The binocular intraocular lens power difference in eyes with different axial lengths

AIM:To investigate the binocular intraocular lens(IOL)power difference in eyes with short,normal,and long axial lengths(AL)using Lenstar LS 900 optical biometry.METHODS:A total of 716(1432 eyes)participants were included.The groups were categorized into short(group A:AL<22 mm),normal(group B:22 mm≤AL≤25 mm),and long AL groups(group C:AL>25 mm).The central corneal thickness(CCT),anterior chamber depth(ACD),lens thickness(LT),AL,anterior corneal keratometry,whiteto-white(WTW),pupil diameter(PD),as well as IOL power calculated using embedded Barrett formula were assessed.Bland-Altman plots were used to test the agreement of the binocular parameters.RESULTS:In group A,the CCT of the right eye was significantly thinner than that of the left eye(P=0.044)with a difference of-2±8μm[95%limits of agreement(LoA),-17.8 to 13.2μm].For group B,the PD and IOL power in the right eye were significantly lower than those of the left eye(P=0.001,<0.001)with a difference of-0.05±0.32 mm(95%LoA,-0.68 to 0.58 mm)and-0.18±1.01 D(95%LoA,-2.2 to 1.8 D).The AL of right eye was longer than that of the left eye(P=0.002)with a difference of 0.04±0.25 mm(95%Lo A,-0.45 to 0.52 mm).No significant difference was observed for all the binocular parameters in group C.The percentage of participants with binocular IOL power difference within±0.5 D were 62%(31/50),68.3%(339/496),and 38.8%(66/170)in groups A,B,and C,respectively.CONCLUSION:The binocular parameters related to IOL power are in good agreement,but the binocular IOL power difference of more than half of participants with long AL is more than 0.50 D.

Impact of multifocal gas-permeable lens designs on short-term choroidal response, axial length, and retinal defocus profile

AIM:To investigate the impact of multifocal gas permeable contact lens(MFGPCL)in various add power and distance/near area allocation on short-term changes of choroidal thickness(ChT),axial length(AL),and retinal defocus profile in young adults.METHODS:Seventeen young adults(2 males and 15 females;age 23.17±4.48y)were randomly assigned to wear two designs binocularly with a one-week washout period in between.Total of four MFGPCL designs were assessed.All designs were distance-center that varied in two add power(+1.50 and 3.00 D)and/or two distance zone(DZ)diameters(1.50 and 3.00 mm;design A:DZ 1.5/add 3.0,B:DZ 1.5/add 1.5,C:DZ 3.0/add 3.0,D:DZ 3.0/add 1.5).ChT,AL,and peripheral refraction data were collected on each subject at baseline,on days 1 and 7 of MFGPCL daily wear.ChT was assessed in four quadrants using a spectraldomain optical coherence tomography.RESULTS:AL was shortened by-26±44μm with lens C,-18±27μm with lens D,-13±29μm with lens A,and-8±30μm with lens B(all P<0.05).A significant overall increase in ChT was observed with all 4 designs(lens A:+6±6μm,B:+3±7μm,C:+8±7μm,and D:+8±7μm).Temporal and superior choroid exhibited more choroidal thickening associated with MFGPCL.All designs induced significant relative peripheral myopia(RPM)beyond the central 20o across the horizontal meridian in both nasal and temporal fields(P<0.05).CONCLUSION:MFGPCLs show a significant influence on ChT and AL,which are associated with significant increase in RPM after short-term wear.The reliability and feasibility of quantifying short-term changes in ChT support its use as a promising marker for the long-term efficacy of myopia-controlling treatments.

Axial length,vitreoretinal pathology,and anterior chamber depth can predict postoperative refractive outcomes in phacovitrectomy/silicone oil removal

AIM:To evaluate the postoperative refractive prediction error(PE)and determine the factors that af fect the refractive outcomes of combined pars plana vitrectomy(PPV)or silicone oil removal(SOR)with cataract surgery.METHODS:The study is a retrospective,case-series study.Totally 301 eyes of 301 patients undergoing combined PPV/SOR with cataract surgery were enrolled.Eligible individuals were separated into four groups according to their preoperative diagnoses:silicone oil-filled eyes after PPV(group 1),epiretinal membrane(group 2),macular hole(group 3),and primary retinal detachment(RD;group 4).The variables af fecting postoperative refractive outcomes were analyzed,including age,gender,preoperative best-corrected visual acuity(BCVA),axial length(AL),keratometry average,anterior chamber depth(ACD),intraocular tamponade,and vitreoretinal pathology.The outcome measurements include the mean refractive PE and the proportions of eyes with a PE within±0.50 diopter(D)and±1.00 D.RESULTS:For all patients,the mean PE was-0.04±1.17 D,and 50.17%of patients(eyes)had a PE within±0.50 D.There was a significant difference in refractive outcomes among the four groups(P=0.028),with RD(group 4)showing the least favorable refractive outcome.In multivariate regression analysis,only AL,vitreoretinal pathology,and ACD were strongly associated with PE(all P<0.01).Univariate analysis revealed that longer eyes(AL>26 mm)and a deeper ACD were correlated with hyperopic PE,and shorter eyes(AL<26 mm)and a shallower ACD were correlated with myopic PE.CONCLUSION:RD patients have the least favorable refractive outcome.AL,vitreoretinal pathology,and ACD are strongly associated with PE in the combined surgery.These three factors affect refractive outcomes and thus can be used to predict a better postoperative refractive outcome in clinical practice.

Axial length shortening in myopic children with Stickler syndrome after repeated low-level red-light therapy

AIM:To report the myopia-controlling effect of repeated low-level red-light(RLRL)therapy in patients with Stickler syndrome(STL),an inherited collagenic disease typically presenting with early onset myopia.METHODS:Three STL children,aged 3,7,and 11y,received RLRL therapy throughout the follow-up period of 17,3,and 6mo,respectively after exclusion of fundus anomalies.Data on best-corrected visual acuity(BCVA),intraocular pressure,cycloplegic subjective refraction,ocular biometrics,scanning laser ophthalmoscope,optical coherence tomography,genetic testing,systemic disease history,and family history were recorded.RESULTS:At the initiation of the RLRL therapy,the spherical equivalent(SE)of 6 eyes from 3 patients ranged from-3.75 to-20.38 D,axial length(AL)were from 23.88 to 30.68 mm,and BCVA were from 0.4 to 1.0(decimal notation).Myopia progression of all six eyes slowed down after RLRL therapy.AL in five out of the six eyes shortened-0.07 to-0.63 mm.No side effects were observed.CONCLUSION:Three cases of STL whose progression of myopic shift and AL elongation are successfully reduced and even reversed after RLRL therapy.

Axial length and anterior chamber indices in elderly population: Tehran Geriatric Eye Study

AIM:To determine the normative distribution of axial length(AL),anterior chamber depth(ACD),anterior chamber volume(ACV),anterior chamber angle(ACA),and some of their associated factors in subjects aged 60 and over.METHODS:In this cross-sectional study,160 clusters were sampled using multi-stage cluster sampling in Tehran,Iran.After a preliminary interview,the participants underwent optometric examinations including visual acuity and refraction measurement followed by slit lamp biomicroscopy.Finally,ocular imaging was done using the Pentacam AXL to measure AL,ACD,ACV,and ACA.RESULTS:A total of 4519 eyes of 2436 participants were evaluated,of whom 58.0%(n=1412)were female.The mean age of the subjects was 67.32±6.05y(range:60-95y).The mean AL,ACD,ACV,and ACA was 23.22 mm(23.18-23.27 mm),2.61 mm(2.59-2.62 mm),126.56 mm3(125.08-128.04 mm3),and 30.61°(30.3°-30.92°),respectively.In the multivariable model,after adjusting for the effect of both eyes,the longest and shortest AL was seen in myopic and hyperopic subjects,respectively.AL,ACD,ACV and ACA were significantly larger in men compared to women(P<0.001).Except ACA,other evaluated parameters showed an inverse correlation with age(P<0.001),however,this correlation was insignificant for AL(P=0.623).CONCLUSION:Normative value of AL,and other biometric parameters are specific for each ethnicity,age and sex group.Any alteration in these parameters and their effect on refraction should be considered in this age group,especially in case of cataract surgery.

One-year results for myopia control of orthokeratology with different back optic zone diameters: a randomized trial using a novel multispectral-based topographer

AIM:To present the 1-year results of a prospective cohort study investigating the efficacy,potential mechanism,and safety of orthokeratology(ortho-k)with different back optic zone diameters(BOZD)for myopia control in children.METHODS:This randomized clinical study was performed between Dec.2020 and Dec.2021.Participants were randomly assigned to three groups wearing ortho-k:5 mm BOZD(5-MM group),5.5 mm BOZD(5.5-MM group),and 6 mm BOZD(6-MM group).The 1-year data were recorded,including axial length,relative peripheral refraction(RPR,measured by multispectral refractive topography,MRT),and visual quality.The contrast sensitivity(CS)was evaluated by CSV-1000 instrument with spatial frequencies of 3,6,12,and 18 cycles/degree(c/d);the corneal higher-order aberrations(HOAs)were measured by iTrace aberration analyzer.The one-way ANOVA was performed to assess the differences between the three groups.The correlation between the change in AL and RPR was calculated by Pearson’s correlation coefficient.RESULTS:The 1-year results of 20,21,and 21 subjects in the 5-MM,5.5-MM,and 6-MM groups,respectively,were presented.There were no statistical differences in baseline age,sex,or ocular parameters between the three groups(all P>0.05).At the 1-year visit,the 5-MM group had lower axial elongation than the 6-MM group(0.07±0.09 vs 0.18±0.11 mm,P=0.001).The 5-MM group had more myopic total RPR(TRPR,P=0.014),with RPR in the 15°–30°(RPR 15–30,P=0.015),30°–45°(RPR 30–45,P=0.011),temporal(RPR-T,P=0.008),and nasal area(RPR-N,P<0.001)than the 6-MM group.RPR 15–30 in the 5.5-MM group was more myopic than that in the 6-MM group(P=0.002),and RPR-N in the 5-MM group was more myopic than that in the 5.5-MM group(P<0.001).There were positive correlations between the axial elongation and the change in TRPR(r=0.756,P<0.001),RPR 15–30(r=0.364,P=0.004),RPR 30–45(r=0.306,P=0.016),and RPR-N(r=0.253,P=0.047).The CS decreased at 3 c/d(P<0.001),and the corneal HOAs increased in the 5-MM group(P=0.030).CONCLUSION:Ortho-k with 5 mm BOZD can control myopia progression more effectively.The mechanism may be associated with greater myopic shifts in RPR.

Distribution and correlation of refractive parameters in children with different corneal curvatures in southeast China

AIM:To analyze the distribution of refractive status in school-age children with different corneal curvatures(CC)and the correlation between CC and refractive status.METHODS:A total of 2214 school-aged children of grade 4 in Hangzhou who were screened for school myopia were included.Uncorrected distance visual acuity(UCDVA),non-cycloplegic refraction,axial length(AL),horizontal and vertical corneal curvature(K1,K2)were measured and spherical equivalent(SE),corneal curvature radius(CCR)and axial length/corneal radius of curvature ratio(AL/CR)were calculated.UCDVA<5.0 and SE≤-0.50 D were classified as school-screening myopia.According to the different CCRs,the patients were divided into the lower corneal curvature(LCC)group(CCR≥7.92)and the higher corneal curvature(HCC)group(CCR<7.92).Each group was further divided into the normal AL subgroup and the long AL subgroup.The refractive parameters were compared to identify any differences between the two groups.RESULTS:Both SE and AL were greater in the LCC group(P=0.013,P<0.001).The prevalence of myopia was 38% in the LCC group and 44% in the HCC group(P<0.001).The proportion of children without screening myopia was higher in the LCC group(62%)than in the HCC group(56%).Among these children without screening myopia,the proportion of long AL in the LCC group(24%)was significantly higher than that in the HCC group(0.012%;P<0.001).The change of SE in the LCC group was less affected by the increase of AL than that in the HCC group.CONCLUSION:School-aged children in the LCC group have a lower incidence of screening myopia and longer AL.Low CC can mask SE reduction and AL growth to some extent,and the change of AL growth change more in children with low CC than high CC.Before the onset of myopia,its growth rate is even faster than that after the onset of myopia.

Insight into small eyes: a practical description from phenotypes presentations to the management

This narrative review aimed to have an algorithmic approach to microphthalmos by a systematic search.The definition can be related to a number of special phenotypes.In the more challenging cases of complex microphthalmos,relative anterior microphthalmos,and nanophthalmos,the surgeon can approach these cases more safely if they have a deep understanding of the anatomical variations and ideal formulae for intraocular lens computation and knows how to avoid intra-and post-operative complications.In this article,we review the criteria by which we recognize and describe pre-,intra-,and post-operative considerations,as well as discuss the ideal intraocular lenses for microphthalmos,given the intricate varieties of small eye phenotypes.

Internal limiting membrane peeling combined with silicone oil or air tamponade for highly myopic foveoschisis

AIM:To compare the efficacy of pars plana vitrectomy(PPV)combined with internal limiting membrane(ILM)and silicone oil or sterile air tamponade for the treatment of myopic foveoschisis(MF)in highly myopic eyes.METHODS:This retrospective study included 48 myopic eyes of 40 patients with MF and axial lengths(ALs)ranging from 26-32 mm treated between January 2020 and January 2022.All patients were underwent PPV combined with ILM peeling followed by sterile air or silicone oil tamponade and followed up at least 12mo.Based on the features on spectral-domain optical coherence tomography(SD-OCT),the eyes were divided into the MF-only group(Group A,n=15 eyes),MF with central foveal detachment group(Group B,n=20 eyes),and MF with lamellar macular hole group(Group C,n=13 eyes).According to AL,eyes were further divided into three groups:Group D(26.01-28.00 mm,n=12 eyes),Group E(28.01-30.00 mm,n=26 eyes),and Group F(30.01-32.00 mm,n=10 eyes).The best-corrected visual acuity(BCVA),central foveal thickness(CFT),and complications were recorded.RESULTS:The patients included 16 males and 24 females with the mean age of 56±9.82y.The BCVA and CFT improved in all groups after surgery(P<0.01),while there was no significant difference of the CFT in Group A,B,and C postoperatively(P>0.05).The intergroup differences of BCVA and CFT postoperatively were statistically significant in Group D,E,and F.Twenty eyes were injected with sterile air,and 28 eyes were injected with silicone oil for tamponade based on the AL.However,there was no statistically significant difference among Groups D,E,and F in terms of the results of sterile air or silicone oil tamponade.The mean recovery time was 5.9mo for MF patients subjected to silicone oil tamponade and 7.7mo for patients subjected to sterile air tamponade,and the difference was not statistically significant.CONCLUSION:PPV and ILM peeling combined with silicone oil or sterile air tamponade can achieve good results for MF in highly myopic eyes with ALs≤32 mm.

Ocular surface in patients with different degrees of myopia

AIM:To investigate the clinical features of the ocular surface in patients with different degrees of myopia.METHODS:A cross-sectional study was conducted involving 122 participants with myopia in Beijing Tongren Hospital from February to June,2023.After completing the Ocular Surface Disease Index(OSDI)score scale,measurements were taken for refraction,biometric parameters and ocular surface parameters.The prevalence,severity and related parameters of the dry eye among different groups based on axial length(AL)were compared.Correlation analysis was performed between ocular surface parameters and refraction/biometric measurement parameters.RESULTS:Statistically significant differences were observed in refractive error,corneal thickness,anterior chamber depth,and subfoveal choroidal thickness among the groups(all P<0.05).With the increase in AL,the incidence and severity of dry eye increased significantly(P<0.05).Moreover,the tear film break-up time(BUT)shortened(P<0.05),and the corneal fluorescein staining(CFS)points increased significantly(P<0.05).OSDI scores were positively correlated with AL and spherical equivalent(SE;both P<0.05);BUT was negatively correlated with AL,SE,and corneal astigmatism(AST;all P<0.05);Schirmer I test(SIT)results were negatively correlated with AL and SE(both P<0.05).CONCLUSION:AL elongation is a risk factor for dry eye onset in myopic participants.The longer the AL,the more severe the dry eye is,with the increased CFS spots and tear film instability.Additionally,SE and AST exhibit negative correlations with dry eye symptom scores and ocular surface parameters.

Accuracy of axial length measurements from immersion B-scan ultrasonography in highly myopic eyes

AIM:To evaluate the accuracy of axial length(AL)measurements obtained from immersion B-scan ultrasonography(immersion B-scan)for intraocular lens(IOL)power calculation in patients with high myopia and cataracts.METHODS:Immersion B-scan,contact A-scan ultrasonography(contact A-scan),and the IOLMaster were used to preoperatively measure the AL in 102 eyes from 102 patients who underwent phacoemulsification and IOL implantation.Patients were divided into two groups according to the AL:one containing patients with22 mm≤AL【26 mm(group A)and the other containing patients with AL≥26 mm(group B).The mean error(ME)was calculated from the difference between the AL measurement methods predicted refractive error and the actual postoperative refractive error.RESULTS:Ingroup A,ALs measured byimmersion Bscan(23.48±1.15)didn’t differ significantly from those measured by the IOLMaster(23.52±1.17)or from those by contact A-scan(23.38±1.20).In the same group,the standard deviation(SD)of the mean error(ME)of immersion B-scan(-0.090±0.397 D)didn’t differ significantly from those of IOLMaster(-0.095±0.411 D)and contact A-scan(-0.099±0.425 D).In group B,ALs measured by immersion B-scan(27.97±2.21 mm)didn’t differ significantly from those of the IOLMaster(27.86±2.18 mm),but longer than those measured by Contact A-scan(27.75±2.23 mm,P=0.009).In the same group,the standard deviation(SD)of the mean error(ME)of immersion B-scan(-0.635±0.157 D)didn’t differ significantly from those of the IOLMaster(-0.679±0.359 D),but differed significantly from those of contact A-scan(-0.953±1.713 D,P=0.028).CONCLUSION:ImmersionB-scanexhibitsmeasurement accuracy comparable to that of the IOLMaster,and is thus a good alternative in measuring AL in eyes with high myopia when the IOLMaster can’t be used,and it is more accurate than the contact A-scan.

Comparison axial length measurements from three biometric instruments in high myopia

AIM： To compare the axial lengths （ALs） measured with Lenstar, IOLMaster and A-scan contact ultrasound （Ultrasound） in normal and high myopia （HM）. METHODS： Eighty-four normal eyes and 49 HM eyes were included. Three consecutive measurements were performed on each eye in the following order： Lenstar, IOLMaster, and Ultrasound. The repeatabilities of the AL measurements for each instrument were assessed by calculating the pooled coefficients of variation （CVs） of 18 eyes in each group. Comparisons between the HM and normal groups were made with independent sample t-tests. The inter-device agreements were evaluated with Bland-Altman analyses and paired two-tailed t-tests. RESULTS： For normal group, the CVs of the AL measurements taken with the Lenstar, IOLMaster and Ultrasound were 0.001%, 0.01% and 0.14%, respectively. The corresponding CVs for the HM group were 0.005%, 0.02% and 0.15%, respectively. There was significant difference between the Lenstar and the IOLMaster in normal group （P=0.031） but not in HM group （n=0.100）. In the two groups, the Lenstar and the IOLMaster produced higher values than did the Ultrasound （all P〈 0.001）. All three instruments exhibited good agreement in terms of AL values. For the intraocular lens （IOL） power calculation using SRK II formula, the Lenstar and the IOLMaster showed 0.5 D higher than Ultrasound in both groups （all P〈0.001）. No significant difference existed between the Lenstar and the IOLMaster for the IOL power calculation in both normal （n=0.474） and HM group （P= 0.103）. CONCLUSION： The three devices exhibited excellent intra-visit repeatabilities in the AL measurements. The AL and IOL power difference between partial coherence interferometry and ultrasound instruments should be noticed.

Photopic pupil size change in myopic orthokeratology and its influence on axial length elongation

AIM:To explore the photopic pupil size behavior in myopic children undergoing overnight orthokeratology(ortho-k)over 1-year period and its effects on the axial elongation.METHODS:A total of 202 Chinese myopic children were enrolled in this prospective clinical trial.Ninetyfive subjects in ortho-k group and eighty-eight subjects in spectacle group completed the 1-year study.Axial length(AL)was measured before enrollment and every 6mo after the start of ortho-k.The photopic pupil diameter(PPD)was determined using the Pentacam AXL and measured in an examination room with lighting of 300-310 Lx.Stepwise multiple linear regression analysis was used to identify variables contribution to axial elongation.RESULTS:Compared with spectacle group,the average 1-year axial elongation was significantly slower in the ortho-k group(0.25±0.27 vs 0.44±0.23 mm,P<0.0001).In ortho-k group,PPDs significantly decreased from 4.21±0.62 mm to 3.94±0.53 mm after 1mo of lens wear(P=0.001,Bonferroni correction)and the change lasts for 3-month visit.No significantly change during the other follow-up visits was found(P>0.05,Bonferroni correction).The 4.81 mm PPD may be a possible cutoff point in the ortho-k group.Subjects with PPD below or equal to 4.81 mm tended to have smaller axial elongation compared to subjects with PPD above 4.81 mm after 1-year period(t=-3.09,P=0.003).In ortho-k group,univariate analyses indicated that those with older age,greater degree of myopia,longer AL,smaller baseline PPD(PPDbaseline)experienced a smaller change in AL.In multivariate analyses,older age,greater AL and smaller PPDbaseline were associated with smaller increases in AL.In spectacle group,PPD tended to be stable(P>0.05,Bonferroni correction)and did not affect axial growth.CONCLUSION:PPDs experience significantly decreases at 1-month and 3-month ortho-k treatment.Children with smaller PPD tend to experience slower axial elongation and may benefit more from ortho-k.

Associations of lens thickness and axial length with outcomes of laser peripheral iridotomy

AIM:To investigate the association of axial length(AL),lens thickness(LT),and lens vault(LV)with postoperative anterior chamber angle metrics after laser peripheral iridotomy(LPI).METHODS:Prospective observational study of 69 patients(97 eyes)were diagnosed as primary angle-closure suspect(PACS),primary angle closure(PAC)or primary angle-closure glaucoma(PACG).AL,LT,anterior central chamber depth(ACD),angle opening distance(AOD),trabecular iris angle(TIA),and angle recess area(ARA)were measured before and 1 wk after LPI.The association between AL,LT,LV with ACD,AOD,TIA,ARA were analyzed by comparing the differences between preoperative and postoperative measurements for anterior segment biometric parameters.RESULTS:ACD,AOD,TIA,and ARA were significantly increased after LPI(all P<0.05).Greater LT was significantly associated with greater postoperative increases in ACD,AOD,TIA,and ARA(all P<0.05).AL was not significantly associated with changes of anterior segment biometric parameters.Greater LV was significantly associated with greater postoperative increases in ACD,AOD,and TIA(all P<0.05),but was not significantly associated with changes of ARA.CONCLUSION:Greater baseline LT and LV measurements are associated with greater increases in anterior segment biometric parameters after laser peripheral iridotomy.AL are not associated with the change of anterior segment biometric parameters.

Effect of axial length and anterior chamber depth on the peripheral refraction profile

AIM:To evaluate the effect of axial length(AL)and anterior chamber depth(ACD)on peripheral refractive profile in myopic patients compared to emmetropic participants.METHODS:This cross-sectional study was conducted in right eyes of 58 participants of whom 38 were emmetropic and 20 were myopic.Central and peripheral refraction were measured at 10°,20°,and 30°eccentricities in nasal and temporal fields using an open-field autorefractor.The Lenstar LS900 was used to measure ACD and AL.The participants were divided into three groups of short(<22.5 mm),normal(22.5-24.5 mm),and long eye(>24.5 mm)according to AL and three groups of low ACD(<3.00 mm),normal ACD(3.00-3.60 mm),and high ACD(>3.60 mm)according to ACD.RESULTS:The mean age of the participants was 22.26±3.09 y(range 18-30 y).The peripheral mean spherical refractive error showed a hypermetropic shift in myopic and emmetropic groups although this shift was more pronounced in the myopic group.The results showed significant changes in the spherical equivalent,J0,and J45 astigmatism in all gazes with an increase in eccentricity(P<0.001).The pattern of refractive error changes was more noticeable in long and short eyes versus normal AL eyes.Moreover,the pattern of peripheral refractive changes was much more prominent in the high ACD group versus the normal ACD group and in the normal ACD group versus the low ACD group.CONCLUSION:Peripheral refraction changes are greater in participants with AL values outside the normal range and deeper ACD values compared to participants with normal AL and ACD.

Novel compact and lightweight coaxial C-band transit-time oscillator

Compactness and miniaturization have become increasingly important in the development of high-power microwave devices.Based on this rising demand,a novel C-band coaxial transit-time oscillator(TTO)with a low external guiding magnetic field is proposed and analyzed.The proposed device has the following advantages:simple structure,short axial length,high power conversion efficiency,and low external guiding magnetic field,which are of great significance for developing the compact and miniaturized high-power microwave devices.The application of a shorter axial length is made possible by the use of a transit radiation mechanism.Also,loading the opening foil symmetrically to both ends of the buncher helps reduce the external magnetic field of the proposed device.Unlike traditional foils,the proposed opening foil has a circular-hole;therefore,the electron beam will not bombard the conductive foil to generate plasma.This makes it possible to realize long pulse and high repetition rate operation of the device in future experiments.Through numerical calculation and PIC particle simulation,the stability of the intense relativistic electron beam(IREB)and the saturation time of the device are improved by using the conductive foil.The voltage and current of the diode are 548 kV and 11.4 kA,respectively.Under a 0.4-T external guiding magnetic field,a C-band output microwave with a frequency of 4.27 GHz and power of 1.88 GW can be generated.The power conversion efficiency of the proposed device is about 30%.

Association between axial length and toric intraocular lens rotation according to an online toric back-calculator

AIM: To assess the relationship between axial length(AL) and intraocular lens(IOL) rotation among eyes receiving a toric IOL and subsequently entered into an online toric back-calculator database.METHODS: Retrospective analysis of data collected online via astigmatismfix.com, a freely available online toric back-calculator where surgeons enter pre-and postoperative information to help manage residual postoperative astigmatism.Included records were deemed valid with entry of AL and IOL orientation between January 2017 and March 2019.Rotation was determined by a difference of ≥5° between pre-operative intended IOL orientation and actual post-operative IOL orientation.Frequency and magnitude of rotation are presented with means and associated standard deviation(SD).Linear regression models of this association are presented.RESULTS: Records of 6752 eyes were included in the analysis, of which 74.8% were determined to have a rotated IOL.The magnitude of rotation increased with each millimeter(mm) increase in AL with a mean rotation of 13.3°(SD: 12.8°) for eyes with AL 20-20.9 mm and a maximum mean rotation of 30.6°(SD: 30.3°) among eyes with AL 29-29.9 mm.General linear modeling demonstrated a significant association(P<0.0001) with a parameter estimate of 1.19(standard error: 0.159) and R;of 0.0083.CONCLUSION: Analysis from an online database indicates that toric IOLs inserted into eyes with longer AL are more likely to rotate and to rotate more degrees from the target axis.The findings from this study are clinically relevant for surgeons implanting toric IOLs.

Accuracy of segmented measurement of axial length in ultra-high myopia filled with silicone oil using immersion B-scan ultrasonography

AIM:To evaluate the accuracy of segmented measurement of axial length(AL)in high myopia filled with silicone oil by immersion B-scan ultrasonography(immersion B-scan).METHODS:From June 2016 to June 2020,a total of 67 ultra-high myopia inpatients(67 eyes)who underwent silicone oil removal combined with cataract extraction and intraocular lens(IOL)implantation were retrospectively enrolled.The preoperative axial length(AL)of 31 patients with severe cataract were segmented measured using immersion B-scan(B-scan group)and another 36 patients with mild or moderate cataract were measured using IOLMaster 500(IOLMaster group).The post-operative ALs in two groups were both measured using IOLMaster 500.The IOL power was calculated with Haigis formula.The differences in ALs between pre-and post-surgery,as well as the postoperative refractive spherical equivalent,absolute refractive error,the prediction deviation of postoperative refraction and best corrected visual acuity(BCVA)were compared.RESULTS:The pre-and post-operative ALs were 30.46±1.63 mm(range 28.09-33.51 mm)and 30.42±1.70 mm(range 28.03-33.90 mm)in B-scan group(t=0.644,P=0.542)and 30.51±1.21 mm(range 28.03-33.90 mm)and 30.43±1.27 mm(range 28.54-33.50 mm)in IOLMaster group(t=1.843,P=0.074),respectively.Three months after surgery,BCVA were 0.45±0.13(range 0.3-0.9)and 0.44±0.20(range 0.2-1.0)in B-scan and IOLMaster group respectively(t=0.086,P=0.932).There was no significant difference of the postoperative spherical equivalent(-3.11±0.65 D vs-3.21±0.51 D,t=0.671,P=0.505)and the absolute refractive error(0.589±0.340 vs 0.470±0.245 D,t=1.615,P=0.112)between two groups.In B-scan group,absolute refractive error within±0.50 D was found in 18 eyes(58.1%),within±1.00 D in 26 eyes(83.9%),and within±1.50 D in 31 eyes(100%).In IOLMaster group,absolute refractive error within±0.50 D was found in 23 eyes(63.9%),within±1.00 D in 34 eyes(94.4%),and within±1.50 D in 36 eyes(Z=0.757,P=0.449).CONCLUSION:The segmented measurement of ALs by immersion B-scan shows comparable measurement accuracy with that of IOLMaster 500 in ultra-high myopia patients with severe cataract secondary to silicone oil filling and can obtain an ideal postoperative refractive state.

Evaluation of axial length/total corneal refractive power ratio as a potential marker for ocular diagnosis of Marfan’s syndrome in children

AIM:To investigate whether the axial length(AL)/total corneal refractive power(TCRP)ratio is a sensitive and simple factor that can be used for the early diagnosis of Marfan’s syndrome(MFS)in children.METHODS:The relationship between the AL/TCRP ratio and the diagnosis of MFS for 192 eyes in 97 children were evaluate.The biological characteristics,including age,sex,AL,and TCRP,were collected from medical records.Receiver operating characteristic(ROC)curve analysis was performed to investigate whether the AL/TCRP ratio effectively distinguishes MFS from other subjects.The Youden index was used to re-divide the whole population into two groups according to an AL/TCRP ratio of 0.59.RESULTS:Of 96 subjects(mean age 7.46±3.28 y)evaluated,56(110 eyes)had a definite diagnosis of MFS in childhood based on the revised Ghent criteria,41(82 eyes)with diagnosis of congenital ectopia lentis(EL)were included as a control group.AL was negatively correlated with TCRP,with a linear regression coefficient of-0.36(R2=0.08).A significant correlation was found between age and the AL/TCRP ratio(P=0.023).ROC curve analysis showed that the AL/TCRP ratio distinguished MFS from the other patients at a threshold of 0.59.MFS patients were present in 24/58(41.38%)patients with an AL/TCRP ratio of≤0.59 and in 34/39(87.18%)patients with an AL/TCRP ratio of>0.59.CONCLUSION:An AL/TCRP ratio of>0.59 is significantly associated with the risk of MFS.The AL/TCRP ratio should be measured as a promising marker for the prognosis of children MFS.Changes in the AL/TCRP ratio should be monitored over time.

Ultrasonic Evaluation of the Lens Thickness to Axial Length Factor in Primary Closure Angle Glaucoma

Ultrasonic biometry was done in 232 normal eyes and 138 eyes with primary angle closure glaucoma (ACG), using Ultrascan Digital B System IV (10 MHz). The ratio between the lens thickness and the axial length (lens thickness to axial length factor, LAF) was evaluated as a biometric index for assessing the eye with primary ACG in Chinese. LAF of 2.00 was found to be ideal point of demarcation between ACG and normal eyes (i.e., lens thickness equals to 1/5 of axial length). It appears that LAF is helpful i...