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PubMed2004

Magnitude and determinants of refractive error in Omani school children.

OBJECTIVE: To estimate the magnitude and determinants of refractive error in school children, a study was undertaken to review the school screening and refraction data. METHODS: Trained physicians screened 416,157 students to evaluate their visual status and identified 28,765 students with defective vision. Refractionists refracted 25,733 (89.5%) of them, determined the refractive error and prescribed spectacles. Students with ocular co-morbidity and visual disability were re-examined and treated by the ophthalmologists. This study was conducted between June 2003 and December 2003 in the Ministry of Health, Muscat, Sultanate of Oman. RESULTS: The prevalence of myopia was 4.1% (95% confidence interval [CI] 4.06-4.18). It was higher among female than male students [rate ratio (RR) 1.69 (95% CI 1.64-1.74)]. The rate was more in students of higher age groups (chi2 = 11,179 degrees of freedom = 2 p<0.00001). Regional variation in myopic trend was marked. The prevalence of hypermetropia was 0.4% (95% CI 0.37-0.41). However, it could be an underestimation as presence of accommodative spasm was not taken into account. The risk of low vision disability was significantly higher in male students than female students. The prevalence of ambiopia was 0.3%. It was significantly higher in male than female students. First primary students had strabismus of 0.5%. CONCLUSION: The study enabled to understand trends of refractive error in Omani children (Arabic tribe) and demonstrated the importance of vision screening in providing timely eye care and identifying visually disabled school children.

Adolescent↗
PubMed1997

Refractive errors in children born before 32 weeks gestation.

PURPOSE: To document the refractive errors in a cohort of children born before 32 weeks gestation. METHODS: All children born before 32 weeks gestation between 1 January 1990 and 31 December 1991 to mothers resident in the Northern Region of the National Health Service were examined at 2 years old (n = 558). RESULTS: Stage 3 or worse retinopathy of prematurity (ROP) was associated with myopia. In those not developing stage 3 or worse ROP, the refractive errors were myopia in 1.5%, hypermetropia > 4 dioptres (D) in 5.4%, anisometropia > 1 D in 1.1% and astigmatism > 1.25 D in 5.7%. CONCLUSION: The incidence of refractive errors in those not developing stage 3 or worse ROP was similar to that in the general population.

Acute Disease↗
PubMed2005

Use of refractive direct ophthalmoscopy for estimation of refractive error.

The purpose of this study was to find if direct ophthalmoscopy, a simple technique, could be used to give an approximate value of the refractive correction for a patient. This would shorten the time and lessen the effort to be expended during the following retinoscopic examination done for finding the patient's refractive correction. The use of direct ophthalmoscopy for this specific purpose is especially desirable where retinoscopic examination is quite tedious, e.g. uncooperative patients like children, bed-ridden patients and mentally retarded subjects, in patients with a large central corneal opacity and in patients having a large refractive error. The study was divided into two phases. In phase I, refractive direct ophthalmoscopy followed by classical retinoscopy was done for 92 subjects (184 eyes) in the age group of 11-35 years. The method of regression analysis was used to find a regression equation relating the readings to refractive error determined by the two above techniques. In phase II of study, the refractive correction needed for 50 other subjects in the similar age group was estimated using this regression equation by inserting their respective direct ophthalmoscopy readings. Then, these estimated values and classical retinoscopic examination values were compared. The refractive error determined after retinoscopy and that derived from regression equation (incorporating direct ophthalmoscopy readings) was statistically comparable (t = 0.52, p = 0.60). The correlation coefficient (r value) between the two methods was 0.37. Direct ophthalmoscopic lens reading can be used to give a fairly accurate estimate of refractive error in a patient's eye by using a linear regression equation, which relates these two examination techniques. The magnitude of astigmatic error, however, cannot be obtained.

Adolescent↗
PubMed1993

Effect of uncorrected refractive errors upon central visual field testing.

An investigation of the effects of uncorrected refractive errors upon a central visual field examination has been made with a view to establishing what the likely effects would be of omitting a refractive correction when screening the visual field with a threshold related, supra-threshold strategy on the Henson CFA3000. The results indicate that, while a linear relationship exists between the extent of threshold elevation and the product of residual refractive error and pupil size, the scatter in the results means that accurate predictions cannot be made in individual cases. The threshold elevation was found to be independent of eccentricity (within the central 21 degrees from fixation) and did not increase the variability of results. These last two findings indicate that uncorrected refractive errors are unlikely to affect the sensitivity of the threshold related, supra-threshold strategy to localized visual field defects.

Adult↗
PubMed1986

Stereopsis angle in relation to proximity and induced refractive errors.

Dependence of stereoacuity (SA) angle on the reciprocal of the test distance with positive, negative, and zero values of induced refractive errors is demonstrated with the three-rod test and the mean errors statistical method. Two male emmetropes and one hyperope showed linearly increasing dependence of SA angle on the reciprocal of the test distance within the subject's range of clear vision extended at both ends by 1 D. Linear regression coefficients were not influenced by the value of induced refractive error within +/- 2 D. Correlation coefficients in the case of corrected refractive error were about 0.90, but their mean value in the case of induced refractive errors was 0.83.

Adult↗
PubMed2003

The biological basis of myopic refractive error.

Myopia is among the most common refractive errors and is associated with the greatest risk of pathological outcomes. Most animals, including humans, are born with hyperopic errors. During development, axial elongation of the eye occurs and is regulated through a vision-dependent process, known as emmetropisation The extremely rapid changes in the prevalence of myopia and the dependence of myopia on the level of education indicate that there are very strong environmental impacts on the development of myopia. This conflicts with the common occurrence of familial patterns of inheritance of myopia, which suggests a role for genetic determination. There are more than 150 defined genetic syndromes in which familial high myopia is one of the features, including some that are not associated with other syndromes. The evidence for the roles of both nature and nurture in the aetiology of myopia is discussed. This review also examines the experimentally induced refractive errors associated with form-deprivation, recovery from form deprivation and the effects of both negative and positive lenses. In addition, it looks at the local and optical control of eye growth. Finally, the various control pathways for growth are considered. These include dopamine, ZENK-glucagon, retinoic acid and retinoic acid receptors, crystallin, seratonin and melatonin, vasoactive intestinal peptide and enkephalins, nitric oxide and various growth factors.

Accommodation, Ocular↗
PubMed2003

Refractive errors and visual impairment in 900 adults with intellectual disabilities in the Netherlands.

PURPOSE: To collect data on refractive errors and visual impairment in adults with an intellectual disability (ID) in the Netherlands. PATIENTS: A randomized sample of 2100 participants was drawn from a base population of 9000 adults with intellectual disabilities in the Netherlands. This article reports on the first 900 participants. METHODS: All participants underwent a protocol-based on-site ophthalmological assessment carried out by skilled investigators. RESULTS: Co-operation was classified according to the number of tests that could be carried out reliably and was good or excellent in 80% of subjects, average in 13% and poor in 7%. Refraction could be reliably assessed in 505/900 (56%) subjects. There was an increased risk of visual impairment in all subgroups compared to the general Dutch population. Visual acuity (VA) was related to the level of ID, but refractive errors were not. New spectacles were prescribed in 106 cases (12%). Of 374 people in whom both monocular VA and the refractive error of the right eye could be reliably assessed, 153 (41%) had a pretest prescription, 16 (10%) of which we found to be inadequate. Of the 221 participants without a pretest prescription, 41 (19%) benefited from correction. Only 38/84 (45%) subjects aged 50 years or older, who could benefit from correction for near vision, had near spectacles. New correction increased the mean distant VA significantly from 0.44 to 0.65 (p < 0.0005). CONCLUSIONS: With some adaptations, visual screening is feasible in a majority of adults with ID. Visual impairment and refractive errors are much more prevalent in adults with ID than in the normal population. Accurate spectacle correction resulted in significant improvement in distant VA.

Adult↗
PubMed1995

Studies on the role of the retinal dopamine/melatonin system in experimental refractive errors in chickens.

We have found that development of both deprivation-induced and lens-induced refractive errors in chickens implicates changes of the diurnal growth rhythms in the eye (Fig. 1). Because the major diurnal oscillator in the eye is expressed by the retinal dopamine/melatonin system, effects of drugs were studied that change retinal dopamine and/or serotonin levels. Vehicle-injected and drug-injected eyes treated with either translucent occluders or lenses were compared to focus on visual growth mechanisms. Retinal biogenic amine levels were measured at the end of each experiment by HPLC with electrochemical detection. For reserpine (which was most extensively studied) electroretinograms were recorded to test retinal function [Fig. 3 (C)] and catecholaminergic and serotonergic retinal neurons were observed by immunohistochemical labelling [Fig. 3(D)]. Deprivation myopia was readily altered by a single intravitreal injection of drugs that affected retinal dopamine or serotonin levels; reserpine which depleted both serotonin and dopamine stores blocked deprivation myopia very efficiently [Fig. 3(A)], whereas 5,7-dihydroxy-tryptamine (5,7-DHT), sulpiride, melatonin and Sch23390 could enhance deprivation myopia (Table 1, Fig. 5). In contrast to other procedures that were previously employed to block deprivation myopia (6-OHDA injections or continuous light) and which had no significant effect on lens-induced refractive errors, reserpine also affected lens-induced changes in eye growth. At lower doses, the effect was selective for negative lenses (Fig. 4). We found that the individual retinal dopamine levels were very variable among individuals but were correlated in both eyes of an animal; a similar variability was previously found with regard to deprivation myopia. To test a hypothesis raised by Li, Schaeffel, Kohler and Zrenner [(1992) Visual Neuroscience, 9, 483-492] that individual dopamine levels might determine the susceptibility to deprivation myopia, refractive errors were correlated with dopamine levels in occluded and untreated eyes of monocularly deprived chickens (Fig. 6). The hypothesis was rejected. Although it has been previously found that the static retinal tissue levels of dopamine are not altered by lens treatment, subtle changes in the ratio of DOPAC to dopamine were detected in the present study. The result indicates that retinal dopamine might be implicated also in lens-induced growth changes. Surprisingly, the changes were in the opposite direction for deprivation and negative lenses although both produce myopia. Currently, there is evidence that deprivation-induced and lens-induced refractive errors in chicks are produced by different mechanisms. However, findings (1), (3) and (5) suggest that there may also be common features. Although it has not yet been resolved how both mechanisms merge to produce the appropriate axial eye growth rates, we propose a scheme (Fig. 7).

5,7-Dihydroxytryptamine↗
PubMed1987

The effect of refractive error on automated global analysis program G-1.

We determined the effect of induced refractive errors on the visual field indices of the Octopus global analysis program G-1. After cycloplegia, refractive errors were introduced randomly in ten nonglaucomatous eyes of ten patients. Mean defect values (+/- S.D.) were lowest (2.4 +/- 0.8 dB) with full cycloplegic correction. With increasing ametropia, the mean defect increased significantly; it was 3.6 +/- 0.8 dB (P less than .0001) with the addition of +1.00 diopter and 5.3 +/- 0.9 dB (P less than .0001) with +2.00 diopters of sphere over the full cycloplegic correction. No significant differences in corrected loss variance, skew, short-term fluctuation, or reliability factor could be determined with changes in refractive error.

Adult↗
PubMed1994

[Relation between postoperative refraction errors and decentration of the intraocular lens].

In a group of 51 patients the authors measured the position of the intraocular lens (the method was based on mathematical analysis of the Purkinje images position) and calculated the postoperative refractive error. The dependence of the postoperative refractive error on IOL position was analyzed and the results of the analysis were compared with the presumptions based on theoretical calculations. The results obtained from the measurement are very close to that assessed by the theoretical calculations. The IOL decentration in the eye causes the the shift of the postoperative refractive error towards myopia and it is probably the cause of the part of the postoperative refractive error.

Humans↗
PubMed2004

Prevalence of refractive errors in a rural South Indian population.

PURPOSE: To report the prevalence of refractive errors in a rural south Indian population. METHODS: Four thousand eight hundred subjects (age, >39 years) from rural south India were enumerated for a population-based study. All participants underwent complete ophthalmic evaluation. Subjects who were phakic in the right eye with best corrected visual acuity of 20/40 or better were included for analysis. Association of refractive errors with age, sex, cataract, and diabetes mellitus were analyzed. RESULTS: Of the 3924 responders, 2508 were eligible. The unadjusted prevalence of emmetropia (spherical equivalent [SE], -0.50 to +0.50 diopter sphere [DS]), myopia (SE < -0.50 DS), high myopia (SE < -5.00 DS), and hyperopia (SE > 0.50 DS) were 50.60%, 26.99%, 3.71%, and 18.70% and age and gender adjusted for the rural Tamil Nadu population were 46.77%, 30.97%, 4.32%, and 17.94%, respectively. The prevalence of emmetropia decreased significantly with age (P < 0.0001), and the prevalence of myopia and high myopia increased significantly with age (P < 0.001) and were significantly associated with nuclear sclerosis (P < 0.001). The prevalence of hyperopia increased until 60 years of age and then decreased. Hyperopia was more common among women than men (P < 0.001) and was negatively associated with nuclear sclerosis (P < 0.001) and positively with diabetes mellitus (P = 0.008). Of the participants with astigmatism (cylindrical error greater than 0.50 DC), 9.80% had with-the-rule (WTR) and 77.44% against-the-rule (ATR) astigmatism. The prevalence of WTR and ATR astigmatism significantly decreased (P < 0.001) and increased (P = 0.006) with age, respectively. CONCLUSIONS: The pattern of refractive errors in this rural south Indian population is similar to those reported in other tropical regions of the world.

Adult↗
PubMed2002

[The role of light in pathogenesis of refractive errors].

PURPOSE: To present and account the results of newest experimental and clinical investigations on the subject of the light effect on the creation of refractive errors. MATERIAL AND METHODS: A review of literature concerning the role of the light in the refractive errors' pathogenesis has been performed. RESULTS: The influence of continuous light and night adaptation on the eyeball development as well as on the creation of refractive errors in experimental conditions are discussed. The anatomical and biochemical changes taking place in the course of experimental myopia are described. The entities of diseases predisposing to the creation of myopia are characterized. The results of the newest clinical investigations in which was shown that myopia and hyperopia might be associated with sleeping in lighted rooms up to the age of two are presented as well as accounted. CONCLUSIONS: Light and darkness play an important role in the proper eye development. Disturbance of the diurnal cycle over the time during which refraction forms may create refractive errors.

Adaptation, Physiological↗
PubMed2005

Occurrence of refractive errors among students who before the age of two grew up under the influence of light emitted by incandescent or fluorescent lamps.

PURPOSE: The aim of the study was to determine whether the development of refractive errors could be associated with exposure to light emitted by incandescent or fluorescent lamps. MATERIAL AND METHODS: 3636 students were examined (1638 boys and 1998 girls, aged 6-18 years, mean age 12.1, SD 3.4). The examination included skiascopy with cycloplegia. Myopia was defined as refractive error < or = -0.5 D, hyperopia as refractive error > or = +1.5 D, astigmatism as refractive error > 0.5 DC. Anisometropia was diagnosed when the difference in the refraction of both eyes was > 1.0 D. The parents of all the students examined completed a questionnaire on the child's light exposure before the age oftwo. Data were analyzed statistically with the chi2 test. P values of less than 0.05 were considered statistically significant. RESULTS: It was observed that sleeping until the age of two in a room with a light turned on is associated with an increase in the occurrence of anisometropia (p < 0.02) as well as with a reduction in the prevalence of emmetropia (p < 0.05). It was also found that light emitted by fluorescent lamps leads to more frequent occurrence of astigmatism (p < 0.01).

Adolescent↗
PubMed2005

Laser in situ keratomileusis for refractive error after cataract surgery.

PURPOSE: To evaluate the safety and efficacy of laser in situ keratomileusis (LASIK) to correct refractive error following cataract surgery. SETTING: The Eye Institute, Sydney, Australia. METHODS: This retrospective study reviewed 23 eyes (19 patients; 10 female, 9 male) treated with LASIK for refractive error following cataract surgery. The Summit Apex Plus and Ladarvision excimer laser and the SKBM microkeratome were used. The mean age was 63.5 years (range 50 to 88 years). The mean length of follow-up was 8.4 months (range 1 to 12 months) and mean interval between cataract surgery and LASIK was 12 months (range 2.5 to 46 months). RESULTS: The mean preoperative spherical equivalent refraction (SEQ) for myopic eyes was -3.08 +/- 0.84 diopters (D) (range -4.75 to -2.00 D) and for hyperopic eyes was +1.82 +/- 1.03 D (range +0.75 to +3.00 D). The mean improvement following LASIK surgery was greater for myopic than hyperopic eyes (myopic, 2.54 +/- 1.03 D versus hyperopic, 1.73 +/- 0.62 D; P=.033). The percentage of patients within +/-0.5 D of intended refraction post-LASIK surgery was 83.3% for myopic eyes and 90.9% for hyperopic eyes and all eyes were within +/-1.0 D of intended (P<.001). The percentage of eyes with uncorrected visual acuity of 20/40 or better in the myopic group improved from none preoperatively to 91.7% postoperatively (P<.001) and in the hyperopic group improved from 27.3% preoperatively to 90.9% postoperatively (P=.008). No eyes lost 2 or more lines of best corrected visual acuity. CONCLUSION: Laser in situ keratomileusis appears to be effective in correcting refractive error following cataract surgery. Longer-term studies are required to determine refractive stability.

Aged↗
PubMed1989

Corneal asphericity and refractive error.

The relationship between corneal curvature measured by classical keratometry and refractive error raises the question of a possible systematic relationship between refractive error and the degree of corneal asphericity. A recomputation and analysis of previously published data leads to the conclusion that the different refractive groups have similar values of the parameter 'p' and differ only in the apical radius of the cornea.

Cornea↗
PubMed2004

Intraocular pressure associations with refractive error and axial length in children.

AIM: To assess whether intraocular pressure (IOP) is associated with refractive error or axial length in children. METHODS: Of subjects from the Singapore Cohort Study of the Risk Factors for Myopia (SCORM), 636 Chinese children aged 9-11 years from two elementary schools underwent non-contact tonometry, cycloplegic autorefraction, and A-scan biometry during 2001. For analyses, refractive error was categorised into four groups; hypermetropia (spherical equivalent refraction (SE) > or = +1.0D), emmetropia (-0.5D<SE< +1.0D), low myopia (-3.0D<SE< or = -0.5D) and high myopia (SE< or = -3.0D). RESULTS: Of the 636 children examined, 50.6% were male. The mean IOP was 16.6 (SD 2.7) mm Hg. There were no significant IOP differences between low (mean IOP = 16.4 (2.8) mm Hg) or high myopes (16.7 (2.5) mm Hg) and emmetropes (16.7 (2.9) mm Hg), p = 0.57. IOP was not correlated with spherical equivalent refraction (Spearman correlation, r = 0.009) or axial length (r = 0.030). In regression analyses adjusting for diastolic blood pressure, neither spherical equivalent (regression coefficient = 0.014) nor axial length (regression coefficient = 0.027) were significantly associated with IOP. CONCLUSION: These findings do not support an association between IOP and refractive error or axial length in children. This questions postulated roles of IOP in the pathogenesis of myopia.

Biometry↗
PubMed2001

Genes and environment in refractive error: the twin eye study.

PURPOSE: A classical twin study was performed to examine the relative importance of genes and environment in refractive error. METHODS: Refractive error was examined in 226 monozygotic (MZ) and 280 dizygotic (DZ) twin pairs aged 49 to 79 years (mean age, 62.4 years). Using a Humphrey-670 automatic refractor, continuous measures of spherical equivalent, total astigmatism, and corneal astigmatism were recorded. Univariate and bivariate maximum likelihood model fitting was used to estimate genetic and environmental variance components using information from both eyes. RESULTS: For the continuous spectrum of myopia/hyperopia, a model specifying additive genetic and unique environmental factors showed the best fit to the data, yielding a heritability of 84% to 86% (95% confidence interval [CI], 81%-89%). If myopia and hyperopia (< or = -0.5 D and > or = 0.5 D, respectively) were treated as binary traits, the heritability was 90% (95% CI, 81%-95%) for myopia and 89% (95% CI, 81%-94%) for hyperopia. For total and corneal astigmatism, modeling showed dominant genetic effects are important; dominant genetic effects accounted for 47% to 49% of the variance of total astigmatism (95% CI, 37%-55%) and 42% to 61% of corneal astigmatism variance (95% CI, 8%-71%), with additive genetic factors accounting for 1% to 4% and 4% to 18%, respectively (95% CIs, 0%-13% and 0%-60%, respectively). CONCLUSIONS: Genetic effects are of major importance in myopia/hyperopia; astigmatism appears to be dominantly inherited.

Aged↗
PubMedDate not supplied

Laser in situ keratomileusis and photorefractive keratectomy for residual refractive error after phakic intraocular lens implantation.

PURPOSE: To determine the visual and refractive outcome of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) in eyes with prior posterior chamber phakic intraocular lens implantation for high myopia. METHODS: We studied a series of 37 consecutive eyes of 31 patients who underwent LASIK or PRK for residual refractive error following collamer posterior chamber intraocular lens (IOL) (Staar Surgical Implantable Contact Lens) implantation into a phakic eye. Twenty-eight eyes had LASIK and nine eyes had PRK. Mean follow-up was 8.1 +/- 4.7 months after laser ablation (range, 3 to 18 mo). RESULTS: The preoperative mean spherical equivalent refraction prior to phakic posterior chamber IOL implantation was -17.74 +/- 4.89 D (range, -9.75 to -28.00 D). Following phakic IOL implantation and prior to LASIK or PRK, mean spherical equivalent refraction was -2.56 +/- 2.34 D (range, -0.25 to -8.75 D). One month following LASIK or PRK, mean spherical equivalent refraction was -0.24 +/- 0.52 D (range, -1.50 to +1.50 D), 3 months following LASIK or PRK, mean spherical equivalent refraction was -0.19 +/- 0.50 D (range, -1.50 to +1.00 D). The refraction was within +/-1.00 D of emmetropia in 36 eyes (97.2%) and within +/-0.50 D in 31 eyes (83.7%). Three eyes developed anterior subcapsular opacities several weeks after laser ablation, one eye developed macular hemorrhage 4 weeks after laser ablation, and one eye had corticosteroid induced ocular hypertension. CONCLUSIONS: LASIK or PRK can be used to treat the residual refractive error following posterior chamber phakic IOL implantation.

Adult↗