Generalised models of the vertebrate eye.

PURPOSE: To present a set of closed-form analytical equations to create a consistent eye model balance based on clinically measured input parameters in a single step. These models complement the existing iterative approaches in the literature. METHODS: Two different approaches are presented, both considering the cornea and lens as equivalent thin lenses. The first, called the Gaussian model, starts by defining the refractive error as the difference between the axial power (or dioptric distance) and the whole eye power, which can be expanded by filling in the formulas for each power. The resulting equation can be solved for either the refractive error, axial length, corneal power, lens power or the distance between the cornea and the lens as a function of the other four parameters. The second approach uses vergence calculations to provide alternative expressions, assuming that the refractive error is located at the corneal plane. Both models are explored for a biometric range typically found in adult human eyes. RESULTS: The Gaussian and vergence models each instantly balance the input data into a working eye model over the human physiological range and far beyond as demonstrated in various examples. The equations of the Gaussian model are more complicated, while the vergence model experiences more singularities, albeit in trivial or highly unlikely parameter combinations. CONCLUSIONS: The proposed equations form a flexible and robust platform to create eye models from clinical data. Possible applications lie in creating animal eye models or providing a generic reference for real biometric data and the relationships between the ocular dimensions.

Suitability of multifunction devices Myah and Myopia Master for monitoring myopia progression in children and adults.

PURPOSE: To assess the feasibility of using multifunction instruments to measure axial length for monitoring myopia progression in children and adults. METHODS: Axial length was measured in 60 children (aged 6-18 years) and 60 adults (aged 19-50 years) with multifunction instruments (Myah and Myopia Master) and stand-alone biometers (Lenstar LS900 and IOLMaster 700). Repeatability (measurements by the same examiner) and reproducibility (measurements by different examiners) were computed as the within-subject standard deviation (Sw) and 95% limits of agreement (LoA). Inter-instrument agreement was computed as intraclass correlation coefficients. The threshold for detecting myopic progression was taken as 0.1 mm. Measures were repeated only in children following the administration of 1% tropicamide to determine the impact of cycloplegia on axial length. RESULTS: Overall, the IOLMaster 700 had the best repeatability in children (0.014 mm) and adults (0.009 mm). Repeatability Sw values for all devices ranged from 0.005 to 0.021 mm (children) and 0.003 to 0.016 mm (adults). In children, reproducibility fell within 0.1 mm 95% of the time for the Myah, Myopia Master and IOLMaster 700. Agreement among all devices was classified as excellent (ICC 0.999; 95% CI 0.998-0.999), but the 95% LoA among the Myah, Myopia Master and Lenstar LS900 was ≥0.1 mm. Cycloplegia had no statistically significant effect on axial length (all p > 0.13). CONCLUSIONS: The Myah and Myopia Master multifunction instruments demonstrated good repeatability and reproducibility, and their accuracy was comparable to stand-alone biometers. Axial length measurements using different instruments can be considered interchangeable but should be compared with some caution. Accurate axial length measurements can be obtained without cycloplegia. The multifunction instruments Myah and Myopia Master are as well suited for monitoring myopia progression in children as the stand-alone biometers IOLMaster 700 and Lenstar LS900.

The influence of variations in ocular biometric and optical parameters on differences in refractive error.

PURPOSE: To present a paraxial method to estimate the influence of variations in ocular biometry on changes in refractive error (S) at a population level and apply this method to literature data. METHODS: Error propagation was applied to two methods of eye modelling, referred to as the simple method and the matrix method. The simple method defines S as the difference between the axial power and the whole-eye power, while the matrix method uses more accurate ray transfer matrices. These methods were applied to literature data, containing the mean ocular biometry data from the SyntEyes model, as well as populations of premature infants with or without retinopathy, full-term infants, school children and healthy and diabetic adults. RESULTS: Applying these equations to 1000 SyntEyes showed that changes in axial length provided the most important contribution to the variations in refractive error (57%-64%), followed by lens power/gradient index power (16%-31%) and the anterior corneal radius of curvature (10%-13%). All other components of the eye contributed <4%. For young children, the largest contributions were made by variations in axial length, lens and corneal power for the simple method (67%, 23% and 8%, respectively) and by variations in axial length, gradient lens power and anterior corneal curvature for the matrix method (55%, 21% and 14%, respectively). During myopisation, the influence of variations in axial length increased from 54.5% to 73.4%, while changes in corneal power decreased from 9.82% to 6.32%. Similarly, for the other data sets, the largest contribution was related to axial length. CONCLUSIONS: This analysis confirms that the changes in ocular refraction were mostly associated with variations in axial length, lens and corneal power. The relative contributions of the latter two varied, depending on the particular population.

Estimating the astigmatic power of the crystalline lens and eye from ocular biometry.

PURPOSE: To estimate the astigmatic power of the crystalline lens and the whole eye without phakometry using a set of linear equations and to provide estimates for the astigmatic powers of the crystalline lens surfaces. METHODS: Linear optics expresses astigmatic powers in the form of matrices and uses paraxial optics and a 4 × 4 ray transfer matrix to generalise Bennett's method comprehensively to include astigmatic elements. Once this is established, the method is expanded to estimate the contributions of the front and back lens surfaces. The method is illustrated using two examples. The first example is of an astigmatic model eye and compares the calculated results to the original powers. In the second example, the method is applied to the biometry of a real eye with large lenticular astigmatism. RESULTS: When the calculated powers for the astigmatic model eye were compared to the actual powers, the difference in the power of the eye was 0.03 0.13 0.04 T D $$ {\left(0.03\kern0.5em 0.13\kern0.5em 0.04\right)}^{\mathrm{T}}\ \mathrm{D} $$ (where T represents the matrix transpose) and for the crystalline lens, the difference was 0.08 0.29 0.08 T D $$ {\left(0.08\kern0.5em 0.29\kern0.5em 0.08\right)}^{\mathrm{T}}\ \mathrm{D} $$ (power vector format). A second example applies the method to a real eye, obtaining lenticular astigmatism of -5.84 × 175. CONCLUSIONS: The method provides an easy-to-code way of estimating the astigmatic powers of the crystalline lens and the eye.

Five-year changes in macular thickness in the elderly population: A cohort study.

BACKGROUND: The aim of this study is to determine the 5-year changes in macular thickness and related factors. METHODS: Data were from the second (2014) and third (2019) phases of the Shahroud Eye Cohort Study. Examinations included measurement of uncorrected and best-corrected visual acuity, non-cycloplegic autorefraction, slit-lamp biomicroscopy, and funduscopy. Participants underwent Cirrus HD-OCT 4000 (Carl Zeiss Meditec, Dublin, CA). RESULTS: The 5-year changes (95% confidence interval) of central and overall macular thicknesses were - 3.48 ± 8.16 µ (-3.92, -3.03) and - 0.79 ± 4.06 µ (-1.03, -0.54), respectively. The median and IQR of 5-year changes in the central subfield thickness were -3 and 10, although they were 0 and 5 in the overall macular thickness, respectively. Multiple regression model showed the central macular thickness (CMT) decreased with a U-shape pattern with increasing age. The 5-year changes in CMT were significantly lower in females compared to males ß = -1.55; (-2.78, -0.32) and in smokers compared to non-smokers ß = -1.92; (-3.55, -0.28). Moreover, higher body mass index ß = -0.12; (-0.22, -0.02) and CMT at baseline ß = -0.08; (-0.10, -0.06) were significantly associated with lower CMT changes. The average 5-year changes in overall macular thickness showed a non-linear decrease with age and was significantly higher in females ß = 0.93; (0.4, 1.43). These changes were directly related to the anterior chamber depth ß = 0.87; (0.10, 1.64) in the baseline. CONCLUSIONS: The macular thickness decreased slightly after 5 years; however, this change is not clinically significant. Demographic factors such as age and sex and refractive errors were significantly related to macular thickness changes.

Determination of progressive endothelial cell loss after posterior chamber phakic intraocular lens implantation.

Comments about endothelial cell loss after posterior chamber phakic intraocular lens are provided, with a particular emphasis on the importance of determining progressive postoperative cell density reduction, excluding that related to surgical trauma.

Refraction and ocular biometric parameters of preschool children in the Beijing whole childhood eye study: the first-year report.

BACKGROUND: Prevention of myopia should begin before school age. However, few population-based cohort studies have investigated refractive status in preschool children with cycloplegia. This study aimed to investigate the post-COVID-19 refraction and ocular biometric parameters of preschool children in Beijing Tongzhou District. METHODS: A population-based cohort study of kindergarten children in Tongzhou District, Beijing, commenced in November 2021. The present study reports data from the first year of the aforementioned population-based study. We selected children aged 3-6 years from nine kindergartens. Biometric parameters, including axial length (AL), anterior chamber depth (ACD), and corneal radius of curvature (CR), were collected before cycloplegia. Cycloplegic refraction was also measured. The spherical equivalent (SE), lens power (LP), and AL-to-CR ratio were calculated. Multiple linear regression analysis was used to analyse the correlation between refraction and ocular biometric parameters. RESULTS: A total of 1,505 children completed the examination, and a mean SE of 1.24 ± 0.91 D was found. The overall prevalence of myopia was 1.93%. The mean AL, ACD, CR, LP, and AL-to-CR ratio were 22.24 ± 0.70 mm, 3.28 ± 0.26 mm, 7.77 ± 0.26 mm, 26.01 ± 1.56 D, and 2.86 ± 0.07, respectively. Longer AL, deeper ACD, larger AL-to-CR ratio, and lower LP were associated with older age; the CR was not significantly different among different ages. In the multiple linear regression analysis, after adjusting for sex and age, the model that included AL, CR, and LP explained 87% of the SE variation. No differences were observed in the prevalence of myopia or the SE in this particular age range. CONCLUSION: The findings of this study suggest that a large proportion of preschool children in Beijing are mildly hyperopic, with a considerably low prevalence of myopia. In preschool children, refractive development was found to present mild hyperopia rather than emmetropia or myopia, a phenomenon that is characteristic of this age range.

Effects of atropine and tropicamide on ocular biological parameters in children: a prospective observational study.

BACKGROUND: The effectiveness of cycloplegia in delaying the progression of myopia and its application in refractive examination in children have been extensively studied, but there are still few studies on the effects of atropine/tropicamide on ocular biological parameters. Therefore, the purpose of this study was to explore the effects of atropine/tropicamide on children's ocular biological parameters in different age groups and the differences between them. METHODS: This was a prospective observational study in which all school children were examined for dioptres and ocular biological parameters in the outpatient clinic, and 1% atropine or tropicamide was used for treatment. After examination, we enrolled the patients grouped by age (age from 2 to 12 years treated by atropine, 55 cases; age from 2 to 10 years treated by tropicamide, 70 cases; age from 14 to 17 years treated by tropicamide, 70 cases). The ocular biological parameters of each patient before and after cycloplegia were measured, and the difference and its absolute value were calculated for statistical analysis using an independent-samples t test. RESULTS: We compared the value and the absolute value of the differences in ocular biological parameters before and after cycloplegia in the same age group, and we found that the differences were not statistically significant (P > 0.05). There were significant differences in the corresponding values of AL, K1 and ACD among the different age groups (P < 0.05). Before cycloplegia, there were significant differences in AL, K, K1, K2 and ACD in different age groups (P < 0.05). However, the differences in AL, K, K1, K2 and ACD among different age groups disappeared after cycloplegia (P > 0.05). CONCLUSIONS: This study demonstrated that atropine/tropicamide have different effects on cycloplegia in children of different ages. The effects of atropine/tropicamide on ocular biological parameters should be fully considered when evaluating the refractive state before refractive surgery or mydriasis optometry for children of different ages.

Investigation of ocular biometry in 4- to 9-year-old Chinese children.

PURPOSE: To investigate the distribution and changes in ocular biometry in 4-to to 9-year-old Chinese children and to compare the differences between age and genders in these parameters. METHODS: This was a school-based cross-sectional study. A total of 1,528 Chinese children, aged 4-9 years, from one primary school and 12 kindergartens, were included in the study. Axial length, corneal curvature, anterior chamber depth, and corneal diameter were measured for each child. RESULTS: AL and anterior chamber depth gradually increased with age in both genders. No significant changes in corneal curvature or corneal diameter were detected at different ages in either genders group. The mean ALs of males and females were 22.94 ± 0.80 mm and 22.38 ± 0.79 mm, respectively. The mean corneal curvatures of males and females were 43.05 ± 1.37 D and 43.75 ± 1.48 D, respectively. The mean anterior chamber depth of males and females were 3.47 ± 0.24 mm and 3.38 ± 0.25 mm, respectively. The mean corneal diameter of males and females were 12.08 ± 0.43 mm and 11.94 ± 0.44 mm, respectively. Females had consistently shorter ALs, shorter anterior chamber depth, smaller corneal diameter, and steeper corneal curvatures than males at any age. CONCLUSIONS: Boys had larger dimensions than girls for all ocular parameters except corneal curvature (flatter). Boys and girls showed similar trends for all parameters. Axial length and anterior chamber depth increased from 4 to 9 years of age, whereas corneal diameter and curvature did not change with age in either genders.

Evaluation and comparison of ocular biometric parameters obtained with Tomey OA-2000 in silicone oil-filled aphakic eyes.

PURPOSE: To evaluate a new non-contact instrument (OA-2000) measuring the ocular biometry parameters of silicone oil (SO)-filled aphakic eyes, as compared with IOLMaster 700. METHODS: Forty SO-filled aphakic eyes of 40 patients were enrolled in this cross-sectional clinical trial. The axial length (AL), central corneal thickness (CCT), keratometry ((flattest keratometry) Kf and (steep keratometry, 90° apart from Kf) Ks), and axis of the Kf (Ax1) were measured with OA-2000 and IOLMaster 700. The coefficient of variation (CoV) was calculated to assess the repeatability. The correlation was evaluated by the Pearson coefficient. Bland-Altman analysis and paired t test were used to analyze the agreements and differences of parameters measured by the two devices, respectively. RESULTS: The mean AL obtained with the OA-2000 was 23.57 ± 0.93 mm (range: 21.50 to 25.68 mm), and that obtained with the IOLMaster 700 was 23.69 ± 0.94 mm (range: 21.85 to 25.86 mm), resulting in a mean offset of 0.124 ± 0.125 mm (p < 0.001). The mean offset of CCT measured by OA-2000 and IOLMaster 700 was 14.6 ± 7.5 µm (p < 0.001). However, the Kf, Ks and Ax1 values from the two devices were comparable (p > 0.05). All the measured parameters of the two devices showed strong linear correlations (all r ≥ 0.966). The Bland-Altman analysis showed a narrow 95% limits of agreement (LoA) of Kf, Ks and AL, but 95%LoA of CCT and Ax1 was wide, which were - 29.3 ~ 0.1 µm and-25.9 ~ 30.7°respectively. The CoVs of the biometric parameters obtained with OA-2000 were lower than 1%. CONCLUSION: In SO-filled aphakic eyes, the ocular parameters (including AL, Kf, Ks, Ax1, and CCT) measured by the OA-2000 and IOLMaster 700 had a good correlation. Two devices had an excellent agreement on ocular biometric measurements of Kf, Ks and AL. The OA-2000 provided excellent repeatability of ocular parameters in SO-filled aphakic eyes.

The association between time spent on screens and reading with myopia, premyopia and ocular biometric and anthropometric measures in 6- to 7-year-old schoolchildren in Ireland.

PURPOSE: More time spent on near tasks has consistently been associated with the promotion of myopia. The World Health Organization advises limiting daily screentime to less than 2 h for children aged five and over. This study explored the relationship between time spent on screens and reading/writing with refractive status, ocular biometric and anthropometric factors in 6- to 7-year-olds in Ireland. METHODS: Participants were 723 schoolchildren (377 boys [51.8%]), mean age 7.08 (0.45) years. The examination included cycloplegic autorefraction (1% cyclopentolate hydrochloride), ocular biometry (Zeiss IOLMaster), height (cm) and weight (kg). Screentime and reading/writing time were reported by parents/legal guardians by questionnaire. Myopia (≤-0.50D) and premyopia (>-0.50D ≤ 0.75D) risk assessments were performed using logistic regression, and multivariate linear regression was used to analyse continuous variables. RESULTS: Reported daily screentimes were 31% <1 h, 49.5% 1-2 h, 15.6% 2-4 h and 3.9% >4 h. Reading/writing times were 42.2% frequently, 48.0% infrequently and 9.8% seldom/never. Linear regression, controlling for age and ethnicity, revealed >2 h/day on screens was associated with a more myopic spherical equivalent [ß = -1.15 (95% confidence intervals {CIs}: 1.62-0.69, p < 0.001)], increased refractive astigmatism (ß = 0.29, CI: 0.06-0.51, p = 0.01), shorter corneal radius (ß = 0.12, CI: 0.02-0.22, p = 0.02), higher axial length/corneal radius (ß = 0.06, CI: 0.03-0.09, p < 0.001), heavier weight (ß = 1.60, CI: 0.76-2.45, p < 0.001) and higher body mass index (BMI) (ß = 1.10, CI: 0.28-1.12, p < 0.001). Logistic regression, controlling for age and ethnicity, revealed daily screentime >2 h was associated with myopia (OR = 10.9, CI: 4.4-27.2, p = 0.01) and premyopia (OR = 2.4, CI: 1.5-3.7, p < 0.001). Frequent reading/writing was associated with screentime ≤2 h/day (OR = 3.2, CI: 1.8-5.8, p < 0.001). CONCLUSION: Increased screentime was associated with a more myopic refraction, higher axial length/corneal radius ratio, increased odds of myopia, premyopia, higher degrees of astigmatism, increased weight, BMI and decreased reading/writing time. Dedicated education programmes promoting decreased screentime in children are vital to prevent myopia and support eye and general health.

Refractive development I: Biometric changes during emmetropisation.

PURPOSE: Although there are many reports on ocular growth, these data are often fragmented into separate parameters or for limited age ranges. This work intends to create an overview of normal eye growth (i.e., in absence of myopisation) for the period before birth until 18 years of age. METHODS: The data for this analysis were taken from a search of six literature databases using keywords such as "[Parameter] & [age group]", with [Parameter] the ocular parameter under study and [age group] an indication of age. This yielded 34,409 references that, after screening of title, abstract and text, left 294 references with usable data. Where possible, additional parameters were calculated, such as the Bennett crystalline lens power, whole eye power and axial power. RESULTS: There were 3422 average values for 17 parameters, calculated over a combined total of 679,398 individually measured or calculated values. The age-related change in refractive error was best fitted by a sum of four exponentials (r2  = 0.58), while all other biometric parameters could be fitted well by a sum of two exponentials and a linear term ('bi-exponential function'; r2 range: 0.64-0.99). The first exponential of the bi-exponential fits typically reached 95% of its end value before 18 months, suggesting that these reached genetically pre-programmed passive growth. The second exponentials reached this point between 4 years of age for the anterior curvature and well past adulthood for most lenticular dimensions, suggesting that this part represents the active control underlying emmetropisation. The ocular components each have different growth rates, but growth rate changes occur simultaneously at first and then act independently after birth. CONCLUSIONS: Most biometric parameters grow according to a bi-exponential pattern associated with passive and actively modulated eye growth. This may form an interesting reference to understand myopisation.

Feasibility and repeatability of ocular biometry measured with IOLMaster 700 in a large population-based study.

PURPOSE: To evaluate the feasibility and repeatability of IOLMaster 700 biometry measurements in an adult population. Furthermore, to assess the value of the Quality Indicators (QIs) provided by the device. METHOD: As part of the large population-based Leipzig Research Centre for Civilization Diseases (LIFE) Adult-Study, randomly selected participants from Leipzig, Germany were evaluated with the ZEISS IOLMaster 700. Age range was 26-85 years, with 53% of participants above 70 years of age. Axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT) and keratometry (K) were assessed in 1767 right eyes. Measurements were repeated twice and in a subset of 1331 eyes, three times. Measurement feasibility was evaluated for three levels; successful, with warnings and failed, using the inbuilt QIs. Repeatability was assessed as within-subject standard deviation (SD) and repeatability limits were calculated. RESULTS: First measurement success rate for phakic eyes was over 99% for AL, CCT, ACD, over 98% for LT and over 97% for K. K had 16% eyes with warnings and the recommendation to repeat the measurement. Excluding the measurements with warnings resulted in a reduction of mean SD for AL from 48 to 4 µm and for mean K from 0.08 to 0.04 D. Repeatability for phakic eyes was 8 µm for AL, CCT, ACD and LT and 2.3 µm for CCT; 0.07 D and 0.12 D for mean K and delta K, respectively, for phakic cases without warnings (two measurements). CONCLUSIONS: In our population-based sample, the IOLMaster 700 collected data for AL, CCT, ACD, LT and K from the vast majority of eyes. Considering the built-in QIs improved the measurement variability substantially. Repeatability measurements indicate that clinically meaningful changes can be detected reliably with this instrument.

Effect of low-dose atropine (0.01%) on crystalline lens power among school-aged children with progressive myopia.

PURPOSE: To evaluate the change in crystalline lens power (LP) in a cohort of Indian children with progressive myopia receiving atropine (0.01%) compared with an untreated control group. DESIGN: Nonrandomised clinical trial. METHODS: The study included 120 children (70 in the atropine group; 50 in the control group) with progressive myopia (≥0.5 D/year) with a 1-year follow-up. The atropine group received 0.01% atropine eye drops once daily in both eyes, whereas the control group received no treatment. Changes in cycloplegic spherical equivalent, axial length (AL), keratometry (KER), anterior chamber depth (ACD) and lens thickness (LT) were recorded. LP was calculated using the formula proposed by Bennett. RESULTS: Mean myopia progression at year 1 was significantly less in the atropine group (-0.18 D [0.2]) than in the control group (-0.59 [0.21]; p < 0.001). The increase in AL was significantly different between the two groups (atropine: 0.21 mm [0.12]; control: 0.29 mm [0.11], p < 0.001). A significantly greater loss of LP was noted in the atropine group (-0.67 D [0.34]) than in the placebo group (-0.28 D [0.42]; p < 0.001). The change in LT was significantly different between the atropine and control groups (p = 0.02), whereas the change in ACD and KER was similar in the two groups. CONCLUSION: The greater loss of LP could contribute to the anti-myopia effect of atropine and should therefore be evaluated in studies reporting the efficacy of atropine on myopia to assess its actual effect on myopic progression.

Phakic iris-claw intraocular lens: calculations of power and long-term endothelial cells loss.

A correction about phakic intraocular lens power calculation process, as it was stated by Li, Song & Song, is provided. It is explained that this calculation is based on the Van der Heijde formula and not on biometric formulas. A comment about the mechanisms of late endothelial cell loss following phakic intraocular lenses is done.

Associations between anterior segment biometry and high axial myopia in 3438 cataractous eyes in the Chinese population.

BACKGROUND: To investigate the associations between anterior segment biometry and high axial myopia in cataractous eyes in the Chinese population. METHODS: Data on 3438 eyes from 3438 subjects were analyzed in this cross-sectional study. Anterior segment biometry, axial length measurements, and intraocular pressure evaluation were implemented using an Oculus Pentacam HR, a Zeiss IOLMaster 500, and a Nidek TonoRef II, respectively. A multivariate-adjusted logistic model and a multivariate-adjusted linear model were used for statistical analysis. RESULTS: The mean age of the subjects was 62.2 ± 10.6 years, and 56.4% were female. There were 2665 subjects with high axial myopia (axial length, ≥26.50 mm) and 773 without (axial length, < 26.50 mm). The characteristics independently associated with high axial myopia included lower total corneal refractive power, a more negative Q value, greater total corneal astigmatism, greater white-to-white corneal diameter, greater anterior chamber depth, and higher intraocular pressure (all P <  0.05). In addition, greater axial length correlated with a thicker temporal cornea and a thinner nasal cornea (both P <  0.001). CONCLUSIONS: For cataractous eyes, high axial myopia was associated with corneal flattening, increased total corneal astigmatism, anterior segment enlargement, and intraocular pressure elevation. The findings may inform the choice of intraocular lenses and the calculation of their power, help improve the surgical practice of refractive cataract procedures, and provide useful information on the centration and stability of intraocular lenses.

Ocular biometry with swept-source optical coherence tomography-based optical biometer in Japanese patients with EYS-related retinitis pigmentosa: a retrospective study.

BACKGROUND: This study aimed to identify the features of ocular biometry in patients with EYS-related retinitis pigmentosa using IOLMaster 700. METHODS: We retrospectively reviewed the medical records of patients with retinitis pigmentosa. Patients with records of the following were included: (1) ocular biometry measurements using the IOLMaster 700 and (2) genetic diagnostic tests. Axial length, keratometry, anterior chamber depth, aqueous depth, lens thickness, central corneal thickness (CCT), and corneal diameter (white to white) measurements were extracted. Based on keratometry measurements, (1) standard keratometric astigmatism, (2) posterior corneal astigmatism, and (3) total corneal astigmatism were obtained. Demographics and biometric parameters were compared between patients with EYS-related retinitis pigmentosa and other patients with retinitis pigmentosa. RESULTS: A total of 86 eyes of 44 patients (23 females and 21 males; mean age: 47.7 years) with retinitis pigmentosa were included. Of these, 18 were identified as having EYS variants. CCT was significantly thinner (P < 0.001) and the posterior corneal curvature at the steepest meridian was significantly smaller (P = 0.024) in patients with EYS-related retinitis pigmentosa than in other patients with retinitis pigmentosa. The magnitudes of all corneal astigmatism measurements was higher in patients with EYS-related RP, although these differences were not statistically significant. CONCLUSION: Patients with EYS-related retinitis pigmentosa had unique features in ocular biometry, such as thinner central corneal thickness and smaller posterior corneal curvature radius at the steepest meridian compared with other patients with retinitis pigmentosa. The findings suggest that patients with retinitis pigmentosa have different ocular dimension features among the different causative genes.

Normal range of ocular biometry in healthy children: A systemic review and meta-analysis of 33,559 individuals under seven years of age.

PURPOSE: To conduct a systemic review and meta-analysis on the normative range of ocular biometry in healthy children under seven years of age. METHODS: A literature search was performed using the PubMed (MEDLINE) database. The main outcomes were normative values of axial length (AL), central corneal thickness (CCT), cornea curvature (CC), anterior chamber depth (ACD), lens thickness (LT) and vitreous chamber depth (VCD). Pooled estimates were obtained with a random-effects meta-analysis. Multivariate meta-regressions ascertained the moderator-related trends. RESULTS: We included 47 studies for a total of 33,559 subjects. The pooled ALs for 0.0-1.9 years, 2.0-3.9 years and 4.0-6.9 years were 18.33 mm (95% confidence interval [CI] 17.57-19.09), 21.71 mm (21.49-21.93) and 22.37 mm (22.29-22.45), respectively. Children aged 0.0-1.9 years had a greater CCT (576.70 µm, 567.20-586.21), steeper cornea (7.41 mm, 7.16-7.65) and shallower ACD (2.46 mm, 2.23-2.69). LT ranged from 3.65 to 3.74 mm for 0-6 years, and VCD increased from 11.94 mm at birth to 15.36 mm at 4.0-6.9 years. Differences in AL between East Asian and non-East Asian children were found below two years of age (17.30 mm vs. 18.40 mm, p = 0.008) and for CC at 4.0-6.9 years of age (7.82 mm vs. 7.79 mm, p = 0.004). In a multivariate meta-regression, AL, CC, ACD and VCD increased with age (p < 0.05 for all), while CCT decreased with age (p = 0.0007). CONCLUSIONS: This study reports normative data for ocular biometry in children. Few differences were found with ethnicity in the ocular biometry of infants and pre-schoolers.

Ciliary muscle thickness in adults with Down syndrome.

PURPOSE: The relationship between ciliary muscle thickness (CMT), age and refractive error was investigated to determine if CMT, like other anterior ocular anatomy, differs in adults with Down syndrome (DS). METHODS: The CMT of 33 adults with DS was imaged using anterior segment optical coherence tomography. Images from the right eye obtained 45 minutes after cycloplegia (1% tropicamide, 2.5% phenylephrine) were analysed to calculate thickness at 1, 2 and 3 mm posterior to the scleral spur (CMT1, CMT2, CMT3), maximum thickness (CMTMAX) and apical thickness (AT = CMT1 - CMT2). Spherical equivalent refractive error was determined by clinical refraction using both non-dilated and dilated measures. Multivariate regression analysis evaluated the relationship between CMT and refractive error while controlling for subject age. RESULTS: Images were analysed from 26 subjects (mean age (SD) 29 years; mean refractive error (SD): -0.90 (5.03) D, range: -15.75 to +5.13D). Mean (SD) CMT decreased with posterior position (CMT1: 804 (83) µm; CMT2: 543 (131) µm; CMT3: 312 (100) µm). Mean (SD) CMTMAX and AT was 869 (57) µm and 260 (84) µm, respectively. There was a significant linear correlation indicating thinning CMT with increasing age for CMT1 and CMT2 (p ≤0.05). CMT2 and CMT3 had a significant negative correlation (thicker muscle with increasing myopic refractive error) (p ≤0.01). AT had a significant positive correlation (thicker muscle with increasing hyperopic refractive error) (p <0.01). CONCLUSIONS: Ciliary muscle thickness in participants with DS was found to be in a similar range with similar refractive error trends to previous reports of individuals without DS. However, it is important to note that the refractive error trends were driven by individuals with moderate to high levels of myopia.

In vivo analysis of ciliary muscle in myopic Chinese young adults using ArcScan Insight® 100.

OBJECTIVE: To analyse the morphological characteristics of the ciliary muscle (CM) and to explore its relationship with different ocular biometric parameters in myopic young Chinese adults. METHODS: This observational, cross-sectional study included 50 right eyes from 50 myopic adults. The CM area (CMA), CM thickness (CMT) and CM length (CML) were measured using the ArcScan Insight® 100. CMT was determined at three points: 1.0 mm (CMT-1), 2.0 mm (CMT-2) and 3.0 mm (CMT-3) posterior to the scleral spur. CML was measured on the scleral (CMLs) and vitreous (CMLv) aspects. The spherical equivalent refraction (SER), axial length (AL) and subfoveal choroidal thickness (SFCT) were examined to determine their associations with CM parameters (CMA, CML and CMT). RESULTS: The mean SER and AL were -4.39 ± 2.29 D and 25.61 ± 1.15 mm, respectively. Compared with the nasal CMA, CML and CMT (CMT-1, CMT-2 and CMT-3) findings, the temporal CM parameters (CMA, CMLs, CMLv, CMT-1, CMT-2 and CMT-3) were found to be significantly thicker (all p < 0.001, except CMLv and CMT-1; p < 0.01). The nasal CMA was associated with the average corneal curvature (r = 0.30, p = 0.03) and SER (r = -0.30, p = 0.04). Nasal and temporal CMT-2 were negatively correlated with SER (r = -0.33 and -0.32, respectively, both p < 0.05). There was no correlation between CM parameters (except nasal CMLs, r = 0.31, p = 0.03) and SFCT, or between CM parameters and either the AL or anterior chamber depth (all p > 0.05). CONCLUSION: These results suggest that there is temporal versus nasal asymmetry of the CM. CMA, CMT or CML did not vary with axial growth of the eye. The CM is not simply stretched as the eye elongates in myopic young adults.