Ocular Component Growth Curves among Singaporean Children with Different Refractive Error Status (original) (raw)
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Understanding the normal functioning of the human lens and its role in the development of disorders of vision, such as presbyopia and cataract, requires a thorough knowledge of how the lens grows and how its properties change with age. Many of these properties can be obtained only by studying the isolated organ in vitro. In addition, because of the difficulties in obtaining human tissues, animal lenses are frequently used as models for the human lens. Information is needed for these as well. In this review, current knowledge of lens growth and factors that affect growth are examined in a variety of species. Topics covered include changes in lens weight, dimensions, stiffness and refractive index distribution with age and the influence of other factors such as gender, environment and body size. From these, it has become clear that lens growth is not greatly affected by external influences. Although there are many similarities in the growth of lenses from different species, humans (and probably all primates) have distinctly different growth patterns, with prenatal and postnatal growth having different regulatory mechanisms. As a result, human lens properties are different from those of other species. Unfortunately, many of the published data are unreliable, presumably because of post-mortem changes, making it difficult to extrapolate in vitro observations to the in vivo situation. Figure 7. The relationship between (A) lens diameter and (B) thickness and age. Data were obtained from Glasser and Campbell 19 ( ), Jones and colleagues 20 ( ), Larsen 21 (᭹), Moffatt, Atchison and Pope 22 ( ), Pierscionek and Augusteyn 23 ( ), Rosen and associates 24 ( ), Schacchar 25 , ( ) and Smith 26 ( ). Growth of the lens Augusteyn Figure 11. Refractive index gradients along (A) the equatorial and (B) the sagittal axes for a 27-year-old ( ) and a 63-year-old ( ) lens. The data, which were kindly supplied by Drs C Jones and J Pope, were obtained using MRI. 46
Comparison of Ocular Component Growth Curves among Refractive Error Groups in Children
Investigative Ophthalmology & Visual Science, 2005
PURPOSE. To compare ocular component growth curves among four refractive error groups in children. METHODS Cycloplegic refractive error was categorized into four groups: persistent emmetropia between Ϫ0.25 and ϩ1.00 D (exclusive) in both the vertical and horizontal meridians on all study visits (n ϭ 194); myopia of at least Ϫ0.75 D in both meridians on at least one visit (n ϭ 247); persistent hyperopia of at least ϩ1.00 D in both meridians on all visits (n ϭ 43); and emmetropizing hyperopia of at least ϩ1.00 D in both meridians on at least the first but not at all visits (n ϭ 253). Subjects were seen for three visits or more between the ages of 6 and 14 years. Growth curves were modeled for the persistent emmetropes to describe the relation between age and the ocular components and were applied to the other three refractive error groups to determine significant differences. RESULTS At baseline, eyes of myopes and persistent emmetropes differed in vitreous chamber depth, anterior chamber depth, axial length, and corneal power and produced growth curves that showed differences in the same ocular components. Persistent hyperopes were significantly different from persistent emmetropes in most components at baseline, whereas growth curve shapes were not significantly different, with the exception of anterior chamber depth (slower growth in persistent hyperopes compared with emmetropes) and axial length (lesser annual growth per year in persistent hyperopes compared with emmetropes). The growth curve shape for corneal power was different between the emmetropizing hyperopes and persistent emmetropes (increasing corneal power compared with decreasing power in emmetropes). CONCLUSIONS Comparisons of growth curves between persistent emmetropes and three other refractive error groups showed that there are many similarities in the growth patterns for both the emmetropizing and persistent hyperopes, whereas the differences in growth lie mainly between the emmetropes and myopes.
Growth of the human lens in the Indian adult population: Preliminary observations
Indian Journal of Ophthalmology, 2012
The eye lens grows throughout life by the addition of new cells inside the surrounding capsule. How this growth affects the properties of the lens is essential for understanding disorders such as cataract and presbyopia. Aims: To examine growth of the human lens in the Indian population and compare this with the growth in Western populations by measuring in vitro dimensions together with wet and dry weights. Settings and Design: The study was conducted at the research wing of a tertiary eye care center in South India and the study design was prospective. Materials and Methods: Lenses were removed from eye bank eyes and their dimensions measured with a digital caliper. They were then carefully blotted dry and weighed before being placed in 5% buffered formalin. After 1 week fixation, the lenses were dried at 80 °C until constant weight was achieved. The constant weight was noted as the dry weight of the lens. Statistical Analysis Used: Lens parameters were analyzed as a function of age using linear and logarithmic regression methods. Results: Data were obtained for 251 lenses, aged 16-93 years, within a median postmortem time of 22 h. Both wet and dry weights increased linearly at 1.24 and 0.44 mg/year, respectively, throughout adult life. The dimensions also increased continuously throughout this time. Conclusions: Over the age range examined, lens growth in the Indian population is very similar to that in Western populations.
Axial Growth and Lens Power Loss at Myopia Onset in Singaporean Children
Investigative Opthalmology & Visual Science
PURPOSE. We studied biometry changes before and after myopia onset in a cohort of Singaporean children. METHODS. All data were taken from the Singapore Cohort Study of the Risk Factors for Myopia (SCORM). Participants underwent refraction and biometry measurements with a follow-up of 3 to 6 years. The longitudinal ocular biometry (spherical equivalent refraction, axial length, and lens power) changes were compared between children who suffered myopia during the study (N ¼ 303), emmetropic children (N ¼ 490), and children myopic at baseline (N ¼ 509). RESULTS. At myopia onset, the myopic shift increased to 0.50 diopters (D)/y or more in new myopes compared to the minor changes in emmetropes of the same age. New myopes had higher axial growth rates than emmetropes, even years before myopia onset (0.37 and 0.14 mm/y, respectively; ANOVA with Bonferroni post hoc test, P < 0.001). After onset, the change in both parameters slowed down gradually, but significantly (P < 0.05). In new myopes, lens power loss (À0.71 D/y) was significantly higher up to 1 year before myopia onset compared to emmetropes (À0.46 D/y), after which lens power loss slows down rapidly. At age 7 years, (future) new myopes had lens power values close to those of emmetropes (25.12 and 25.23 D, respectively), while later these values approached those of children who were myopic at baseline (23.06 and 22.79 D, respectively, compared to 23.71 D for emmetropes; P < 0.001). CONCLUSIONS. New myopes have higher axial growth rates and lens power loss before myopia onset than persistent emmetropes.
Eye growth changes in myopic children in Singapore
British Journal of Ophthalmology, 2005
Aims: To assess the longitudinal changes in biometric parameters and associated factors in young myopic children aged 7-9 years followed prospectively in Singapore. Methods: Children aged 7-9 years from three Singapore schools were invited to participate in the SCORM (Singapore Cohort study Of the Risk factors for Myopia) study. Yearly eye examinations involving biometry measures were performed in the schools. Only myopic children (n = 543) with 3 year follow up data were included in this analysis.
Corneal and Crystalline Lens Dimensions Before and After Myopia Onset
Optometry and Vision Science, 2012
Purpose-To describe corneal and crystalline lens dimensions before, during, and after myopia onset compared to age-matched emmetropic values. Methods-Subjects were 732 children 6 to 14 years of age who became myopic and 596 emmetropic children participating between 1989 and 2007 in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error Study. Refractive error was measured using cycloplegic autorefraction, corneal power using a hand-held autokeratometer, crystalline lens parameters using video-based phakometry, and vitreous chamber depth (VCD) using A-scan ultrasonography. Corneal and crystalline lens parameters in children who became myopic were compared to age-, gender-, and ethnicity-matched model estimates of emmetrope values annually from 5 years before through 5 years after the onset of myopia. The comparison was made without, then with statistical adjustment of emmetrope component values to compensate for the effects of longer VCDs in children who became myopic. Results-Before myopia onset, the crystalline lens thinned, flattened, and lost power at similar rates for emmetropes and children who became myopic. The crystalline lens stopped thinning, flattening, and losing power within ±1 year of onset in children who became myopic compared to emmetropes statistically adjusted to match the longer vitreous chamber depths of children who became myopic. In contrast, the cornea was only slightly steeper in children who became myopic compared to emmetropes (<0.25 D) and underwent little change across visits. Conclusions-Myopia onset is characterized by an abrupt loss of compensatory changes in the crystalline lens that continue in emmetropes throughout childhood axial elongation. The mechanism responsible for this decoupling remains speculative, but might include restricted equatorial growth from internal mechanical factors.
Understanding the normal functioning of the human lens and its role in the development of disorders of vision, such as presbyopia and cataract, requires a thorough knowledge of how the lens grows and how its properties change with age. Many of these properties can be obtained only by studying the isolated organ in vitro. In addition, because of the difficulties in obtaining human tissues, animal lenses are frequently used as models for the human lens. Information is needed for these as well. In this review, current knowledge of lens growth and factors that affect growth are examined in a variety of species. Topics covered include changes in lens weight, dimensions, stiffness and refractive index distribution with age and the influence of other factors such as gender, environment and body size. From these, it has become clear that lens growth is not greatly affected by external influences. Although there are many similarities in the growth of lenses from different species, humans (and probably all primates) have distinctly different growth patterns, with prenatal and postnatal growth having different regulatory mechanisms. As a result, human lens properties are different from those of other species. Unfortunately, many of the published data are unreliable, presumably because of post-mortem changes, making it difficult to extrapolate in vitro observations to the in vivo situation. Figure 7. The relationship between (A) lens diameter and (B) thickness and age. Data were obtained from Glasser and Campbell 19 ( ), Jones and colleagues 20 ( ), Larsen 21 (᭹), Moffatt, Atchison and Pope 22 ( ), Pierscionek and Augusteyn 23 ( ), Rosen and associates 24 ( ), Schacchar 25 , ( ) and Smith 26 ( ). Growth of the lens Augusteyn Figure 11. Refractive index gradients along (A) the equatorial and (B) the sagittal axes for a 27-year-old ( ) and a 63-year-old ( ) lens. The data, which were kindly supplied by Drs C Jones and J Pope, were obtained using MRI. 46
Growth of the eye lens II Allometric studies
It has long been known, from casual observation in the laboratory and elsewhere, that there are huge variations, not only in the size, but also in the properties of the eye lens, throughout the animal kingdom. Soft, easily deformed almost spherical lenses are found in the birds while those from most rodents and fish are also almost spherical, but rock-hard. Lenses from the higher order mammals are generally of intermediate hardness and ellipsoid in shape. Optical power varies because of differences in lens curvature and in the refractive index distribution. How such differences arise is not understood and little is known about the nature of factors which determine the final properties of the lens. Allometry offers a means for exploring some aspects of these.