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At least 289 records · Page 16Linked to original sources
PubMed2003

Quantification of recti eye muscle paths in high myopia.

PURPOSE: To elucidate the etiology of an acquired, restrictive motility disorder in patients with high myopia. METHODS: Thirty-three orbits were imaged using a Siemens Magnetom or Siemens Vision (both 1.5 Tesla) MRI (magnetic resonance imaging) scanner, applying a head coil. Coronal T1-weighted, spin-echo images were obtained. Orbits of three different patient groups were analyzed. Group 1 (n = 14): patients with high axial myopia and restricted eye motility (average axial length = 31.4 mm; refractive error more than -15 D). Group 2 (n = 8): subjects with high axial myopia and normal eye motility (average axial length = 29.2 mm). Controls (n = 11): emmetropic subjects with normal eye motility. RESULTS: Highly myopic patients showed significant displacements of recti EOMs in comparison to the controls. Mean displacements as measured in the plane 3 mm anterior to the globe-optic nerve junction in primary gaze were, in group 1: lateral rectus (LR) 2.9 mm (2.5 downward, 1.4 medial), medial rectus (MR) 1.3 mm downward. In group 2: LR 1.4 mm (1.3 downward, 0.6 medial) and MR 1.2 mm downward. In both groups 1 and 2, the inferior rectus (IR) was displaced 1.3 mm medially and upwards. In both groups of myopic patients the superior rectus (SR) was displaced 1.5 mm medially and downwards. CONCLUSIONS: In patients with high axial myopia, displacements of all recti EOMs can be detected by MRI. However, displacement of the LR into the lateral and inferior quadrant of the orbit is significantly greatest. We therefore assume LR displacement to be a major pathophysiological factor for the restrictive motility disorder in high myopia. EOM dislocations can be explained by myopia-associated alterations in the orbital connective tissues confining EOM positions in relation to the orbital wall.

Case-Control Studies↗
PubMed2005

Can alcohol lead to inhibition or disinhibition? Applying alcohol myopia to animal experimentation.

AIMS: Animal experimentation often demonstrates that alcohol leads to disinhibited behaviour, such as increased aggression, increased social behaviour, or increased impulsivity. However, human experimentation demonstrates that alcohol can have either disinhibiting or inhibiting effects on behaviour, depending on salient environmental cues. Our aim was to illustrate how alcohol myopia theory could be applied to the literature assessing the effects of alcohol on behaviour in animals. METHODS: The effects of alcohol on animal behaviour were reviewed in several domains, including aggression, social behaviours, and impulsivity. Suggestions for testing alcohol myopia with animal research paradigms were provided. RESULTS: Current animal research paradigms are often designed in such a way that alcohol myopia cannot be tested. To test alcohol myopia, we recommend manipulating the salience of both impelling and inhibiting environmental cues. CONCLUSIONS: Disinhibition alone cannot explain alcohol's effects on behaviour. We contend that alcohol myopia theory helps to explain some contradictory findings in the human and animal literature. We encourage animal researchers to develop research paradigms to provide tests of alcohol myopia.

Aggression↗
PubMed2001

Inhibition of myopia development in chicks using himbacine: a role for M(4) receptors?

The success of the M(1)-selective muscarinic antagonist pirenzepine in preventing myopia development in animal models implicates a role for the M(1) receptor. However, the relatively high dose of pirenzepine required may indicate that the drug acts through another receptor subtype. This study examined whether the M(4)-selective antagonist, himbacine, could also prevent myopia. Daily intravitreal injections of himbacine inhibited the inducement of myopia in chick eyes in a dose- dependent manner. Doses < or = 200 microg caused no significant inhibition of induced myopia compared to controls (-13.7 +/- 2.3 vs -16.2 +/- 0.9D, ANOVA p = 0.37), whilst a dose of 800 microg almost completely inhibited the induced myopia (-2.4 +/- 2.0, p < 0.01). Findings demonstrate himbacine is effective at preventing the development of myopia in chick and implicates a role for the M4 receptor.

Age Factors↗
PubMed1996

Clinical findings before the onset of myopia in youth: 3. Heterophoria.

BACKGROUND: Some contemporary theories of the etiology of youth onset myopia suggest differences in accommodation and convergence function. Previous studies have related esophoria to various aspects of myopia development. This paper examines whether differences in phorias exist before the onset of myopia. METHODS: A cohort of initially emmetropic children had eye and vision examinations at 6-month intervals for a period of 3 years. Dissociated phorias were measured by the von Graefe method. These prospective data were analyzed by: (1) comparing phorias in children who became myopic to those in children who remained emmetropic; (2) determination of sensitivity and specificity of phorias to distinguish between children who became myopic and those who did not; and (3) determining the change in phorias with time. These same analyses were also performed as additional analyses of some previously published retrospective private practice data. RESULTS: Distance phorias were not significantly different in the became-myopic and remained-emmetropic group by the Mann Whitney U test in either the private practice data or the prospective data. The near phoria was more convergent in the became-myopic group than in the remained-emmetropic group in the private practice data (p < 0.02 by Mann Whitney U test). In the prospective data there were proportionately more children who became myopic outside the near phoria range of 3 delta exo to 1 delta eso (p < 0.05 by chi 2 test). In both data sets the near phoria showed an eso shift with time in the children who became myopic, beginning before and continuing after the onset of myopia. The children in the remained-emmetropic groups did not show eso shifts in near phoria. CONCLUSIONS: A near phoria which is not close to orthophoria appears to be a risk factor for youth onset myopia, but sensitivity and specificity were not as high as those for other variables such as corneal power, axial length to corneal radius ratio, positive relative accommodation (PRA), and midpoint of the near fusional vergence range. The onset of myopia is associated with an eso (convergent) shift in the near phoria.

Child↗
PubMed1998

Role of the cornea in emmetropia and myopia.

The purpose of this paper is to review the available evidence concerning the role of the cornea in achieving and maintaining emmetropia, as well as its role in the development and progression of myopia. The role of the cornea in emmetropization is most evident at the two extremes of life. During infancy, when the axial length increases rapidly, both the cornea and the lens become flatter, moving the refractive state of the eye toward emmetropia; during the later years of life, when the axial length remains constant or even shortens, the cornea appears to steepen somewhat. When myopia develops, in some cases the cornea may undergo a "paradoxical" steepening, which accelerates, rather than retards, the development of myopia. The effect of the cornea on the development and progression of myopia is evident when the ratio of axial length to corneal radius--the AL/CR ratio--is considered. Recent studies suggest that a high AL/CR ratio, which has a value of approximately 3.0 in the emmetropic eye, is a risk factor for youth-onset myopia. Several studies have shown that myopic eyes have greater mean corneal powers than emmetropic eyes; this may be mostly due to greater corneal powers being a risk factor for youth-onset myopia.

Accommodation, Ocular↗
PubMed1999

Effects of spectacle intervention on the progression of myopia in children.

The literature on myopigenesis suggests an active emmetropization mechanism regulated by optical defocus. The strongest evidence comes from compensatory ocular growth in response to lens-induced defocus in different species of animals. Based on these results, it has been suggested that, however useful, spectacle intervention for the optical correction of human myopia would lead to its exacerbation. The present study seeks to evaluate the progression of juvenile-onset myopia in children differentiated by their lens wear patterns. Data from 43 myopes from our longitudinal study of refraction were evaluated, with myopia defined as a spherical equivalent of at least -0.50 D. Refractions were obtained in the laboratory by noncycloplegic retinoscopy performed by one experienced optometrist at regular intervals. Information regarding the subjects' prescription lens-wearing history was obtained from the subjects and their eye care providers. Based on their wearing patterns, subjects were divided into four categories: (1) full-time wearers; (2) myopes who switched from distance to full-time wear; (3) distance wearers; and (4) nonwearers. Exponential functions were fit to the individual refraction data. The age of onset of myopia, the mean myopia at onset of spectacle wear, and the refractive shift over a period of at least 3 years were derived from these fits. Results show that the 3-year refractive shifts are not significantly different among the four groups. A comparison of the extreme conditions, i.e., full-time vs. nonwear categories, also revealed no significant difference when the data were corrected for age effects despite the fact that the nonwearers exhibited an age-adjusted 3-year progression approximately one-half that of the full-time wearers. In summary, the present study failed to demonstrate any overall effects of spectacle intervention on the progression of human myopia. Further investigation using a larger sample is warranted.

Age of Onset↗
PubMed1999

A 2-year longitudinal study of myopia progression and optical component changes among Hong Kong schoolchildren.

This study investigated refractive error and optical component changes in a group of 142 Hong Kong schoolchildren from age 6 to 17 years over a 2-year period between 1991 and 1993. Subjects were refracted subjectively and corneal curvatures and ocular dimensions were measured. At the end of the 2-year study, the mean spherical equivalent refraction (SER) was -1.86 D (SD 1.99 D) and 62% of the schoolchildren were myopic. The annual incidence of myopia was 11.8%. Children aged 10 years and under had a greater change in SER toward myopia than older children. The annual rate of myopia progression for the myopic children was -0.46 D (SD 0.40 D) and the rate of progression was greatest between age 6 and 10 years old. Vitreous depth/axial length elongation was the main component contributing to the progression of myopia. Hong Kong schoolchildren develop myopia as early as 6 years old and myopia progresses at a greater rate compared with children of European extraction.

Adolescent↗
PubMed1999

Role of genetic factors in the etiology of juvenile-onset myopia based on a longitudinal study of refractive error.

In an attempt to determine the role of genetic factors in the development of myopia, we examined the relationship of infantile refractive error and parental history to juvenile-onset myopia and analyzed 43 pedigrees affected by juvenile-onset myopia. Refraction data collected at regular intervals from a sample of juvenile subjects participating in a 24-year longitudinal study of refractive error were used. Results showed that children with two myopic parents were 6.42 times as likely to become myopic as children with one or no myopic parents. Furthermore, children who had refractions in the lower half of the distribution at 6 to 12 months of age were 4.33 times as likely to develop myopia as children who had refractions in the upper half of the distribution at 6 to 12 months of age. The pedigree analysis indicated that 63% of individuals considered at risk for developing juvenile-onset myopia actually became myopic, with an equal number of affected males and females. These results suggest that juvenile-onset myopia of moderate amounts may be inherited as a complex trait involving both genetic and environmental factors.

Adolescent↗
PubMed1999

The effect of having myopic parents: an analysis of myopia in three generations.

PURPOSE: The etiology of myopia has been attributed to both genetic and environmental factors. The purpose of this paper is to attempt to distinguish between genetic and environmental factors in three generations of subjects from three locations. METHODS: Noncycloplegic autorefraction and distance visual acuity were measured in 3131 Chinese children 7 to 17 years old from Hong Kong, Tianjin, and Ban Chau. Data on the refractive status of the parents and grandparents were collected using questionnaires. Myopia was defined operationally as spherical equivalent refractive error (SER) of at least -1.00 D and uncorrected vision worse than logMAR 0.18 (6/9). RESULTS: The odds of having myopia for the grandparents', parents', and children's generations were 0.06, 0.26, and 0.35, respectively. Having myopic parents increased the odds ratio for having myopia (odds ratio 1.85 for children's generation and 6.71 for parents' generation), showing a genetic influence. However, the odds of having myopia also increased in offspring of nonmyopic parents between generation 2 and 3, suggesting an environmental influence. Results of prevalence and odds ratios from the three locations also demonstrated an environmental effect on development of myopia. CONCLUSION: We propose that myopic development in Chinese follows a multifactorial and polygenic model in which the genetic input has remained constant while the environmental influence has increased over the last three generations.

Adolescent↗
PubMed1999

Optical correction of induced axial myopia in the tree shrew: implications for emmetropization.

PURPOSE: To determine whether an active emmetropization mechanism is involved in the recovery from axial myopia through the use of a mammalian model of refractive development. Specifically, we sought to establish whether the emmetropization mechanism is visually guided by the level of clarity of the image falling on the retina, or if recovery is driven by a mechanism sensitive to abnormal eye shape. METHODS: Young tree shrews had axial myopia induced by monocular deprivation (MD) of pattern vision and then the myopic eye was either: (1) accurately corrected with a negative lens or (2) had a zero-powered lens placed in front of it. Their emmetropization response was monitored, both through the use of ocular refractive and biometric measures, as well as through the assessment of scleral dry weight and glycosaminoglycan synthesis, as indicators of scleral metabolism. RESULTS: Corrective lenses prevented recovery from induced myopia (-6.8 +/- 0.7 D after 5 days MD vs. -6.6 +/- 0.6 D after 5 days of lens wear), whereas animals fitted with zero-powered lenses displayed near full recovery from the induced myopia (-6.6 +/- 0.6 D vs. -1.7 +/- 0.3 D). Significant reductions in scleral dry weight (-4.6 +/- 1.3%) and glycosaminoglycan synthesis (-28.6 +/- 7.3%) were found in the posterior sclera of animals wearing corrective lenses. Conversely, animals wearing zero-powered lenses displayed elevated levels of glycosaminoglycan synthesis (+62.3 +/- 11.1%) in conjunction with scleral dry weights that did not differ significantly between treated and fellow control eyes (-1.5 +/- 2.6%). CONCLUSIONS: Accurate correction of induced axial myopia prevents the refractive, biometric and scleral metabolic responses that are normally observed in tree shrew eyes recovering from induced myopia. These findings support the hypothesis that recovery is driven by an active emmetropization response dependent on the clarity of image falling on the retina and not by a mechanism that is sensitive to abnormal eye shape.

Accommodation, Ocular↗
PubMed2000

Longitudinal changes in corneal asphericity in myopia.

PURPOSE: To report the change in shape of the peripheral cornea (asphericity, Q) as it relates to myopia progression in adolescence. METHODS: Forty-eight subjects with initial ages between 11 and 13 years of age were observed for 5 years. Each subject had participated in a variety of soft contact lens studies and all had worn daily wear soft contact lenses successfully for the 2 years before collection of the second data set. RESULTS: Myopia increased by an average of 1.46 D and was strongly correlated with a 0.56-mm increase in axial length. There was no contribution to the change in myopia from the change in central radius of the cornea. A significant (p < 0.01, one tail) correlation was found between Q and the progression of myopia. Principal axis analysis yielded a slope of -0.04 in Q per diopter of increase in myopia. CONCLUSION: These data show a shift to a more positive Q (in the oblate direction) with increased myopia.

Adolescent↗
PubMed2004

Prevalence of myopia in a group of Hong Kong microscopists.

PURPOSE: To study the prevalence and magnitude of myopia in a group of Hong Kong Chinese microscopists and compare it with that observed in microscopists working in the United Kingdom. METHODS: Forty-seven microscopists (36 women and 11 men) with a median age of 31 years and working in hospital laboratories throughout Hong Kong were recruited to the study. Information about past refractive corrections, microscopy work, and visual symptoms associated with microscope use were collected. All subjects had a comprehensive eye examination at The Hong Kong Polytechnic University Optometry Clinic, including measures of refractive error (both noncycloplegic and cycloplegic), binocular vision functions, and axial length. RESULTS: The prevalence of myopia in this group of microscopists was 87%, the mean (+/- SD) refractive error was -4.45 +/- 3.03 D and mean axial length was 25.13 +/- 1.52 mm. No correlation was found between refractive error and years spent working as a microscopist or number of hours per day spent performing microscopy. Subjects reporting myopia progression (N = 22) did not differ from the refractively stable group (N = 19) in terms of their microscopy working history, working hours, tonic accommodation level, or near phoria. However, the AC/A ratio of the progressing group was significantly greater than that of the stable group (4.59 delta/D cf. 3.34 delta/D). CONCLUSION: The myopia prevalence of Hong Kong Chinese microscopists was higher than that of microscopists in the United Kingdom (87% cf. 71%), as well as the Hong Kong general population (87% cf. 70%). The average amount of myopia was also higher in the Hong Kong Chinese microscopists than the Hong Kong general population (-4.45 D cf. -3.00 D). We have confirmed that the microscopy task may slightly exacerbate myopia development in Chinese people.

Adult↗
PubMed1995

A clinical study of the development of posterior vitreous detachment in high myopia.

PURPOSE: The correlation of age, axial length, and myopic chorioretinal atrophy with vitreous changes in high myopia were analyzed to investigate the development of posterior vitreous detachment (PVD) in high myopia. METHODS: The vitreous condition of 329 consecutive eyes with high myopia (more than -8.25 diopters (D) and more than 26.0 mm of axial length) was examined biomicroscopically with a +90-D preset lens and a Goldmann three-mirror contact lens. RESULTS: The prevalence of PVD in high myopia was 12.5% in patients between 20 and 29 years of age, and it increased with age. The incidence of PVD in eyes with axial length of more than 30.0 mm was 60.7% and was statistically higher than the prevalence in eyes with an axial length of less than 29.9 mm (P < 0.01). Multiple logistic regression analysis showed that age and axial length were statistically significant factors in the development of PVD and lacuna formation in high myopia (P < 0.01), but the influence of chorioretinal atrophy was not significant. CONCLUSION: The results of this study suggest that liquefaction of the vitreous begins at a relatively young age in patients with high myopia and progresses with age and axial elongation, thus resulting in a frequent occurrence of PVD.

Adult↗
PubMed2004

Myopia: precedents for research in the twenty-first century.

The myopic eye is generally considered to be a vulnerable eye and, at levels greater than 6 D, one that is especially susceptible to a range of ocular pathologies. There is concern therefore that the prevalence of myopia in young adolescent eyes has increased substantially over recent decades and is now approaching 10-25% and 60-80%, respectively, in industrialized societies of the West and East. Whereas it is clear that the major structural correlate of myopia is longitudinal elongation of the posterior vitreous chamber, other potential correlates include profiles of lenticular and corneal power, the relationship between longitudinal and transverse vitreous chamber dimensions and ocular volume. The most potent predictors for juvenile-onset myopia continue to be a refractive error </=+0.50 D at 5 years of age and family history. Significant and continuing progress is being made on the genetic characteristics of high myopia with at least four chromosomes currently identified. Twin studies and genetic modelling have computed a heritability index of at least 80% across the whole ametropic continuum. The high index does not, however, preclude an environmental precursor, sustained near work with high cognitive demand being the most likely. The significance of associations between accommodation, oculomotor dysfunction and human myopia is equivocal despite animal models that have demonstrated that sustained hyperopic defocus can induce vitreous chamber growth. Recent optical and pharmaceutical approaches to the reduction of myopia progression in children are likely precedents for future research, for example progressive addition spectacle lens trials and the use of the topical M1 muscarinic antagonist pirenzepine.

Animals↗
PubMed2003

Prevalence of myopia among primary school children in eastern Sydney.

BACKGROUND: Worldwide there is concern that the prevalence of myopia is increasing but the prevalence of myopia in Australian school children has not been analysed in detail. This study examines the prevalence of refractive errors in a large unselected population of primary school children in the eastern suburbs of Sydney. METHODS: Children visiting the Vision Education Centre at the School of Optometry and Vision Science, University of New South Wales, on a school excursion during the first half of the 1990s were refracted by non-cycloplegic retinoscopy. Spherical equivalents were computed and analysis of variance carried out. RESULTS: There were 1,459 boys and 1,076 girls in the study, a total of 2,535 children of whom approximately 40 per cent were born overseas or were first generation Australians. Overall, there was no significant difference in refractive error between girls and boys, although there were age/gender interactions with older girls exhibiting more hyperopia than boys. The refractive error ranged from -0.25 to +1.25 D spherical equivalent in 87.3 per cent of children. Mean spherical equivalent for the group was +0.50 +/- 0.82 D. There was a significant shift (p < 0.001) towards increasing myopia with age. The prevalence of myopia greater than -0.50 D rose from 1.0 per cent of four-year-olds to 8.3 per cent of 12-year-olds. CONCLUSIONS: The prevalence of myopia found in a large multi-ethnic group of non-clinical primary school children in eastern Sydney is lower than expected from other studies in the USA and Asia. Compared with Australian data from the 1970s and 1980s, only a weak increase in the prevalence of myopia is revealed.

Age Distribution↗
PubMed1993

Accommodative adaptation and age of onset of myopia.

Tonic accommodation in an empty field and accommodative adaptation, defined as accommodation shift after 2 min viewing of a 4 D near task, were measured using an infrared optometer. Subjects were classified into three types: emmetropes (n = 18), early onset myopes (n = 18) and late onset myopes (n = 15). The relationship between accommodative adaptation and the onset age of myopia were compared. There was no statistical difference in the pre-task tonic accommodation among the three subject groups. However, the accommodative adaptation differed in the three groups during the 5 min post-task period. The average accommodative adaptation of emmetropia, early onset myopia and late onset myopia were 0.66, 0.27 and 1.19 D, respectively. Accommodative adaptation in the late onset myopia group was significantly higher than in the emmetropia group. Furthermore, the accommodative adaptation in the early onset myopia group was significantly lower than in the emmetropia group. Two possible aetiologies of myopia are discussed: one for the group which shows low accommodative adaptation that has no relationship with the age of onset and another for the group which shows high accommodative adaptation that has a relationship to an onset age of 15 years or later. The aetiology is also considered with regard to a potentiating chemical effect on the synapses of the ciliary muscle.

Accommodation, Ocular↗
PubMed1996

Animal models of myopia. A review.

The discovery that myopia can be induced in animals has resulted in renewed interest in the condition and it is hoped that information gained about the production, manipulation and prevention of myopia in animals might provide information about naturally occurring myopia in humans. Early experimental work was carried out using monkeys as subjects, but the high cost involved, and the difficulty of obtaining monkeys in adequate numbers for good experimental design and control, made researchers look for more suitable experimental animals. Myopia has also been induced in other animals species such as the domestic cat, the tree shrew, the marmoset, the guinea pig and, most successfully, the domestic chicken. The parallels between experimentally induced myopia, which can only be induced in infant animals, and human myopia which typically develops well after infancy, have still to be established.

Animals↗
PubMed2005

Monovision slows juvenile myopia progression unilaterally.

AIM: To evaluate the acceptability, effectivity, and side effects of a monovision spectacle correction designed to reduce accommodation and myopia progression in schoolchildren. METHODS: Dominant eyes of 11 year old children with myopia (-1.00 to -3.00 D mean spherical equivalent) were corrected for distance; fellow eyes were uncorrected or corrected to keep the refractive imbalance <or=2.00 D. Myopia progression was followed with cycloplegic autorefraction and A-scan ultrasonography measures of vitreous chamber depth (VCD) for up to 30 months. Dynamic retinoscopy was used to assess accommodation while reading. RESULTS: All children accommodated to read with the distance corrected (dominant) eye. Thus, the near corrected eye experienced myopic defocus at all levels of accommodation. Myopia progression in the near corrected eyes was significantly slower than in the distance corrected eyes (inter-eye difference=0.36 D/year (95% CI: 0.54 to 0.19, p=0.0015, n=13); difference in VCD elongation=0.13 mm/year (95% CI: 0.18 to 0.08, p=0.0003, n=13)). After refitting with conventional spectacles, the resultant anisometropia returned to baseline levels after 9-18 months. CONCLUSIONS: Monovision is not effective in reducing accommodation in juvenile myopia. However, myopia progression was significantly reduced in the near corrected eye, suggesting that sustained myopic defocus slows axial elongation of the human eye.

Accommodation, Ocular↗