Prediction model for best focus, power, and spherical aberration of the cornea: Raytracing on a large dataset of OCT data

Purpose To analyse corneal power based on a large optical coherence tomography dataset using raytracing, and to evaluate corneal power with respect to the corneal front apex plane for different definitions of best focus. Methods A large OCT dataset (10,218 eyes of 8,430 patients) from the Casia 2 (Tomey, Japan) was post-processed in MATLAB (MathWorks, USA). Using radius of curvature, corneal front and back surface asphericity, central corneal thickness, and pupil size (aperture) a bundle of rays was traced through the cornea. Various best focus definitions were tested: a) minimum wavefront error, b) root mean squared ray scatter, c) mean absolute ray scatter, and d) total spot diameter. All 4 target optimisation criteria were tested with each best focus plane. With the best-fit keratometer index the difference of corneal power and keratometric power was evaluated using a multivariate linear model. Results The mean corneal powers for a/b/c/d were 43.02±1.61/42.92±1.58/42.91±1.58/42.94±1.59 dpt respectively. The root mean squared deviations of corneal power from keratometric power (nK = 1.3317/1.3309/1.3308/1.3311 for a/b/c/d) were 0.308/0.185/0.171/0.209 dpt. With the multivariate linear model the respective RMS error was reduced to 0.110/0.052/0.043/0.065 dpt (R² = 0.872/0.921/0.935/0.904). Conclusions Raytracing improves on linear Gaussian optics by considering the asphericity of both refracting surfaces and using Snell’s law of refraction in preference to paraxial simplifications. However, there is no unique definition of best focus, and therefore the calculated corneal power varies depending on the definition of best focus. The multivariate linear model enabled more precise estimation of corneal power compared to the simple keratometer equation.

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Refractive, Topographic, and Aberrometric Results at 2-Year Follow-Up for Accelerated Corneal Cross-Link for Progressive Keratoconus

Journal of Ophthalmology ◽

10.1155/2017/5714372 ◽

2017 ◽

Vol 2017 ◽

pp. 1-6 ◽

Cited By ~ 7

Author(s):

Ercüment Bozkurt ◽

Engin Bilge Ozgurhan ◽

Betul Ilkay Sezgin Akcay ◽

Tugba Kurt ◽

Yusuf Yildirim ◽

...

Keyword(s):

Visual Acuity ◽

Spherical Aberration ◽

Corneal Thickness ◽

Corneal Topography ◽

Wavefront Aberration ◽

Distance Visual Acuity ◽

Uncorrected Distance Visual Acuity ◽

Wavefront Error ◽

The Mean

Purpose. To report the visual, refractive, and corneal topography and wavefront aberration results of accelerated corneal cross-linking (CXL) during a 24-month follow-up.Methods. Forty-seven eyes underwent riboflavin-ultraviolet A-induced accelerated CXL treatment (30 mW/cm2with a total dose of 7.2 joules/cm2). Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical and cylindrical values, keratometry (K) measurements (Ksteep,Kflat,Kavg, andKapex), central corneal thickness, and anterior corneal aberrometric analyses including total wavefront error (WFE), total high order aberration (HOA), astigmatism, trefoil, coma, quadrafoil, secondary astigmatism, and spherical aberration were evaluated.Results. The mean UDVA and CDVA were significantly improved at 1 (p=0.003andp=0.004, resp.) and 2 years after treatment (p=0.001andp=0.001, resp.). The meanKsteep,Kflat,Kaverage, andKapexvalues were significantly lower than baseline at 12 months (p=0.008,p=0.024,p=0.001, andp=0.014, resp.) and 24 months (p=0.014,p=0.017,p=0.001, andp=0.012, resp.). Corneal thickness showed a significant decrease at 1 month. Total HOA and coma decreased significantly at the 12-month (p=0.001andp=0.009, resp.) and 24-month visits (p=0.001andp=0.007, resp.).Conclusion. Accelerated CXL (30 mW/cm2) was found to be effective in improving UDVA, CDVA, corneal topography readings, total HOA, and coma aberrations during the 24-month follow-up.

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Evaluation of the Relationships between Corneal Parameters, Ocular Biometry, and Myopia Magnitude

Sains Malaysiana ◽

10.17576/jsm-2021-5010-20 ◽

2021 ◽

Vol 50 (10) ◽

pp. 3077-3084

Author(s):

Mohd Izzuddin Hairol ◽

Norlaili Arif ◽

Pui Theng Yong ◽

Mariah Asem Shehadeh Saleh Ali ◽

Nik Nor Adlina Nik Idris ◽

...

Keyword(s):

Axial Length ◽

Corneal Thickness ◽

Anterior Chamber Depth ◽

Radius Of Curvature ◽

Corneal Curvature ◽

Ocular Biometry ◽

Corneal Asphericity ◽

Corneal Radius ◽

The Difference ◽

The Relationship

Axial length of the eye correlates with the magnitude of myopia. However, there are conflicting reports on the relationship between certain corneal parameters with myopia magnitude. The objective of this study was to compare ocular biometry and corneal parameters between emmetropic and myopic groups. Participants (n=127) were categorized as emmetropia (spherical equivalent, SE, ±0.50D), low myopia (-0.75D≤SE<-6.00D) and high myopia (SE≥-6.00D). The difference in axial length, anterior chamber depth, and vitreous chamber depth between emmetrope, low myope, and high myope were highly significant (one-way ANOVA, all p<0.001) with significant correlations between SE and all these parameters (simple regressions, all p<0.001). However, central corneal thickness, corneal radius of curvature, and corneal asphericity between these groups, and the correlations between the ocular parameters with SE were not significantly different (all p>0.05). Corneal curvature correlated significantly with axial length (p=0.001) but not with myopia magnitude (p=0.91). Rather than myopia magnitude, axial length appears to be more sensitive to detect changes in corneal curvature in myopes. In conclusion, myopic patients’ axial length should be carefully considered for interventions that involve the cornea, such as orthokeratology and refractive surgery.

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Refractive accuracy in eyes undergoing combined cataract extraction and Descemet membrane endothelial keratoplasty

British Journal of Ophthalmology ◽

10.1136/bjophthalmol-2020-317247 ◽

2021 ◽

pp. bjophthalmol-2020-317247

Author(s):

Jack A Campbell ◽

John G Ladas ◽

Kendrick Wang ◽

Fasika Woreta ◽

Divya Srikumaran

Keyword(s):

Corneal Thickness ◽

Cataract Extraction ◽

Absolute Error ◽

Corneal Dystrophy ◽

Endothelial Keratoplasty ◽

Descemet Membrane Endothelial Keratoplasty ◽

Optical Biometry ◽

Corneal Power ◽

Descemet Membrane ◽

The Difference

PurposeTo evaluate the refractive accuracy of current intraocular lens (IOL) formulas and propose a modification in calculation of corneal power in eyes undergoing combined cataract extraction and Descemet membrane endothelial keratoplasty (DMEK).DesignRetrospective cohort study.MethodsPatients with Fuchs endothelial corneal dystrophy undergoing uncomplicated combined cataract surgery and DMEK at a single institution were included. The Hoffer Q, SRK/T, Holladay I, Barrett Universal II and Haigis formulas were compared. A modified corneal power was calculated using a thick lens equation based on anterior and posterior corneal radii and corneal thickness from Pentacam imaging. Error calculations were adjusted based on the difference in optical biometry and the modified corneal power. Mean absolute error (MAE) for each formula was compared between the corneal power modification and optical biometry corneal power.ResultsIn 86 eyes, the mean error ranged from 0.90 D for the Barrett Universal II formula to −0.10 D for the Haigis formula, with 4 of 5 formulas resulting in a mean hyperopic error. The corneal power modification resulted in a significantly lower MAE for the Hoffer Q (0.82 D), Holladay I (0.85 D), SRK/T (0.85 D) and Barrett Universal II (0.90 D) formulas compared with optical biometry corneal power for the Hoffer Q (1.02 D; p<0.005), Holladay I (0.97 D; p<0.005), SRK/T (0.93 D; p<0.01) and Barrett Universal II (1.16 D; p<0.005) formulas.ConclusionsAll formulas except the Haigis formula resulted in a hyperopic error. The corneal power modification significantly reduced error in four out of five IOL formulas.

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Accelerated cross-linking technique using a protective corneal donor flap in the treatment of progressive keratoconus on «thin» corneas

Fyodorov journal of ophthalmic surgery ◽

10.25276/0235-4160-2021-2-26-31 ◽

2021 ◽

pp. 26-31

Author(s):

A.V. Tereshchenko ◽

◽

I.G. Trifanenkova ◽

S.K. Dem'yanchenko ◽

Y.Y. Golubeva ◽

...

Keyword(s):

Visual Acuity ◽

Corneal Thickness ◽

Cross Linking ◽

Donor Cornea ◽

Corrected Visual Acuity ◽

Uncorrected Visual Acuity ◽

The Difference ◽

Definition Of ◽

Thin Cornea ◽

Observation Period

Purpose. To develop a method of accelerated ultraviolet crosslinking with an initial corneal thickness equal to or less than 400 microns using a protective donor corneal flap. Definition of safety and effectiveness of this method in the treatment of progressive keratoconus. Material and methods. 20 patients (20 eyes) with a diagnosis of progressive keratoconus 2–3 stages were included in the study. The accelerated crosslinking was carried out with an IROC-VX-2000 device (Switzerland). A protective donor corneal flap was cut out by using a Femto LDV Z8 femtosecond laser (Ziemer, Switzerland). The thickness of the protective flap of the donor cornea was determined as the difference between 450 μm and the obtained value of the patient's pachymetry in 30 minutes of saturation with Dextralink in μm. Results. Indicators of uncorrected visual acuity and corrected visual acuity returned to the level of preoperative values and did not tend to decrease until the end of the observation period for 6 months. The average keratometry indices gradually decreased: after 3 months – 50.3 ± 1.5 μm, after 6 months – 48.9 ± 1.8 μm, by 12 months – 46.7 ± 2.1 μm. A decrease in elevation indicators of the anterior and posterior surfaces was marked on elevation maps throughout the observation period. Conclusion. The proposed ultraviolet crosslinking technique using a protective donor corneal flap in patients with corneal thickness 400 μm or less is reproducible. This technique proves its effectiveness and safety and allows to stabilize the condition in patients with progressive keratoconus with adequate visual function. This makes this technique necessary, taking into account the lack of adequate cross-linking technology with a thin cornea. Keywords: progressive keratoconus, thin cornea, ultraviolet crosslinking, protective donor corneal flap.

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Structural distributions in the multivariate linear model

Optimization ◽

10.1080/02331937608842371 ◽

1976 ◽

Vol 7 (5) ◽

pp. 679-683

Author(s):

Michael Nussbaum

Keyword(s):

Linear Model ◽

Multivariate Linear Model

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The Distinction between [P] and [S]

10.23943/princeton/9780691161006.003.0018 ◽

2017 ◽

Author(s):

Galen Strawson

Keyword(s):

Personal Identity ◽

Radical Change ◽

Legal Responsibility ◽

The Difference ◽

Definition Of ◽

Over Time

This chapter examines the difference between John Locke's definition of a person [P], considered as a kind of thing, and his definition of a subject of experience of a certain sophisticated sort [S]. It first discusses the equation [P] = [S], where [S] is assumed to be a continuing thing that is able to survive radical change of substantial realization, as well as Locke's position about consciousness in relation to [P]'s identity or existence over time as [S]. It argues that Locke is not guilty of circularity because he is not proposing consciousness as the determinant of [S]'s identity over time, but only of [S]'s moral and legal responsibility over time. Finally, it suggests that the terms “Person” and “Personal identity” pull apart, in Locke's scheme of things, but in a perfectly coherent way.

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L'anglicisme dans la langue française

Digital Press Social Sciences and Humanities ◽

10.29037/digitalpress.43286 ◽

2019 ◽

Vol 3 ◽

pp. 00013

Author(s):

Danny Susanto

Keyword(s):

English Language ◽

Oil Industry ◽

English Word ◽

Public Institutions ◽

Font Size ◽

The World ◽

French Speaking ◽

The Difference ◽

Definition Of ◽

Bibliographic Study

The purpose of this study is to analyze the phenomenon known as “anglicism”: a loan made to the English language by another language. Anglicism arose either from the adoption of an English word as a result of a translation defect despite the existence of an equivalent term in the language of the speaker, or from a wrong translation, as a word-by-word translation. Said phenomenon is very common nowadays and most languages of the world including making use of some linguistic concepts such as anglicism, neologism, syntax, morphology etc, this article addresses various aspects related to Anglicisms in French through a bibliographic study: the definition of Anglicism, the origin of Anglicisms in French and the current situation, the areas most affected by Anglicism, the different categories of Anglicism, the difference between French Anglicism in France and French-speaking Canada, the attitude of French-speaking society towards to the Anglicisms and their efforts to stop this phenomenon. The study shows that the areas affected are, among others, trade, travel, parliamentary and judicial institutions, sports, rail, industrial production and most recently film, industrial production, sport, oil industry, information technology, science and technology. Various initiatives have been implemented either by public institutions or by individuals who share concerns about the increasingly felt threat of the omnipresence of Anglicism in everyday life.

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Goldmann Tonometry and Corneal Biomechanics

Applied Sciences ◽

10.3390/app11094025 ◽

2021 ◽

Vol 11 (9) ◽

pp. 4025

Author(s):

Dario Messenio ◽

Marco Ferroni ◽

Federica Boschetti

Keyword(s):

Mechanical Properties ◽

Anterior Chamber ◽

Pressure Transducer ◽

Pearson Correlation ◽

Corneal Thickness ◽

Applanation Tonometry ◽

In Vitro Tests ◽

Goldmann Tonometry ◽

The Difference

Glaucoma is the second cause of irreversible blindness in the world. Intraocular pressure (IOP) is a recognized major risk factor for the development and progression of glaucomatous damage. Goldmann applanation tonometry (GAT) is internationally accepted as the gold standard for the measurement of IOP. The purpose of this study was to search for correlations between Goldmann tonometry and corneal mechanical properties and thickness by means of in vitro tests. IOP was measured by the Goldmann applanation tonometer (GIOP), and by a pressure transducer inserted in the anterior chamber of the eye (TIOP), at increasing pressure levels by addition of saline solution in the anterior chamber of enucleated pig eyes (n = 49). Mechanical properties were also determined by inflation tests. The GAT underestimated the real measurements made by the pressure transducer, with most common differences in the range 15–28 mmHg. The difference between the two instruments, highlighted by the Bland–Altman test, was confirmed by ANOVA, normality tests, and Mann–Whitney’s tests, both on the data arranged for infusions and for the data organized by pressure ranges. Pearson correlation tests revealed a negative correlation between (TIOP-GIOP) and both corneal stiffness and corneal thickness. In conclusion, data obtained showed a discrepancy between GIOP and TIOP more evident for softer and thinner corneas, that is very important for glaucoma detection.

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Matched comparison of corneal higher order aberrations induced by SMILE to femtosecond assisted LASIK and to PRK in correcting moderate and high myopia: 3.00mm vs. 6.00mm

BMC Ophthalmology ◽

10.1186/s12886-021-01987-3 ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Mohammad Miraftab ◽

Hassan Hashemi ◽

Mohammadreza Aghamirsalim ◽

Shiva Fayyaz ◽

Soheila Asgari

Keyword(s):

Visual Acuity ◽

High Myopia ◽

Spherical Aberration ◽

Corneal Thickness ◽

Higher Order ◽

Laser In Situ Keratomileusis ◽

Higher Order Aberrations ◽

Surgical Methods ◽

Matched Comparison ◽

Surgical Group

Abstract Background The refractive surgeries induce corneal higher order aberrations (C-HOAs). In this study, change of C-HOAs after small-incision lenticule extraction (SMILE) compared to femtosecond assisted laser in situ keratomileusis (femto-LASIK), and to photorefractive keratectomy with mitomycin-C (PRK) under photopic and mesopic conditions. Methods In this prospective study, age, gender, and apical corneal thickness (ACT) matched cases with moderate myopia [spherical equivalent (SE) 3.00 to 6.00D) to high myopia (SE > 6.00D)] were enrolled. In addition to visual acuity and refraction, total C-HOA, coma, spherical aberration (SA), and trefoil in the 3- and 6-mm zones were measured before and 3 and 6 months after surgery. Results Overall, 372 moderate myopia cases (124 eyes of 124 individuals in each surgical group) and 171 high myopia cases (57 eyes of 57 individuals in each surgical group) were enrolled. At baseline, the differences in age, gender, ACT, uncorrected and corrected visual acuity, and SE were not statistically significant between subgroups of surgical methods within each myopia group (all P > 0.05). At 12 months, in the moderate myopia group, there was less increase in 6-mm zone total C-HOA, coma, and SA with SMILE compared to the other groups (all P < 0.05). In the high myopia group, there was greater increase in photopic total C-HOA and trefoil and less increase in mesopic SA with SMILE (all P < 0.05). Conclusions In correction of moderate myopia, SMILE has better results in mesopic condition. In high myopia correction, femto-LASIK and PRK have better results in photopic and SMILE in mesopic condition.

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Identity, Community and Belonging in gcc States

Sociology of Islam ◽

10.1163/22131418-00604004 ◽

2018 ◽

Vol 6 (4) ◽

pp. 401-428

Author(s):

Miriam R. Lowi

Keyword(s):

Religious Affiliation ◽

Protective Role ◽

The Other ◽

National Project ◽

Scholarly Literature ◽

National Community ◽

The Difference ◽

Definition Of

Studies of identity and belonging in Gulf monarchies tend to privilege tribal or religious affiliation, if not the protective role of the ruler as paterfamilias. I focus instead on the ubiquitous foreigner and explore ways in which s/he contributes to the definition of national community in contemporary gcc states. Building upon and moving beyond the scholarly literature on imported labor in the Gulf, I suggest that the different ‘categories’ of foreigners impact identity and the consolidation of a community of privilege, in keeping with the national project of ruling families. Furthermore, I argue that the ‘European,’ the non-gcc Arab, and the predominantly Asian (and increasingly African) laborer play similar, but also distinct roles in the delineation of national community: while they are differentially incorporated in ways that protect the ‘nation’ and appease the citizen-subject, varying degrees of marginality reflect Gulf society’s perceptions or aspirations of the difference between itself and ‘the other(s).’

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