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At least 145 records · Page 8Linked to original sources
PubMed2000

Effects of scleral buckling of refraction and ocular growth in young rabbits.

BACKGROUND: There have been a series of reports indicating that scleral buckling (SB) surgery may induce high myopia in advanced retinopathy of prematurity. The mechanism of SB on refractive change in children, however, is not clearly known. We designed this study to investigate the effects of SB on refractive error and ocular growth in young rabbits and demonstrate their mechanisms. METHODS: For the study, SB surgery was performed on the right eyes of nine 5-week-old rabbits and 11 8-week old rabbits, with encircling buckle. The left eyes were monitored for control. Spherical equivalent, corneal power, and axial length were measured before SB and postoperatively at 2, 4, and 8 weeks. We compared the experimental group with the control group and analyzed the influence of age at the time of operation. RESULTS: In the control group of eyes, corneal power decreased, axial length increased, and spherical equivalent developed emmetropization with aging. In all eyes that underwent SB surgery, high myopia developed, with the increase in axial length as a major factor in inducing myopia. These changes were greater in the 5-week-old group than in the 8-week-old group. In the eyes that underwent SB surgery, axial length increased more than the eyes in the control group up to 2 weeks after surgery, but ocular growth was arrested after that time. CONCLUSIONS: SB in young rabbits effects ocular growth and results in high myopia, and an increase of axial length plays a major role in this mechanism. Also, the difference in the effects of SB according to age at the time of surgery may suggest that SB in premature infants could induce a significant axial myopia and secondary amblyopia.

Aging↗
PubMed1980

Refraction, nearwork and education. A population study in Newfoundland.

There is little information directly relating ocular refraction and nearwork habits in representative human populations. Ocular refraction (diopters), nearwork (hours per day), and education (years) were therefore measured for 957 persons comprising 80% of the population aged 5 years and above of 3 communities in western Newfoundland. Refraction was moderately, consistently and significantly correlated with nearwork from ages 5 to 60, and remained so after adjustments for the association of refraction and nearwork levels with age, sex and education. Multiple regression coefficients relating refraction to nearwork decreased from -0.43 D/h at ages 5-14 years to -0.22 D/h at ages 60 years and up. The magnitude of this association, and its consistency and persistence over a wide age range, suggest that large amounts of nearwork in childhood may contribute to the prevalence of clinical myopia.

Adolescent↗
PubMed1999

Refractive errors and ocular motility disorders in preterm babies with and without retinopathy of prematurity.

Ocular motility, refraction and visual acuity (VA) were evaluated at the age of 4 years in 136 preterm infants with gestational ages (GAs) at birth of less than 32 weeks. Group 1 (non-retinopathy of prematurity, ROP) included 87 children that had never developed ROP. Group 2 contained 19 children whose ROP had regressed spontaneously. Group 3 (cryo-ROP) was composed of 30 patients who had undergone cryotherapy for severe ROP. Strabismus was found in 13.9% of the total population. chi(2) analysis revealed that strabismus was significantly (p < 0.01) associated with prematurity (i.e. GA <29 weeks), ROP and cryotherapy. Myopia of more than 3 dpt was significantly (p < 0.001) more common in the cryo-ROP infants than in the regressed-ROP and non-ROP groups. The distribution of hypermetropia was similar in all three groups. VA was measured with the E chart. Of the 272 eyes examined, 251 (92.3%) displayed VA of more than 20/25. The majority of these eyes were from the non-ROP group (65.4%), 15.3% had regressed ROP and 21.1% belonged to the cryo-ROP group. Fifteen eyes (8 non-ROP, 3 regressed ROP and 4 cryo-ROP) presented VAs between 20/25 and 20/60. VA of less then 20/60 was found in 6 eyes (2 non-ROP, 1 regressed ROP, 3 cryo-ROP). Cryotherapy did not appear to preclude the development of good VA.

Child Development↗
PubMed1995

Mechanisms of emmetropization in the aging eye.

Refraction and its components were measured on 96 subjects consisting of 48 Young Adults (19 to 31 years old) and 48 Mature Adults (49 to 61 years old) having refractive errors in the range from +2.50 to -2.50 D. Subjects for the two groups were matched on the basis of sex and refractive error. A quota sampling technique was used to obtain subjects for myopic, emmetropic, and hyperopic refractive-error categories. An autorefractor was used to measure refractive error, an autokeratometer was used to measure corneal radius of curvature, and an A-scan ultrasonometer was used to determine the axial dimensions. Crystalline lens radii were determined by submitting Purkinje image data to a ray-tracing program, with the assumption that the index of refraction of the ocular media is constant throughout life. By comparing the results for the two groups of subjects, it was found that there were no significant age-related differences in mean corneal radius of curvature or in mean axial length. However, the following significant age-related differences were found: the Mature Adult eyes had shallower anterior chambers, thicker lenses, shorter vitreous chambers, steeper anterior and posterior lens surfaces (shorter radii of curvature), more highly powered lenses, and higher ocular refracting power than the Young Adult eyes. It was concluded that a decrease in the gradient-index of the lens occurs with increasing age, acting as an emmetropizing mechanism by compensating for the steepening of both the front and back surfaces of the lens.(ABSTRACT TRUNCATED AT 250 WORDS)

Accommodation, Ocular↗
PubMed1990

Refractive state, ocular anatomy, and accommodative range of the sea otter (Enhydra lutris).

Sea otters are carnivorous, amphibious mammals that are active both above and under water. Accordingly, it might be expected that their eyes are adapted for both aerial and aqueous vision. We examined the anatomy and physiological optics of the sea otter eye with a view towards describing and explaining its amphibious visual characteristics. We employed photokeratoscopy to measure the refractive power of the sea otter cornea, which we found to be 59 D. Using video dynamic photorefraction, we found that sea otters can focus targets clearly both in air and water, relying on accommodation to compensate for the refractive loss of their corneas upon immersion in water. Our anatomical investigations revealed that the anterior epithelium of the cornea is extensively developed, as is the iris musculature, meridional ciliary muscle, and the corneoscleral venous plexus. The first feature is most likely an adaptation to the salinity of the marine environment. We believe the latter features are part of a novel, well-developed lenticular accommodative mechanism.

Accommodation, Ocular↗
PubMed1986

Comparison of subjective lens preference to objective refractive error measurements in pigtail macaques.

Two measurements can be taken to determine the refractive error in human beings: a subjective, lens preference measurement and objective retinoscopy. This study determined the subjective refractive error in eight pigtailed monkeys by placing lenses of different powers in front of peepholes in a solid wall cage and recording the amount of time each subject used the holes. Retinoscopy measurements were then taken and compared to the subjective findings to determine the degree of similarity between these two refraction methods. The results showed a high correlation between the subjective measurements and the vertical ocular refraction (VOR) and spherical equivalent (SE) (rho = 0.96), further supporting generalizations made from nonhuman primate vision studies to human beings.

Animals↗
PubMed2004

Effect of hyperbaric oxygen on guinea pig lens optical quality and on the refractive state of the eye.

The main objective of this study was to investigate the effect of in vivo hyperbaric oxygen (HBO) treatment of albino guinea pigs on ocular refractive state and optical properties of the lens in vitro, as well as on the integrity of the mitochondria of the lens. The animals were treated 30-35 times (2.5-3 months) or 70 times (6 months) with HBO. An increased level of lens nuclear light scattering was evident by slit-lamp at 30 treatments, and this increased at 70 treatments. After 30-35 HBO treatments a myopic shift in refractive state of the eye was seen in two separate studies with two different refractionists. Also, the average back vertex distance of the lens was significantly shorter after 35 HBO treatments while spherical aberration (focal variability) increased after 70 treatments. No difference in refractive state was noted after 70 HBO treatments (a reversal of the initial myopic effect). The mitochondrial distribution and morphology of the lens epithelium and the superficial cortical fibre cells were normal after both 35 and 70 HBO treatments, highlighting that HBO treatment does not affect the superficial cortex of the lens. The results of the in vitro lens optical analysis carried out in this study correlate with the myopia observed after 30-35 HBO in vivo treatments. A similar reversible myopia and increase in lens nuclear light scattering is known to occur in humans treated with HBO for extended periods and the results suggest that the myopia was caused by a change in the refractive index of the lens. The significant loss of sharp focus after 70 HBO treatments can be correlated with previous reports of biochemical and morphological changes associated with HBO-induced loss of lens nuclear transparency in mature guinea pigs. The guinea pig HBO model may be a useful approach for the study of lens development and refractive error.

Animals↗
PubMed2002

Neuroretinal basis of visual impairment in the very elderly.

PURPOSE: To evaluate the effects of senescence on the morphology and neural function of the retinal nerve fiber layer (NFL) in the very elderly. METHODS: The NFL thickness about the optic nerve head and the neural activity of its neurons were quantified by scanning laser polarimetry and pattern reversal electroretinograms (PERGs), respectively, in a group of young healthy volunteers ( n=27; mean ocular refraction -1.59+/-0.45 D) between 20 and 31 years of age, and a group of healthy elderly volunteers ( n=27; mean ocular refraction +0.11+/-0.40 D) between 75 and 88 years of age. RESULTS: Relative to the young group, the elderly subjects showed an overall thinning of the NFL of some 22.5%; however, the superior quadrant was attenuated by about 30.0%. The function of the ganglion cell axons in the NFL as reflected by the N95 component of the PERG was reduced by about 28.8% in the elderly compared with the young. CONCLUSION: Aging caused a thinning of the NFL, particularly in the superior quadrant. The evoked potentials from the neurons comprising this layer were attenuated by near equivalent amount. These findings have clinical implications in the differential diagnosis of normal aging versus disease-related alterations in the structure and function of the NFL in the very elderly sector of our population.

Adult↗
PubMedDate not supplied

The factors influencing visual development in blepharophimosis-ptosis-epicanthus inversus syndrome.

PURPOSE: To investigate the factors influencing visual development in blepharophimosis-ptosis-epicanthus inversus syndrome. MATERIALS AND METHODS: The study population comprised 20 patients with blepharophimosis-ptosis-epicanthus inversus syndrome who were referred for an oculoplastic opinion. The ocular examination included measurement of Snellen visual acuity, cycloplegic refraction, ocular movements and alignment, and the presence of amblyopia. Patients were treated with spectacle correction, occlusion therapy, strabismus surgery, and oculoplastic surgery if necessary. Minimum follow-up was 2 years. RESULTS: Nine (45%) patients had amblyopia; 5 (25%) of these patients had unilateral amblyopia and 4 (20%) had bilateral amblyopia. Six (67%) patients with amblyopia had a significant coexisting strabismus. A significant strabismus was present in 11 (55%) patients; 6 (55%) of these patients had unilateral or bilateral amblyopia. Patients with strabismus were more likely to have amblyopia than those without. A total of 14 (70%) patients had refractive error; 6 (43%) of these patients had amblyopia. CONCLUSIONS: Patients with blepharophimosis-ptosis-epicanthus inversus syndrome had a high rate of amblyopia, especially bilateral amblyopia. Patients with strabismus were more likely to have amblyopia than those without. Patients also had a high incidence of refractive errors.

Adult↗
PubMed2004

Prevalence of myopia in Taiwanese schoolchildren: 1983 to 2000.

INTRODUCTION: To determine time trends in myopia over a 20-year period in Taiwan, we conducted 5 nationwide surveys pertaining to the ocular refraction of schoolchildren in 1983, 1986, 1990, 1995 and 2000. MATERIALS AND METHODS: The sampling technique used herein involved the assessment of stratified systematic clusters, with the unweighted myopic rate being represented using data derived from different sectors of the population, such as metropolitan, city, town, and aboriginal. The mean values for the spherical equivalent of the cycloplegic refractive status and the dimension of corneal radii as determined by the autorefractometer were used for the calculation. RESULTS: In our review of 5 nationwide myopia surveys, we found that the mean prevalence of myopia among 7 year olds increased from 5.8% in 1983 to 21% in 2000. At the age of 12, the prevalence of myopia was 36.7% in 1983 increasing to 61% in 2000, corresponding figures for 15-year-olds being 64.2% and 81%, respectively. The prevalence of myopia increased from 74% in 1983 to 84% in 2000 for children aged between 16 and 18 years, and, in addition, the prevalence of high myopia (over -6.0 D) increased from 10.9% in 1983 to 21% of 18-year-old students of Taiwan in 2000. The mean refractive status at the age of 12 deteriorated from -0.48 D in 1983 to -1.45 D in 2000, and from -1.49 D to -2.89 D for children aged 15, whilst for individuals aged 18, it deteriorated from -2.55 D in 1983 to -3.64 D in 2000. The mean ocular refraction began to progress to a myopic condition at the age of 11 in 1983, this becoming an age of 8 years in 2000. There appeared to be significant difference in both the prevalence and the degree of myopia between study participants residing in cities and villages. CONCLUSIONS: We conclude that the cause of the relative increasing severity of myopia among the schoolchildren was due to the onset of myopia at a very young, and progressively-decreasing, age over the study period. Thus, to reduce the prevalence and severity of myopia, we should pay more attention to the eye care of pre-schoolchildren.

Adolescent↗
PubMed1980

The prevalence of refractive and ocular anomalies among 1242 institutionalized mentally retarded persons.

The population of a large Canadian institution, providing rehabilitative and health care for the mentally retarded, received oculo-visual assessments in an optometric clinic established in the hospital by the University of Waterloo, School of Optometry. The ocular and visual anomalies of 1242 residents have been compiled and analyzed. This paper reports the results and discusses their implications. The size of the sample makes the data useful in planning vision care delivery to the mentally retarded. Comparisons are made to similar data obtained from a concurrent study of a community sample and to studies from vision literature.

Adolescent↗
PubMed1998

Ocular status of boys with fragile X syndrome: a prospective study.

PURPOSE: The purpose of this study was to determine whether the high rates of ocular problems described in previous retrospective reports of individuals with fragile X syndrome were present in a prospective sample of young boys. Fragile X syndrome is currently considered the leading hereditary cause of mental retardation, with prevalence estimates of 1:2500 to 1:5000 males. METHODS: Forty-eight boys with fragile X syndrome between the ages of 2.5 and 11 years were evaluated for ocular abnormalities. They received complete ophthalmic evaluations including assessment of visual acuity, cycloplegic refraction, ocular motility assessment, and dilated fundus examination. RESULTS: Approximately 25% of the children had clinically significant ocular findings that included refractive errors (17%, primarily hyperopia and astigmatism) and strabismus (8%). Of the 42 children with quantifiable visual acuities, only 1 child, with diagnoses of nystagmus and hyperopia, had a Snellen visual acuity that was not within normal limits for his age. Three of the 5 children with gross measures of visual acuity had clinically significant findings: 2 had hyperopia greater than 3.5 diopters and 1 had esotropia. The other 2 children with gross measures of acuity and the 1 child without visual acuity assessment had cycloplegic refractions of +1.25 to +1.5 and ocular motility appeared normal. CONCLUSIONS: These results suggest that previous reports of high rates of vision problems, particularly strabismus, in boys with fragile X syndrome may have resulted from selection bias. Although we did observe a higher prevalence of strabismus than that found in the general population (8% vs 0.5% to 1%), the proportion of children having strabismus in our sample was much smaller than that reported in other studies of children with fragile X syndrome (30% to 40%). However, 17% of the sample did have significant refractive errors. In addition to evaluating the ocular motility of children with fragile X syndrome, cycloplegic refraction should also be performed to determine whether refractive problems are present.

Child↗