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PubMed1992

Retinoscopic measurement of the refractive state of the rat.

Using retinoscopy, we measured the refractive state of 96 eyes of three different strains of rats: albino Sprague-Dawley, Royal College of Surgeons (RCS) with and without inherited retinal dystrophy, and lean and obese varieties of Zucker rats. Contrary to previous reports, we do not find consistent high hyperopia in the rat, but rather refractions that range from near emmetropia (-0.12 D) to extreme hyperopia (+18.95 D). This range of refractive errors suggests a poorly developed emmetropization mechanism in the rat, and that individual refractions should be performed on animals utilized in experiments where refractive state is critical.

Albinism, Ocular↗
PubMed1993

Chromatic aberration and accommodation: their role in emmetropization in the chick.

The roles of chromatic aberration and accommodation as cues to emmetropization in the chick were investigated. Myopia was induced monocularly by lid suture for a period of 1-2 weeks from hatching, after which eyes were reopened and the recovery process followed. Monochromatic light (ML) rearing conditions and ciliary nerve section surgery were used to eliminate chromatic aberration and accommodative activity respectively. Control animals were reared in white light (WL). When accommodation was left intact, chickens reared under monochromatic light were able to recover normally. However, ciliary nerve section produced hyperopia, deepening of the anterior chamber and a tendency towards axial lens thinning, irrespective of the light conditions used. Hyperopic refractive errors peaked at 4 weeks (mean refractive errors: +5.7 D, +4.21 D for ML, WL groups respectively, 4 weeks), with the ML group still exhibiting significant hyperopia at 7 weeks. Ciliary nerve section did not prevent the myopic response to lid suture (mean refractive errors: -22.65 D; -25 D for ML, WL groups respectively, 1 week) nor the elimination of myopia when eyes were reopened. These data indicate that neither accommodation nor chromatic aberration are fundamental to the gross operation of the emmetropization process although they may be essential for the fine tuning of refraction.

Accommodation, Ocular↗
PubMed2005

Optic disk size correlated with refractive error.

PURPOSE: To evaluate for which range of refractive error the optic disk size depends on, or is independent of, the refractive error. DESIGN: Clinical observational study. METHODS: The study included 1999 eyes of 1011 subjects with a mean refractive error of -0.97 +/- 2.72 diopters (range, -24.25 to +9.4 diopters). Optic disk photographs were morphometrically evaluated. RESULTS: The relation between optic disk area and refractive error showed a curvilinear shape, with a steep increase toward high myopia starting at -8 diopters, and a decrease toward high hyperopia starting at +4 diopters. CONCLUSION: The optic disk size depends on the refractive error with an increase in highly myopic eyes beyond -8 diopters and a decrease in highly hyperopic eyes beyond +4 diopters. Confirming histomorphometric studies, the limits of -8 diopters and +4 diopters may be discussed to refine the definitions of high hyperopia and high myopia.

Chronic Disease↗
PubMed2006

Correctable and non-correctable visual impairment in a population-based sample of 12-year-old Australian children.

PURPOSE: To document the prevalence of correctable and non-correctable visual impairment in a representative sample of Australian children, predominantly age 12 years. DESIGN: Population-based cross-sectional study. METHODS: Logarithm of the minimum angle of resolution (logMAR) visual acuity was measured in both eyes unaided, with spectacles if worn, and after subjective refraction if required, in 2353 children, examined during 2004 to 2005. Cycloplegic autorefraction (using cyclopentolate) and dilated fundus examination were performed. Using a cut-off of 0.3 logMAR units (<20/40), presenting visual impairment was defined using unaided visual acuity if spectacles were not worn or with usual correction if spectacles were worn. Impairment not eliminated by refraction was considered non-correctable; any difference between this and presenting impairment was defined as correctable impairment. Myopia was defined as spherical equivalent refraction (SER) < or =-0.50 diopters (D), hyperopia as SER > or =+2.0 diopters, anisometropia as SER difference > or =1.00 diopters, and astigmatism as cylinder > or =1.0 diopters. Amblyopia was defined as corrected visual acuity <0.3 logMAR not attributable to an underlying structural eye or visual pathway abnormality. RESULTS: Visual impairment was found in the worse eye of 117 children (5.0%) and comprised correctable (82%) and non-correctable impairment (18%). Correctable impairment was due to myopia in 67 (69.8%), hyperopia in 11 (11.5%) and astigmatism in 32 subjects (33.3%). Causes of non-correctable impairment were: amblyopia 66.7%, congenital glaucoma 9.5%, optic nerve hypoplasia 9.5%, congenital nystagmus 4.8%, and cortical blindness 4.8%. CONCLUSIONS: Visual impairment had a relatively low prevalence in this older childhood population, a large proportion of which was correctable by refraction alone.

Adolescent↗
PubMed2006

Factors associated with a previous diagnosis of strabismus in a population-based sample of 12-year-old Australian children.

PURPOSE: To describe the prevalence of strabismus and factors associated with its diagnosis in a representative sample of older Australian children. DESIGN: Cross-sectional, population-based study. METHODS: A representative stratified random cluster sample of 2353 children (aged 12 years) attending 21 secondary schools in Sydney, Australia was examined in 2004 to 2005 (response 75.3%). Cover testing was performed at near (30 cm) and distance (6 m); cycloplegic autorefraction, visual acuity, and stereoacuity were assessed. Previous strabismus diagnosis was obtained from parental questionnaires. RESULTS: Strabismus was evident in 64 children (2.7%); 21 (33%) had esotropia, 27 (42%) had exotropia, and 16 (25%) had microstrabismus. There were no gender (P = .2) or ethnicity (P = .6) associations. Previous diagnosis by an eye practitioner was noted in 27 (42%). This was related to hyperopia (P = .04), esotropia (P = .001), and amblyopia (P = .001). CONCLUSIONS: Strabismus was relatively infrequent in this Australian childhood sample. Its diagnosis was strongly related to presence of esotropia, hyperopia, and amblyopia.

Child↗
PubMed2005

Patterns of spectacle use in young Australian school children: findings from a population-based study.

PURPOSE: To describe the patterns of spectacle use in a population-based sample of Australian Year 1 school children (mostly aged 6 years). METHODS: Logarithm of the minimum angle of resolution (logMAR) visual acuity was measured in both eyes before and after pinhole correction, and using spectacles if worn. Cycloplegic autorefraction (cyclopentolate) and detailed dilated fundus examination were performed. Visual impairment was defined as visual acuity <40 logMAR letters (ie, <20/40 Snellen equivalent). Myopia was defined as spherical equivalent (SE) refraction < or = -0.50 diopters (D), and hyperopia as SE refraction > or = +2.0D, deemed significant when > or = +3.0D. Astigmatism was defined as cylinder > or =1.0D and anisometropia as SE refraction difference between the two eyes at least 1.0D. RESULTS: One thousand seven hundred forty predominantly 6-year-old school children were examined during 2003 to 2004. Spectacle use was documented in 77 children (4.4% of sample). Uncorrected visual impairment was found in the worse eye of 71 children (4.1%) and refractive error accounted for the majority (69.0%). Astigmatism was the most common refractive error causing visual impairment, accounting for 46.5%. Hyperopia, with or without astigmatism, was the most frequent reason for spectacle use, documented in 40.3%. Spectacle use in the absence of significant refractive error, amblyogenic risk factors, or visual impairment was noted in 26 children (33.8% of spectacle wearers). The prescription of spectacles could have benefited a further 26 children (1.5% of sample), mostly for correction of astigmatism. CONCLUSION: This study documents a significant disparity between spectacle use and need. Astigmatism was the most common cause of visual impairment due to refractive error.

Child↗
PubMed2006

Evaluation of the accuracy of estimation retinoscopy.

BACKGROUND: Some children are unable to cooperate for retinoscopy because they object strongly to the placement of lenses close to their faces. For these children, it would be ideal to obtain an accurate estimate of refractive error without using lenses. Techniques of estimation retinoscopy include sliding the sleeve of the Copeland retinoscope downward or moving closer to the patient until neutrality is achieved. The purpose of this study was to evaluate the accuracy of estimation techniques by comparing results to standard retinoscopy with loose lenses in cooperative children. METHODS: A Copeland retinoscope was calibrated using a schematic eye and loose lenses. A scale was created adjacent to the sleeve of the retinoscope which allowed an estimate of refractive error based on the position of the top of the sleeve. Estimation retinoscopy followed by standard retinoscopy with loose lenses was done on 100 eyes of 50 children after cycloplegia. RESULTS: Estimation of spherical equivalent for myopia less than 4 D and hyperopia less than 2 D correlated strongly with results obtained by standard retinoscopy with loose lenses (r = 0.87). Estimation retinoscopy had a sensitivity of 88%, specificity of 67%, positive-predictive value of 58%, and negative-predictive value of 92% in the detection of amblyogenic refractive errors. CONCLUSIONS: Estimation retinoscopy has very good accuracy for low levels of myopia, hyperopia, and astigmatism. Techniques of estimation may be useful in excluding amblyogenic refractive errors, particularly in children who object to loose lenses held close to them.

Child↗
PubMed2006

Ocular phenotype correlations in patients with TWIST versus FGFR3 genetic mutations.

BACKGROUND/PURPOSE: Despite the similar clinical phenotype of the Saethre-Chotzen and Muenke craniosynostoses, the 2 syndromes are now genotypically distinct. Patients with Saethre-Chotzen and Muenke syndromes carry mutations in the TWIST and fibroblast growth factor receptor (FGFR) 3 genes, respectively. We sought to assess possible ocular phenotypic differences in patients with mutations of either gene previously grouped according to phenotype only. METHODS: A retrospective chart review was performed for 21 children with known mutations of the TWIST (n=10) or the FGFR3 (n=11) genes. Data gathered included patient sex, age, family craniofacial history, craniofacial and ophthalmic surgeries, type of strabismus, ptosis, cycloplegic refraction, visual acuity, the presence of amblyopia, nasolacrimal duct obstruction (NLDO), nystagmus, hypertelorism, epicanthal fold anomalies, and any ocular structural abnormalities. RESULTS: In the TWIST group, ptosis was present in 90%, amblyopia in 70%, horizontal strabismus in 70%, vertical strabismus in 60%, NLDO in 60%, astigmatism in 50%, inferior oblique overaction (IOOA) in 40%, hyperopia in 40%, myopia in 30%, nystagmus in 30%, and optic nerve findings in 30%. In the FGFR3 group, ptosis was present in 36%, amblyopia in 18%, horizontal strabismus in 55%, vertical strabismus in 36%, NLDO in 0%, astigmatism in 9%, IOOA in 45%, hyperopia in 27%, myopia in 18%, nystagmus in 18%, and optic nerve findings in 27%. CONCLUSIONS: Patients with TWIST gene mutations may have more ophthalmic abnormalities, including more strabismus, ptosis, NLDO, astigmatism, vertical deviations, and amblyopia compared with patients with FGFR3 gene mutations.

Abnormalities, Multiple↗
PubMed2006

Ocular abnormalities in Apert syndrome: genotype/phenotype correlations with fibroblast growth factor receptor type 2 mutations.

BACKGROUND/PURPOSE: Apert syndrome, a disorder of craniosynostosis, syndactyly, and other craniofacial malformations, is caused by point mutations (Ser252Trp or Pro253Arg) in the fibroblast growth factor receptor 2 gene. This study's goal was to determine ophthalmic phenotype/genotype correlations in patients with either mutation. METHODS: A retrospective chart review of demographic and ophthalmologic data was performed for 18 children carrying either the S252W (11) or the P253R (7) mutation. Fisher exact tests were performed to determine significance of variable phenotypes between the two mutation groups. RESULTS: In the P253R group, 85% had strabismus (14% required surgery), 71% had ptosis, 43% had amblyopia, 14% had nasolacrimal duct obstruction, 14% had myopia, 14% had hyperopia, and 14% had astigmatism. In the S252W group, 91% had strabismus (64% required surgery), 73% had ptosis, 73% had amblyopia, 100% had nasolacrimal duct obstruction, 36% had myopia, 9% had hyperopia, and 82% had astigmatism. Overall, S252W and P253R groups showed significantly different numbers of patients with strabismus requiring surgery (p = 0.039), superior rectus muscle underaction (p = 0.024), nasolacrimal duct obstruction (p = 0.0002), and astigmatism (p = 0.005). CONCLUSIONS: Compared with patients with the P253R mutation, Apert syndrome patients with the S252W mutation may have more severe ocular phenotypes with a higher likelihood of developing strabismus, especially vertical deviation. They also are more likely to develop astigmatic refractive errors and tearing secondary to nasolacrimal system anomalies.

Acrocephalosyndactylia↗
PubMed2004

Phototherapeutic keratectomy in children: 5-year results.

PURPOSE: To evaluate the efficacy and safety of phototherapeutic keratectomy (PTK) for the treatment of superficial corneal opacities, surface irregularities, epithelial instability, and reepithelialization failure in pediatric patients and study the visual and refractive changes after combined PTK and photorefractive keratectomy (PRK). SETTING: Department of Ophthalmology, Masaryk University Hospital, Brno, Czech Republic. METHODS: This retrospective clinical study comprised children who had PTK or PTK combined with PRK from September 1996 to January 2000. The goals of treatment were to improve visual acuity and reduce or eliminate subjective ocular discomfort (eg, pain, lacrimation, and photophobia). A Nidek EC-5000 excimer laser was used in PTK mode with a 3.0 to 6.0 mm optical zone and a 4.0 to 7.5 mm transition zone. RESULTS: Forty-one pediatric patients (41 eyes) were included. Twenty-three eyes had PTK only, and 18 eyes had PTK combined with PRK to reduce preoperative myopia (11 eyes) or hyperopia (7 eyes). The mean patient age was 11.4 years (range 8 to 18 years) and the mean follow-up, 4.8 years (range 3 to 6 years). The best spectacle-corrected visual acuity (BSCVA) improved in all patients, and episodes of ocular pain or discomfort, lacrimation, and photophobia diminished. The mean preoperative BSCVA of 6/38 (range 6/10 to 1/60) improved to 6/12 (range 6/6 to 6/38) at the last postoperative examination. Eight eyes gained 5 or more Snellen lines of BSCVA; 11 gained 4 lines, 9 gained 3 lines, 7 gained 2 lines, 5 gained 1 line, and 1 eye was unchanged. No eye lost a line of BSCVA. The mean preoperative spherical equivalent (SE) decreased from -5.32 to -1.16 diopters (D) in the 11 myopic eyes and from +4.72 to +1.51 D in the 7 hyperopic eyes within 3 years of the combined procedure. CONCLUSIONS: Phototerapeutic keratectomy is an effective and safe procedure for the treatment of various surface corneal disorders in children. It can improve best corrected visual acuity and eliminate ocular pain and irritation. Preoperative myopia and hyperopia were effectively reduced by a combination of PTK and PRK.

Adolescent↗
PubMed2004

Prevalence of refractive error in Bangladeshi adults: results of the National Blindness and Low Vision Survey of Bangladesh.

PURPOSE: To determine the prevalence of refractive errors and to investigate factors associated with refractive error in adults 30 years of age and older in Bangladesh. DESIGN: Cross-sectional study. PARTICIPANTS: A nationally representative sample of 12 782 adults 30 years of age and older. METHODS: The sample of subjects was selected based on multistage, cluster random sampling with probability-proportional-to-size procedures. The examination protocol consisted of an interview that included measures of literacy, education, occupation, and refractive correction. Visual acuity testing (logarithm of the minimum angle of resolution [logMAR]), automated refraction, and optic disc examination were performed for all subjects. Subjects with <6/12 (0.3 logMAR) acuity in either eye were graded additionally for cataract and underwent a dilated fundal examination. Subjects for whom no refractive error was recorded (312 subjects; 2.7%) or who had undergone cataract surgery (123 subjects; 1.1%) were excluded from the analysis. MAIN OUTCOME MEASURES: Refractive error and socioeconomic variables (literacy, education, occupation). RESULTS: Eleven thousand six hundred twenty-four subjects were examined (90.9% response rate; mean age+/-standard deviation, 44+/-12.6 years). Five thousand four hundred eighty-nine subjects (49.1%) were men and 5700 subjects (50.9%) were women. Mean spherical equivalent was -0.19 diopters (D; +/-1.50 D). Six thousand four hundred twelve subjects (57.3%) were emmetropic, 2469 (22.1%) were myopic (<-0.5 D), and 2308 (20.6%) were hypermetropic (>+0.5 D). Two hundred six subjects (1.8%) were highly myopic (<-5 D). Myopia was more common in men (26.3%) than in women (21.0%), whereas hyperopia was more common in women (27.4%) than in men (15.8%). Overall, myopia increased with age (17.5% of those aged 30-39 years were myopic, compared with 65.5% of those age 70 years and older). A subanalysis of subjects without cataract showed increasing hyperopia with age and an association between myopia and higher education. Myopia was more common among the employed than in unemployed subjects. Astigmatism (>0.5 D), present in 3625 subjects (32.4%), was more common among women, illiterate subjects, and unschooled subjects. Against-the-rule astigmatism was more common (58.7%) than oblique astigmatism (29.3%), which was more common than with-the-rule (WTR) astigmatism (12.1%). Against-the-rule astigmatism and oblique astigmatism increased with age, unlike WTR astigmatism. Of 830 (7.5%) subjects, women were more commonly anisometropic (>1.0 D). Anisometropia increased with age. CONCLUSIONS: Refractive error data are described for a country and region that previously have lacked population-based data. Prevalence and factors associated with refractive error are presented, with a detailed comparison with other population-based surveys regionally and internationally.

Adult↗
PubMed2005

Refractive error and visual impairment in school-age children in Gombak District, Malaysia.

PURPOSE: To assess the prevalence of refractive error and visual impairment in school-age children in Gombak District, a suburban area near Kuala Lumpur city. DESIGN: Population-based, cross-sectional survey. PARTICIPANTS: Four thousand six hundred thirty-four children 7 to 15 years of age living in 3004 households. METHODS: Random selection of geographically defined clusters was used to identify the study sample. Children in 34 clusters were enumerated through a door-to-door survey and examined in 140 schools between March and July 2003. The examination included visual acuity measurements; ocular motility evaluation; retinoscopy and autorefraction under cycloplegia; and examination of the external eye, anterior segment, media, and fundus. MAIN OUTCOME MEASURES: Distance visual acuity and cycloplegic refraction. RESULTS: The examined population was 70.3% Malay, 16.5% Chinese, 8.9% Indian, and 4.3% of other ethnicity. The prevalence of uncorrected (unaided), presenting, and best-corrected visual impairment (visual acuity < or =20/40 in the better eye) was 17.1%, 10.1%, and 1.4%, respectively. More than half of those in need of corrective spectacles were without them. In eyes with reduced vision, refractive error was the cause in 87.0%, amblyopia in 2.0%, other causes in 0.6%, and unexplained causes in 10.4%, mainly suspected amblyopia. Myopia (spherical equivalent of at least -0.50 diopter [D] in either eye) measured with retinoscopy was present in 9.8% of children 7 years of age, increasing to 34.4% in 15-year-olds; and in 10.0% and 32.5%, respectively, with autorefraction. Myopia was associated with older age, female gender, higher parental education, and Chinese ethnicity. Hyperopia (> or =2.00 D) with retinoscopy varied from 3.8% in 7-year-olds, 5.0% with autorefraction, to less than 1% by age 15, with either measurement method. Hyperopia was associated with younger age and "other" ethnicity. Astigmatism (> or =0.75 D) was present in 15.7% of children with retinoscopy and in 21.3% with autorefraction. CONCLUSIONS: Visual impairment in school-age children in urban Gombak District is overwhelmingly caused by myopia, with a particularly high prevalence among children of Chinese ethnicity. Eye health education and screening may help address the unmet need for refractive correction.

Adolescent↗
PubMed2006

Refractive error and patterns of spectacle use in 12-year-old Australian children.

PURPOSE: To document the prevalence of visual impairment resulting from refractive error and to describe patterns of spectacle use in a representative sample of 12-year-old Australian school children. DESIGN: Population-based cross-sectional study. PARTICIPANTS: Two thousand three hundred fifty-three predominantly 12-year-old children examined from 2004 through 2005. METHODS: Logarithm of the minimum angle of resolution (logMAR) visual acuity (VA) was measured unaided and with spectacles if worn. Subjective refraction, cycloplegic autorefraction (with cyclopentolate), and detailed dilated fundus examination were performed. MAIN OUTCOME MEASURES: Myopia was defined as spherical equivalent (SE) refraction < or =-0.50 diopters (D), hyperopia as SE refraction > or =2.0 D, and astigmatism as cylinder > or =1.0 D. Uncorrected visual impairment was defined using unaided VA, and presenting visual impairment was defined using spectacle-corrected VA, if worn. Visual impairment was defined as VA <20/40 (<40 logMAR letters) for both better and worse eyes. Spectacle need was defined as uncorrected visual impairment in the better eye, improving by at least 2 lines with refraction, and undercorrection as presenting impairment in the better eye, improving by at least 2 lines with refraction. RESULTS: Uncorrected and presenting visual impairment in at least 1 eye because of refractive error was found in 10.4% and 3.7%, respectively. Spectacle use was reported by 448 children (19.0%); 204 (46.3%) had myopia, 48 (10.9%) had hyperopia, and 96 (21.8%) had astigmatism in at least 1 eye; 38.3% had no significant refractive error in either eye. Eight children were in need of spectacles and 37 children (8.3% of spectacle users) were undercorrected. Nonrefractive spectacle users were more likely to report eyestrain and headache or to have had learning difficulty at school (P<0.0001). CONCLUSIONS: This study documents a relatively low prevalence of undercorrected refractive error in a population of Australian children. Nonrefractive prescription of spectacles is common.

Adolescent↗
PubMed2006

High myopia and glaucoma susceptibility the Beijing Eye Study.

OBJECTIVE: To evaluate whether marked myopia, compared with moderate myopia and low myopia, is associated with a higher prevalence of glaucomatous optic nerve damage. DESIGN: Population-based cross-sectional study. PARTICIPANTS: Four thousand four hundred thirty-nine of 5324 subjects 40 years or older were invited to participate (response rate, 83.4%). The group was stratified according to refractive error into high myopia (myopia > -8 diopters [D]), marked myopia (<-6 to -8 D), moderate myopia (<-3 to -6 D), low myopia (<-0.5 to -3 D), emmetropia (-0.5 to + <2 D), and hyperopia (>+ 2 D) subgroups. METHODS: Morphologic assessment of optic disc monoscopic photographs. MAIN OUTCOME MEASURES: Morphologic optic disc parameters and intraocular pressure (IOP). RESULTS: For 4319 (97.3%) subjects (8484 eyes), optic disc photographs were evaluated. Prevalence of glaucomatous optic nerve atrophy as defined by the glaucomatous optic nerve head appearance did not vary significantly (P = 0.77; odds ratio [OR], 1.2; 95% confidence interval [CI], 0.38-3.81) between the highly myopic group and the group with marked myopia. In both refractive groups combined, glaucoma frequency seemed to be higher (P = 0.075; OR, 2.28; 95% CI, 0.99-5.25) higher than in the group with moderate myopia; it was significantly (P = 0.001; OR, 3.5; 95% CI, 1.71-7.25) higher than in the group with low myopia; significantly (P<0.001; OR, 7.56; 95% CI, 3.98-14.35) higher than in the group with emmetropia; and significantly (P = 0.005; OR, 4.23; 95% CI, 1.57-11.45) higher than in the group with hyperopia. Glaucoma frequency did not vary significantly between the hyperopic group and the emmetropic group (P = 0.17), the group with low myopia (P = 0.83), and the group with moderate myopia (P = 0.32). Intraocular pressure did not vary significantly (P>0.10) between any of the subgroups. Similar results were obtained for the frequency of glaucoma defined as glaucomatous optic disc appearance and visual field defects. In binary logistic regression analysis, presence of glaucoma was significantly associated with the myopic refractive error (P<0.001), age (P<0.001), and IOP (P<0.001). CONCLUSIONS: Marked to high myopia with a myopic refractive error exceeding -6 D may be a risk factor associated with glaucomatous optic neuropathy.

Adult↗
PubMed2006

Normal development of refractive state and ocular dimensions in guinea pigs.

PURPOSE: This study investigated changes in refraction, corneal curvature, axial components and weight of posterior sclera in guinea pig eyes during the normal development from birth. METHODS: Sixty-four guinea pigs were assigned to eight groups (n=8 each). Each group underwent a series of ocular measurements at one of the eight time-points (0, 1, 2, 3, 5, 7, 9 and 11 weeks), including refraction (streak retinoscopy), corneal radius of curvature (CRC; keratometry), anterior segment length (AS: corneal thickness and depth of the anterior chamber), thickness of the crystalline lens (CL), vitreous chamber length (VC; all A-scan ultrasonography) and dry weight of a circular 6mm diameter punch in the posterior sclera (electronic balance). Results of all the measurements were statistically compared between right eye and left eye, male and female and among different age groups. Artifacts of retinoscopy due to small eye artifact were also estimated at different ages. RESULTS: The refraction in guinea pig eyes was +5.22+/-0.23 D (Mean, SE) at birth. This value decreased rapidly during the first 3 weeks followed by a slow decline. The overall decrease in refraction was highly significant from birth to 11 weeks (p<0.001 one way ANOVA). The small eye artifact was approximately 4.00 D at birth, which reduced to 2.76 D at 11 weeks. The guinea pig eyes were emmetropic by 3 weeks of age when the small eye artifact was taken into account. The CRC (3.24+/-0.01 mm at birth), AS (1.20+/-0.01 mm at birth), CL (2.72+/-0.03 mm at birth) and VC (3.28+/-0.01 mm at birth) increased within the first 3 weeks despite a transient decrease in the CRC within the first week. The increase in CRC, CL and VC continued after 3 weeks, however, the AS remained constant after this age. The increase in VC was better correlated to the decline of hyperopia (R(2)=0.70) than the other components (R(2)=0.33-0.39). Dry weight of the posterior sclera increased linearly from birth (p<0.001 between any two close time-points from 3 to 9 weeks) and had a moderately linear correlation with the VC (R(2)=0.60). There were no significant differences between the right eye and left eye or between male and female in all the measurements. CONCLUSIONS: In guinea pigs, the hyperopia present at birth rapidly reduces to emmetropia within the first 3 weeks of age. The emmetropization process in guinea pigs is mainly related to the increase in the vitreous chamber length. This relationship in guinea pigs is similar to that in chickens, tree shrews, primates and humans. The axial development of the vitreous chamber in guinea pigs appears to be associated with tissue growth of the posterior sclera.

Animals↗
PubMed1996

Ocular findings in Down's syndrome.

PURPOSE: To identify the most common ocular findings in a pediatric group of patients with Down's syndrome. METHODS: A total of 152 children with Down's syndrome between two months and 18 years of age prospectively underwent ocular examination, including visual acuity assessment, slit-lamp biomicroscopy, ocular motility, cycloplegic retinoscopy, and ophthalmoscopy. RESULTS: Ocular findings in decreasing prevalence were the following: upward slanting of the palpebral fissure with the outer canthus 2 mm or higher than the inner canthus (82%), epicanthal folds (61%), astigmatism (60%), iris abnormalities (52%), strabismus (38%), lacrimal system obstruction (30%), blepharitis (30%), retinal abnormalities (28%), hyperopia (26%), amblyopia (26%), nystagmus (18%), cataract (13%), and myopia (13%). Visual acuity was assessed, and the Teller acuity cards were the most useful method of examination. The patients younger than five years old had a higher prevalence of hyperopia than did those in other age groups; patients between five and 12 years old had a higher prevalence of astigmatism; and patients older than 12 years of age had more iris abnormalities, strabismus, and cataract. Myopia and myopic astigmatism were more common in the patients with cardiac malformations. CONCLUSION: The early diagnosis of the ocular abnormalities in patients with Down's syndrome, by using Teller acuity cards in assessing visual acuity facilitates the treatment of refractive errors, strabismus, and amblyopia and may minimize handicaps.

Adolescent↗
PubMed2000

Refractive Error Study in Children: results from Shunyi District, China.

PURPOSE: To assess the prevalence of refractive errors and vision impairment in school-age children in Shunyi District, northeast of Beijing, the Peoples Republic of China. METHODS: Random selection of village-based clusters was used to identify a sample of children 5 to 15 years of age. Resident registration books were used to enumerate eligible children in the selected villages and identify their current school. Ophthalmic examinations were conducted in 132 schools on children from 29 clusters during May 1988 to July 1998, including visual acuity measurements, cycloplegic retinoscopy, cycloplegic autorefraction, ocular motility evaluation, and examination of the external eye, anterior segment, media, and fundus. Independent replicate measurements of all children with reduced vision and a sample of those with normal vision were done for quality assurance monitoring in three schools. RESULTS: A total of 6,134 children from 4,338 households were enumerated, and 5,884 children (95.9%) were examined. The prevalence of uncorrected, presenting, and best visual acuity 0.5 (20/40) or worse in at least one eye was 12.8%, 10.9%, and 1.8%, respectively; 0.4% had best visual acuity 0.5 or worse in both eyes. Refractive error was the cause in 89.5% of the 1,236 eyes with reduced vision, amblyopia in 5%, other causes in 1.5%, with unexplained causes in the remaining 4%. Myopia -0.5 diopter or less in either eye was essentially absent in 5-year-old children, but increased to 36.7% in males and 55.0% in females by age 15. Over this same age range, hyperopia 2 diopters or greater decreased from 8.8% in males and 19.6% in females to less than 2% in both. Females had a significantly higher risk of both myopia and hyperopia. CONCLUSIONS: Reduced vision because of myopia is an important public health problem in school-age children in Shunyi District. More than 9% of children could benefit from prescription glasses. Further studies are needed to determine whether the upward trend in the prevalence of myopia continues far beyond age 15 and whether the development of myopia is changing for more recent birth cohorts.

Adolescent↗
PubMed2000

Refractive Error Study in Children: results from Mechi Zone, Nepal.

PURPOSE: To assess the prevalence of refractive error and vision impairment in school age children in the terai area of the Mechi zone in Eastern Nepal. METHODS: Random selection of village-based clusters was used to identify a sample of children 5 to 15 years of age. Children in the 25 selected clusters were enumerated through a door-to-door household survey and invited to village sites for examination. Visual acuity measurements, cycloplegic retinoscopy, cycloplegic autorefraction, ocular motility evaluation, and anterior segment, media, and fundus examinations were done from May 1998 through July 1998. Independent replicate examinations for quality assurance monitoring took place in all children with reduced vision and in a sample of those with normal vision in seven villages. RESULTS: A total of 5,526 children from 3,724 households were enumerated, and 5,067 children (91.7%) were examined. The prevalence of uncorrected, presenting, and best visual acuity 0.5 (20/40) or worse in at least one eye was 2.9%, 2.8%, and 1.4%, respectively; 0.4% had best visual acuity 0.5 or worse in both eyes. Refractive error was the cause in 56% of the 200 eyes with reduced uncorrected vision, amblyopia in 9%, other causes in 19%, with unexplained causes in the remaining 16%. Myopia -0.5 diopter or less in either eye or hyperopia 2 diopters or greater was observed in less than 3% of children. Hyperopia risk was associated with female gender and myopia risk with older age. CONCLUSIONS: The prevalence of reduced vision is very low in school-age children in Nepal, most of it because of correctable refractive error. Further studies are needed to determine whether the prevalence of myopia will be higher for more recent birth cohorts.

Adolescent↗