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.

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.

Corneal Biomechanical Parameters and Asymmetric Visual Field Damage in Patients with Untreated Normal Tension Glaucoma

Background： High intraocular pressure （IOP） and low central corneal thickness （CCT） are important validated risk factors for glaucoma, and some studies also have suggested that eyes with more deformable corneas may be in higher risk of the development and worsening of glaucoma. In the present study, we aimed to evaluate the association between corneal biomechanical parameters and asymmetric visual field （VF） damage using a Corvis-ST device in patients with untreated normal tension glaucoma （NTG）. Methods： In this observational, cross-sectional study, 44 newly diagnosed NTG patients were enrolled. Of these, 31 had asymmetric VF damage, which was defined as a 5-point difference between the eyes according to the Advanced Glaucoma Intervention Study scoring system. Corneal biomechanical parameters were obtained using a Corvis-ST device, such as time from start until the first and second applanation is reached （time A 1 and time A2, respectively）, cord length of the first and second applanation （length A 1 and length A2, respectively）, corneal speed during the first and second applanation （velocity A1 and velocity A2, respectively）, time from start until highest concavity is reached （time HC）, maximum amplitude at the apex of highest concavity （def ampl HC）, distance between the two peaks at highest concavity （peak dist HC）, and central concave curvature at its highest concavity （radius HC）. Results： Time A 1 （7.19 q- 0.28 vs. 7.37 ~ 0.41 ms, P = 0.010）, length A 1 （1.73 [ 1.70-1.76] vs. 1.78 [ 1.76-1.79] mm, P = 0.007）, length A2 （1.58 [1.46-1.70] vs. 1.84 [h76-1.92] mm, P 〈 0.001）, peak dist HC （3.53 [3.08-4.00] vs. 4.33 [3.92-4.74] mm, P = 0.010）, and radius HC （6.20 ± 0.69 vs. 6.59 i h 18 mm, P = 0.032） were significantly lower in the worse eyes than in the better eyes, whereas velocity A 1 and def ampl HC were significantly higher （0.156 [0.149-0.163] vs. 0.145 [0.138-0.152] m/s, P= 0.002 and 1.19 ± 0.13 vs. 1.15 ± 0.13 mm, P = 0.005, respectively）. There was no significant difference in time A2, velocity A2, and time HC between the two groups. In addition, no difference was observed in lOP, CCT, and axial length. In the univariate and multivariate analyses, some of the Corvis-ST parameters, including time A1 and def ampl HC, were correlated with known risk factors for glaucoma, and there was also a significant positive correlation between def ampl HC and age. Conclusions： There were differences in dynamic corneal response parameters but not IOP or CCT between the paired eyes of NTG patients with asymmetric VF damage. We suggest that the shape of the cornea is more easily altered in the worse eyes of asymmetric NTG patients.

Effects of biomechanical parameters of spinal manipulation: A critical literature review

Spinal manipulation is a manual treatment technique that delivers a thrust,using specific biomechanical parameters to exert its therapeutic effects.These parameters have been shown to have a unique dose-response relationship with the physiological responses of the therapy.So far,however,there has not been a unified approach to standardize these biomechanical characteristics.In fact,it is still undetermined how they affect the observed clinical outcomes of spinal manipulation.This study,therefore,reviewed the current body of literature to explore these dosage parameters and evaluate their significance,with respect to physiological and clinical outcomes.From the experimental studies reviewed herein,it is evident that the modulation of manipulation’s biomechanical parameters elicits transient physiological responses,including changes in neuronal activity,electromyographic responses,spinal stiffness,muscle spindle responses,paraspinal muscle activity,vertebral displacement,and segmental and intersegmental acceleration responses.However,to date,there have been few clinical trials that tested the therapeutic relevance of these changes.In addition,there were some inherent limitations in both human and animal models due to the use of mechanical devices to apply the thrust.Future studies evaluating the effects of varying biomechanical parameters of spinal manipulation should include clinicians to deliver the therapy in order to explore the true clinical significance of the dose-response relationship.

Comparisons of corneal biomechanical and tomographic parameters among thin normal cornea,forme fruste keratoconus,and mild keratoconus

Background:To compare the dynamic corneal response(DCR)and tomographic parameters of thin normal cornea(TNC)with thinnest corneal thickness(TCT)(≤500μm),forme fruste keratoconus(FFKC)and mild keratoconus(MKC)had their central corneal thickness(CCT)matched by Scheimpflug imaging(Pentacam)and corneal visualization Scheimpflug technology(Corvis ST).Methods:CCT were matched in 50 eyes with FFKC,50 eyes with MKC,and 53 TNC eyes with TCT≤500μm.The differences in DCR and tomographic parameters among the three groups were compared.The receiver operating characteristic(ROC)curve was used to analyze the diagnostic significance of these parameters.Back propagation(BP)neural network was used to establish the keratoconus diagnosis model.Results:Fifty CCT-matched FFKC eyes,50 MKC eyes and 50 TNC eyes were included.The age and biomechanically corrected intraocular pressure(bIOP)did not differ significantly among the three groups(all P>0.05).The index of height asymmetry(IHA)and height decentration(IHD)differed significantly among the three groups(all P<0.05).IHD also had sufficient strength(area under the ROC curves(AUC)>0.80)to differentiate FFKC and MKC from TNC eyes.Partial DCR parameters showed significant differences between the MKC and TNC groups,and the deflection amplitude of the first applanation(A1DA)showed a good potential to differentiate(AUC>0.70)FFKC and MKC from TNC eyes.Diagnosis model by BP neural network showed an accurate diagnostic efficiency of about 91%.Conclusions:The majority of the tomographic and DCR parameters differed among the three groups.The IHD and partial DCR parameters assessed by Corvis ST distinguished FFKC and MKC from TNC when controlled for CCT.