Subjective Straylight Index: A Visual Test for Retinal Contrast Assessment as a Function of Veiling Glare.

Spatial aspects of visual performance are usually evaluated through visual acuity charts and contrast sensitivity (CS) tests. CS tests are generated by vanishing the contrast level of the visual charts. However, the quality of retinal images can be affected by both ocular aberrations and scattering effects and none of those factors are incorporated as parameters in visual tests in clinical practice. We propose a new computational methodology to generate visual acuity charts affected by ocular scattering effects. The generation of glare effects on the visual tests is reached by combining an ocular straylight meter methodology with the Commission Internationale de l'Eclairage's (CIE) general disability glare formula. A new function for retinal contrast assessment is proposed, the subjective straylight function (SSF), which provides the maximum tolerance to the perception of straylight in an observed visual acuity test. Once the SSF is obtained, the subjective straylight index (SSI) is defined as the area under the SSF curve. Results report the normal values of the SSI in a population of 30 young healthy subjects (19 ± 1 years old), a peak centered at SSI = 0.46 of a normal distribution was found. SSI was also evaluated as a function of both spatial and temporal aspects of vision. Ocular wavefront measures revealed a statistical correlation of the SSI with defocus and trefoil terms. In addition, the time recovery (TR) after induced total disability glare and the SSI were related; in particular, the higher the RT, the greater the SSI value for high- and mid-contrast levels of the visual test. No relationships were found for low contrast visual targets. To conclude, a new computational method for retinal contrast assessment as a function of ocular straylight was proposed as a complementary subjective test for visual function performance.

Peripheral refraction under different levels of illuminance.

Peripheral refraction is believed to be involved in the development of myopia. The aim of this study was to compare the relative peripheral refraction (RPR) at four different levels of illuminance, ranging from photopic conditions to complete darkness, using an open-field autorefraction method. The RPR was calculated for each eccentricity by subtracting central from peripheral autorefraction measurements. The study included 114 myopic eyes from 114 subjects (mean age of 21.81 ± 1.91 years) and the mean difference in RPR between scotopic and photopic conditions (0 and 300 lux, respectively) was +0.32 D at 30° temporal and +0.37 D at 30° in the nasal visual field (NVF). Statistically significant differences were observed between 0 and 300 lux at 30° in the temporal visual field and at 30° and 20° in the NVF. Our results revealed a significant increase in relative peripheral hyperopia with increasing visual field eccentricity along the horizontal visual field in myopic eyes of young adults. Furthermore, this relative peripheral hyperopia increased as illumination decreased. These findings suggest that an increase in peripheral illuminance may protect against myopic eye growth.

Corneal retardation time as an ocular hypertension disease indicator.

Objective.A detailed analysis of the corneal retardation timeτas a highly related parameter to the intraocular pressure (IOP), and its plausible role as an indicator of ocular hypertension disease.Approach.A simple theoretical expression forτis derived within the corneal viscoelastic model of Kelvin-Voigt with 3 elements. This retardation time can be easily calculated from the well-known signal and pressure amplitudes of non-contact tonometers like the Ocular Response Analyzer (ORA). Then, a population-based study was performed where 100 subjects aged from 18 to 30 were analyzed (within this group, about 10% had an elevated IOP with more than 21 mmHg).Main results.A clear relationship between the corneal retardation time and the corneal-compensated intraocular pressure (IOPcc) was found, underlying the risk for ocular hypertensive (OHT) subjects with lowerτvalues to develop hypertension illnesses (due to the inability of poorly viscoelastic corneas to absorb IOP fluctuations, resulting in probable optic nerve damage).Significance.Our results might provide an useful tool to systematically discern which OHT patients (and even those with normal IOP values) are more likely to suffer glaucoma progression and, consequently, ensure an early diagnosis.

Relationship between corneal tissue and shape in short-term soft contact lens wear.

PURPOSE: To investigate which morphometric and ocular surface tissue parameters are affected by short-term soft contact lens (CL) wear and to assess whether they carry related or independent information. METHODS: Twenty-two healthy participants wore silicone hydrogel (SiHy; MyDay, CooperVision) soft CLs for 8 h in their left eye. Corneal tomography and corneoscleral topography were captured before and immediately after CL wear. Central corneal thickness (CCT), corneoscleral parameters (limbus position and corneoscleral junction [CSJ] angle) and corneal tissue parameters (corneal transparency and homogeneity) were evaluated. RESULTS: Corneoscleral parameters (limbus position and CSJ angle) were independent of corneal tissue parameters (transparency and homogeneity) at baseline and after CL wear. CCT was independent of all the other parameters examined at baseline, but baseline values of corneal tissue parameters were moderately correlated with CCT change (transparency: r = -0.51; p = 0.007), homogeneity: r = -0.46; p = 0.02). CONCLUSIONS: A complete characterisation of ocular surface changes following CL wear should consider corneoscleral topography and corneal densitometry simultaneously, since they carry complementary information.

The influence of soft contact lens material on the corneoscleral profile.

PURPOSE: To objectively quantify changes in corneoscleral profile, as evaluated by the limbus position and corneoscleral junction (CSJ) angle, as a consequence of wearing different soft contact lens (CL) materials. METHODS: Twenty-two healthy participants wore silicone hydrogel (SiHy, MyDay, CooperVision) and hydrogel (Hy, Biomedics 1 day extra, CooperVision) soft CLs for 8 h per lens in their left eye. In each session, corneoscleral topography was captured before and immediately after CL removal with an Eye Surface Profiler. Previously validated automatic and objective algorithms for limbal position and CSJ angle calculation were applied to 360 semi-meridians to investigate the effect of short-term CL wear on corneoscleral topography, globally and by sectors, depending on the soft CL material worn. RESULTS: Short-term soft CL wear significantly impacted limbal position (SiHy: 120 ± 97 µm, Hy: 128 ± 85 µm) and CSJ angle (SiHy: 0.57 ± 0.36°, Hy: 0.55 ± 0.40°); all p < 0.05. A statistically significant difference was found between the sectors with regard to limbus position and CSJ angle before CL wear that remained following lens wear (all pairwise comparisons, p < 0.001). Although individual differences were observed, there was no evidence that one material caused more substantial corneoscleral alterations. CONCLUSION: Corneoscleral profile parameters were altered significantly following 8 h of soft CL wear. The observed changes in limbus position and CSJ angle support the importance of participant-material biocompatibility.

Optical Quality Variation of Different Intraocular Lens Designs in a Model Eye: Lens Placed Correctly and in an Upside-Down Position.

INTRODUCTION: Intraocular lenses (IOLs) may lose their optical quality if they are not correctly placed inside the capsular bag once implanted. One possible malpositioning of the IOL could be the implantation in an upside-down position. In this work, three aspheric IOLs with different spherical aberration (SA) have been designed and numerically tested to analyse the optical quality variation with the IOL flip, and misalignments, using a theoretical model eye. METHODS: Using the commercial optical design software OSLO, the effect of decentration and tilt was evaluated by numerical ray tracing in two conditions: in their designed position and flipped with respect to the planned position (IOL is implanted upside down). The theoretical model eye used was the Atchison model eye. Seven IOL designs of +27.00 diopters were used: a lens with negative SA to correct the corneal SA, a lens to partially correct the corneal SA, and a lens to not add any SA to the cornea (aberration-free IOL). These lenses were designed with the aspherical surface located on the anterior and posterior IOL surface. A lens with no aspherical surfaces was also included. For the optical quality analysis, the modulation transfer function (MTF) was used, together with the Zernike wavefront aberration coefficients of defocus, astigmatism, and primary coma. RESULTS: Off-centring and tilting the IOL reduced overall MTF values and increased wavefront aberration errors. With the IOL correctly positioned within the capsular bag, an aberration-free IOL is the best choice for maintaining optical quality. When the IOL is flipped inside the capsular bag, the optical quality changes, with the aberration-free IOL and the IOL without aspheric surfaces providing the worst results. With the lens in an upside-down position, an IOL design to partially correct corneal SA shows the best optical quality results in decentration and tilt, in terms of MTF and wavefront aberrations. CONCLUSION: The aberration-free IOL is the best choice when minimal postoperative errors of decentration or tilt are predicted. With IOL flip, the negative SA lens design is the best choice, regarding the root mean square wavefront aberrations. However, in a proper IOL implantation, the IOL designed to partially compensate the corneal SA including asphericity on its posterior surface is the better possible option, even in the presence of decentration or tilt.

Peripheral Refraction of Two Myopia Control Contact Lens Models in a Young Myopic Population.

Peripheral refraction can lead to the development of myopia. The aim of this study was to compare relative peripheral refraction (RPR) in the same cohort of uncorrected (WCL) and corrected eyes with two different soft contact lenses (CL) designed for myopia control, and to analyze RPR depending on the patient's refraction. A total of 228 myopic eyes (114 healthy adult subjects) (−0.25 D to −10.00 D) were included. Open-field autorefraction was used to measure on- and off- axis refractions when uncorrected and corrected with the two CLs (dual focus (DF) and extended depth of focus (EDOF)). The RPR was measured every 10° out to 30° in a temporal-nasal orientation and analyzed as a component of the power vector (M). The average RPR for all subjects was hyperopic when WCL and when corrected with EDOF CL design, but changed to a myopic RPR when corrected with DF design. Significant differences were found between RPR curves with both CLs in all the eccentricities (Bonferroni correction p < 0.008, except 10°N). An incremental relationship between relative peripheral refraction at 30 degrees and myopia level was found. It is concluded that the two CLs work differently at the periphery in order to achieve myopia control.

Corneal tissue changes following short-term soft contact lens wear of different materials.

PURPOSE: To study the effect of different soft contact lens (CL) materials during short-term wear on corneal tissue. METHODS: Twenty-two healthy participants wore both silicone hydrogel (MyDay, CooperVision) and hydrogel soft CLs (Biomedics 1 day extra, CooperVision) for 8 h per lens. In each session, Scheimpflug images were captured before and immediately after CL removal. Images were analysed using the densitometry distribution analysis, a technique from which two parameters, α (corneal transparency) and ß (corneal homogeneity), were estimated. In addition, the central corneal thickness changes after CL wear and the influence of the CL material on corneal transparency were evaluated. RESULTS: The ß parameter (homogeneity) increased by 5% after wearing both CL materials (paired t-test, p < 0.001). However, the α parameter (transparency) only increased in half of the participants. No material was found to be more determinant in causing the corneal densitometry changes. Statistically significant but not clinically relevant changes in corneal thickness were observed. CONCLUSIONS: Biomarkers of corneal tissue integrity (α and ß) were affected by short-term soft contact lens wear. The observed changes in corneal transparency and homogeneity were not clinically relevant but support the importance of participant-material biocompatibility.

Superpixel-Based Optic Nerve Head Segmentation Method of Fundus Images for Glaucoma Assessment.

Glaucoma disease is the second leading cause of blindness in the world. This progressive ocular neuropathy is mainly caused by uncontrolled high intraocular pressure. Although there is still no cure, early detection and appropriate treatment can stop the disease progression to low vision and blindness. In the clinical practice, the gold standard used by ophthalmologists for glaucoma diagnosis is fundus retinal imaging, in particular optic nerve head (ONH) subjective/manual examination. In this work, we propose an unsupervised superpixel-based method for the optic nerve head (ONH) segmentation. An automatic algorithm based on linear iterative clustering is used to compute an ellipse fitting for the automatic detection of the ONH contour. The tool has been tested using a public retinal fundus images dataset with medical expert ground truths of the ONH contour and validated with a classified (control vs. glaucoma eyes) database. Results showed that the automatic segmentation method provides similar results in ellipse fitting of the ONH that those obtained from the ground truth experts within the statistical range of inter-observation variability. Our method is a user-friendly available program that provides fast and reliable results for clinicians working on glaucoma screening using retinal fundus images.

Effect of decentration, tilt and rotation on the optical quality of various toric intraocular lens designs: a numerical and experimental study.

Toric intraocular lenses (T-IOLs) may lose their optical quality if they are not correctly positioned inside the capsular bag once implanted. In this work, T-IOLs with cylinder powers of +1.50, +4.50 and +7.50 D and differing degrees of spherical aberration have been designed, manufactured and tested in vitro using a commercial optical bench that complies with the requirements of standard ISO 11979-2. Moreover, the effect of tilt and rotation on optical quality was assessed by means of numerical ray tracing on an astigmatic eye model, while the effect of decentration was evaluated numerically and experimentally.

Corneal hysteresis and intraocular pressure are altered in silicone-hydrogel soft contact lenses wearers.

PURPOSE: The aim of this work is to determinate the effects in the physical parameters in terms of intraocular pressure (IOP) and central corneal thickness (CCT) and corneal biomechanics in terms of corneal resistance factor (CRF) and corneal hysteresis (CH) of wearing silicone-hydrogel soft contact lenses (SiH-CLs) in young adult subjects during a short-term follow-up. METHODS: 40 eyes of 20 healthy patients with a mean age of 22.87 ± 4.14 were involved in this study. Subjects with corneal diseases, dry eye, irregular astigmatism or who have been previous contact lens wearers were excluded. The ocular response analyzer (Reichert Ophthalmic Instruments) was used to measure CH, CRF and IOP and Scheimpflug imaging (the GALILEI™ Dual Scheimpflug camera analyzer, Ziemer) was used to measure CCT before and 10 days (Group 1) and 20 days (Group 2) after wearing the SiH-CLs. RESULTS: IOP was significantly decreased 10 days after using the SiH-CLs (p = 0.009). Within the 20 days' period, Group 2 revealed an even more pronounced decrease in IOP (p = 0.003) while CH increased significantly (p = 0.04). CCT and CRF did not show a significant change during the period of SiH-CLs use. Our finding allowed obtaining an empirical expression that relates IOP, CCT, CRF and CH within a biomechanical compensation experimental model. CONCLUSIONS: Corneal biomechanical parameters and physical properties of the cornea may be altered due to SiH-CLs use. Our findings could have an impact on the management of glaucoma progression and ocular hypertension.

On the Relationship between Corneal Biomechanics, Macrostructure, and Optical Properties.

Optical properties of the cornea are responsible for correct vision; the ultrastructure allows optical transparency, and the biomechanical properties govern the shape, elasticity, or stiffness of the cornea, affecting ocular integrity and intraocular pressure. Therefore, the optical aberrations, corneal transparency, structure, and biomechanics play a fundamental role in the optical quality of human vision, ocular health, and refractive surgery outcomes. However, the inter-relationships of those properties are not yet reported at a macroscopic scale within the hierarchical structure of the cornea. This work explores the relationships between the biomechanics, structure, and optical properties (corneal aberrations and optical density) at a macro-structural level of the cornea through dual Placido-Scheimpflug imaging and air-puff tonometry systems in a healthy young adult population. Results showed correlation between optical transparency, corneal macrostructure, and biomechanics, whereas corneal aberrations and in particular spherical terms remained independent. A compensation mechanism for the spherical aberration is proposed through corneal shape and biomechanics.

Iterative-Trained Semi-Blind Deconvolution Algorithm to Compensate Straylight in Retinal Images.

The optical quality of an image depends on both the optical properties of the imaging system and the physical properties of the medium in which the light travels from the object to the final imaging sensor. The analysis of the point spread function of the optical system is an objective way to quantify the image degradation. In retinal imaging, the presence of corneal or cristalline lens opacifications spread the light at wide angular distributions. If the mathematical operator that degrades the image is known, the image can be restored through deconvolution methods. In the particular case of retinal imaging, this operator may be unknown (or partially) due to the presence of cataracts, corneal edema, or vitreous opacification. In those cases, blind deconvolution theory provides useful results to restore important spatial information of the image. In this work, a new semi-blind deconvolution method has been developed by training an iterative process with the Glare Spread Function kernel based on the Richardson-Lucy deconvolution algorithm to compensate a veiling glare effect in retinal images due to intraocular straylight. The method was first tested with simulated retinal images generated from a straylight eye model and applied to a real retinal image dataset composed of healthy subjects and patients with glaucoma and diabetic retinopathy. Results showed the capacity of the algorithm to detect and compensate the veiling glare degradation and improving the image sharpness up to 1000% in the case of healthy subjects and up to 700% in the pathological retinal images. This image quality improvement allows performing image segmentation processing with restored hidden spatial information after deconvolution.

Misalignment and tilt effect on aspheric intraocular lens designs after a corneal refractive surgery.

PURPOSE: To numerically evaluate and compare the tolerance to misalignment and tilt of aspheric intraocular lenses (IOLs) designed for three eyes: with standard cornea and with simulated corneas after myopic and hyperopic laser ablation surgery. METHODS: Three aspheric IOLs of +20.00 diopter (D) with different spherical aberration (SA) ([Formula: see text]) values have been designed using a theoretical model eye. Drastic changes on the theoretical eye anterior corneal asphericity have been performed to simulate myopic and hyperopic refractive surgeries. The effect of IOL misalignment and tilt on the image quality has been evaluated using a commercial optical software design for the three eye models. Image quality was assessed from the modulation transfer function (MTF), root mean square (RMS) values of defocus, astigmatism, coma and spherical aberration ([Formula: see text]), and retinal images obtained from a visual simulator using an aleatory optotype of 0.00 LogMar visual acuity (VA). RESULTS: IOL misalignment and tilt reduced MTF values in general, and increased wavefront aberrations errors. Aberration-free IOLs maintained best the MTF values when misalignments were applied, together with good on-axis optical quality. IOLs with negative SA ([Formula: see text]) correction decreased the MTF value under 0.43 for misalignments values higher than 0.50 mm with the three corneas. The effect of misalignment on RMS astigmatism and coma was correlated with the IOL SA ([Formula: see text]) and with the three corneas. CONCLUSIONS: This theoretical study shows that the largest degradation in image quality arises for the IOL with the highest amount of spherical aberration ([Formula: see text]). Moreover, it has been found that the aspherical design has a more influential role in misalignment tolerance than in tilt tolerance.

Biomechanical Stability of Three Intraocular Lenses With Different Haptic Designs: In Silico and In Vivo Evaluation.

PURPOSE: To assess the biomechanical stability of three different marketed intraocular lenses (IOLs) with different haptic designs (four-loop IOL [Micro F FineVision model] and double C-loop IOL [POD F and POD FT models], all manufactured by PhysIOL), in silico (computer simulation) and in vivo (in the context of lens surgery). METHODS: An in silico simulation investigation was performed using finite element modeling (FEM) software to reproduce the compression test defined by the International Organization for Standardization and in vivo implantation in patients in the context of lens surgery was evaluated 1 day and 3 months postoperatively. IOL decentration and rotation were tested. In addition, the stress and strains were analyzed with the finite element method. RESULTS: In the in silico evaluation, the compression force for the POD F IOL was slightly lower than for the POD FT IOL and Micro F IOL for all compression diameters. The axial displacement was maximum for the POD FT IOL and the tilt, rotation, and lateral decentration were substantially lower than the acceptable tolerance limits established in ISO 11979-2. In the in vivo evaluation, a total of 45 eyes from 45 patients were selected, 15 eyes for each IOL model under assessment. Statistically significant differences were found between the Micro F and POD F IOLs for lateral decentration in x-direction (in absolute value) at 3 months postoperatively (P = .03). CONCLUSIONS: Although statistically significant differences have been found when comparing the displacement, tilt, and rotation between the different lenses, these differences cannot be considered clinically relevant, which would suggest that all three IOL models yield excellent stability in those terms. FEM appears to be a powerful tool for numerical studies of the biomechanical properties of IOLs. [J Refract Surg. 2020;36(9):617-624.].

Wide-field direct ocular straylight meter.

The impact of the intraocular straylight (IOS) on the visual performance and retinal imaging is still a challenging topic. Direct optical methods to measure IOS avoid psychophysical approaches and interaction with the patient. In this work, we developed an optical instrument providing direct imaging measurement of IOS based on the double-pass technology. The system was tested in an artificial eye IOS model constructed with holographic diffusers and validated with theoretical simulations.

Evaluation of the optical performance for aspheric intraocular lenses in relation with tilt and decenter errors.

PURPOSE: To evaluate and compare the effect of misalignment and tilt on the optical performance of different aspheric intraocular lens (IOL) designs. METHODS: Three aspheric IOLs with a different quantity of spherical aberration (SA) have been designed and the effect of IOL misalignment and tilt on the imaging quality of an eye model has been numerically assessed using a commercial optical design software. The prototypes have been manufactured by lathe turning and tested in vitro using the same optical bench (PMTF, Lambda-X) that complies with International Organization for Standardization standard 11979-2 requirements. Image quality was evaluated from the modulation transfer functions (MTFs), through-focus modulation transfer functions (TF-MTFs), root mean square (RMS) values of defocus, astigmatism and coma, and images of the United States Air Force (USAF) target were taken. A comparison with the optical performance of spherical IOLs has also been performed. RESULTS: Intraocular lens misalignment and tilt increased wavefront aberrations; the effect of misalignment on root mean square (RMS) astigmatism and coma was positively correlated with the spherical aberration of the IOL. Aberration-free IOLs showed the highest MTF for all misalignment values and for IOLs with negative SA correction the MTF decays below 0.43 when they are decentered 0.50 mm. CONCLUSIONS: Aspherical IOLs are more sensitive than spherical IOLs to misalignment or tilt, depending on their SA correction. The optical degradation caused by IOL misalignment had a greater effect on IOL designs with a higher amount of negative spherical aberration. In contrast, the effect of tilt on the optical performance was less sensitive to the IOL design.

Bifocal and Multifocal Contact Lenses for Presbyopia and Myopia Control.

Bifocal and multifocal optical devices are intended to get images into focus from objects placed at different distances from the observer. Spectacles, contact lenses, and intraocular lenses can meet the requirements to provide such a solution. Contact lenses provide unique characteristics as a platform for implementing bifocality and multifocality. Compared to spectacles, they are closer to the eye, providing a wider field of view, less distortion, and their use is more consistent as they are not so easily removed along the day. In addition, contact lenses are also minimally invasive, can be easily exchangeable, and, therefore, suitable for conditions in which surgical procedures are not indicated. Contact lenses can remain centered with the eye despite eye movements, providing the possibility for simultaneous imaging from different object distances. The main current indications for bifocal and multifocal contact lenses include presbyopia correction in adult population and myopia control in children. Considering the large numbers of potential candidates for optical correction of presbyopia and the demographic trends in myopia, the potential impact of contact lenses for presbyopia and myopia applications is undoubtedly tremendous. However, the ocular characteristics and expectations vary significantly between young and older candidates and impose different challenges in fitting bifocal and multifocal contact lenses for the correction of presbyopia and myopia control. This review presents the recent developments in material platforms, optical designs, simulated visual performance, and the clinical performance assessment of bifocal and multifocal contact lenses for presbyopia correction and/or myopia progression control.