Astigmatic Lens Research Articles

Astigmatic lens approach of defocus measurement using Computer Generated Hologram

Measurement of defocus using the astigmatic lens approach is a very simple, fast and effective technique. The approach uses an astigmatic lens to incorporate astigmatism into the test beam and the measurement of defocus is done from the intensity measurement at the focal plane of the lens. The present research is on the use of computer generated hologram in the astigmatic lens approach for measuring the strength of defocus present in the test beam. The use of a computer generated hologram in conjunction with a liquid crystal spatial light modulator allows a dynamic change in the strength of astigmatism without disturbing the measurement setup. The strength of astigmatism incorporated by the astigmatic lens on the other hand is a very important parameter that determines the sensitivity, dynamic range and resilience to cross-talk of the technique. Therefore, a dynamic change in the strength of astigmatism is very important to switch to a different mode of operation as per the demand of the applications. This is not possible with an astigmatic lens as any change in the strength of astigmatism can be achieved only by replacing the lens itself, thereby disturbing the whole measurement setup. In this paper, we provide a brief discussion on the principle of an astigmatic defocus sensor followed by the process of its implementation using computer generated hologram. Simulation is carried out to validate the technique. The simulation results are further verified experimentally with the help of a proof of principle laboratory setup. The technique is validated for all three modes of operation, i.e. maximum sensitivity, higher dynamic range and resilience to cross-talk.

On the issue of diagnostic accuracy of methods for analyzing the parameters of regular astigmatism

This study evaluates the diagnostic accuracy of various methods for measuring the parameters of regular astigmatism. The study included 83 patients (122 eyes) with regular astigmatism exceeding 1.0 D. Three groups were formed depending on the type of astigmatism. Spherical and cylindrical (power and axis) components of refraction were determined using automatic refractometry. The results were refined with subjective tests: power and axis tests with a cross-cylinder. The criterion for diagnostic accuracy was the level of corrected visual acuity. To assess the impact of cylinder position on visual acuity, discrete deviations of the axis of trial astigmatic lenses from the correct position (determined based on subjective tests) were modeled at 5, 10, and 15 degrees in both clockwise and counterclockwise directions. In the overall sample of observations, coincidence of results was found only in one-third of cases, with a tendency for discrepancies in data between the two methods in nearly 70% of cases. Statistical processing revealed significant differences only in the magnitude of the cylinder in the group with against-the-rule astigmatism (p<0.0005). An increase in maximum visual acuity corrected based on subjective test data was noted. With a deviation of the cylinder axis from the correct position by 10-15 degrees, regardless of the type of astigmatism, a significant tendency for a decrease in visual acuity was identified. At the same time, with a deviation of the cylinder axis within 5 degrees, a significant decrease in visual acuity was noted only in with-the-rule astigmatism and counterclockwise deviation. To achieve maximum visual acuity in the correction of regular astigmatism, objective method data must be refined with subjective tests. The results of modeling the deviation of the axis of the corrective lens from the proper position can be considered when evaluating the functional outcomes of TIOL implantation.

Биоптический подход к эксимерлазерной хирургии при сочетанной патологии роговицы и хрусталика

Purpose. To consider a biooptical approach to excimer laser surgery for combined pathology of the cornea and lens. Material and methods. The work is based on 20-year clinical observations of the results of excimer laser refractive, opto-reconstructive and medical surgery in combined pathology of the cornea and lens based on a biooptical approach (more than 1500 operations). Particular emphasis was placed on the cycloplegic functional test and the use of stromal saturation with 0.25% chilled to +5–7 °C isotonic riboflavin solution during photoablation. The studies used modern diagnostic devices OPD-scan, RTVue XR100 and TMS-5 and excimer ophthalmic lasers from various companies. Results. In case of combined refractive pathology of the cornea and lens, the cycloplegic test made it possible to more accurately determine the degree of ametropia, its accommodative component with compensation of corneal astigmatism, and the presence of lens astigmatism. In all cases, the determination of the volume of photorefractive ablation was calculated taking into account the contribution of the cornea and lens to the formation of ametropia and aberrations of the optical system of the eye. The diameter of the optical and transition zone during photorefractive ablation was calculated depending on the state of the pupil diameter in photopic and mesopic conditions. Obtained in the course of studies on the OPD-Scan device, objective information on the difference between the pupil width in mesopic and photopic conditions made it possible to individualize the sizes of the optical and transition zones during photorefractive ablation, to avoid the «Halo» and «Gler» effects. Photoablation with saturation of tecorneal stroma with riboflavin reduced the response of aseptic inflammatory and regenerative reactions, the severity and duration of the corneal syndrome, and provided earlier stabilization of optical refractive indices. Conclusion. When performing excimer laser refractive, opto-reconstructive and therapeutic operations with combined pathology of the cornea and lens, a biooptical approach is required, taking into account the leading role of the cornea and lens in the formation of the optical system of the eye and visual acuity. Keywords: biooptics, photoablation, excimer laser corneal surgery

Functional visual tests to evaluate the effect of small astigmatism correction with toric contact lenses.

The prescription of daily contact lenses does not often include a full astigmatic correction. We question here whether this full astigmatic correction (for low to moderate astigmatism) provides a substantial improvement in the overall visual performance compared to a more conservative approach based only on the prescription of spherical contact lenses. The visual performance of 56 contact lens neophytes divided in two contact lens fitting groups (toric versus spherical lens fit) was assessed using standard visual acuity and contrast sensitivity tests. A new set of functional tests simulating everyday tasks was also used. Results showed that subjects with toric lenses had significantly better visual acuity and contrast sensitivity than those with spherical lenses. Functional tests did not render significant differences between groups, which was explained by several factors like i) the visual demand of the functional tests, ii) the dynamic blur due to misalignments and iii) small misfits between the available and measured axis of the astigmatic contact lens.

Changes of Surgically Induced Corneal Astigmatism and Position of Artificial Intraocular Lens over Time

To analyze changes in surgically induced corneal astigmatism and articial intraocular lens (IOL) stability over time following cataract surgery. To compare the interchangeability of measurements between an automatic keratorefractometer (AKRM) and a biometer. In this prospective observational study, the above-mentioned parameters were collected from 25 eyes (25 subjects) on the first day, first week, first and third month after uncomplicated cataract surgery. We used IOL-induced astigmatism (difference between refractometry and keratometry) as an indirect indicator of IOL stability change. We used the Blant-Altman method to analyze consistency between devices. At the above time points, surgically induced astigmatism (SIA) decreased as follows: 0.65 D; 0.62 D; 0.60 D and 0.41 D (in the first day, week, month and third month respectively). Astigmatism induced by changes of the position of the IOL varied as follows: 0.88 D; 0.59 D; 0.44 D and 0.49 D. Changes in both parameters were statistically significant (p0.05). Both surgically induced astigmatism and astigmatism induced by IOL decreased over time, in which both changes were statistically significant. The decrease in SIA was most pronounced between the first and third month after surgery. For IOL-induced astigmatism, the greatest decrease was within the first month after surgery. The differences in measurement between the biometer and AKRM were statistically insignificant, but the clinical interchangeability between the given methods is questionable, especially with regard to measurement of the astigmatism angle.

Aspherical, sphero-cylindrical, toroidal, and ellipsoidal surfaces for designing astigmatic spectacle lenses with axis orientation

In this paper, formulas for aspherical, sphero-cylindrical, toroidal, and ellipsoidal surfaces with astigmatic axes are derived. Based on this, four types of curved surfaces were designed to correct astigmatism with axis, and, subsequently, the lenses were simulated, fabricated, and measured. A total of ten spectacle lenses in two groups were designed. Those in the first group used identical optical parameters. The spherical and cylindrical powers and maximum and minimum edge thicknesses of aspherical, sphero-cylindrical, and ellipsoidal surfaces were compared. The results indicated that the power of the lens constructed using the toroidal surface was more accurate than those of the other three lenses. Moreover, the minimum edge thickness of the toroidal surface was 1.2%, 4.98%, and 4.87% lower than those of the aspherical, sphero-cylindrical, and ellipsoidal surfaces, respectively. The powers and edge thicknesses of toroidal surfaces with different diopters were compared in the second group. The minimum and maximum edge thicknesses were observed to be reduced by 8.97% and 6.05%, respectively, corresponding to the conic constants obtained via ray tracing. The conclusion will be significant for clinical ophthalmology and optical design for the patients with astigmatism.

Refractive and visual outcomes of plate-haptic toric intraocular lens implantation for astigmatic correction after uncomplicated microincision cataract surgery.

Objective: To evaluate visual and refractive outcomes with plate-haptic toric intraocular lens implantation (ph-toric) after uncomplicated microincision cataract surgery (MICS) to correct moderate-to-severe astigmatism. Design: Prospective cross-sectional study. Methods: The study was conducted at a tertiary eye care center in New Delhi, India, on patients with visually-significant cataract and moderate-to-severe astigmatism (>1.00 diopters [D]). Preoperative parameters like visual-acuity, keratometry and astigmatism values and lens power calculation were noted. After MICS via 1.8 mm incision, a ph-toric IOL was implanted. The outcome measures noted were uncorrected and corrected distant visual-acuity (UDVA, CDVA), decrease in astigmatism and rotational stability. Follow-up was done on day 1, day 7, 1-month and 3-months postoperative. Results: This study involved 30 eyes of 30 patients. 27 patients (90%) gained UDVA of 6/ 9 or better. Out of these, 27 patients (90%) achieved CDVA of 6/ 6. Mean CDVA changed from 0.967 ± 0.101 postoperative to 0.176 ± 0.82 preoperatively (p<0.001). The mean preoperative astigmatism was 2.08 ± 0.59 D and the mean postoperative astigmatism was 0.35 ± 0.39 D. The mean correction achieved was 1.28 ± 0.32 D. Statistically significant (p<0.001) correction of astigmatism was observed by use of ph-toric IOL. The mean reduction in astigmatism was 84.16 ± 10.61 with excellent reduction in 43.3%. IOL rotation was <10 degrees in all the eyes. No complications were observed. Patients had satisfaction with the procedure and visual outcomes. Conclusion: Implantation of a plate-haptic toric IOL after uncomplicated MICS via 1.8 mm incision is a feasible and safe option in cataract cases with astigmatism to provide good visual and refractive outcomes. No major drawbacks were observed attributable to ph-toric IOL. Abbreviations: SIA - surgically induced astigmatism, D - diopters, MICS - microincision cataract surgery, ph-toric IOL - plate-haptic toric IOL, IOL - intraocular lens, UDVA - uncorrected distant visual acuity, CDVA - corrected distant visual acuity.

Corneal Astigmatism and Intraocular Lens Power Calculation before and after Pterygium Surgery

Corneal Astigmatism and Intraocular Lens Power Calculation before and after Pterygium Surgery

Leftover Astigmatism: The Missing Link Between Measured and Calculated Posterior Corneal Astigmatism.

To quantify the total eye astigmatism that is not accounted for by measurement of anterior corneal astigmatism and posterior corneal astigmatism and knowledge of intraocular lens (IOL) astigmatism and assess whether it is correlated with candidate sources of or correlates with leftover astigmatism. Vector subtraction of anterior corneal, posterior corneal, and IOL astigmatism from total eye astigmatism as represented by spectacle astigmatism to yield a value of "leftover" astigmatism that is neither corneal nor lenticular. This value was derived in a series of eyes following cataract surgery. This novel entity was examined for correlation with candidate sources of or correlates with leftover astigmatism. In 103 pseudophakic eyes with known IOL toricity, mean leftover astigmatism was 0.71 ± 0.43 diopters. This was significantly correlated with against-the-rule anterior corneal astigmatism (P < .001). Leftover astigmatism is clinically substantial. Because it is included in IOL cylinder power calculations based on refractive outcome, it may explain why methods of IOL cylinder power calculation using refractive outcome-based adjustments to anterior corneal astigmatism (previously described as adjustments for "posterior corneal astigmatism") are more successful than adjustment on the basis of measured posterior corneal astigmatism. [J Refract Surg. 2022;38(9):559-564.].

Недостаточная или оптимальная коррекция

Purpose. To develop a new approach to assessing the quality of vision in children with habitual correction, or in its absence, to determine reasonable indications for the appointment of a certain type of correction of ametropia. Material and methods. On the basis of the Doctor Sorokin office, 195 children (390 eyes) aged 5 to 18 years who applied for an appointment were examined. anamnesis about the beginning of the manifestation of ametropia, the time of the first treatment and the time of the first correction of ametropia were carried out. All applicants were divided into 4 groups: No correction, complete and incomplete correction, excessive correction and control group. All applicants underwent a complete ophthalmological examination: Determination of relative, absolute visual acuity and visual acuity with habitual correction (Shin Nippon CP), refractometry without mydriasis and with mydriasis, retinoscopy, keratometry (Huvitz HRK 7000), keratotopography. Biometrics, biomicroscopy with aspherical lens (spruce lamp Shin Nippon SL-40), direct and indirect ophthalmoscopy (Welch Allyn ophthalmoscope with retinoscopy nozzle). Optical coherence tomography – angiography (optical coherence tomography with Optovue Avanti angiography module). Full optical correction, portable eyeglass and contact vision correction (spherical, astigmatic, de-focal and ORT lenses). A study on the contrast of vision before correction and after complete correction of vision. A survey was conducted on the quality of vision before correction and after different correction options. We used traditional indicators of descriptive statistics – the number of observations (n), arithmetic mean (M), standard deviation (SD). To identify statistically significant differences between the groups, the nonparametric Mann – Whitney criterion was used, within each group parametric data were compared using the Student's t-test. The differences were considered significant at p &lt; 0.05. Results. At this stage, 195 children aged 5 to 18 years of different genders were examined. All are divided into 4 groups [7]: Group 1 – no correction Group 2 – complete and incomplete correction Group 3 – excessive correction Group 4 – control group All children also underwent a study to determine the quality of vision with different levels of contrast. A trend is revealed showing an increase in the contrast of vision with a full-fledged correction. These are preliminary data that require further observation and statistical confirmation. Conclusion. The results revealed a trend confirming the already established fact that under-correction of myopia at the initial stage is not a successful therapeutic method of preventing myopia, and that full correction should be used to correct myopia. It is necessary to work out new tactical approaches in earlier diagnosis and timely full - fledged correction of any ametropia in the younger and middle age group. To strengthen explanatory work among parents and children, including through the mass media, about the need for early and full-fledged vision correction. About the need for regular preventive monitoring and treatment by ophthalmologists for the timely detection of ametropia. Keyword: refraction, insufficient correction, myopia, eyeglass correction, contact lenses, full correction.

Astigmatic Stokes lens revisited.

Stokes lenses are variable power astigmatic lenses comprising of, in its standard version, two pure cylindrical lenses of equal but contrary power that rotate in opposite directions. Here, we present an optical device with variable and continuous astigmatic power which is based on a modified Stokes lens where two sphero-cylindrical lenses (in the form of pure astigmatic lenses) are combined in the classical way but merged with another fixed pure astigmatic lens for improving the capabilities of the resulting optical device concerning the expansion of the astigmatic range without worsening the dioptric power step resolution. The performance of this device is theoretically analyzed in virtue of the power vectors formalism including a three-dimensional (3-D) representation of the generated dioptric power as a function of both the meridian and the rotation angle between the cylinder's axes. In addition, we have assembled a lab-made prototype of the proposed modified Stokes lens and validated its theoretical behavior by dioptric power measurements with an automatic focimeter. As conventional Stokes lenses, the applications of this new optical device range from astigmatism compensation in optical instruments to measurement of refractive error in subjective routines with the previously commented improved capabilities.

Comparison Study of the Two Biometers Based on Swept-Source Optical Coherence Tomography Technology.

This research aimed to investigate the potential differences in the parameters, including axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), flat keratometry (Kf), steep keratometry (Ks), mean keratometry (Km), astigmatism, white-to-white (WTW) distance, acquired rate, and intraocular lens (IOL) power, between the two swept-source optical coherence tomography (SS-OCT) biometers, the ANTERION (biometer A) and IOLMaster 700 (biometer B). In a prospective observational comparative case series study, we enrolled 198 eyes undergoing cataract surgery. The AL, CCT, ACD, LT, Kf, Ks, Km, astigmatism, WTW, acquired rate, and IOL power were assessed. McNemar tests compared the acquired rate, and the paired sample t-test compared the quantitative measurement results between the groups. Nineteen eyes were excluded owing to missing AL data for either biometer. Finally, data from 179 eyes were analyzed. Between the two devices, no significant difference was found in AL, astigmatism magnitude, J0, and J45, while significant differences existed in CCT, ACD, LT, Kf, Ks, Km, WTW, astigmatism axis, and IOL power; no statistical significance was found in the AL acquired rate (biometer A, 90.9% and biometer B, 93.9%). Approximately 65.4% of eyes demonstrated ≥0.5-D difference in IOL power between the two biometers. In conclusion, the two biometers showed significant differences in all measurements (CCT, ACD, LT, K, WTW, astigmatism axis, and IOL power), except for AL.

Thermally induced depolarization in a silicon (c-Si) single crystal.

Single-crystal silicon is one of the most promising materials for producing test masses for the new generation of laser interferometers intended for the detection of gravitational waves. We studied the thermally induced depolarization of radiation in single-crystal silicon with [001] orientation at a wavelength of 1940 nm at room temperature. The value of the piezo-optical anisotropy ratio was found to be ξ = -0.63 ± 0.05 for one manufacturer and ξ = 0.62 ± 0.05 for another. The physical reason for the different signs was not established, and the search for this reason will continue. For the single-crystal silicon with the negative piezo-optical anisotropy ratio, the directions of the special orientations [C] and [P] for which thermally induced depolarization and thermal lens astigmatism vanish, respectively, were determined. When ξ is close to -0.5, the special orientations are close to [111], making this orientation preferable to the other traditionally used orientation, [001].

A systematic review and meta-analysis on intraocular lens implantation with different performances for the treatment of cataract.

Cataract is one of the common eye diseases. At present, Phacoemulsification combined with traditional intraocular lens (IOL) implantation can achieve satisfactory rejuvenation effects. However, the correction of corneal astigmatism is limited, while Toric IOL implantation can provide good astigmatism correction treatment. We retrieved randomized controlled trials (RCTs) on the treatment of cataracts published in the PubMed, EBSCO, MEDLINE, EMBASE, Science Direct, Cochrane Library, China National Knowledge Infrastructure (CNKI), Wanfang, and Weipu databases. Professional journals were searched manually to avoid omissions. The research subject search terms included cataract, astigmatism, IOL, and intraocular lens. The observation indicators search terms included uncorrected distance visual acuity (UDVA), best-corrected distance visual acuity (BDVA), residual corneal astigmatism, and cataract cure rate. A total of 12 articles were included. The articles were tested for heterogeneity of UDVA measured using the Logarithm of Mininal Angle Resolution (LogMAR) visual acuity chart, and the results showed that Chi-squared test (Chi2) =75.21, degree of freedom (df) =11, and I2=85%>50%, so the random effects model (REM) was adopted for analysis. The results indicated that the differences between the Toric and Non-Toric IOL groups statistically significant, and the Toric IOL group had a significant therapeutic effect [Z =2.18, mean difference (MD) =-0.05, 95% confidential interval (CI): -0.09, -0.00, P=0.03]. The fixed effects model (FEM) was adopted to analyze the determination of BDVA by LogMAR visual acuity chart in 6 articles. The results suggested that the difference between the Toric IOL and non-Toric IOL groups was not statistically significant (Z =0.29, MD =-0.00, 95% CI: -0.02, 0.01, P=0.77). Heterogeneity analysis was performed on three articles in terms of residual corneal astigmatism, which showed that Chi2=75.55, df =3, I2=96%>50%, and P<0.00001. The REM analysis results revealed that the difference between the two groups was not statistically significant, and the Toric IOL group had low residual corneal astigmatism (Z =1.35, MD =-0.34, 95% CI: -0.83, 0.15, P=0.18). The meta-analysis results confirmed that Toric IOL implantation showed obvious advantages in improving UDVA and corneal residual astigmatism in cataract patients.

Evolution of a C-antidipole or C-dipole passing through an astigmatic lens

• After passage of a C-antidipole through a lens, four C-points appear. • The position and degree of polarization of the same C-point may change. • The evolution of a C-dipole passing through the lens is more complicated. • Handedness reversal, creation and disappearance of C-points may occur. The evolution of a C-antidipole and a C-dipole embedded in Gaussian beams in the presence of an astigmatic lens is studied, respectively. After the passage of the beams carrying a C-antidipole through the lens, four C-points with the same topological charges appear in the fields. Their position and degree of polarization may change, but their number and the handedness don't change with variations of the propagation distance, the off-axis parameter and the astigmatic coefficient. On the other hand, the evolution of the C-dipole passing through the lens is more complicated. In addition to the change of their position and degree of polarization, the handedness of the same C-point may change, and the creation or disappearance of C-dipoles may occur by varying the relevant parameters.

Delicate balance: the relationship between internal astigmatism and lens astigmatism

Background: Due to lack of equipment for directly measuring crystal morphology, there has been little research on lenticular astigmatism. The purpose of this study was to accurately explore the correlation between internal astigmatism and lens astigmatism in patients with ametropia. Methods: This is a cross-sectional study conducted in the Affiliated Hospital of North Sichuan Medical College, China, in September 2020. Diopter values (refractive astigmatism, RA) of patients with ametropia was recorded, and the corneal and lens biological parameters were measured by CASIA2 (corneal/anterior segment optical correlation tomography analyzer). Biometric parameters, including the total corneal astigmatism (total corneal astigmatism, TCA), anterior and posterior curvature radius of the lens (anterior curvature radius of the lens, ACL; posterior curvature radius of the lens, PCL), internal astigmatism (internal astigmatism, IA), anterior and posterior astigmatism of the lens (anterior astigmatism of the lens, AAL; posterior astigmatism of the lens, PAL) were measured. Grouping and comparisons were made according to gender and age. Results: In total, 151 participants (293 eyes) were included in the analysis. There were significant ( P&lt;0.05) differences in the IA ( Z=-2.194, P=0.028) according to gender, but not in the other parameters. By age group, there were statistically significant differences in the TCA ( H=10.609, P=0.005), IA ( F=3.722, P=0.025), and PAL ( H=8.254, P=0.016), but not in the others. The IA was positively correlated with the age ( r=0.155, P=0.008), RA ( r=0. 534, P&lt;0.001), AAL ( r=0.308, P&lt;0.001), and was negatively correlated with the TCA ( r=-0.244, P&lt;0.001). The regression equation between the IA and AAL was: Y (IA) =-0.626 +0.447 X (AAL). Conclusions: Internal astigmatism is mainly related to the anterior astigmatism of the lens, and the higher the anterior astigmatism of the lens, the higher the internal astigmatism; At the same time, internal astigmatism increases with age.

Thermo-optic refraction based switchable optical mode converter

The temporally switchable optical mode conversion is crucial for optical communication and computing applications. This research demonstrates such optically switchable mode converter driven by thermo-optic refraction. The MoS2 nanofluid is used as a medium where the thermal microlens is created by a focused laser beam (pump). The convective thermal plume generated above the focal point of the pump beam within the nanofluid acts as an astigmatic thermal lens. It is discovered that mode conversion of the Laguerre-Gaussian (LG) to the Hermite-Gaussian (HG) beam (vice versa) takes place upon passing through the thermal lens. The topological charge of the LG beam can be easily determined using the proposed mode converter. The mode transformation is explained theoretically as the Fourier components of the LG beam undergoing different optical paths while propagating through the convective plume.

Delicate balance: the relationship between internal astigmatism and lens astigmatism

Background: Due to lack of equipment for directly measuring crystal morphology, there has been little research on crystal astigmatism. The purpose of this study was to accurately explore the correlation between internal astigmatism and lens astigmatism in patients with ametropia. Methods: This is a cross-sectional study conducted in the Affiliated Hospital of North Sichuan Medical College, China, in September 2020. Diopter values (refractive astigmatism, RA) of patients with ametropia was recorded, and the corneal and lens biological parameters were measured by CASIA2 (corneal/anterior segment optical correlation tomography analyzer). Biometric parameters, including the total corneal astigmatism (TCA), anterior and posterior curvature radius of the lens (ACL, PCL), internal astigmatism (IA), anterior and posterior astigmatism of the lens (AAL, PAL) were measured. Grouping and comparisons were made according to gender and age. Results: In total, 151 participants (293 eyes) were included in the analysis. There were significant (P&lt;0.05) differences in the IA (Z=-2.194, P=0.028) according to gender, but not in the other parameters. By age group, there were statistically significant differences in the TCA (H=10.609, P=0.005), IA (F=3.722, P=0.025), and PAL (H=8.254, P=0.016), but not in the others. The IA was positively correlated with the age (r=0.155, P=0.008), RA (r=0. 534, P&lt;0.001), AAL (r=0.308, P&lt;0.001), and was negatively correlated with the TCA (r=-0.244, P&lt;0.001). The regression equation between the IA and AAL was: Y (IA) =-0.626 +0.447X (AAL). Conclusions: There is a delicate balance between internal astigmatism and intraocular astigmatism. There were no significant differences in the other parameters except IA for different gender groups. For different ages, there are symbol differences in the TCA, IA and PAL, but not in the other parameters. In the analysis of IA with lens astigmatism, it was found that internal astigmatism was mainly related to AAL, but not to PAL.

Ratio of torus and equivalent power to refractive cylinder and spherical equivalent in phakic lenses - a Monte-Carlo simulation study.

Spherical and astigmatic powers for phakic intraocular lenses are frequently calculated using fixed ratios of phakic lens refractive power to refractive spherical equivalent, and of phakic lens astigmatism to refractive cylinder. In this study, a Monte-Carlo simulation based on biometric data was used to investigate how variations in biometrics affect these ratios, in order to improve the calculation of implantable lens parameters. A data set of over sixteen thousand biometric measurements including axial length, phakic anterior chamber depth, and corneal equivalent and astigmatic power was used to construct a multidimensional probability density distribution. From this, we determined the axial position of the implanted lens and estimated the refractive spherical equivalent and refractive cylinder. A generic data model resampled the density distributions and interactions between variables, and the implantable lens power was determined using vergence propagation. 50 000 artificial data sets were used to calculate the phakic lens spherical equivalent and astigmatism required for emmetropization, and to determine the corresponding ratios for these two values. The spherical ratio ranged from 1.0640 to 1.3723 and the astigmatic ratio from 1.0501 to 1.4340. Both ratios are unaffected by the corneal spherical / astigmatic powers, or the refractive cylinder, but show strong correlation with the refractive spherical equivalent, mild correlation with the lens axial position, and moderate negative correlation with axial length. As a simplification, these ratios could be modelled using a bi-variable linear regression based on the first two of these factors. Fixed spherical and astigmatic ratios should not be used when selecting high refractive power phakic IOLs as their variation can result in refractive errors of up to ±0.3 D for a 8 D lens. Both ratios can be estimated with clinically acceptable precision using a linear regression based on the refractive spherical equivalent and the axial position.

Mutation spectrum and genotype-phenotype correlations in Chinese congenital ectopia lentis patients

PurposeTo identify the spectrum and frequency of mutations in congenital ectopia lentis (CEL) and to investigate the correlations between genotype and clinical phenotype in Chinese CEL patients. MethodsNinety-three participants with CEL were enrolled from March 2017 to April 2020. Ocular and systemic examinations were performed for each included patient. Genomic DNA from the included patients was analysed by whole-exome sequencing to detect mutations. Clinical manifestations were compared for different mutation subgroups. ResultsGene mutations were detected in 79 patients. Sixty-five were FBN1-associated, and most were related to Marfan syndrome (MFS). The FBN1 mutations mainly consisted of missense mutations (49/65) and were concentrated in the 5′ region. Probands with missense mutations tend to show high corneal astigmatism (χ2 = 3.98, P = 0.046) and severe lens dislocation (t = 2.90, P = 0.006) compared to premature termination codon (PTC) mutations. ConclusionsMost Chinese CEL patients were identified as having FBN1 mutations. Those with missense mutations commonly showed severe ocular phenotypes; therefore, reinforced follow-up and long-term observation are required. These correlations implicated the crucial role of missense and cysteine-involving mutations in ocular phenotypes, which might be explained by dominant-negative and nonsense-mediated mRNA decay (NMD).