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.

Agreement of corneal curvature and central corneal thickness obtained from a swept-source OCT and Pentacam in ectopia lentis patients

AIM:To assess the inter-device consistency of corneal curvature and central corneal thickness between Pentacam and a swept-source Fourier-domain anterior segment optical coherence tomography(AS-OCT)in ectopia lentis patients.METHODS:Totally 72 eyes of ectopia lentis patients were recruited.Central corneal thickness(CCT),corneal curvature values and corneal astigmatism were obtained from both the Pentacam and AS-OCT(CASIA2).Repeatability was evaluated for both devices.The coef ficient of repeatability(COR)and the relative COR was calculated.Bland-Altman plots were conducted to evaluate the interdevice agreement of measurement.Orthogonal linear regression was used to examine any proportional bias.RESULTS:The mean difference of CCT,steep anterior corneal cur vature(anterior K_S),flat anterior corneal curvature(anterior K_f),anterior corneal astigmatism(ACA),steep posterior corneal cur vature(posterior K_S),flat posterior corneal cur vature(posterior K_f),posterior corneal astigmatism(PCA),steep true net power(TNP K_S),flat true net power(TNP K_f)and total corneal astigmatism(TCA)between Pentacam and CASIA2 were 7.03±9.70μm,-0.19±0.41 D,-0.27±0.35 D,0.04±0.47 D,-0.17±0.23 D,-0.11±0.11 D,-0.02±1.02 D-0.41±0.43 D,-0.52±0.46 D,and-0.15±0.96 D,respectively.For measurement of TNP K_f with the Pentacam and CASIA2,a mean difference of 0.52 D and COR of 0.90 with P=0.02 was detected.There was no significant difference in CCT(P=0.393),anterior K_f(P=0.107),anteriorKs(P=0.414),ACA(P=0.131),posterior K_f(P=0.286),posterior Ks(P=0.418),PCA(P=0.105),TNP Ks(P=0.054),and TCA(P=0.977)between Pentacam and CASIA2.CONCLUSION:Our study reveals good agreement of CCT,corneal curvature and corneal astigmatism measured by CASIA2 and Pentacam in ectopia lentis patients.However,there was significant difference for CCT and corneal curvature values obtained by the two devices.

Changes in corneal curvature and aberrations after cataract surgery

Background:Surgically induced astigmatism(SIA)and corneal high-order aberrations(HOAs)are the two main causes of poor visual quality after cataract surgery.Changes in the parameters of corneal HOAs after cataract surgery and their effects on and relationships with changes in corneal curvature have not yet been reported.This study aimed to explore changes in anterior,posterior and total corneal curvature,astigmatism and HOAs after microincision cataract surgery.Methods:Sixty-one age-related cataract patients(61 eyes)were included in this prospective study.The total,anterior and posterior corneal astigmatism and corneal HOAs were analyzed by anterior segment optical coherence tomography(AS-OCT)and iTrace before,one day,one week and three months after 2.2 mm temporal microincision coaxial phacoemulsification to evaluate the changes in anterior,posterior and total corneal curvature,astigmatism and corneal HOAs.Results:The mean J0 and J45 values of anterior,posterior and total corneal curvature obtained by ASOCT showed no statistically significant difference between preoperatively and any postoperative followup.SIA occurred on the anterior,posterior and total corneal surfaces and showed no statistically significant difference at any postoperative follow-up.No significant changes in 3rd-order oblique trefoil,vertical coma or 4th-order spherical aberrations were observed after surgery except for a significant increase in horizontal coma at postoperative day 1(POD1).Conclusions:There were no significant changes in corneal curvature after 2.2 mm temporal microincision coaxial phacoemulsification,and the corneal HOAs were not changed significantly except for the increase in horizontal coma at POD1,which may be one of the main reasons of poor visual quality at POD1 in some cataract patients who have good uncorrected or corrected distance vision.

Impact of corneal parameters on intraocular pressure measurements in different tonometry methods

AIM: To evaluate the impact of central corneal thickness(CCT) and corneal curvature on intraocular pressure(IOP) measurements performed by three different tonometers. METHODS: IOP in 132 healthy eyes of 66 participants was measured using three different tonometry techniques: Goldmann applanation tonometer(GAT), Pascal dynamic contour tonometer(DCT), and ICare rebound tonometer(RT). CCT and corneal curvature were assessed. RESULTS: In healthy eyes, DCT presents significantly higher values of IOP than GAT(17.34±3.69 and 15.27±4.06 mm Hg, P<0.0001). RT measurements are significantly lower than GAT(13.56±4.33 mm Hg, P<0.0001). Compared with GAT, DCT presented on average 2.51 mm Hg higher values in eyes with CCT<600 μm and 0.99 mm Hg higher results in eyes with CCT≥600 μm. The RT results were lower on average by 1.61 and 1.95 mm Hg than those obtained by GAT, respectively. Positive correlations between CCT in eyes with CCT<600 μm were detected for all IOP measurement techniques, whereas a similar relationship was not observed in eyes with thicker corneas. A correlation between IOP values and keratometry in the group with CCT<600 μm was not detected with any of the tonometry methods. In thicker corneas, a positive correlation was found for GAT and mean keratometry values(R=0.369, P=0.005). CONCLUSION: The same method should always be chosen for routine IOP control, and measurements obtained by different methods cannot be compared. All analysed tonometry methods are dependent on CCT;thus, CCT should be taken into consideration for both diagnostics and monitoring.

Posterior corneal astigmatism modifications after cataract surgery and its role on total corneal astigmatism

Background:In recent years posterior corneal astigmatism and its effect on total corneal astigmatism has been studied,with research showing that this can impact total astigmatism.This study aims to ascertain if there is significant change in the posterior corneal astigmatism after cataract surgery and its impact on the total astigmatism.Methods:Analysis of 76 eyes that underwent cataract surgery with monofocal intraocular lens implantation.Corneal topography was performed with Pentacam(OCULUS®)pre-and post-operatively.Total corneal astigmatism was calculated with the algorithm of vergence tracing.We compared preoperative and postoperative changes in the magnitude and axis differences of anterior corneal curvature astigmatism,posterior corneal curvature astigmatism and the calculated total corneal astigmatism.We calculated the correlation between the total preoperative astigmatism and the difference between total corneal astigmatism and anterior corneal astigmatism.Results:The mean preoperative and postoperative posterior astigmatism was 0.31±0.02 D,showing no significant differences before and after surgery(P=0.989).Statistically significant differences between the calculated total corneal astigmatism and anterior corneal astigmatism were registered preoperatively and postoperatively in the with-the-rule anterior(WTR)corneal astigmatism(P=0.004,P<0.0001);against-the-rule(ATR)anterior corneal astigmatism(P<0.0001,P<0.0001)and in the oblique(P=0.026,P=0.019)subgroups.The posterior corneal astigmatism and the total corneal astigmatism correlated positively with the differences between the total corneal and anterior corneal astigmatism(R=0.378,P=0.001).Conclusions:There were statistically significant differences between the magnitude of the total astigmatism and anterior corneal astigmatism,underlining the impact of posterior corneal astigmatism.A positive correlation between the preoperative posterior astigmatism and the difference between the total corneal and the anterior corneal astigmatism suggests a specially relevant role of posterior corneal astigmatism when evaluating patients with higher degrees of astigmatism.

Comparison of Goldmann applanation tonometry,rebound tonometry and dynamic contour tonometry in normal and glaucomatous eyes

AIM: To compare the intraocular pressure(IOP)measurements obtained with the rebound tonometry(RT), dynamic contour tonometry(DCT) and Goldmann applanation tonometry(GAT) in normal and glaucomatous eyes and investigate the effects of central corneal thickness(CCT) and corneal curvature(CC) on IOP measurements.METHODS: One hundred and twenty-four eyes of 124 subjects were enrolled in this cross-sectional study.Fifty-six of participants were healthy individuals and 68 of them were glaucomatous patients. IOP was measured on each subject always in the same order, ICare RT-Pascal DCT-GAT, after a minimum interval of 10 min between measurements. CCT and CC were measured using a rotating Scheimpflug camera before the IOP measurements in all subjects. One way repeated measures ANOVA, Pearson correlation coefficient and regression analysis, and Bland-Altman analysis was used for the statistical assessment.RESULTS: Mean IOP for all enrolled eyes was 16.00±3.80 mm Hg for GAT, 16.99 ±4.91 mm Hg for RT, and20.40 ±4.44 mm Hg for DCT. Mean differences between GAT and RT was-1.75±3.41 mm Hg in normal(P <0.001)and-0.37 ±3.00 mm Hg in glaucomatous eyes(P =0.563).Mean differences between GAT and DCT was-4.06 ±3.42 mm Hg in normal(P < 0.001) and-4.67 ±3.12 mm Hg in glaucomatous eyes(P <0.001). GAT and RT were significantly positive correlated with CCT in normal(r2=0.101, P =0.017 and r2=0.331, P <0.001, respectively) and glaucomatous eyes(r2=0.084, P =0.016 and r2=0.123,P =0.003, respectively). DCT was also significantly positive correlated with CCT in normal eyes( r2=0.179,P =0.001) but not in glaucomatous eyes(r2=0.029, P =0.165).All tonometers were unaffected by CC.CONCLUSION: IOP measurements by RT and DCT were significantly higher than GAT. DCT has highest IOP measurements among these tonometers. RT was most influenced tonometer from CCT although all tonometers were significantly positive correlated with CCT except DCT in glaucomatous eyes. CC did not influence IOP measurements.

Proportion and characteristic of emmetropia in schoolchildren aged 6-11y:the Shenzhen elementary school eye study

AIM:To investigate the proportion and characteristic of emmetropia in schoolchildren aged 6-11,especially estimate the normal value of ocular biometric parameters of emmetropia.METHODS:A population-based cross-sectional study was conducted on children aged 6-11 y in Shenzhen.Totally,2386 schoolchildren from two primary schools were involved.The axial length(AL)and the corneal radius of curvature(CRC)were measured by partial coherence laser interferometry.Noncycloplegic refraction and refractive astigmatism(RA)was measured using autorefraction.The axial length-to-corneal radius of curvature ratio(AL/CRC),corneal astigmatism(CA)and spherical equivalent refraction(SER)were calculated.RESULTS:The proportion of emmetropia in elementary school students was 41.30%.This percentage decreased gradually from 6 to 11 years of age and decreased rapidly after 9 years of age.The mean and 95%CI of each parameter were provided for boys and girls aged 6 to 11 years of age with emmetropia according to each age group.The change trend of parameters of boys and girls are similar.After 7 years of age,the AL of non-emmetropia started to increase faster than that of emmetropia.The change trend of AL/CRC was the same as that of AL.The other parameters tend to be stable after 7 years of age.CONCLUSION:The age of 7-9 is an important period for the changes of refractive state and ocular biometric parameters of primary school students,and it is a special focus period for children myopia prevention.The normal value and variation of ocular biometric parameters of emmetropia can provide the basis for the clinical judgment of whether or not children’s ocular biometric parameters obtained by single measurement and changes obtained by multiple measurements are abnormal.