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16 pages, 1682 KiB

Open AccessArticle

A Refined Model for Ablation Through Cavitation Bubbles with Ultrashort Pulse Lasers

by Shwetabh Verma and Samuel Arba Mosquera

Photonics 2024, 11(11), 1047; https://doi.org/10.3390/photonics11111047 - 7 Nov 2024

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Abstract

(1) Background: Ultrashort high-energy laser pulses may cause interaction mechanisms, including photodisruption and plasma-induced ablation in the medium. It is not always easy to distinguish between these two processes, as both interaction mechanisms rely on plasma generation and overlap. The purpose of this [...] Read more.

(1) Background: Ultrashort high-energy laser pulses may cause interaction mechanisms, including photodisruption and plasma-induced ablation in the medium. It is not always easy to distinguish between these two processes, as both interaction mechanisms rely on plasma generation and overlap. The purpose of this paper is to discuss prominent cavitation bubble models describing photodisruption and plasma-induced ablation and to explore their nature for different threshold energies. This exploration will help to better distinguish the two interaction mechanisms. As a second aim, we present an alternative model for the low-energy regime close to the laser-induced optical breakdown (LIOB) threshold, representing the phenomenological effect of the plasma-induced ablation regime. (2) Methods: The cavitation bubble models for photodisruption and plasma-induced ablation were used to calculate the bubble radius for a series of threshold energies (E_Th = 30, 50, 70, and 300 nJ) that loosely represent commercial systems currently used in ultrashort-pulse tissue ablation. Taking a photodisruption model coefficient commonly used in the literature, the root mean square error between the two interaction models was minimized using the generalized reduced gradient fitting method to calculate the optimum scaling factors for the plasma model. The refined models with optimized coefficients were compared for a range of pulse and threshold energies. (3) Results: For low E_Th (30, 50, and 70 nJ), the plasma-induced ablation model dominates for low energies that are close to the threshold energy. The photodisruption model dominates for high energies that are well above the threshold energy. At very high pulse energies, for all the simulated cases, the photodisruption model transitions and crosses over to the plasma-induced ablation model. The cross-over points from which the photodisruption model dominates tend to be reduced for larger E_Th. A new universally applicable model for plasma-induced ablation has been hypothesized that considers the cavitation bubble volume and potentially better explains the bubble dynamics during intrastromal processes. (4) Conclusions: This theoretical exploration and the comparison of the outcomes to empirical data substantiate that inadvertently using the photodisruption model to explain the cavitation bubble dynamics for the entire spectrum of pulse energies and laser systems might provide erroneous estimates of cavitation bubble sizes. A reliable estimate of the true size (the maximum radius) of the cavitation bubble can be reasonably retrieved as the maximum predicted size from the fit of the photodisruption model and the newly proposed plasma-induced ablation model at any given pulse energy. Full article

(This article belongs to the Special Issue Visual Optics)

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14 pages, 841 KiB

Open AccessArticle

A Closed-Form Analytical Conversion between Zernike and Gatinel–Malet Basis Polynomials to Present Relevant Aberrations in Ophthalmology and Refractive Surgery

by Masoud Mehrjoo, Damien Gatinel, Jacques Malet and Samuel Arba Mosquera

Photonics 2024, 11(9), 883; https://doi.org/10.3390/photonics11090883 - 20 Sep 2024

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Abstract

The Zernike representation of wavefronts interlinks low- and high-order aberrations, which may result in imprecise clinical estimates. Recently, the Gatinel–Malet wavefront representation has been introduced to resolve this problem by deriving a new, unlinked basis originating from Zernike polynomials. This new basis preserves [...] Read more.

The Zernike representation of wavefronts interlinks low- and high-order aberrations, which may result in imprecise clinical estimates. Recently, the Gatinel–Malet wavefront representation has been introduced to resolve this problem by deriving a new, unlinked basis originating from Zernike polynomials. This new basis preserves the classical low and high aberration subgroups’ structure, as well as the orthogonality within each subgroup, but not the orthogonality between low and high aberrations. This feature has led to conversions relying on separate wavefront reconstructions for each subgroup, which may increase the associated numerical errors. This study proposes a robust, minimised-error (lossless) analytical approach for conversion between the Zernike and Gatinel–Malet spaces. This method analytically reformulates the conversion as a nonhomogeneous system of linear equations and computationally solves it using matrix factorisation and decomposition techniques with high-level accuracy. This work fundamentally demonstrates the lossless expression of complex wavefronts in a format that is more clinically interpretable, with potential applications in various areas of ophthalmology, such as refractive surgery. Full article

(This article belongs to the Special Issue Visual Optics)

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10 pages, 1695 KiB

Open AccessArticle

Analysis of the Effective and Actual Lens Position by Different Formulas. Postoperative Application of a Ray-Tracing-Based Simulated Optical Model

by Diana Gargallo Yebra, Laura Remón Martín, Iván Pérez Escorza and Francisco Javier Castro Alonso

Photonics 2024, 11(8), 711; https://doi.org/10.3390/photonics11080711 - 30 Jul 2024

Viewed by 805

Abstract

(1) Background: This study compares the effective lens position (ELP) and intraocular lens power (IOLP) derived from SRK/T, Hoffer Q, Holladay I, and Haigis formulas with the actual lens position (ALP) and the implanted IOLP after cataract surgery. Additionally, it aims to optimize [...] Read more.

(1) Background: This study compares the effective lens position (ELP) and intraocular lens power (IOLP) derived from SRK/T, Hoffer Q, Holladay I, and Haigis formulas with the actual lens position (ALP) and the implanted IOLP after cataract surgery. Additionally, it aims to optimize ALP using a ray-tracing-based simulated optical model to achieve emmetropia. (2) Methods: A retrospective observational study was conducted on 43 eyes implanted with the same monofocal intraocular lens (IOL). Preoperative and postoperative biometric data were collected using the Lenstar LS900. Postoperative measurements included ALP, subjective refraction, and refraction error (RE). Optical simulations (OSLO EDU 6.6.0) were utilized to optimize ALP for emmetropia (ALP_IDEAL). (3) Results: Paired t-test results between RE_OSLO-RE_OBJ (p-value = 0.660) and RE_OSLO-RE_SUB (p-value = 0.789) indicated no significant statistical differences. However, statistically significant differences were found between ALP and ALP_IDEAL (p < 0.05), with a difference of −0.04 ± 0.45 mm [ranging from −1.00 to 1.20 mm]. A significant correlation was observed between ΔALP (ΔALP = ALP − ALP_IDEAL) and RE_SUBJ. (4) Conclusions: This customized ray-tracing eye model effectively achieves refractive outcomes similar to those obtained both subjectively and objectively post-surgery. Additionally, it has enabled optical simulations to optimize the IOL position and achieve emmetropia. Full article

(This article belongs to the Special Issue Visual Optics)

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9 pages, 522 KiB

Open AccessArticle

Model of the Effects of Femtosecond Laser Pulse Energy on the Effective Z-Position of the Resulting Cut after Laser-Induced Optical Breakdown

by Simas Sobutas and Samuel Arba Mosquera

Photonics 2024, 11(8), 685; https://doi.org/10.3390/photonics11080685 - 23 Jul 2024

Viewed by 682

Abstract

Presented in this study is a validated semiempirical model of the effects of femtosecond laser pulse energy on the effective z-position of the resulting cut after laser-induced optical breakdown. Different energy levels (for the same spot spacings, i.e., different doses) running from 1.07 [...] Read more.

Presented in this study is a validated semiempirical model of the effects of femtosecond laser pulse energy on the effective z-position of the resulting cut after laser-induced optical breakdown. Different energy levels (for the same spot spacings, i.e., different doses) running from 1.07 × (~60 nJ) to 3.8 × (~215 nJ) of the laser-induced optical breakdown (LIOB) threshold (~56 nJ) were used to perform flat cuts within flat poly(methyl methacrylate) (PMMA) samples at the same nominal focus position (depth within the material). The z-locations of the effective cut and the anterior surface of the PMMA were confocally determined. The difference (PMMA_surface—Cut_plane) was used as a surrogate for the effective shift in the z-position of the cut. A consistent and continuous shift towards less deep cuts was observed for increasing pulse energies. The z-shift spreads by up to 22 µm thinner cuts for the largest pulse energy (3.8× LIOBTh, ~215 nJ). Higher pulse energies seem to significantly reduce the cutting depth. The results for PMMA are in good agreement with the moving LIOB model. Full article

(This article belongs to the Special Issue Visual Optics)

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10 pages, 1039 KiB

Open AccessArticle

Repeatability of Subjective Refraction in Different Age Groups

by Carlos Carpena-Torres, Laura Batres, María Serramito and Gonzalo Carracedo

Photonics 2024, 11(7), 634; https://doi.org/10.3390/photonics11070634 - 2 Jul 2024

Viewed by 803

Abstract

Background: The purpose of this study was to assess the inter-examiner repeatability of subjective refraction across diverse age cohorts, an aspect not previously investigated. Methods: A cross-sectional, randomized study enrolled 86 participants (mean age: 37.0 ± 18.0 years), distributed into three groups: youth, [...] Read more.

Background: The purpose of this study was to assess the inter-examiner repeatability of subjective refraction across diverse age cohorts, an aspect not previously investigated. Methods: A cross-sectional, randomized study enrolled 86 participants (mean age: 37.0 ± 18.0 years), distributed into three groups: youth, non-presbyopic adults, and presbyopic adults. Each participant underwent three subjective refractions by three different optometrists on separate days. Repeatability analysis encompassed all refractive variables (M, J0, and J45). Results: There were no significant differences between optometrists in all refractive variables for either the overall sample or across age groups (p ≥ 0.05). Additionally, no correlation was found between participants’ age and the mean difference in refractive variables across optometrists (p ≥ 0.05). The 95% confidence interval of repeatability (r) for the total sample was ±0.70 D for M, ±0.29 for J0, and ±0.21 D for J45. Conclusions: Based on these findings and previous research, it is suggested to establish 95% limits of agreement of ±0.75 D for M, and between ±0.25 D and ±0.50 D for both J0 and J45 when validating new refraction systems compared to subjective refraction as the gold standard, regardless of the age of the subjects evaluated. Full article

(This article belongs to the Special Issue Visual Optics)

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16 pages, 5258 KiB

Open AccessArticle

A Comprehensive Study on Elasticity and Viscosity in Biomechanics and Optical Properties of the Living Human Cornea

by Francisco J. Ávila, Óscar del Barco, María Concepción Marcellán and Laura Remón

Photonics 2024, 11(6), 524; https://doi.org/10.3390/photonics11060524 - 31 May 2024

Viewed by 731

Abstract

Corneal biomechanics is a hot topic in ophthalmology. The biomechanical properties (BMPs) of the cornea have important implications in the management and diagnosis of corneal diseases such as ectasia and keratoconus. In addition, the characterization of BMPs is crucial to model the predictability [...] Read more.

Corneal biomechanics is a hot topic in ophthalmology. The biomechanical properties (BMPs) of the cornea have important implications in the management and diagnosis of corneal diseases such as ectasia and keratoconus. In addition, the characterization of BMPs is crucial to model the predictability of a corneal surgery intervention, the outcomes of refractive surgery or the follow-up of corneal diseases. The biomechanical behavior of the cornea is governed by viscoelastic properties that allow, among other structural implications, the damping of excess intraocular pressure and the reduction of damage to the optic nerve. Currently, the most versatile and complete methods to measure corneal viscoelasticity are based on air-puff corneal applanation. However, these methods lack the ability to directly measure corneal viscosity. The aim of this work is to propose a new methodology based on the analysis of corneal air-puff measurements through the standard linear solid model (SLSM) to provide analytical expressions to separately calculate the elastic and time-dependent (corneal retardation time and viscosity) properties. The results show the mean values of elasticity (E), viscosity (Ƞ) and corneal retardation time (τ) in a sample of 200 young and healthy subjects. The influence of elasticity and viscosity on viscoelasticity, high-order corneal aberrations and optical transparency is investigated. Finally, the SLSM fed back from experimental E and Ƞ values is employed to compare the creep relaxation response between a normal, an ocular hypertension patient and an Ortho-K user. Corneal biomechanics is strongly affected by intraocular pressure (IOP); however, corneal hysteresis (CH) analysis is not enough to be employed as a risk factor of glaucoma progression. Low values of CH can be accompanied by high or low corneal elasticity and viscosity depending on the IOP threshold from which the time-dependent biomechanical properties trends are reversed. Full article

(This article belongs to the Special Issue Visual Optics)

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11 pages, 2290 KiB

Open AccessEditor’s ChoiceArticle

Optimization of the Spot Spacings for Reducing Roughness in Laser-Induced Optical Breakdown Processes for Corneal Laser Vision Correction

by Helen Amann and Samuel Arba Mosquera

Photonics 2024, 11(2), 114; https://doi.org/10.3390/photonics11020114 - 26 Jan 2024

Cited by 2 | Viewed by 1322

Abstract

The aim of this work is to implement an algorithm that simulates a simplified cutting surface based on laser-induced optical breakdown (LIOB). The algorithm includes the definition of a possible positioning of the laser pulses and calculation of the roughness for different parameter [...] Read more.

The aim of this work is to implement an algorithm that simulates a simplified cutting surface based on laser-induced optical breakdown (LIOB). The algorithm includes the definition of a possible positioning of the laser pulses and calculation of the roughness for different parameter settings (including LIOB threshold, pulse energies, and spot spacings) as the difference between simulated and ideal target cut (local differences within the cut, i.e., the waviness of the simulated cut vs. the homogeneity of the ideal target cut). Furthermore, optimizations of specific variables, such as spot distance (along the pathway), track distance (between lines/tracks), and pulse energy, are performed. The simulations suggest that lower pulse energies (well above the LIOB threshold) combined with asymmetric spacings (spot-to-track distance ratio >> 1) may be effective to lower the roughness of laser cuts generated by LIOB processes. The importance of lowering pulse energies (well above the threshold) emphasizes the need for the LIOB threshold to remain low (as low as possible). Reducing roughness by decreasing spacings (thus, increasing dose for same pulse energies) may have negative implications in visual recovery (risk for overdose). In all cases, the roughness is multiple times larger (rougher) than equivalent simulations for ablative procedures. Full article

(This article belongs to the Special Issue Visual Optics)

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8 pages, 1117 KiB

Open AccessArticle

Numerical Analysis of the Effect of Decentered Refractive Segmented Extended Depth of Focus (EDoF) Intraocular Lenses on Predicted Visual Outcomes

by Scott García, Luis Salvá, Salvador García-Delpech, Anabel Martínez-Espert and Vicente Ferrando

Photonics 2023, 10(7), 850; https://doi.org/10.3390/photonics10070850 - 22 Jul 2023

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Abstract

This study aimed to evaluate the optical performance of a rotationally asymmetric intraocular lens (IOL) when it is decentered relative to the visual axis. The FEMTIS Comfort IOL (Teleon Surgical B.V., Spankeren, The Netherlands) was assessed using ray tracing software in the Atchison [...] Read more.

This study aimed to evaluate the optical performance of a rotationally asymmetric intraocular lens (IOL) when it is decentered relative to the visual axis. The FEMTIS Comfort IOL (Teleon Surgical B.V., Spankeren, The Netherlands) was assessed using ray tracing software in the Atchison model eye at apertures of 3.0 mm and 4.5 mm. The metric used for assessment was the through-the-focus area under the modulation transfer function (TF-MTFa). Decentrations of 0.2 mm and 0.4 mm were considered. Our results indicated that the MTFa defocus curves exhibited significant differences depending on the direction of vertical decentration. Downward decentrations shifted the MTFa curve towards virtual vergences, resulting in improved optical quality at far distances but decreased optical quality at intermediate and near vision. Conversely, upward decentrations produced the opposite effect. Since, on one hand, this lens is fixed within the capsulorhexis during surgery, demonstrating excellent stability, and on the other hand, the precise centration of the capsulorhexis can be made accurately off the visual axis, these results provide surgeons with the opportunity to plan various clinical scenarios to optimize surgical outcomes with this IOL by selecting the optimal location for capsulorhexis centration in each patient. Full article

(This article belongs to the Special Issue Visual Optics)

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6 pages, 226 KiB

Open AccessArticle

Accuracy of Haigis Formula Using Total Keratometry for IOL Power Calculation in Eyes with Previous Myopic and Hyperopic LASIK and PRK

by Alice Galzignato, Virgilio Galvis, Alejandro Tello, Juan F. Urrea, Kenneth J. Hoffer, Catarina P. Coutinho, Domenico Schiano-Lomoriello and Giacomo Savini

Photonics 2023, 10(6), 624; https://doi.org/10.3390/photonics10060624 - 28 May 2023

Cited by 1 | Viewed by 1831

Abstract

Background: this retrospective study aimed to analyze the results of the combination of the Haigis formula and total keratometry (TK) in calculating the IOL power in eyes with previous corneal refractive surgery. Methods: the TK value provided by the IOL Master 700 (Carl [...] Read more.

Background: this retrospective study aimed to analyze the results of the combination of the Haigis formula and total keratometry (TK) in calculating the IOL power in eyes with previous corneal refractive surgery. Methods: the TK value provided by the IOL Master 700 (Carl Zeiss Meditec) was introduced into the Haigis formula; the mean prediction error (PE), mean absolute error (MAE), median absolute error (MedAE) and percentage of eyes with a PE within ±0.25 D, ±0.5 D, ±0.75 D and ±1.00 D were calculated. Results: ninety-three eyes of 93 patients with previous laser refractive surgery were evaluated. Two groups were defined: the Myopic Group included 51 previously myopic eyes and the Hyperopic Group included 42 previously hyperopic eyes. The mean PE in the Myopic Group was +0.09 ± 0.44 D and 76.47% of eyes had a PE within ±0.50 D. In the Hyperopic Group, the mean PE was −0.15 ± 0.46 D and 66.67% of eyes had a PE within ±0.50 D. Discussion: when compared to the results previously published with other formulas or methods, the Haigis formula combined with TK provided very accurate refractive outcomes for IOL power calculation in eyes with prior myopic and hyperopic corneal refractive surgery. In such eyes the results are similar to or better than those reported in previous studies. Full article

(This article belongs to the Special Issue Visual Optics)

10 pages, 1657 KiB

Open AccessArticle

Corneal Densitometry with Galilei Dual Scheimpflug Analyzer

by Alejandra Consejo, Silvia Basabilbaso and Laura Remon

Photonics 2023, 10(4), 467; https://doi.org/10.3390/photonics10040467 - 19 Apr 2023

Cited by 2 | Viewed by 1611

Abstract

This study aims to apply the densitometry distribution analysis (DDA) method to study corneal densitometry depending on age and corneal region from Galilei Dual Scheimpflug Analyzer tomography. A total of 83 healthy participants aged 39.02 ± 18.34 years (range 9–81 years) were screened [...] Read more.

This study aims to apply the densitometry distribution analysis (DDA) method to study corneal densitometry depending on age and corneal region from Galilei Dual Scheimpflug Analyzer tomography. A total of 83 healthy participants aged 39.02 ± 18.34 years (range 9–81 years) were screened using a Ziemer Galilei G2. Images were analysed using the DDA, and two parameters, α (corneal transparency) and β (corneal homogeneity), were estimated. A two-way ANOVA analysis was performed to investigate whether α and β are influenced by age, corneal región (four concentric areas were considered), and their interaction. The parameters α and β statistically change with age and corneal region. A statistically significant interaction effect of 13% (α) and 11% (β) exists between age and corneal region. However, the corneal region plays a more significant role than aging in corneal densitometry; 31% (α) and 51% (β) of the variance can be attributed to the corneal region, while 28% (α) and 5% (β) can be attributed solely to aging. Corneal densitometry can be objectively assessed from Galilei G2 images using the DDA method. The corneal region plays a more significant role than aging in corneal densitometry. Consequently, general results on corneal densitometry and aging should be taken cautiously. Full article

(This article belongs to the Special Issue Visual Optics)

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11 pages, 2823 KiB

Open AccessArticle

Changes in Wavefront Error of the Eye for Different Accommodation Targets under the Application of Phenylephrine Hydrochloride

by María Mechó-García, Iñaki Blanco-Martínez, Paulo Fernandes, Rute J. Macedo-de-Araújo, Miguel Faria-Ribeiro and José Manuel González-Méijome

Photonics 2023, 10(4), 381; https://doi.org/10.3390/photonics10040381 - 30 Mar 2023

Cited by 2 | Viewed by 1421

Abstract

Pharmacological dilation of the eye to have a larger pupil diameter may allow a better understanding of the wavefront error changes with accommodation. This work aimed to investigate whether dilation of the pupil with Phenylephrine Hydrochloride (PHCl) application changes the accommodative response and [...] Read more.

Pharmacological dilation of the eye to have a larger pupil diameter may allow a better understanding of the wavefront error changes with accommodation. This work aimed to investigate whether dilation of the pupil with Phenylephrine Hydrochloride (PHCl) application changes the accommodative response and the Zernike coefficient magnitude with accommodative demand when computed to a common pupil size. Sixteen right eyes of healthy young subjects were measured with the commercial Hartmann–Shack aberrometer IRX3 (Imagine Eyes, Orsay, France) 30 min after two drops of 1.0% PHCl were applied. The eye wavefronts for accommodative demands from 0 to 5 D were measured in natural conditions and after pupil dilatation. Statistically significant differences between both conditions were found for the Zernike coefficients

C_{3}^{- 1}

,

C_{3}^{1},

C_{4}^{0}

and

C_{6}^{0}

. Without the effect of PHCl, higher values were found for all higher-order Zernike coefficients (HOA). With increased accommodative response, an increase of

C_{3}^{- 1}

and a decrease of

C_{3}^{1}

was observed and the

C_{4}^{0}

becomes more negative; the change from positive to negative is shown in the accommodative demand of 1.5 D. Conversely,

C_{6}^{0}

increases with increasing accommodative demand. To conclude, the results demonstrated that the mydriatic effect of PHCl causes changes in the magnitude of HOA when accommodation is stimulated. The trends observed in the different Zernike coefficients were the same reported in previous studies. Full article

(This article belongs to the Special Issue Visual Optics)

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10 pages, 1480 KiB

Open AccessArticle

Luminous Flux in Ex-Vivo Porcine Eyes during Endoillumination and during Transscleral Illumination Depending on the Transmission Properties of the Eyewall

by Nicole Fehler and Martin Heßling

Photonics 2023, 10(4), 362; https://doi.org/10.3390/photonics10040362 - 23 Mar 2023

Viewed by 1225

Abstract

(1) Background: During eye surgery, it is important that sufficient light enlightens the inside of the eye for small structures to become visible. The intraocular brightness is influenced by the luminous flux of the illumination system. However, the intraocular luminous flux during surgery [...] Read more.

(1) Background: During eye surgery, it is important that sufficient light enlightens the inside of the eye for small structures to become visible. The intraocular brightness is influenced by the luminous flux of the illumination system. However, the intraocular luminous flux during surgery has not been investigated so far. Insufficient luminous flux makes vision difficult for the surgeon, whereas excessive luminous flux can cause damage to the retina. Therefore, the luminous flux in lightly and strongly pigmented eyes is determined by endoillumination and diaphanoscopic illumination. (2) Methods: First, the luminous flux emitted from a diaphanoscopic illumination fiber is measured. For determining the intraocular luminous flux, this is multiplied with the transmission properties of the eyewall, which are determined for ex vivo porcine eyes. In order to compare the luminous flux of transscleral illumination with that of endoillumination, the luminous flux of various endoillumination fibers is examined. (3) Results: The results reveal that the total transmission of the eyewall is up to 2.5 times higher for blue/lightly pigmented eyes than for brown/strongly pigmented eyes. With this, the intraocular luminous flux in ex vivo porcine eyes is around 95% higher for less pigmented eyes than for strong pigmented eyes, considering intraocular reflections. (4) Conclusion: To obtain the same brightness in blue and brown eyes, the surgeon can reduce the intensity of the light source when illuminating blue eyes to reduce their retinal risk. Full article

(This article belongs to the Special Issue Visual Optics)

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11 pages, 1536 KiB

Open AccessArticle

Photostress Recovery Time after Flash-Lighting Is Increased in Myopic Eyes

by Francisco J. Ávila, Pilar Casado and Jorge Ares

Photonics 2023, 10(1), 86; https://doi.org/10.3390/photonics10010086 - 12 Jan 2023

Cited by 1 | Viewed by 2987

Abstract

Background: It is well-known that non-pathological axial myopic eyes present physiological and functional differences in comparison with emmetropic eyes due to altered retinal anatomy. Photostress tests have shown very significant capabilities to discriminate a normal retina from an abnormal retina. Accordingly, the aim [...] Read more.

Background: It is well-known that non-pathological axial myopic eyes present physiological and functional differences in comparison with emmetropic eyes due to altered retinal anatomy. Photostress tests have shown very significant capabilities to discriminate a normal retina from an abnormal retina. Accordingly, the aim of this work was to investigate the differences between myopic and emmetropic eyes in the measured photostress recovery time (PSRT) after retinal light-flashing in a population of young healthy subjects. Methods: A coaxial illumination total disability glare instrument was employed to measure the recovery time after photostress was induced by a 240 milliseconds flash-lighting (535 nm) exposure on 66 myopic and 66 emmetropic eyes. The measurements were carried out for different combinations of glare angles and contrasts of the visual stimuli. Results: In general terms, PSRT in myopic eyes was found at a statistically higher than in emmetropic eyes (Bonferroni correction). For both groups, the measured recovery strongly depends on the contrast of the test object used to measure baseline recovery function and markedly less on the source of glare angles explored. When the PSRTs obtained for different glare angles are averaged, the differences between PSRTs drastically increase with the reduction in the contrast of the stimuli between both groups of study. Conclusions: PSRT is higher for myopic than for young healthy emmetropic eyes (1.2 s and 0.2 s for 5% and 100% contrast test object, respectively). Though seemingly small, the magnitude of this finding can be relevant when flash-lighting happens while driving a car or while performing actions where the reaction time after a visual stimulus can be critical. Full article

(This article belongs to the Special Issue Visual Optics)

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5 pages, 614 KiB

Open AccessOpinion

The Centration Dilemma in Refractive Corrections: Why Is It Still a Dilemma and How to Cope?

by Samuel Arba Mosquera and Shwetabh Verma

Photonics 2024, 11(9), 822; https://doi.org/10.3390/photonics11090822 - 30 Aug 2024

Cited by 1 | Viewed by 652

Abstract

(1) Background: Defining the optimum center for laser refractive corrections is difficult, with many of the available approaches having pros and cons. Decentered ablations result in undesirable side effects like halos, glare, monocular diplopia, and a reduction in visual acuity; (2) Methods: The [...] Read more.

(1) Background: Defining the optimum center for laser refractive corrections is difficult, with many of the available approaches having pros and cons. Decentered ablations result in undesirable side effects like halos, glare, monocular diplopia, and a reduction in visual acuity; (2) Methods: The ideal centration in refractive corrections should fulfil three requirements: covering a scotopic pupil; respecting the visual axis; and minimizing tissue removal. The implications of different centration strategies are discussed and shown graphically; (3) Results: Oversized asymmetric offset ablation faces fewer difficulties in registering static cyclotorsion, features less tissue wastage compared to a symmetric offset, and includes a certain amount of coma (and trefoil) in the profile, benefiting eyes with a pupil offset, which typically present with relevant amounts of coma and trefoil corneal aberrations due to decentered optics; (4) Conclusions: There is a need for a flexible choice of centration in refractive procedures to design customized and non-customized treatments optimally. An ideal optical zone covering the pupil with the widest entrance may be as important as a centration reference. Full article

(This article belongs to the Special Issue Visual Optics)

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