone.0267028Translation model for CW chord to angle Alpha derived from a Monte-Carlo simulation based on raytracing.Achim LangenbucherNóra SzentmáryAlan CaylessJohannes WeisenseeJascha WendelsteinPeter Hoffmann<h4>Background</h4>The Chang-Waring chord is provided by many ophthalmic instruments, but proper interpretation of this chord for use in centring refractive procedures at the cornea is not fully understood. The purpose of this study is to develop a strategy for translating the Chang-Waring chord (position of pupil centre relative to the Purkinje reflex PI) into angle Alpha using raytracing techniques.<h4>Methods</h4>The retrospective analysis was based on a large dataset of 8959 measurements of 8959 eyes from 1 clinical centre, using the Casia2 anterior segment tomographer. An optical model based on: corneal front and back surface radius Ra and Rp, asphericities Qa and Qp, corneal thickness CCT, anterior chamber depth ACD, and pupil centre position (X-Y position: PupX and PupY), was defined for each measurement. Using raytracing rays with an incident angle IX and IY the CW chord (CWX and CWY) was calculated. Using these data, a multivariable linear model was built up in terms of a Monte-Carlo simulation for a simple translation of incident ray angle to CW chord.<h4>Results</h4>Raytracing allows for calculation of the CW chord CWX/CWY from biometric measures and the incident ray angle IX/IY. In our dataset mean values of CWX = 0.32±0.30 mm and CWY = -0.10±0.26 mm were derived for a mean incident ray angle (angle Alpha) of IX = -5.02±1.77° and IY = 0.01±1.47°. The raytracing results could be modelled with a linear multivariable model, and the effect sizes for the prediction model for CWX are identified as Ra, Qa, Rp, CCT, ACD, PupX, PupY, IX, and for CWY they are Ra, Rp, PupY, and IY.<h4>Conclusion</h4>Today the CW chord can be directly measured with any biometer, topographer or tomographer. If biometric measures of Ra, Qa, Rp, CCT, ACD, PupX, PupY are available in addition to the CW chord components CWX and CWY, a prediction of angle Alpha is possible using a simple matrix operation.https://doi.org/10.1371/journal.pone.0267028 |
| spellingShingle | Achim Langenbucher Nóra Szentmáry Alan Cayless Johannes Weisensee Jascha Wendelstein Peter Hoffmann Translation model for CW chord to angle Alpha derived from a Monte-Carlo simulation based on raytracing. PLoS ONE |
| title | Translation model for CW chord to angle Alpha derived from a Monte-Carlo simulation based on raytracing. |
| title_full | Translation model for CW chord to angle Alpha derived from a Monte-Carlo simulation based on raytracing. |
| title_fullStr | Translation model for CW chord to angle Alpha derived from a Monte-Carlo simulation based on raytracing. |
| title_full_unstemmed | Translation model for CW chord to angle Alpha derived from a Monte-Carlo simulation based on raytracing. |
| title_short | Translation model for CW chord to angle Alpha derived from a Monte-Carlo simulation based on raytracing. |
| title_sort | translation model for cw chord to angle alpha derived from a monte carlo simulation based on raytracing |
| url | https://doi.org/10.1371/journal.pone.0267028 |
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