Changes in corneal biomechanics and posterior corneal surface elevation after FS-LASIK

AIM:To investigate the changes in corneal biomechanics and posterior corneal surface elevation after femtosecond laser-assisted in situ keratomileusis(FS-LASIK).METHODS:Totally 197 eyes of 100 patients who underwent the FS-LASIK from April 2022 to November 2022 were included.They were divided into three groups according to the ratio of residual corneal stroma thickness/corneal thickness(RCST/CT):Group I(50%≤RCST/CT<55%,63 eyes of 32 patients),Group II(55%≤RCST/CT<60%,67 eyes of 34 patients),and Group III(RCST/CT≥60%,67 eyes of 34 patients).The intraocular pressure(IOP),corneal compensated IOP(IOPcc),corneal hysteresis(CH)and corneal resistance factor(CRF)were measured immediately,1,and 3mo postoperatively by ocular response analyzer(ORA)and the posterior elevation difference(PED)was measured by Pentacam.RESULTS:After operation,IOP,CH,CRF,and PED were statistically different among the three groups(F=12.99,31.148,23.998,all P<0.0001).There was no statistically significant difference in IOPcc among the three groups(F=0.603,P>0.05).The IOP,IOPcc,CH,and CRF were statistical changed after surgery(F=699.635,104.125,308.474,640.145,all P<0.0001).The PED of Group I was significantly higher than that of Group II(P<0.05),and Group II was significantly higher than that of Group III(P<0.05).The PED value of 3mo after surgery decreased in each group compared with 1mo after surgery,but there was no statistical difference(Group I:t=0.82,P=0.41;Group II:t=0.17,P=0.87;Group III:t=1.35,P=0.18).The correlation analysis of corneal biomechanical parameter changes with PED at 1mo and 3mo after surgery showed thatΔIOP,ΔIOPcc,ΔCH,andΔCRF were not correlated with PED value in three groups(P>0.05).CONCLUSION:The smaller the RCST/CT,the greater effect on corneal biomechanics and posterior surface elevation.There is no correlation between changes in corneal biomechanics and posterior corneal surface elevation in the range of RCST/CT≥50%.

Comparison of corneal biomechanics in Sjogren's syndrome and non-Sjogren's syndrome dry eyes by Scheimpflug based device

AIM：To compare the corneal biomechanics of Sj？gren＇s syndrome（SS） and non-SS dry eyes with Corneal Visualization Scheimpflug Technology（CorV is ST）.METHODS：Corneal biomechanics and tear film parameters, namely the Schirmer I test value, tear film break-up time（TBUT） and corneal staining score（CSS） were detected in 34 eyes of 34 dry eye patients with SS（SSDE group） and 34 dry eye subjects without SS（NSSDE group） using CorV is ST. The differences of the above parameters between the two groups were examined, and the relationship between corneal biomechanics and tear film parameters were observed. RESULTS：The differences in age, sex, intraocular pressure（IOP） and central corneal thickness（CCT） were not significant between the two groups（P〉0.05）. The tear film parameters had significant differences between the SSDE group and NSSDE group（all P〈0.05）. Patients in the SSDE group had significantly lower A1-time and HC-time, but higher DA（P=0.01, 0.02, and 0.02, respectively） compared with the NSSDE group. In the SSDE group, DA was negatively correlated with TBUT（rho=-0.38, P=0.03）; HC-time was negatively correlated with CSS（rho=-0.43, P=0.02）. In the NSSDE group, HC-time was again negatively correlated with CSS（rho=-0.39, P=0.02）.CONCLUSION：There are differences in corneal biomechanical properties between SSDE and NSSDE. The cornea of SSDE tends to show less ＂stiffness＂, as seen by a significantly shorter A1-time and HC-time, but larger DA, compared with the cornea of NSSDE. Biomechanical parameters can be influenced by different tear film parameters in both groups.

Changes in corneal biomechanics and intraocular pressure following Femto-LASIK using Goldman applanation tonometry and ocular response analyzer

AIM:To compare intraocular pressure(IOP)measurements before and after laser in situ keratomileusis(LASIK)with a femtosecond laser for flap creation using ocular response analyzer(ORA)and Goldmann applanation tonometry,and to identify factors that may influence the preoperative and postoperative IOP.METHODS:A prospective study conducted on myopic patients who underwent LASIK using a femtosecond laser for flap fashioning.Enrolled patients were evaluated preoperatively,6 wk and 3 mo postoperatively for manifest refraction(MR),keratometric(K)readings and central corneal thickness(CCT)using a scheimpflug-based topography.Corneal resistance factor(CRF),corneal hysteresis(CH),Goldmann correlated IOP(IOPg)and corneal compensated IOP(IOPcc)were measured using ORA besides IOP assessment by Goldman applanation tonometry(GAT).RESULTS:There was a statistically significant decrease in measures of IOPg by 3.35±0.83 mm Hg,followed by GAT which decreased by 2.2±0.44 mm Hg,and the least affected by operation was IOPcc which decreased only by 0.87±0.1 mm Hg after 6 wk.After 3 mo follow up there was a statistically significant decrease in IOPcc which decreased only by 0.76±0.4 mm Hg,followed by IOP GAT by 1.6±0.5 mm Hg,and the most affected by operation was IOPg which decreased by 2.3±0.3 mm Hg.Correspondingly,there was a statistically significant decrease in CH and CRF after 6 wk and 3 mo.At 3 mo,the preoperative MR and preoperative GAT were prominent significant predictors of the postoperative GAT changes.The prediction equation was subsumed.CONCLUSION:IOP measurements and corneal biomechanical factors reduce significantly after LASIK with a femtosecond laser for flap creation.The IOPcc values are less influenced by changes in corneal properties than IOPg and GAT,indicating that IOPcc may provide the most reliable measurement of IOP after this procedure.

Evaluation of corneal parameter changes under different accommodative stimuli with Scheimpflug imaging-based tomography

AIM:To evaluate the reliability of measurements of corneal changes with accommodation in healthy eyes using a Scheimpflug imaging-based system and how these measurements distribute in the normal population.METHODS:Prospective,non-randomized,comparative study including 27 healthy subjects(54 eyes),including emmetropia(13 eyes),myopia(17 eyes),hyperopia(4 eyes)and astigmatism(20 eyes)groups.In all cases,a complete eye examination was performed,including the analysis of corneal changes with different accommodative stimuli(+2.00,0.00 and-3.00 D)using the Pentacam AXL system.The investigation was structured in 2 phases:repeatability analysis and characterization of accommodation-related corneal changes in healthy populations.RESULTS:In the repeatability analysis,the index of height asymmetry(IHA)showed the greatest variability with the three accommodative stimuli,being the results for the rest of parameters acceptable.The group of emmetropes showed significant differences with accommodative changes in the position of maximum keratometry(Kmax;P<0.05),whereas in the astigmatism group,significant changes were not only observed in the position of Kmax,but also in minimum corneal thickness(MCT),corneal spherical aberration,and total and low order aberration root mean square(all P<0.05).Likewise,a significant difference was found in the displacement of the X position of Kmax with+2.00 D and-3.00 D in the myopia group(P=0.033)as well as in changes with+2.00 D and-3.00 D in the magnitude of the position vector of Kmax in the emmetropia group(P<0.05).No significant changes were found between accommodative stimuli in the displacement of coordinates of MCT(P≥0.109).CONCLUSION:The position of Kmax and MCT in healthy corneas can change significantly when presenting different accommodative stimuli using the accommodation mode of the Pentacam system,with different trends in these accommodation-related corneal changes between refractive errors.Likewise,the consistency of the measurements obtained with Scheimpflug has been confirmed.

Stromal lenticule addition keratoplasty with corneal crosslinking for corneal ectasia secondary to FS-LASIK:a case series

●AIM:To explore the clinical efficacy and safety of stromal lenticule addition keratoplasty(SLAK)with corneal crosslinking(CXL)on patients with corneal ectasia secondary to femtosecond laser-assisted in situ keratomileusis(FS-LASIK).●METHODS:A series of 5 patients undertaking SLAK with CXL for the treatment of corneal ectasia secondary to FS-LASIK were followed for 4-9mo.The lenticules were collected from patients undertaking small incision lenticule extraction(SMILE)for the correction of myopia.Adding a stromal lenticule was aimed at improving the corneal thickness for the safe application of crosslinking and compensating for the thin cornea to improve its mechanical strength.●RESULTS:All surgeries were conducted successfully with no significant complications.Their best corrected visual acuity(BCVA)ranged from 0.05 to 0.8-2 before surgery.The pre-operational total corneal thickness ranged from 345-404μm and maximum keratometry(Kmax)ranged from 50.8 to 86.3.After the combination surgery,both the corneal keratometry(range 55.9 to 92.8)and total corneal thickness(range 413-482μm)significantly increased.Four out of 5 patients had improvement of corneal biomechanical parameters(reflected by stiffness parameter A1 in Corvis ST).However,3 patients showed decreased BCVA after surgery due to the development of irregular astigmatism and transient haze.Despite the onset of corneal edema right after SLAK,the corneal topography and thickness generally stabilized after 3mo.●CONCLUSION:SLAK with CXL is a potentially beneficial and safe therapy for advanced corneal ectasia.Future work needs to address the poor predictability of corneal refractometry and compare the outcomes of different surgical modes.

Consideration of corneal biomechanics in the diagnosis and management of keratoconus: is it important?

Keratoconus is a bilateral,non-inflammatory,degenerative corneal disease.The occurrence and development of keratoconus is associated with corneal thinning and conical protrusion,which causes irregular astigmatism.With the disruption of the collagen organization,the cornea loses its shape and function resulting in progressive visual degradation.Currently,corneal topography is the most important tool for the diagnosis of keratoconus,which may lead to false negatives among the patient population in the subclinical phase.However,it is now hypothesised that biomechanical destabilisation of the cornea may take place ahead of the topographic evidence of keratoconus,hence possibly assisting with disease diagnosis and management.This article provides a review of the definition,diagnosis,and management strategies for keratoconus based on corneal biomechanics.

Comparison of corneal biomechanics among primary open-angle glaucoma with normal tension or hypertension and controls

Background:Normal tension glaucoma(NTG)is a less pressure-dependent type of glaucoma with characteristic optic neuropathy.Recently,the biomechanical mechanism has been thought to account for glaucomatous optic neuropathy to some degree.We intended to compare dynamic corneal response parameters(DCRs)among patients with primary open-angle glaucoma with normal tension or hypertension and controls.The correlations between DCRs and known risk factors for glaucoma were also analyzed.Methods:In this cross-sectional study,49 NTG subjects,45 hypertension glaucoma(HTG)subjects,and 50 control subjects were enrolled.We compared the differences in DCRs using corneal visualization Scheimpflug technology among the NTG,HTG,and control groups.We also analyzed the correlations between DCRs and known risk factors for glaucoma(eg,central corneal thickness[CCT],intraocular pressure[IOP],etc).Results:The maximum inverse concave radius(NTG:0.18[0.17,0.20]mm-1;control:0.17[0.16,0.18]mm-1;P=0.033),deformation amplitude ratio of 2 mm(DAR 2 mm,NTG:4.87[4.33,5.39];control:4.37[4.07,4.88];P<0.001),and DAR 1 mm(NTG:1.62[1.58,1.65];control:1.58[1.54,1.61];P<0.001)were significantly higher in NTG than in the controls.The integrated radius(IR,NTG:8.40±1.07 mm-1;HTG:7.64±1.31 mm-1;P=0.026)and DAR 2 mm(NTG:4.87[4.33,5.39];HTG:4.44[4.12,5.02];P<0.007)were significantly higher,whereas the stiffness parameter at the first applanation(SP-A1,NTG:91.23[77.45,107.45];HTG:102.36[85.77,125.12];P=0.007)was lower in NTG than in HTG.There were no significant differences in the DCRs between HTG and control groups(P>0.05).In the univariate and multivariate analyses,some of the DCRs,such as IR,were negatively correlated with CCT and IOP,whereas SP-A1 was positively correlated with CCT and IOP.Conclusions:The cornea was more deformable in NTG than in HTG or controls.There were no significant differences in corneal deformability between HTG and controls.The cornea was more deformable with the thinner cornea and lower IOP.

Review of in-vivo characterisation of corneal biomechanics

The study of corneal biomechanics in vivo has been evolving fast in recent years.While an organised corneal structure is necessary for its transparency,resistance to occasional external insults and bearing the intraocular pressure(IOP),which several clinically relevant events can disturb.This review focuses on three techniques that are available for clinical use,namely the Ocular Response Analyzer(Reichert Ophthalmic Instruments,Buffalo,NY,USA),the Corvis ST(Oculus Optikgerate GmbH,Wetzlar,Germany)and the Brillouin Optical Scattering System(Intelon Optics Inc.,Lexington,MA,USA).The principles and the main parameters of each device are discussed along with their strategies to improve accuracy in the IOP measurement,corneal ectasia diagnosis,evaluation of corneal cross-linking procedures,and planning of corneal refractive surgeries.

Review of ex-vivo characterisation of corneal biomechanics

The evaluation of the corneal biomechanical behaviour has important clinical applications.To name a few,the accuracy of the intraocular pressure measurement,the study of corneal ectatic diseases and the assessment and optimisation of corneal surgical procedures are all highly influenced by corneal biomechanics.Over the last 45 years different ex-vivo methods were developed to study corneal biomechanical behaviour.Different tissue maintenance,support,loading systems,as well as different monitoring strategies of corneal deformations were employed.In this review,the most important and commonly used methods are outlined,including strip extensiometry,inflation,compression,indentation and tissue separation testing.Their particularities,applications,pros and cons and main applications are discussed.

Comparison of corneal biological parameters between transepithelial and epithelium-off corneal cross-linking in keratoconus

AIM:To evaluate the differences in corneal biological parameters between transepithelial and epithelium-off corneal cross-linking in keratoconus.METHODS:In our prospective clinical trial,40 patients(60 eyes)with progressive keratoconus were randomized to undergo corneal cross-linking with transepithelial(TE group,n=30)or epithelium-off(EO group,n=30)keratoconus.Examinations comprised topography,corneal biomechanical analysis and specular microscopy at 6 mo postoperatively.RESULTS:The keratometer values were not significantly different between the TE and EO corneal cross-linked groups in different periods(each P>0.05).The corneal thickness of the EO group was greater than that of the TE group at 1 wk after the operation(each P<0.05).Regarding corneal biomechanical responses,the EO group showed a longer second applanation length than TE group(P=0.003).Regarding the corneal endothelial function,standard deviation of the endothelial cell size,and coefficient of variation in the cell area,the values of EO group were larger than those of TE group at 1 wk(P=0.011,0.026),and the percentage of hexagonal cells in EO group was lower than that in TE group at 1 and 6 mo(P=0.018,0.019).CONCLUSION:Epithelium-off corneal cross-linking may strengthen corneal biomechanics better than TE procedure can.However,the TE procedure with a lower ultraviolet-A irradiation intensity would be safer for corneal endothelial function.

Short and long term corneal biomechanical analysis after overnight orthokeratology

AIM: To investigate the short and long term corneal biomechanical changes after overnight orthokeratology(OK) and compare them with those occurring in subjects not wearing contact lenses.METHODS: Retrospective case control study enrolling 54 subjects that were divided into three groups 18 subjects each: control group(CG), short term(15 nights) OK(STOK) group, and long term(more than 1 y of OK wear) OK(LTOK) group. Corneal biomechanics were characterized using the Cor Vis? ST system(Oculus), recording parameters such as time [first/second applanation time(AT1, AT2)], speed [velocity of corneal apex at the first/second applanation time(AV1, AV2)], and amplitude of deformation(AD1, AD2) in the first and second corneal flattening, corneal stiffness(SPA1), biomechanically corrected intraocular pressure(b IOP) and corneal(CBI) and tomographic biomechanical indices(TBI).RESULTS: Significantly lower AD1 and standard deviate on of Ambrosio’s relational average thickness related to the horizontal profile(ARTh) values were found in the OK groups compared to CG(P<0.05). Likewise, significantly higher values of CBI were found in STOK and LTOK groups compared to CG(P<0.01). No significant differences between groups were found in integrated radius index(P=0.24), strain stress index(P=0.22), tomographic biomechanical index(P=0.91) and corneal stif fness parameter(SPA1, P=0.97). Significant inverse correlations were found between corneal thickness and CBI in STOK(r=-0.90, P<0.01) and LTOK groups(r=-0.71, P<0.01).CONCLUSION: OK does not seem to alter significantly the corneal biomechanical properties, but special care should be taken when analyzing biomechanical parameters influenced by corneal thickness such as amplitude of deformation, ARTh or CBI, because they change significantly after treatment but mainly due to the reduction and pachymetric progression induced by the corneal molding secondary to OK treatment.

Corneal biomechanical properties changes after coaxial 2,2-mm microincision and standard 3,0-mm phacoemulsification

AIM： To compare the changes in corneal biomechanics measured by ocular response analyzer （ORA） after 2.2-ram microincision cataract surgery and 3.0-mm standard coaxial phacoemulsification. METHODS： The prospective nonrandomized study comprised eyes with cataract that had 2.2-mm coaxial microincision or 3.0 -mm standard incision phacoemulsification. The corneal hysteresis （CH）, corneal resistance factor （CRF）, corneal-compensated intraocular pressure （IOPcc） and Goldmann-correlated intraocular pressure （IOPg） were measured by ORA preoperatively and at ld, 1-, 2-, 3- and 4-week postoperatively. Results were analyzed and compared between groups. RESULTS： In both groups, CH decreased in the immediate postoperative period （P〈0.05）, returned to the preoperative level at one week （P =0.249） in the 2.2-mm group, and at two weeks in the 3.0-mm group （P --0.264）; there was no significant change in CRF values. In 2.2-mm group, mean IOPcc and IOPg increased at ld postoperatively （both ,P〈0.05）, and returned to preoperative level at one week （,0 =0.491 and P =0.923, respectively）. In 3.0-mm group, mean IOPcc and IOPg increased at ld and lwk postoperatively （P =0.005 and ,P =0.029, respectively）, and returned to preoperative level at 2wk （P =0.347 and P =0.887, respectively）. CONCLUSION： Significant differences between preoperative and postoperative corneal biomechanical values were found for CH, IOPcc and IOPg. But the recovery time courses were different between the two groups. The 2.2-mm coaxial microincision cataract surgery group seemed recovery faster compared to the 3.0-mm standard coaxial phacoemulsification group.

Corneal properties in children with congenital isolated growth hormone deficiency

AIM:To compare the corneal parameters of children with congenital isolated growth hormone deficiency and healthy subjects.METHODS:In this cross-sectional,prospective study,50 cases with growth hormone(GH)deficiency treated with recombinant GH and 71 healthy children underwent a complete ophthalmic examination.The corneal hysteresis(CH),corneal resistance factor(CRF),Goldmann-correlated intraocular pressure(IOPg)and corneal-compensated intraocular pressure(IOPcc)were measured with the Ocular Response Analyzer(ORA).Central corneal thickness(CCT)was measured by a ultrasonic pachymeter.RESULTS:The mean age was 13.0±3.0 years in the GH deficiency group consisting of 21 females and 29 males and 13.4±2.4 years in the healthy children group consisting of 41 females and 30 males.There was no statistically significant difference between the groups for gender or age(Chi-square test,P=0.09;independent ttest,P=0.28,respectively).The mean duration of recombinant GH therapy was 3.8±2.4y in the study group.The mean CH,CRF,IOPg and IOPcc values were 11.0±2.0,10.9±1.9,15.1±3.3,and 15.1±3.2 mm Hg respectively in the study group.The same values were 10.7±1.7,10.5±1.7,15.2±3.3,and 15.3±3.4 mm Hg respectively in the control group.The mean CCT values were 555.7±40.6,545.1±32.5μm in the study and control groups respectively.There was no statistically significant difference between the two groups for CH,CRF,IOPg,IOPcc measurements or CCT values(independent t-test,P=0.315,0.286,0.145,0.747,0.13 respectively).CONCLUSION:Our study suggests that GH deficiency does not have an effect on the corneal parameters and CCT values.This observation could be because of the duration between the beginning of disease and the diagnosis and beginning of GH therapy.

Correlation of myopia onset and progression with corneal biomechanical parameters in children

BACKGROUND Recent epidemiological studies have shown that general eye measurement parameters and corneal biomechanical properties can predict the speed of myopic progression in children.AIM To investigate the correlation between the onset and progression of myopia and corneal biomechanical parameters in children.METHODS The study included 102 cases in the emmetropia group,207 cases in the myopic group,and 109 cases in the hyperopic group.The correlation between the change in corneal biomechanical indexes and the change in general ocular measurement parameters was analyzed.A one-way ANOVA test compared general ocular measurement and corneal biomechanical parameters.Pearson’s correlation coefficient was analyzed to correlate corneal biomechanical and general ocular measurement parameters.RESULTS The general ophthalmometric parameters:Spherical equivalent(SE),intraocular pressure(IOP),and axial length(AL),differed significantly among subjects in myopia,emmetropia,and hyperopic groups.Children’s SE positively correlated with corneal biomechanical parameters:Second velocity of applanation(A2V),peak distance(PD),and deformation amplitude(DA)(P<0.05),and second applanation length(A2L)(P<0.05).But it was negatively correlated with PD,DA and integral radius(IR)(P<0.05).Also,IOP was negatively correlated with A2L and IR(P<0.05).AL positively correlated with A2V and negatively correlated with second applanation time(A2T),highest concavity,and PD.Central corneal thickness positively correlated with first applanation length,first applanation time,first applanation deformation amplitude,A2V,A2L,A2T,second applanation deformation amplitude,central curvature radius at highest concavity(HCR),PD,DA,IR,ambrosia relational thickness-horizontal,first applanation stiffness parameter,corvis biomechanical index,topographic and biomechanics index and the first velocity of applanation.The general ocular Km in children positively correlated with corneal biomechanical parameters DA and IR and negatively correlated with A2L,HCR,and PD.There was a positive correlation between the general ocular measurement parametersΔSE and corneal biomechanical parametersΔA2V andΔA2L,and a negative correlation withΔIR.The increase in general ocular measurement parameterΔKm positively correlated with changes in corneal biomechanical parameters,ΔDA andΔIR,and negatively correlated withΔHCR andΔPD.CONCLUSION Myopia development in children was associated with multiple corneal biomechanical parameters.

Agreement of intraocular pressure measurement with Corvis ST,non-contact tonometer,and Goldmann applanation tonometer in children with ocular hypertension and related factors

AIM:To access the agreement of intraocular pressure(IOP)values obtained from biomechanically corrected tonometer[Corvis ST(CST)],non-contact tonometer(NCT),and Goldmann applanation tonometer(GAT)in children with NCT measured-IOP(NCT-IOP)values of 22 mm Hg or more,and related factors.METHODS:A total of 51 eyes with NCT-IOP≥22 mm Hg in children aged 7 to 14y were examined and IOP was measured by CST,NCT,and GAT.Based on GAT measured IOP(GAT-IOP),ocular hypertension(OHT)group(≥22 mm Hg,24 eyes)and the non-OHT group(<22 mm Hg,27 eyes)were defined.We compared the agreement of the three measurements,i.e.,CST measured IOP(CST-IOP),GAT-IOP,and NCT-IOP,and further analyzed the correlation between the differences in tonometry readings,central corneal thickness(CCT),axial length(AL),optic disc rim volume,and age.RESULTS:Compared with the OHT group,thicker CCT,larger rim volume,and higher differences between NCTIOP and GAT-IOP,were found in the non-OHT group.The differences between CST-IOP and GAT-IOP were lower than the differences between NCT-IOP and GAT-IOP in both groups.The mean differences in CST-IOP and GAT-IOP were 1.26 mm Hg(95%limit of agreement ranged from 0.1 to 2.41 mm Hg,OHT group)and 1.20 mm Hg(95%limit of agreement ranged from-0.5 to 3.00 mm Hg,non-OHT group),and the mean differences in NCT and GAT were 3.90 mm Hg(95%limit of agreement ranged from-0.19 to 9.70 mm Hg,OHT group)and 6.00 mm Hg(95%limit of agreement ranged from 1.50 to 10.50 mm Hg,non-OHT group).The differences between CST-IOP and GAT-IOP were not related to CCT,age,and AL in both groups;while the differences between NCT-IOP and GAT-IOP were related to CCT in the OHT group(r=0.93,P<0.001)and to CCT and AL in the non-OHT group(r=0.66,P<0.001,r=-0.81,P<0.001).CONCLUSION:The accuracy of NCT in the diagnosis of pediatric OHT is low.The agreement of CST-IOP and GATIOP was significantly higher in children with and without OHT than in those with NCT-IOP and GAT-IOP.Therefore,CST can be used as a good alternative for IOP measurement in children.The impacts of CCT and AL on NCT measurement need to be fully considered when managing childhood IOP.

Evaluation of Corvis ST tonometer with the updated software in glaucoma practice

AIM: To evaluate the agreement of biomechanically corrected intraocular pressure(b-IOP) and central corneal thickness(CCT) measurements obtained with the updated Corvis ST tonometer versus Goldmann applanation tonometry(GAT) and optical-based corneal pachymetry(OB-CCT) in controls, patients with ocular hypertension(OHT) and primary open angle glaucoma(POAG).Additionally, we examined the differences in corneal deformation parameters provided by the updated Corvis ST among the three groups.METHODS: For each participant, GAT IOP, OB-CCT and measurements with a Corvis ST with updated software were obtained.Bland-Altman analysis was used to assess the agreement between the two measurement methods.RESULTS: A consecutive series of 80 eyes from 80 participants(30 with POAG, 25 with OHT and 25 normal controls) were included in this prospective study.The mean GAT IOP of all eyes was 17.2±3.6 mm Hg, and the mean b-IOP was 15.9±3.7 mm Hg(Spearman’s rho=0.767, P<0.001).The 95% limits of agreement(Lo As) ranged from-3.1 mm Hg to 5.5 mm Hg for GAT IOP and b-IOP.b-IOP was not correlated with OB-CCT(Spearman’s rho=-0.13 P=0.917).Meanwhile there was a weak positive corelation between OB-CCT and GAT IOP–b-IOP difference(Spearman’s rho=0.378, P=0.001).The mean OB-CCT was 549.5±36.4 μm, and the Corvis-CCT was 556.1±41.5 μm(Spearman’s rho=0.900, P<0.001).No statistically significant difference in the new indices provided by the updated Corvis ST was detected among the three groups.Compared with control eyes, POAG eyes had a significantly reduced applanation time 2 after adjusting for OB-CCT and GAT IOP(P=0.048).CONCLUSION: Corvis b-IOP and CCT correlate well with GAT IOP and OB-CCT.b-IOP is not affected by CCT, which might be an advantage, especially in thick or thin corneas.Corvis ST yields shorter applanation time 2 measurements in patients with POAG, which might reflect altered corneal viscoelasticity.

Development of a classification system based on corneal biomechanical properties using artificial intelligence predicting keratoconus severity

Background:To investigate machine-learning(ML)algorithms to differentiate corneal biomechanical properties between different topographical stages of keratoconus(KC)by dynamic Scheimpflug tonometry(CST,Corvis ST,Oculus,Wetzlar,Germany).In the following,ML models were used to predict the severity in a training and validation dataset.Methods:Three hundred and eighteen keratoconic and one hundred sixteen healthy eyes were included in this monocentric and cross-sectional pilot study.Dynamic corneal response(DCR)and corneal thickness related(pachymetric)parameters from CST were chosen by appropriated selection techniques to develop a ML algorithm.The stage of KC was determined by the topographical keratoconus classification system(TKC,Pentacam,Oculus).Patients who were classified as TKC 1,TKC 2 and TKC 3 were assigned to subgroup mild,moderate,and advanced KC.If patients were classified as TKC 1-2,TKC 2-3 or TKC 3-4,they were assigned to subgroups according to the normative range of further corneal indices(index of surface variance,keratoconus index and minimum radius).Patients classified as TKC 4 were not included in this study due to the limited amount of cases.Linear discriminant analysis(LDA)and random forest(RF)algorithms were used to develop the classification models.Data were divided into training(70%of cases)and validation(30%of cases)datasets.Results:LDA model predicted healthy,mild,moderate,and advanced KC eyes with a sensitivity(Sn)/specificity(Sp)of 82%/97%,73%/81%,62%/83%and 68%/95%from a validation dataset,respectively.For the RF model,a Sn/Sp of 91%/94%,80%/90%,63%/87%,72%/95%could be reached for predicting healthy,mild,moderate,and advanced KC eyes,respectively.The overall accuracy of LDA and RF was 71%and 78%,respectively.The accuracy for KC detectionincludina allstho ofKC severity as.93%.in both.models.Conclusion:The RF model showed good accuracy in predicting healthy eyes and various stages of KC.The accuracy was superior with respect to the LDA model.The clinical importance of the models is that the standalone dynamic Scheimpflug tonometry is able to predict the severity of KC without having the keratometric data.

Corneal biomechanical changes in allergic conjunctivitis

Background:To explore corneal biomechanical changes,identify related factors and determine early indicators of keratoconus(KC)development risk in allergic conjunctivitis(AC)patients.Methods:A total of 50 patients,including 20 eyes without AC and 30 eyes with AC were enrolled in this study.All patients underwent a complete ocular examination,including evaluations of clinical manifestations of AC,corneal tomography and densitometry by Pentacam,corneal biomechanics by Corvis ST,and corneal and epithelial thickness mapping by RTvue optical coherence tomography(OCT).Results:The index of surface variance(ISV),index of vertical asymmetry(IVA),keratoconus index(KI),index of height decentration(IHD)and Belin/Ambrosio enhanced ectasia total deviation index(BAD-D)were significantly higher in the AC group than in the non-allergic conjunctivitis(NAC)group(P<0.05).The tomography and biomechanical index(TBl)was also significantly higher in the AC group(P=0.04).The average epithelial thickness in the 2-7 mm annulus was significantly thinner in the AC group than in the NAC group(P<0.05).The average densitometry of the total cornea and the anterior layer were higher in the AC group than in the NAC group(P<0.001).The ISV,IVA,KI,IHD and BAD-D were significantly correlated with the TBI and changes in corneal epithelial thickness in AC patients(P<0.05).The changes in epithelial thickness were closely related to the eye rubbing frequency and allergic sign scores(P<0.05).Conclusions:AC patients should be advised to routinely undergo corneal tomographic and biomechanical measurements,and the TBl could be used as an indicator of KC development risk in AC patients.Trial registration:Corneal Biomechanical Changes of Allergic Conjunctivitis,NCT04299399.Registered March 3,2020-Retrospectively registered.

Development of a classification system based on corneal biomechanical properties using artificial intelligence predicting keratoconus severity

Background:To investigate machine-learning(ML)algorithms to differentiate corneal biomechanical properties between different topographical stages of keratoconus(KC)by dynamic Scheimpflug tonometry(CST,Corvis ST,Oculus,Wetzlar,Germany).In the following,ML models were used to predict the severity in a training and validation dataset.Methods:Three hundred and eighteen keratoconic and one hundred sixteen healthy eyes were included in this monocentric and cross-sectional pilot study.Dynamic corneal response(DCR)and corneal thickness related(pachymetric)parameters from CST were chosen by appropriated selection techniques to develop a ML algorithm.The stage of KC was determined by the topographical keratoconus classification system(TKC,Pentacam,Oculus).Patients who were classified as TKC 1,TKC 2 and TKC 3 were assigned to subgroup mild,moderate,and advanced KC.If patients were classified as TKC 1-2,TKC 2-3 or TKC 3-4,they were assigned to subgroups according to the normative range of further corneal indices(index of surface variance,keratoconus index and minimum radius).Patients classified as TKC 4 were not included in this study due to the limited amount of cases.Linear discriminant analysis(LDA)and random forest(RF)algorithms were used to develop the classification models.Data were divided into training(70%of cases)and validation(30%of cases)datasets.Results:LDA model predicted healthy,mild,moderate,and advanced KC eyes with a sensitivity(S_(n))/specificity(S_(p))of 82%/97%,73%/81%,62%/83%and 68%/95%from a validation dataset,respectively.For the RF model,a S_(n)/S_(p) of 91%/94%,80%/90%,63%/87%,72%/95%could be reached for predicting healthy,mild,moderate,and advanced KC eyes,respectively.The overall accuracy of LDA and RF was 71%and 78%,respectively.The accuracy for KC detection including all subgroups of KC severity was 93%in both models.Conclusion:The RF model showed good accuracy in predicting healthy eyes and various stages of KC.The accuracy was superior with respect to the LDA model.The clinical importance of the models is that the standalone dynamic Scheimpflug tonometry is able to predict the severity of KC without having the keratometric data.

In vivo study of corneal responses to increased intraocular pressure loading

Background:The cornea is responsible for two-thirds of the eye's refractive power which is a function of the shape and refractive index.The aim of this present study is to examine human eyes in vivo for corneal shape changes in response to short-term elevation in intraocular pressure.Methods:Videokeratographic and tonometric assessments at baseline were compared with the same assessments when intraocular pressure was elevated to approximately double(199±22%)the baseline levels using ophthalmodynamometer applanation of the sclera.Composite maps of the cornea and limbus were created by combining topographical assessments for central,nasal,temporal,inferior and superior fixation.Numerical finiteelement simulations were custom built for each subject and the stiffness distribution across corneal surface modified to achieve matches between simulated and experimental data.Results:The stiffness distributions required to achieve simulation-experimental matches showed a consistent trend with the 2.5 mm annulus bounded by the limbus showing a mean stiffness reduction of 47.3±10.8%compared with the central cornea(P=0.001).Conclusions:Corneal structure appears to provide the central cornea with a greater stiffness compared with the peripheral cornea and associated greater tolerance to elevation in intraocular pressure,consistent with the need for stable corneal refraction and vision.The method adopted to examine corneal biomechanical performance in vivo may have applications in additional studies.