Refractive Groups Research Articles

Enhance the viscosity of polydimethylsiloxane by controlling the volume ratio of monomer and chain terminator

The production of polydimethylsiloxane (PDMS) as a vitreous substitute in Indonesia has been carried out. In our previous study, a good quality of low viscosity PDMS was well provided using a low-grade octamethylcyclotetrasiloxane (D4) monomer. We also reported that a new type of PDMS with medium viscosity had been produced. In vitreoretinal surgery, medium-viscosity PDMS has advantages over the other types of PDMS due to its injectability and lower propensity to emulsify. However, to produce a high-quality medium viscosity PDMS and fulfill stringent requirements, the conditions affecting the synthesis results need to be explored. Here, we reported the effect of changing one of the PDMS synthesis parameters, namely, the volume ratio composition of low-grade D4 monomer and chain terminator of hexamethyldisiloxane (MM) in producing medium viscosity PDMS. PDMS with low viscosity was successfully synthesized with a ratio of D4:MM = 26:10. However, only by changing the ratio of D4:MM from 26:10 to 46:10, the resulting PDMS increased in viscosity from low- to medium-viscosity PDMS of 1.81 Pa s. Quality improvement was also indicated by high surface tension and higher yield values. The medium viscosity PDMS had a refractive index and functional group values similar to the PDMS produced in previous studies.

AI-based fully automatic analysis of retinal vascular morphology in pediatric high myopia

PurposeTo investigate the changes in retinal vascular structures associated with various stages of myopia by designing automated software based on an artificial intelligence model.MethodsThe study involved 1324 pediatric participants from the National Children’s Medical Center in China, and 2366 high-quality retinal images and corresponding refractive parameters were obtained and analyzed. Spherical equivalent refraction (SER) degree was calculated. We proposed a data analysis model based on a combination of the Convolutional Neural Networks (CNN) model and the attention module to classify images, segment vascular structures, and measure vascular parameters, such as main angle (MA), branching angle (BA), bifurcation edge angle (BEA) and bifurcation edge coefficient (BEC). One-way ANOVA compared parameter measurements between the normal fundus, low myopia, moderate myopia, and high myopia groups.ResultsThe mean age was 9.85 ± 2.60 years, with an average SER of -1.49 ± 3.16D in the right eye and − 1.48 ± 3.13D in the left eye. There were 279 (12.38%) images in the normal group and 384 (16.23%) images in the high myopia group. Compared with normal fundus, the MA of fundus vessels in different myopic refractive groups was significantly reduced (P = 0.006, P = 0.004, P = 0.019, respectively), and the performance of the venous system was particularly obvious (P < 0.001). At the same time, the BEC decreased disproportionately (P < 0.001). Further analysis of fundus vascular parameters at different degrees of myopia showed that there were also significant differences in BA and branching coefficient (BC). The arterial BA value of the fundus vessel in the high myopia group was lower than that of other groups (P = 0.032, 95% confidence interval [CI], 0.22–4.86), while the venous BA values increased (P = 0.026). The BEC values of high myopia were higher than those of low and moderate myopia groups. When the loss function of our data classification model converged to 0.09, the model accuracy reached 94.19%.ConclusionThe progression of myopia is associated with a series of quantitative retinal vascular parameters, particularly the vascular angles. As the degree of myopia increases, the diversity of vascular characteristics represented by these parameters also increases.

Late Bedtime and Altered Diurnal Axial Length Rhythms of the Eye

Purpose Affecting one-third of the population worldwide and increasing, the sight-threatening condition myopia is causing a significant socio-economic burden. To better understand its etiology, recent studies investigated the role of ocular and systemic rhythms, yet results are conflicting. Here we profiled 24-h variations of axial length of the eye and salivary melatonin concentration in young adults with and without myopia and explored the potential impacts of bedtime on these rhythms. Methods A total of 25 healthy young adults (age 25.0 ± 4.8 years, 13 females) completed this study, including 13 myopes (mean spherical equivalent refractive error −2.93 ± 1.46 diopters) and 12 non-myopes (0.14 ± 0.42 diopters). Saliva sample collection and axial length measurements were repeated for seven times over 24 h starting from 8 am. Information on sleep and chronotype was collected at first visit with the Pittsburgh Sleep Quality Index and the Morningness-Eveningness Questionnaire. Results Significant diurnal rhythms of axial length and salivary melatonin concentration were identified in both refractive groups (both p < 0.001), with no myopia-related rhythm difference (interaction of measurement time-point × myopia, p = 0.9). Late bedtime was associated with altered rhythms (p = 0.009) and smaller diurnal change (p = 0.01) in axial length. Elevated melatonin levels were observed in myopes (p = 0.006) and in late sleepers (p = 0.017). Conclusions These findings suggest that sleep/wake cycles may be involved in the regulation of axial length rhythms. Further research is needed to determine if there exists a causal relationship between the two.

Chromatic cues for the sign of defocus in the peripheral retina.

Detecting optical defocus at the retina is crucial for accurate accommodation and emmetropization. However, the optical characteristics of ocular defocus are not fully understood. To bridge this knowledge gap, we simulated polychromatic retinal image quality by considering both the monochromatic wavefront aberrations and chromatic aberrations of the eye, both in the fovea and the periphery (nasal visual field). Our study revealed two main findings: (1) chromatic and monochromatic aberrations interact to provide a signal to the retina (chromatic optical anisotropy) to discern positive from negative defocus and (2) that chromatic optical anisotropy exhibited notable differences among refractive error groups (myopes, emmetropes and hyperopes). These findings could enhance our understanding of the underlying mechanisms of defocus detection and their subsequent implications for myopia control therapies. Further research is needed to explore the retinal architecture's ability to utilize the optical signals identified in this study.

High-Refractive-Index Cross-Linked Cyclic Olefin Polymers with Excellent Transparency via Thiol-Ene Click Reaction.

High-refractive-index polymers are important optical materials in optoelectronics. Conventional cyclic olefin polymers (COPs), possessing many excellent optical properties, are a class of highly promising optical materials; however, one of the greatest obstacles is their low refractive index of n = 1.52-1.54. Here, one efficient strategy of first incorporating high molar refraction groups, including carbazolyl and indolyl moieties, into unsaturated COPs via ring-opening metathesis polymerization (ROMP) and then introducing another high molar refraction sulfur atom by a subsequent thiol-ene click reaction is presented. The obtained cross-linked COPs bearing both an aromatic group and sulfur possess significantly higher refractive indices (n = 1.611-1.684 at 589 nm) and highly optical transparency (approximately 95%) in the range of vis-NIR. This provides a way toward potential applications of new-generation optical materials.

Increase in choroidal thickness after blue light stimulation of the blind spot in young adults.

Blue light activates melanopsin, a photopigment that is expressed in intrinsically photosensitive retinal ganglion cells (ipRGCs). The axons of ipRGCs converge on the optic disc, which corresponds to the physiological blind spot in the visual field. Thus, a blue light stimulus aligned with the blind spot captures the ipRGCs axons at the optic disc. This study examined the potential changes in choroidal thickness and axial length associated with blue light stimulation of melanopsin-expressing ipRGCs at the blind spot. It was hypothesized that blue light stimulation at the blind spot in adults increases choroidal thickness. The blind spots of both eyes of 10 emmetropes and 10 myopes, with a mean age of 28 ± 6 years (SD), were stimulated locally for 1-minute with blue flickering light with a 460nm peak wavelength. Measurements of choroidal thickness and axial length were collected from the left eye before stimulation and over a 60-minute poststimulation period. At a similar time of day, choroidal thickness and axial length were measured under sham control condition in all participants, while a subset of 3 emmetropes and 3 myopes were measured after 1-minute of red flickering light stimulation of the blind spot with a peak wavelength of 620nm. Linear mixed model analyses were performed to examine the light-induced changes in choroidal thickness and axial length over time and between refractive groups. Compared with sham control (2 ± 1μm, n = 20) and red light (-1 ± 2μm, n = 6) stimulation, subfoveal choroidal thickness increased within 60min after blue light stimulation of the blind spot (7 ± 1μm, n = 20; main effect of light, p < 0.001). Significant choroidal thickening after blue light stimulation occurred in emmetropes (10 ± 2μm, p < 0.001) but not in myopes (4 ± 2μm, p > 0.05). Choroidal thickening after blue light stimulation was greater in the fovea, diminishing in the parafoveal and perifoveal regions. There was no significant main effect of light, or light by refractive error interaction on the axial length after blind spot stimulation. These findings demonstrate that stimulating melanopsin-expressing axons of ipRGCs at the blind spot with blue light increases choroidal thickness in young adults. This has potential implications for regulating eye growth.

Comparison of Refraction Data and Visual Acuity With and Without Cyclopentolate in Children and Young Adults

Purpose. This investigation compared refraction and visual acuity obtained under cycloplegic and non-cycloplegic condition in a Caucasian population. Material and Methods. One eye of 73 subjects, aged 6-29 years, was examined under cycloplegic (C) and non-cycloplegic (NC) condition using autorefraction (AR), subjective refraction (SR) and visual acuity testing. Subjects were subdivided into refractive groups (emmetropia: −0.5 D &lt; SE &lt; +1.00 D, myopia: SE ≤ −0.5 D, hyperopia: SE ≥ +1.00 D). Results. When comparing AR C and SR NC, deviations in SE were largest in hyperopes (∆SE = 0.74 ± 0.57 D; 95% CI: 0.5 – 0.97 D) compared to emmetropes (∆SE = 0.37 ± 0.21 D; 95% CI: 0.24 – 0.45 D) and myopes (∆SE = 0.25 ± 0.32 D; 95% CI: 0.12 – 0.38 D). When comparing SR C and SR NC, deviations in SE were largest in hyperopes (∆SE = 0.54 ± 0.43 D; 95% CI: 0.36 – 0.71 D) compared to emmetropes (∆SE = 0.23 ± 0.26 D; 95% CI: 0.10 – 0.35 D) and myopes (∆SE = 0.12 ± 0.17 D; 95% CI: 0.04 – 0.18 D). In emmetropes and myopes, C and NC refraction did not change visual acuity. For hyperopes, visual acuity reduced by 0.38 ± 0.18 logMAR and 0.22 ± 0.18 logMAR when comparing AR C prescription and SR C prescription to SR NC prescription, respectively. Conclusion. In emmetropes and myopes, C is not indicated. In hyperopes, C prescription may reduce NC visual acuity. For maximum visual acuity, a combination of C and subjective NC refraction is recommended. C refraction must be performed if visual abnormalities are suspected. Keywords Objective refraction, subjective refraction, visual acuity, cycloplegia, cycloplentolate

Grayscale two-photon 3D printed gradient-refractive-index metamaterial lens for dual-band mid-infrared imaging

Gradient refractive index (GRIN) metamaterial lenses can achieve multi-band fusion infrared imaging and has the characteristics of integration, light weight, and achromaticity, compared with existing curved refractive lenses group. Constructing a three-dimensional (3D) GRIN lens for dual-band (3.0–5.0 and 7.5–9.2 µm) mid-infrared imaging is challenging due to the difficulty of fabricating the desired 3D GRIN materials with continuously changing linewidths. Here, we present a 3D self-focusing GRIN lens with a cylindrical symmetry configuration in the mid-infrared band. Such a 3D GRIN lens is designed with gradient woodpile polymer metamaterials based on effective medium theory and fabricated with high fidelity by grayscale two-photon lithography. Simulated and experimental results simultaneously exhibit a 3D GRIN lens possessing dual-band, achromatic, near-diffraction-limit focusing on the wavelengths of 4.5 and 7.5 µm. The protocol for developing the 3D GRIN lens with dual-band fusion imaging would prompt potential applications in integrated light-coupled devices and lightweight infrared imaging devices.

Fitting-Shape-based Strategy for Topography-guided LASIK: A Prospective Study.

To assess and compare the visual acuity and refractive outcomes of topography-guided laser in situ keratomileusis (LASIK) based on the fitting-shape-based refractive compensated and Phorcides software strategies. Consecutive patients who underwent topography-guided LASIK were included in this study. Through double-masked simple randomization, patients were assigned to the Zhang & Zheng Auto-compensate Refraction (ZZ AR) group (the fitting-shape-based refractive compensated strategy using the ZZ AR calculator was used) or the Phorcides group (the topography analysis algorithm in Phorcides software [Phorcides LLC] was used). Only one eye per patient with binocular correction was randomly enrolled. The preoperative and postoperative visual acuities and refraction were analyzed at the 6-month follow-up visit. The ZZ AR and Phorcides groups comprised 156 and 147 eyes, respectively. At the 6-month postoperative follow-up visit, the median (range) absolute residual cylindrical refraction was 0.35 (1.01) and 0.47 (1.63) diopters (D) for the ZZ AR and Phorcides groups, respectively (P < .001). The percentages of patients with residual cylindrical power within 0.25 D were 29.49% and 13.61% for the ZZ AR and Phorcides groups, respectively (P = .001). Based on the percentages of patients with residual cylindrical powers within 0.50 and 1.00 D, the ZZ AR group showed better outcomes (P = .02 and .01). The percentage of patients with visual acuity better than 20/16 was significantly higher for the ZZ AR group than for the Phorcides group (P = .03). The fitting-shape-based refractive compensated strategy for topography-guided LASIK procedures can better optimize the visual acuity and astigmatic refraction than the Phorcides software strategy. [J Refract Surg. 2024;40(5):e336-e343.].

Short-Term Myopic Defocus and Choroidal Thickness in Children and Adults.

Studies report conflicting findings regarding choroidal thickness changes in response to myopic defocus in humans. This study aimed to investigate the choroidal response to myopic defocus in children and adults using automated analysis. Participants (N = 46) were distance-corrected in both eyes and viewed a movie on a screen for 10 minutes. Two optical coherence tomography (OCT) radial scans were collected for each eye, then +3 diopters was added to one eye. Participants continued to watch the movie, OCT scans were repeated every 10minutes for 50minutes, and then recovery was assessed at 60 and 70minutes. Defocus was interrupted for approximately two out of each 10minutes for OCT imaging. OCT images were analyzed using an automated algorithm and trained neural network implemented in MATLAB to determine choroidal thickness at each time point. Repeated-measures ANOVA was used to assess changes with time in three age groups (6-17, 18-30, and 31-45 years) and by refractive error group (myopic and nonmyopic). Choroidal thickness was significantly associated with spherical equivalent refraction, with the myopic group having a thinner choroid than the nonmyopic group (P<0.001). With imposed myopic defocus, there were no significant changes in choroidal thickness at any time point for any age group and for either refractive error group (P>0.05 for all). Findings demonstrate that, using the described protocol, the choroidal thickness of children and adults does not significantly change in response to short-term, full-field myopic defocus, in contrast to several previously published studies.

Effects of short-term exposure to red or near-infrared light on axial length in young human subjects.

To determine whether visible light is needed to elicit axial eye shortening by exposure to long wavelength light. Incoherent narrow-band red (620 ± 10 nm) or near-infrared (NIR, 875 ± 30 nm) light was generated by an array of light-emitting diodes (LEDs) and projected monocularly in 17 myopic and 13 non-myopic subjects for 10 min. The fellow eye was occluded. Light sources were positioned 50 cm from the eye in a dark room. Axial length (AL) was measured before and after the exposure using low-coherence interferometry. Non-myopic subjects responded to red light with significant eye shortening, while NIR light induced minor axial elongation (-13.3 ± 17.3 μm vs. +6.5 ± 11.6 μm, respectively, p = 0.005). Only 41% of the myopic subjects responded to red light exposure with a decrease in AL and changes were therefore, on average, not significantly different from those observed with NIR light (+0.2 ± 12.1 μm vs. +1.1 ± 11.2 μm, respectively, p = 0.83). Interestingly, there was a significant correlation between refractive error and induced changes in AL after exposure to NIR light in myopic eyes (r(15) = -0.52, p = 0.03) and induced changes in AL after exposure to red light in non-myopic eyes (r(11) = 0.62, p = 0.02), with more induced axial elongation with increasing refractive error. Incoherent narrow-band red light at 620 nm induced axial shortening in 77% of non-myopic and 41% of myopic eyes. NIR light did not induce any significant changes in AL in either refractive group, suggesting that the beneficial effect of red laser light therapy on myopia progression requires visible stimulation and not simply thermal energy.

Effect of corneal cross-linking on biomechanical changes following transepithelial photorefractive keratectomy and femtosecond laser-assisted LASIK.

Purpose: To evaluate the change in corneal biomechanics in patients with postoperative ectasia risk when combining two common laser vision correction procedures (tPRK and FS-LASIK) with cross-linking (in tPRK Xtra and FS-LASIK Xtra). Methods: The study included 143 eyes of 143 myopic, astigmatic patients that were divided into non-cross-linked refractive surgery groups (non-Xtra groups, tPRK and FS-LASIK) and cross-linked groups (Xtra groups, tPRK Xtra and FS-LASIK Xtra) according to an ectasia risk scoring system. The eyes were subjected to measurements including the stress-strain index (SSI), the stiffness parameter at first applanation (SP-A1), the integrated inverse radius (IIR), the deformation amplitude at apex (DA), and the ratio of deformation amplitude between apex and 2mm from apex (DARatio2mm). The measurements were taken preoperatively and at 1, 3, and 6months postoperatively (pos1m, pos3m, and pos6m). Posterior demarcation line depth from the endothelium (PDLD) and from the ablation surface (DLA) were recorded at pos1m. Results: SP-A1 significantly decreased, while IIR, deformation amplitude, and DARatio2mm increased significantly postoperatively in all four groups (p < 0.01)-all denoting stiffness decreases. In the FS-LASIK group, the changes in IIR, DA, and DARatio2mm were 32.7 ± 15.1%, 12.9 ± 7.1%, and 27.2 ± 12.0% respectively, which were significantly higher (p < 0.05) compared to 20.1 ± 12.8%, 6.4 ± 8.2%, and 19.7 ± 10.4% in the FS-LASIK Xtra group. In the tPRK group, the change in IIR was 27.3 ± 15.5%, significantly larger than 16.9 ± 13.4% in the tPRK Xtra group. The changes of SSI were minimal in the tPRK (-1.5 ± 21.7%, p = 1.000), tPRK Xtra (8.4 ± 17.9%, p = 0.053), and FS-LASIK Xtra (5.6 ± 12.7%, p = 0.634) groups, but was significant in the FS-LASIK group (-12.1 ± 7.9%, p < 0.01). After correcting for baseline biomechanical metrics, preoperative bIOP and the change in central corneal thickness (△CCT) from pre to pos6m, the changes in the IIR in both FS-LASIK and tPRK groups, as well as DA, DARatio2mm and SSI in the FS-LASIK group remained statistically greater than their corresponding Xtra groups (all p < 0.05). Most importantly, after correcting for these covariates, the changes in DARatio2mm in the FS-LASIK Xtra became statistically smaller than in the tPRK Xtra (p = 0.017). Conclusion: The statistical analysis results indicate that tPRK Xtra and FS-LASIK Xtra effectively reduced the biomechanical losses caused by refractive surgery (tPRK and FS-LASIK). The decrease in corneal overall stiffness was greater in FS-LASIK than in tPRK, and the biomechanical enhancement of CXL was also higher following LASIK than after tPRK.

Variations in choroidal thickness between emmetropic and myopic eyes after caffeine intake.

To investigate the variations in choroidal thinning between emmetropic and myopic subjects after caffeine intake. Forty-five healthy participants (age mean ± standard deviation [SD]: 20.75 ± 1.6 years) recruited in a prospective cross-sectional study. They were divided into three groups, based on refractive error status, emmetropes (spherical equivalent [SE] -0.25 to +0.25D), myopes (SE ≥-0.50D to ˂-6.00D), and high myopes (SE ≥-6.00D). The participants underwent choroidal thickness [ChT] measurements using optical coherence tomography [OCT] (Topcon 3D OCT-1 Maestro System) at baseline, 20, 40, and 60 minutes after consuming 200 mg of caffeine. The measurements of ChT were taken from five different areas horizontally. Compared to baseline measurement, the ChT significantly decreased after 200 mg caffeine intake in all conditions ( P < 0.001). There was a statistically significant difference in ChT at baseline between the refractive groups ( χ2 (2)=6.548, P = 0.038) as the high myope group showed lesser horizontal ChT within Nasal at (1 mm) area compared to the myope group ( P = 0.032), however, no other significant differences in mean scores of horizontal ChT at baseline were found. The thinning in ChT in the high myope group was lesser compared to both emmetrope and myope groups; however, it was not statistically significant ( P > 0.05). The results of this study suggest that the reduction in ChT due to caffeine consumption is not significantly affected by the refractive status of the eye. Thus, it is safe to hypothesize that the vascular part of the choroid behaves identically to vasoconstrictive in both emmetropic and myopic eyes. The choroidal thinning found in myopic and high myopic eyes and/or the reduced choroidal vascularity index were not apparent in this study. Therefore, further longitudinal studies recruiting greater numbers of participants, including myopes and high myopes, and measuring both vascular and stromal layers to investigate such variations are warranted.

Assessment of the effects of myopic and hyperopic anisometropia on choroidal vascular structure in children using SS-OCTA.

To compare large- and medium-sized choroidal vascularity and the choriocapillaris (CC) flow area in children with different refractive errors using swept-source optical coherence tomography angiography (SS-OCTA). Forty-two anisometropic children were enrolled and divided into hyperopic anisometropia (HA) and myopic anisometropia (MA) groups. SS-OCTA was performed to analyse choroidal vascularity. Mean choroidal thickness (CT), choroidal vascularity volume (CVV), choroidal vascularity index (CVI) and CC flow area were compared between the two eyes. The inter-ocular differences between the two groups were also determined. Mean CT and CVV were highest in eyes with shorter axial lengths in both refractive groups, and the difference between the two eyes was positively correlated with the difference in axial length at the foveal region. Significant differences in the CVI in the MA group were only found in the parafoveal region. Inter-ocular differences in the CC were significantly reduced in eyes with longer axial lengths in the foveal and parafoveal regions of the HA and MA groups, respectively. Comparing inter-ocular differences, CC was significantly greater in the parafoveal region of the MA group than the HA group. All layers of choroidal vasculature were thinner in eyes with longer axial lengths in all groups. The inter-ocular CC difference was greater in the MA than in the HA group, with similar differences in axial length. This suggests that both medium-to-large choroidal vascular and choroidal capillaries may play a role in myopia development.

Digital device viewing behaviour in children.

Habitual viewing behaviour is widely believed to be an important contributing factor to the onset and progression of myopia and may be task dependent. The purpose of this study was to quantify the habitual viewing distance of children performing five different tasks on a smartphone digital device. The real-time viewing distance in 38 children with their habitual correction was measured using software (MyopiaApp) on a handheld (Google Pixel 3) device. Five tasks were performed in a randomised sequence: playing a game, watching video in a light (680 lux) and dark (5.5 lux) environment and reading small (8 pt) and large (16 pt) text. ANCOVA statistical analysis was used to evaluate the effect of task, group (myope vs. non-myope) and arm length on the median relative viewing distance. Arm length was not correlated with viewing distance in any of the tasks, and there was no significant difference in viewing distance between any of the tasks. Specifically, a two-way mixed ANCOVA indicated that task, refractive group (myopic vs. non-myopic), age and arm length, as well as all two-way interactions were not significantly associated with viewing distance. Overall, 60% of the total variance in viewing distance was accounted for by individual differences. The average handheld viewing distance was similar across a variety of everyday tasks in a representative sample of myopic and emmetropic children. Neither arm length, age nor refractive group were associated with viewing distance in any of the tasks. Importantly, myopic children of a given size did not hold the smartphone digital device at a different distance for any task than their equally sized non-myopic peers. However, both groups exhibited high inter-individual variability in mean viewing distance, indicating some subjects performed all tasks at further distances while other subjects used at nearer distances.

The effect of multifocal contact lenses on the dynamic accommodation step response.

To measure the dynamic accommodation response (AR) to step stimuli with and without multifocal contact lenses (MFCLs), in emmetropes and myopes. Twenty-two adult subjects viewed alternating distance (0.25D) and near (3D) Maltese crosses placed in free space, through two contact lens types: single vision (SVCL) or centre-distance multifocal (MFCL; +2.50D add). The AR level was measured along with near to far (N-F) and far to near (F-N) step response characteristics: percentage of correct responses, magnitude, latency, peak velocity and duration of step response. There was no difference between N-F and F-N responses, or between refractive groups in any aspect of the accommodation step response dynamics. The percentage of correct responses was unaffected by contact lens type. Through MFCLs, subjects demonstrated smaller magnitude, longer latency, shorter duration and slower peak velocity steps than through SVCLs. When viewing the near target, the AR through MFCLs was significantly lower than through SVCLs. When viewing the distance target with the MFCL, the focal points from rays travelling through the distance and near zones were approximately 0.004D behind and 2.50D in front of the retina, respectively. When viewing the near target, the respective values were approximately 1.89D behind and 0.61D in front of the retina. The defocus error required for accommodation control appears not to be solely derived from the distance zone of the MFCL. This results in reduced performance in response to abruptly changing vergence stimuli; however, these errors were small and unlikely to impact everyday visual tasks. There was a decrease in ocular accommodation during near tasks, which has previously been correlated with a reduced myopic treatment response through these lenses. With MFCLs, the estimated dioptric myopic defocus was the largest when viewing a distant stimulus, supporting the hypothesis that the outdoors provides a beneficial visual environment to reduce myopia progression.

Pupillary Diameter Change and Dynamics in Different Refractive Error Groups after Implantation of a Collamer Lens with a Central Hole Without Viscoelastic Agent

Background: To investigate the pupillary diameter and dynamics in different refractive error groups after non-viscoelastic agent-assisted implantation of a collamer lens with a central hole, so as to evaluate the effect on the pupil of this type of surgery. Methods: Consecutive patients with a range of refractive errors who underwent non-viscoelastic agent-assisted implantation of a collamer lens with a central hole (ICL V4c) were analyzed. OPD-Scan III (NIDEK Japan)was used to measure the pupillary diameter preoperatively and 1 month postoperatively. Pupillary dynamics were assessed by calculating the scotopic pupillary diameter minus the photopic pupillary diameter. All variables were measured under photopic and scotopic conditions. Results: In 53 patients (medium-low myopia group 44 eyes, 23 patients, age 33.3±1.2 years and high myopia group 60 eyes, 30 patients, age 31.7±1.5 years), the postoperative photopic pupil was significantly smaller than preoperatively in both groups, and the postoperative pupillary size was significantly larger in the high myopia group under both the photopic and scotopic conditions. Besides, the high myopia group had a significantly larger photopic-scotopic change postoperatively and greater change in the pupillary dynamics. Conclusion: Implantation of a collamer lens with a central hole without viscoelastic agent assistance affected the pupillary diameter and dynamics at 1 month postoperatively in the medium-low and high myopia groups. The group with medium and low diopters had stronger changes in pupil diameter after surgery, while the group with high diopters was more likely to be affected by changes in visual quality.

Eye Size and Shape in Relation to Refractive Error in Children: A Magnetic Resonance Imaging Study.

The purpose of this study was to determine the association between eye shape and volume measured with magnetic resonance imaging (MRI) and optical biometry and with spherical equivalent (SE) in children. For this study, there were 3637 10-year-old children from a population-based birth-cohort study that underwent optical biometry (IOL-master 500) and T2-weighted MRI scanning (height, width, and volume). Cycloplegic refractive error was determined by automated refraction. The MRI images of the eyes were segmented using an automated algorithm combining atlas registration with voxel classification. Associations among optical biometry, anthropometry, MRI measurements, and RE were tested using Pearson correlation. Differences between refractive error groups were tested using ANOVA. The mean volume of the posterior segment was 6350 (±680) mm3. Myopic eyes (SE ≤ -0.5 diopters [D]) had 470mm3 (P < 0.001) and 970mm3 (P < 0.001) larger posterior segment volume than emmetropic and hyperopic eyes (SE ≥ +2.0D), respectively. The majority of eyes (77.1%) had an oblate shape, but 47.4% of myopic eyes had a prolate shape versus 3.9% of hyperopic eyes. The correlation between SE and MRI-derived posterior segment length (r -0.51, P < 0.001) was stronger than the correlation with height (r -0.30, P < 0.001) or width of the eye (r -0.10, P < 0.001). In this study, eye shape at 10 years of age was predominantly oblate, even in eyes with myopia. Of all MRI measurements, posterior segment length was most prominently associated with SE. Whether eye shape predicts future myopia development or progression should be investigated in longitudinal studies.

Tropicamide Versus Cyclopentolate for Cycloplegic Refraction in Pediatric Patients With Brown Irides: A Randomized Clinical Trial

To compare the final cycloplegic refraction of tropicamide 1% and cyclopentolate 1% in children 3-16 years of age with brown irides. Randomized, controlled, multicenter prospective clinical trial. Included patients were randomized to either cyclopentolate 1% or tropicamide 1% in the first visit with autorefraction measurements. Each subject underwent a second cycloplegic refraction using the other agent on a separate visit with a minimum of 1-week interval and a maximum of 12 weeks. We measured the change in SE (ΔSE) for each eye by deducting the SE before cycloplegia from the SE after cycloplegia. A total of 185 eyes from 94 children aged 3-16 years (average= 8.79 ±3.11 years) were included. The average SE of both eyes before cycloplegia was -0.082 ± 4.8 diopters. The SE after instillation of cyclopentolate and tropicamide in both eyes was 1.07±5.2 and 0.96±5.1, respectively (P value < .001). The average ΔSE after cycloplegia was 1.15±1.2 for cyclopentolate and 1.04±1.2 for tropicamide (P value < .001). The difference between ΔSE of cyclopentolate and tropicamide was found statistically significant at 0.11±1.2 (P < .001), although clinically insignificant. The ΔSE between the 2 drops before and after cycloplegia in both eyes for all refractive error groups was clinically insignificant. The greatest effect of cyclopentolate and tropicamide was in hyperopic eyes with ΔSE of 1.54±1.4 and 1.39±1.4, respectively. Tropicamide might be an effective and safe replacement for cyclopentolate in the refracting nonstrabismic pediatric population 3-16 years of age regardless of their refractive error status.

Cross-Sectional Study of Differences between Intraocular Pressure Measurements using Goldmann, iCare, and Air-Puff Tonometers and their Correlation with Central Corneal Thickness.

To investigate the agreement between the Goldmann tonometer (GAT), the air-puff tonometer, and the iCare tonometer in intraocular pressure (IOP) evaluation as well as their association with central corneal thickness (CCT) in normal participants, glaucoma patients, and patients following refractive surgery. This is a cross-sectional study conducted on 204 eyes from 102 patients. The study consisted of three equal groups: group I (control group, n = 34), group II (glaucoma patients on medication, n = 34), and group III (refractive surgery patients, n = 34). All patients were subjected to examination (complete ocular examination, refraction, and IOP measurement). A total of 102 participants were included in the study with both genders distributed equally. The mean ± standard deviation age was 44.12 ± 12.8 years in the control group while it was 46.29 ± 13.24 years in the glaucoma group and 40.68 ± 15.86 years in the refractive surgery group. Overall, there was a high correlation between the three methods. The mean IOP measured by GAT was 14.03 ± 3.43. The mean IOP measured by iCare was 15.16 ± 3.46. The mean IOP measured by air-puff was 16.66 ± 3.6. The iCare showed the most significant agreement with the GAT (intraclass correlation coefficient [ICC] 0.985, P > 0.05) and the mean difference in IOP between GAT and iCare was 1.1 (95% limits of agreement, -0.62-+2.85 mmHg). The mean difference in IOP between iCare and air-puff was 1.5 and it was 2.6 between GAT and air-puff. There were no significant differences in IOP measurements between GAT and iCare tonometer or between iCare tonometer and air-puff in all groups (P > 0.05). However, there were significant differences in IOP measurements between GAT and air-puff in all groups (P < 0.001). The ICC between all studied methods was strong (ICC > 0.92 for all). Regarding CCT, the mean CCT was 517.14 ± 29.82 μm. There were significant positive correlations between increasing CCT and increasing IOP by GAT, iCare, and air-puff tonometer among the three groups (P < 0.001). In conclusion, the iCare tonometer, specifically the iCare PRO RT model, is a reliable and efficient alternative instrument for assessing IOP. The IOP values obtained with the iCare PRO RT were found to be consistent with those obtained using the air-puff and GAT.