Evaluation of the B/F Ratio Distribution of Cataract Patients Without Corneal Abnormalities and Its Effect on Ocular Parameters

Purpose: To evaluate the distribution of the posterior-anterior corneal radius ratio (B/F ratio; posterior corneal radius/anterior corneal radius) in patients without corneal abnormalities, and to investigate which parameters affect this ratio. Methods: Five thousand eyes from 5,000 patients who underwent cataract surgery were recruited to this study. We explored the linear relationship between B/F ratio and 13 variables using Principal Component-Multivariate Linear Regression Analysis. Results: The B/F ratio was negatively correlated with the difference between simulated keratometry (SimK) and true net power (TNP), central corneal thickness, spherical aberration (SA), and posterior corneal astigmatism and positively correlated with posterior corneal radius, corneal posterior surface, axial length (AL) and anterior corneal radius. Several variables (central corneal thickness, difference between SimK and TNP and asphericity coefficient (Q-value) of the posterior corneal surface) had the highest loading on the final score. B/F ratio reflects the refractive state and anatomical structure of the cornea: thus, higher B/F ratios were associated with larger posterior corneal surface curvature radius, longer axial length, thinner central corneal thickness, lower high order aberrations of the cornea and SA, and the numerical difference between simK and TNP gradually reduced. In clinical practice, for patients with lower B/F ratio, special care should be taken in the choice of system used for intraocular lens (IOL) measurements.

Development of Refractive Parameters in 3- to 6-Year-Old Children and Its Application in Myopia Prediction and Intervention Guidance

Objective. To investigate refractive development and prevalence of myopia in children aged 3-6 years in Hebei Province, China, and to explore the developmental law of refraction, so as to clinically guide the prediction and intervention of myopia. Methods. In May 2019, a total of 6120 people were inspected in 68 kindergartens in 11 cities in Hebei Province. Child refractive refraction was checked under noncycloplegia using a handheld binocular vision screener (SW-800, SUOER, Tianjin, China). Axial length (AL) and corneal radius of curvature (CR) were measured using an ocular biometry (IOLMaster 500, Carl Zeiss, Germany). Myopia was defined as spherical equivalent SE ≤ − 0.75 D . Results. A total of 5506 children aged 3-6 years met the criteria and were included in the statistical analysis. The prevalence of myopia was 3.49% (1.93% at age 3, 2.90% at age 4, 3.78% at age 5, and 3.88% at age 6). Overall, the mean SE was + 0.67 ± 1.05 D ( + 0.81 ± 1.00 D at age 3, + 0.79 ± 1.05 D at age 4, + 0.67 ± 1.08 D at age 5, and + 0.13 ± 1.01 D at age 6); the mean CR was 7.76 ± 0.26 mm ( 7.78 ± 0.26 mm at age3, 7.75 ± 0.25 mm at age 4, 7.77 ± 0.26 mm at age 5, and 7.76 ± 0.25 mm at age 6); the mean AL was 22.31 ± 0.73 mm ( 21.98 ± 0.63 mm at age 3, 22.12 ± 0.69 mm at age 4, 22.34 ± 0.73 mm at age 5, and 22.49 ± 0.73 mm at age 6). Conclusions. Prevalence of myopia increases with age in children aged 3-6 years in Hebei, China. With the increase of age, CR is basically stable, and AL increases gradually. AL/CR, which is closely related to SE, can be used as an indicator to predict myopia and guide clinical work.

Evaluation of the Relationships between Corneal Parameters, Ocular Biometry, and Myopia Magnitude

Axial length of the eye correlates with the magnitude of myopia. However, there are conflicting reports on the relationship between certain corneal parameters with myopia magnitude. The objective of this study was to compare ocular biometry and corneal parameters between emmetropic and myopic groups. Participants (n=127) were categorized as emmetropia (spherical equivalent, SE, ±0.50D), low myopia (-0.75D≤SE<-6.00D) and high myopia (SE≥-6.00D). The difference in axial length, anterior chamber depth, and vitreous chamber depth between emmetrope, low myope, and high myope were highly significant (one-way ANOVA, all p<0.001) with significant correlations between SE and all these parameters (simple regressions, all p<0.001). However, central corneal thickness, corneal radius of curvature, and corneal asphericity between these groups, and the correlations between the ocular parameters with SE were not significantly different (all p>0.05). Corneal curvature correlated significantly with axial length (p=0.001) but not with myopia magnitude (p=0.91). Rather than myopia magnitude, axial length appears to be more sensitive to detect changes in corneal curvature in myopes. In conclusion, myopic patients’ axial length should be carefully considered for interventions that involve the cornea, such as orthokeratology and refractive surgery.

Automatic detection of the cornea location in video captures of fluorescence

Purpose: Fluorescence imaging is a valuable tool for studying tear film dynamics andcorneal staining. Automating the quantification of fluorescence images is a challenging necessary step for making connections to mathematical models. A significant partof the challenge is identifying the region of interest, specifically the cornea, for collected data with widely varying characteristics. Methods: The gradient of pixel intensity at the cornea–sclera limbus is used as the objective of standard optimization to find a circle that best represents the cornea. Results of the optimization in one image are used as initial conditions in the next imageof a sequence. Additional initial conditions are chosen heuristically. The algorithm iscoded in open-source software. Results: The algorithm was first applied to 514 videos of 26 normal subjects, for a total of over 87,000 images. Only in 12 of the videos does the standard deviation in thedetected corneal radius exceed 1% of the image height, and only 3 exceeded 2%. The algorithm was applied to a sample of images from a second study with 142 dry-eye subjects. Significant staining was present in a substantial number of these images. Visual inspection and statistical analysis show good resuls for both normal and dry-eye images. Conclusion: The new algorithm is highly effective over a wide range of tear film andcorneal staining images collected at different times and locations.

Normative data and percentile curves for axial length and axial length/corneal curvature in Chinese children and adolescents aged 4–18 years

PurposeTo develop age-specific and gender-specific reference percentile charts for axial length (AL) and AL/corneal radius of curvature (AL/CR) and, to use percentiles to determine probability of myopia and estimate refractive error (RE).MethodsAnalysis of AL, cycloplegic RE and CR of 14 127 Chinese participants aged 4–18 years from 3 studies. AL and AL/CR percentiles estimated using Lambda-Mu-Sigma method and compared for agreement using intraclass correlation (ICC). Logistic regression was used to model risk of myopia based on age, gender, AL and AL/CR percentiles. Accuracy of AL progression and RE estimated using percentiles was validated using an independent sample of 5742 eyes of children aged 7–10 years.ResultsAge-specific and gender-specific AL and AL/CR (3rd, 5th, 10th, 25th, 50th, 75th, 90th and 95th) percentiles are presented. Concordance between AL and AL/CR percentiles improved with age (0.13 at 4 years to >0.75 from 13 years) and a year-to-year change was observed for all except <10th percentile from 15 years. Increasing age, AL and AL/CR was associated with a more myopic RE (r2=0.45,0.70 and 0.83, respectively). The sensitivity and specificity of the model to estimate probability of myopia was 86.0% and 84.5%, respectively. Estimation of 1-year change in AL using percentiles correlated highly with actual AL (ICC=0.98). Concordance of estimated to actual RE was high (ICC=0.80) and within ±0.50D and ±1.0D of actual RE for 47.4% and 78.9% of eyes, respectively.ConclusionAge-specific and gender-specific AL and AL/CR percentiles provide reference data, aid in identifying and monitoring individuals at risk of myopia and have utility in screening for myopia. AL/CR percentiles were more accurate in estimating probability of myopia in younger children.

Prevalence of myopia in 3–14-year-old Chinese children: a school-based cross-sectional study in Chengdu

Background The prevalence of myopia among children in Chengdu is unknown. The aim of this study was to determine the prevalence of myopia in 3- to 14-year-old Chinese children in Chengdu. Methods This study was a school-based cross-sectional study in children aged 3–14 years. Visual acuity (VA), spherical equivalent error (SER) with noncycloplegic autorefraction, axial length (AL) and corneal radius (CR) were measured. Results A total of 19,455 children were recruited for this study. The prevalence of myopia was 38.1 %; the prevalence of low myopia was 26.6 %, that of moderate myopia was 9.8 %, and that of high myopia was 1.7 %. The prevalence of myopia and SER increased with age from 6 years old. The prevalence of myopia was higher, and the SER indicated more severe myopia in the girls than in the boys (40.1 % vs. 36.2 %, χ2 = 30.67, df = 1, P < 0.001; -0.93 D ± 1.75 D vs. -0.84 D ± 1.74 D, t = 3.613, df=19,453, P < 0.001). The girls had a higher prevalence of myopia and myopic SER than did the boys aged 9 years and older (P < 0.05). Among the myopic children, the rates of uncorrected, undercorrected and fully corrected myopia were 54.8 %, 31.1 and 14.1 %, respectively. AL and AL/CR increased with age from 6 years old, but CR remained stable after 4 years old. The AL was longer, and the CR was flatter in the boys than in the girls aged 3 to 14 years old (P < 0.05). Conclusions The prevalence of myopia, AL and AL/CR increased, and the SER became more myopic with age from 6 years old. The girls had a higher prevalence of myopia and myopic SER than did the boys, but the boys had a longer AL, flatter CR and higher AL/CR ratio than did the girls. The rate of uncorrected myopia was very high in the myopic children. More actions need to be taken to decrease the prevalence of myopia, especially uncorrected myopia in children.

The Correlation of Cycloplegic Refraction with Corneal Radius of Curvature-Adjusted Axial Length in Chinese Preschoolers

Background: In order to master the refractive status and detect severe refractive errors quickly and effectively, this study aimed to investigate the association of axial length after adjusting for corneal radius of curvature with refraction in a group of Chinese preschoolers. Methods: Retrospective review of 716 Chinese children aged from 3 to 6 years, who underwent cycloplegic optometry with 1% atropine eye gel in the ophthalmology department of Children’s Hospital of Fudan University, National Children’s Medical Center in Shanghai. Meanwhile axial length, corneal radius of curvature and cycloplegic autorefraction were obtained and axial length/corneal radius of curvature (AL/CR) ratio was calculated. The correlations of spherical equivalent refraction (SER) with axial length, corneal radius of curvature, AL/CR ratio and corneal radius of curvature-adjusted axial length were analyzed. Results: Only data from the right eye were included in this analysis. Among 716 eyes of 716 Chinese preschoolers, the mean (±SD) SER was 2.28±2.41 diopters (D), of which hyperopia, emmetropia, myopia were 84.64%, 8.54%, 6.84%, respectively. The mean(±SD) axial length, corneal radius of curvature and AL/CR ratio were 21.89±1.01mm, 7.76±0.27 mm, and 2.82±0.13, respectively. The SER was highly negative correlated with both axial length (coefficient –0.722) and AL/CR ratio (coefficient-0.814), and weakly correlated with corneal radius of curvature (coefficient 0.090) and gender(coefficient 0.093). Axial length was weakly correlated with age and gender(coefficient 0.232 and 0.268, respectively), but moderately correlated with corneal radius of curvature (coefficient 0.424). After adjusting for corneal radius of curvature, the correlation coefficient between SER and axial length significantly increased to-0.918. Conclusion: In the samples of 716 3-to 6-year-old Chinese children, axial length was moderately correlated with corneal radius of curvature. After adjusting for corneal radius of curvature, refraction was closely correlated with axial length than axial length alone and AL/CR ratio. Therefore, corneal radius of curvature-adjusted axial length might be a useful tool for pediatric ophthalmologists to detect refractive errors. Key Words: spherical equivalent refraction; corneal radius of curvature; adjusted; axial length; preschoolers.