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PubMed1998

An epidemiologic investigation of unexpected refractive errors following cataract surgery.

OBJECTIVE: To determine the extent and magnitude of unexpected refractive errors following cataract surgery with intraocular lens (IOL) implantation and to determine what characteristics were associated with the errors. DESIGN: In this nonconcurrent prospective study, preoperative, intraoperative and postoperative information was collected from the charts of the 523 consecutive patients who underwent cataract extraction and polymethylmethacrylate IOL implantation performed by one of nine participating surgeons between Jan. 1 and Apr. 30, 1995, or the same dates in 1996. SETTING: University-affiliated eye care centre in Vancouver. OUTCOME MEASURE: Postoperative excess correction, calculated for each patient by subtracting the actual postoperative spherical equivalent from the expected spherical equivalent. Eyes with an excess correction of more than 1.00 dioptre were considered "overcorrected." RESULTS: Univariate analysis showed that the formula used to calculate the lens power, axial length, year of surgery, A-constant/surgeon factor used and lens manufacturer were associated with overcorrection. In a logistic regression model, lens manufacturer was the only variable independently associated with overcorrection. CONCLUSIONS: Routine reporting and follow-up is necessary to identify this kind of "outbreak" and the associated factors. The current guidelines of the Health Protection Branch, Health Canada, for evaluation of IOLs that have changed manufacturers are not adequate to identify the kind of error that we detected.

Aged↗
PubMed1983

An examination of refractive error through computer simulation.

Computer simulation is used to investigate the distribution of refractive error, generating two models based on corneal power, anterior chamber depth, lens power, and axial length for several samples (N = 1000). Discrepancies between simulated and observed data indicate that emmetropization is a more complex process than is accounted for by intercorrelations among components.

Computers↗
PubMed2001

Refractive errors and visual anomalies in Down syndrome.

A comparatively high incidence of ocular and orbital abnormalities has been reported in persons with Down syndrome. Eighty six children (50% male, 50% female) with Down syndrome in several institutions for individuals with learning difficulties (age range 5-18 years, mean 12.5) were examined for visual impairment in order to relate the ocular impairment to the level of learning difficulty. 6% had mild, 7% moderate, 45% severe and 42% profound learning difficulty. 9% of the children had no refractive errors. A significant (P < 0.01) positive correlation was found between progressive amounts of strabismus and ocular pathology with increasing amount of learning difficulty. On the other hand no correlation was found between refractive errors and the level of learning difficulty. Due to the significant number of ocular disorders found it is recommended that all children with Down syndrome should have an eye examination during the first six months of life and annually thereafter.

Adolescent↗
PubMed1991

Refractive errors and axial length among Alaskan Eskimos.

An epidemiological study of the prevalence of refractive errors was made of the Eskimo population of the Norton Sound and Bering Straits region of Alaska. It was possible to determine the subjective refraction in 83.7% of 1673 persons examined: 44.9% were emmetropic, 44.7% myopic and 10.4% hyperopic. Myopia was found more often in women (48.3%) than in men (41.3%), while emmetropia was found more often in men (49.3%) than in women (40.3%). Nine,four percent of the men were hyperopic and 11.4% of the women. The prevalence of myopia increased with age, with a maximum of 67.2% in the age group between 30 and 40 years. Subsequently, the number of myopes decreased rapidly. Little hyperopia was seen before the age of 50 years, it then increased rapidly, up to 71.5% for persons above the age of 80 years. Emmetropia, on the other hand, decreased with age. Ultrasound examination showed that an increasing axial length was associated with more myopia.

Adolescent↗
PubMed1977

Prevalence of refractive errors in adults over 40: a survey of 8102 eyes.

The prevalence of refractive errors was studied in an adult rural population. Of the 8102 eyes studied 18-4% were myopic, 57-1% were emmetropic, and 24-5% were hypermetropic. Mild myopia was commoner in males than in females, and mild hypermetropia was commoner in females than in males. There was increasing hypermetropia with increasing age, probably due to unmasked, latent hypermetropia up to the age of 70 years and to a true shift toward hypermetropia after the age of 70 years.

Adult↗
PubMed2001

Refractive error and glaucoma.

PURPOSE: To study the association between refractive error, glaucoma damage and IOP in a large population. METHODS: We examined 32,918 citizens of the city of Malmö, Sweden, 57-79 years of age, searching for individuals with undetected glaucoma. Refraction was measured with autorefractors. Glaucoma damage was defined as reproducible visual field defects with the Humphrey Full Threshold 24-2 program. RESULTS: Glaucoma prevalence was clearly associated with refractive state, increasing gradually with increasing myopia. This was seen both in males and females and persisted over the full age range. Glaucoma was significantly more common in myopic than in hyperopic eyes with low IOP readings (p=0.024). The overrepresentation of glaucoma in myopic eyes declined with increasing IOP and no relationship was observed in eyes with IOP > or =31 mmHg. CONCLUSION: In this large population, the prevalence of glaucoma increased with increasing myopia. The association between myopia and glaucoma was strong at lower IOP levels, and weakened gradually with increasing IOP. Our findings indicate that myopia is an important risk factor for glaucoma and particularly for normal tension glaucoma.

Aged↗
PubMed2004

Refractive error with optimum intraocular lens power calculation after glaucoma filtering surgery.

PURPOSE: To assess the possibility of deriving an optimum intraocular lens (IOL) power after previous successful trabeculectomy. SETTING: Chang Gung Memorial Hospital, Linko, Taiwan. METHODS: The retrospective study included 1 eye of 22 patients who had cataract surgery after successful trabeculectomy performed by 1 surgeon. Twenty-two eyes that had cataract surgery only performed by the same surgeon were paired as a control group. The IOL power was calculated by the Sanders-Retzlaff-Kraff regression analysis formula based on the data derived after trabeculectomy. The postoperative refractive error at least 1 month after cataract surgery was recorded, and the difference was analyzed by a paired t test and 2-sample t test. RESULTS: Cataract surgery combined with trabeculectomy resulted in a mean spherical equivalent of -0.33 diopter +/- 1.58 (SD). This was not significantly different from the predicted refractive error or the result in the control group (P>.05). CONCLUSION: Although the fluctuation in pseudophakic axial length measurement after glaucoma filtering surgery was logical, a predictable pseudophakic refractive outcome was derived clinically once the intraocular pressure stabilized after trabeculectomy.

Adult↗
PubMed1994

Refractive errors in preterm babies.

Fifty preterm neonates were followed up at the age of 6 months and 1 year. In addition to developmental assessment, a complete ophthalmological examination was done on both visits. The largest (62%) gestational age group was of 34-36 weeks. At 6 months, none of the infants had normal vision. At 1 year of age, 64% of the babies had normal vision while incidence of myopia and hypermetropia was 16% and 20%, respectively. There was an inverse relationship noted between gestation and incidence of refractive errors. It was also noted that with decreasing weight, the incidence of myopia increased. Myopia was seen exclusively among infants of birth weight of 2000 g or less. Birth weight had a significant positive correlation with astigmatism. No correlation of asphyxia with refractive errors was observed. It is recommended that all preterm babies should have an ophthalmological examination at one year of age with follow up later on.

Anisometropia↗
PubMed1994

Comparison of the techniques of videorefraction and static retinoscopy in the measurement of refractive error in infants.

Photorefraction has been suggested as a suitable method of screening for refractive error in infants. The relative performance of cycloplegic and non-cycloplegic videorefraction and cycloplegic retinoscopy was investigated on 150 infants. Under cycloplegic conditions the correlation between findings for spherical error (Rxy = 0.70) was compatible with a previous study. However, where cycloplegia was not used for videorefraction, there was poor agreement between the two techniques in the case of astigmatic error, and all types of ametropia. Interobserver repeatability was very high both for cycloplegic retinoscopy (Rxy = 0.96 spherical error, and Rxy = 0.75 astigmatic error) and for videorefraction measurements (Rxy = 0.95 horizontal meridian of photograph and Rxy = 0.85 vertical meridian). Intraobserver repeatability was also good, both for cycloplegic retinoscopy (Rxy = 0.91 spherical error and 0.82 astigmatic error) and for videorefraction with regard to spherical errors (Rxy = 0.84). Throughout the experiments videorefraction measurements of astigmatic errors proved less consistent when compared with cycloplegic retinoscopy, and to its internal reliability.

Astigmatism↗
PubMed2002

Prevalence rates of refractive errors in Sumatra, Indonesia.

PURPOSE: To determine the prevalence rates of myopia, hyperopia, astigmatism, and anisometropia in a prevalence survey of adults in Sumatra, Indonesia. METHODS: A population-based prevalence survey of 1043 adults 21 or more years of age was conducted in five rural villages and one provincial town of the Riau Province, Sumatra, Indonesia. A one-stage household cluster sampling procedure was used wherein 100 households were selected from each village or town. Refractive error measurements were obtained with one of two handheld autorefractors. Household interviews were conducted to obtain information on relevant lifestyle risk factors. RESULTS: The age-adjusted overall prevalence rates of myopia (SE [spherical equivalent] at least -1.0 D), hyperopia (SE of at least +1.0 D), astigmatism (cylinder of at least -1.0 D), and anisometropia (SE difference of +1.0 D) were 26.1% (95% confidence interval [CI]: 23.4-28.8), 9.2% (95% CI: 7.4-11.0), 18.5% (95% CI: 16.2-20.8), and 15.1% (95% CI: 12.9-17.4), respectively. The age-adjusted overall prevalence rate of high myopia (SE at least -6.0 D) was 0.8% (95% CI: 0.2-1.5). In a multiple logistic regression model, myopia rates varied with age and increased with income. Hyperopia, astigmatism, and anisometropia rates were independently higher in older adults. CONCLUSIONS: The prevalence rates of myopia in provincial Sumatra are higher than the rates in white populations, but lower than the rates in other urbanized Asian countries such as Singapore. The prevalence rate of high myopia is lower than in most other populations, and other refractive errors are common.

Adolescent↗
PubMed1991

The relationship of visual acuity, refractive error, and pupil size after radial keratotomy.

To better define the relationship between residual refractive error, uncorrected visual acuity, and pupil diameter, we compared 42 eyes that had an eight-incision radial keratotomy according to the Prospective Evaluation of Radial Keratotomy Study protocol with 42 matched control eyes. The parameters measured were best corrected visual acuity, uncorrected visual acuity, and the change in cycloplegic refraction with enlarging pupil diameter. The best corrected visual acuity was 20/16 in both the radial keratotomy and control groups, but the variability (SD) was higher in the radial keratotomy group. The average uncorrected visual acuity was 0.35 (35%) better in the radial keratotomy group, but the variability was 1.77 times higher. Change in refraction with dilation occurred in 9% of the controls and 36% of the radial keratotomy patients, indicating a significant difference (P = .002). The change in refraction with dilation in the eyes with radial keratotomy was almost equally split between a hyperopic change (17%) and a myopic change (18%), which was much different than in the control eyes, only 2% of which changed in a hyperopic direction and 7% in a myopic direction. The radial keratotomy patients with a myopic change had the best uncorrected visual acuity, indicating that positive spherical aberration yielded the best aspherical surface for uncorrected visual acuity.

Adult↗
PubMed1992

[Photographic screening for amblyopia, strabismus and refraction errors].

The authors present a photographical method to screen infants on the presence of refractive errors and squint. The photoscreener indicates an absence of focusing in one or both eyes and/or a squint. This method can be used in mass-screening of siblings, the evaluation of glasses, the monitoring of the effects of occlusion and the postoperative follow-up of patients.

Amblyopia↗
PubMed1997

Local changes in eye growth induced by imposed local refractive error despite active accommodation.

We have tested whether defocus imposed on local retinal areas can produce local changes in eye growth, even if accommodation is available to clear part of the imposed defocus. Hemi-field lenses were attached to little leather hoods that were worn by young chickens from day 11-15 post-hatching. The lens segments defocused either the nasal or the temporal visual field, or covered the full field. We found that negative lenses (-7.5 D) were incompletely compensated in all three cases but caused significant myopia in the defocused parts of the visual field (differences to fellow eyes with normal vision: nasal visual field -3.13 +/- 1.56 D, P < 0.001; temporal visual field -4.02 +/- 1.38 D, P < 0.001; full field -3.82 +/- 2.48 D, P = 0.01). Myopia was not enhanced if the lenses covered the entire visual field. Positive lenses (+6.9 D) caused larger changes in refraction than negative lenses and, again, there was no significant difference in the amount of induced hyperopia in the nasal or temporal retina, or in the amount of hyperopia with full-field lenses (difference to fellow eyes with normal vision: nasal visual field +6.2 +/- 2.69 D, P < 0.001; temporal visual field +5.95 +/- 2.22 D, full field +7.22 +/- 2.44 D, P < 0.001). To compare the shapes of the excised eyes after lens treatment, we wrote a fully automated image processing program that traced their outlines in digitized video images. We found that the shapes of the eyes treated with positive lenses did scarcely differ from their fellow eyes with normal vision, indicating that hyperopia over this 4 day period was caused mostly by choroidal thickening. Full field negative lenses produced significant axial eye elongation; the effects of locally imposed defocus on eye shape were less conspicuous and were significant only in some areas. That local compensation of defocus was possible for both negative and positive lenses, suggests that the retina can recognize the sign of defocus without accommodation cues. Even more striking is that the presence of accommodation is apparently ignored since the drift in the plane of focus during accommodation does not disturb the compensation process. We re-analyze previous experimental results that argue for different mechanisms for deprivation myopia and lens-induced refractive errors. We propose that lens-induced refractive errors are compensated by similar retinal mechanisms as the ones proposed by Bartmann and Schaeffel [(1994). Vision Research, 34, pp. 873-876] to explain deprivation myopia. The proposed mechanisms can integrate with long time constants over the spatial frequency content in the retinal image while the viewing distances change, and control both choroidal thickening and scleral growth. However, it turns out that the compensation of imposed myopia cannot be explained if only one constant viewing is available. Apparently, there is more than a retinal blur detector to guide refractive development.

Accommodation, Ocular↗
PubMed2004

Prevalence of refractive errors in teenage high school students in Singapore.

We aimed to study the prevalence of refractive conditions in Singapore teenagers. Grade 9 and 10 students (n = 946) aged 15-19 years from two secondary schools in Singapore were recruited. The refractive errors of the students' eyes were measured using non-cycloplegic autorefraction. Sociodemographic data and information on risk factors for myopia (such as reading and writing) were also obtained using an interviewer-administered questionnaire. The prevalence of refractive conditions was found to be: myopia [spherical equivalent (SE) at least -0.50 D] - 73.9%, hyperopia (SE at least +0.50 D) - 1.5%, astigmatism (cylinder at least -0.50 D) - 58.7% and anisometropia (SE difference at least 1.00 D) - 11.2%. After adjusting for age and gender, currently doing more than 20.5 h of reading and writing a week was found to be positively associated with myopia [odds ratio 1.12 (95% CI 1.04-1.20, p = 0.003)], as was reading and writing at a close distance and a better educational stream. The prevalence of myopia (73.9%) in Singapore teenagers is high. Current reading and writing habits, reading at close distances and a better educational stream are possible risk factors for myopia.

Adolescent↗
PubMed1999

Refractive error consequences of reversed-optic AMO SI-40NB intraocular lens.

OBJECTIVE: To evaluate the refractive consequences of inadvertently implanting a reversed-optic AMO SI-40NB posterior chamber intraocular lens (IOL). DESIGN: Retrospective case series. METHODS: One surgeon (BLH) implanted 457 SI-40NB IOLs over a 2-year period beginning on January 1, 1996, and ending on December 31, 1997. Six of these IOLs (1.3%) were noted to have been implanted with a reversed optic. The authors retrospectively reviewed the target spherical equivalent refractive errors (SEREs) and actual postoperative SEREs for all 457 eyes. MAIN OUTCOME MEASURES: The SRK-II formula was used to predict target SEREs. Actual postoperative SEREs were determined at 1 month after surgery using either a manifest or an automated refraction. Target postoperative SEREs were subtracted from actual postoperative SEREs to calculate diopter surprises, or the degree to which the actual SEREs differed from the target SEREs. RESULTS: The mean (+/-standard deviation) diopter surprise for reversed-optic SI-40NB IOLs was 0.01 (+/-0.89) diopter (D) more myopic than predicted; diopter surprises ranged from -1.39 D to +1.42 D. The mean diopter surprise for nonreversed SI-40NB IOLs was 0.18 (+/-0.81) D more hyperopic than predicted; diopter surprises ranged from -1.88 D to +2.56 D. The difference between the mean diopter surprises (0.19 D) was not statistically significant (t = 0.56, P = 0.57). CONCLUSIONS: A reversed-optic SI-40NB IOL is as likely to produce a satisfactory refractive result as a nonreversed IOL. Therefore, the refractive consequences of a reversed-optic SI-40NB IOL do not warrant the risks associated with repositioning the lens.

Aged↗
PubMed1999

Changes in myopic refractive error with nine months' extended wear of hydrogel lenses with high and low oxygen permeability.

BACKGROUND: A small but significant increase in myopia after extended wear of low oxygen permeability (Dk) hydrogel lenses has been previously reported; however, the specific impact of hypoxia on refractive status and corneal curvature with extended wear are not well documented. The purpose of this study was to compare the refractive changes induced over a period of 9 months' extended wear with high-Dk fluorosiloxane hydrogel lenses and low-Dk hydrogel lenses. METHODS: Adapted daily wear contact lens wearers were randomly assigned to one of two groups. The low-Dk group wore etafilcon A (Dk = 28) for up to 7 days and 6 nights and the high-Dk group wore lotrafilcon A (Dk = 140) for up to 30 days and nights. Refractive error and corneal curvature were measured at 3-month intervals over 9 months of extended wear. RESULTS: The etafilcon A group demonstrated an average increase in myopia of 0.30 D over the 9-month period; however, no change in spherical myopic correction was measured in the lotrafilcon A group. The cylindrical component did not change in either group. A stratified analysis revealed a greater increase in myopia for low myopes than moderate myopes in the etafilcon A group but no difference in the lotrafilcon A group. Keratometric analysis revealed no change in the etafilcon A group and a small degree of central corneal flattening in both major meridians of 0.35 D in the lotrafilcon A group. CONCLUSIONS: Nine months of extended wear of low-Dk lenses is associated with a small degree of myopic progression in adult myopes that appears to be reversible. Wearing fluorosiloxane-hydrogel lenses of high-Dk had no impact on refractive error and may be associated with a small degree of central corneal flattening.

Adult↗
PubMed2002

[The practice guideline 'Refraction errors' from the Dutch College of General Practitioners: response from the perspective of ophthalmology].

The practice guideline 'Refraction errors' from the Dutch College of General Practitioners provides a guideline for referral of persons aged 6 to 65 with gradual loss of vision to either an optician or an ophthalmologist. In this guideline, relevant questions regarding important symptoms are missing, and the value of the proposed examination employing 'diagnostic refraction' has insufficient scientific support. In addition, the possibility to send children between 6 and 10 years of age to the optician may be dangerous for some of the patients, and there are no explicit indications for the urgency of referral to the ophthalmologist. Due to these short-comings, the guideline may fail to provide optimal preventive and therapeutic eye care for the target group of patients concerned.

Adolescent↗
PubMed2005

Delayed visual attention caused by high myopic refractive error.

Delayed visual maturation (DVM) is usually a retrospective diagnosis given to infants who are born with no or poor visually-directed behavior, despite normal acuity on objective testing, but who recover months later. This condition can be organized into several types based on associated neurodevelopmental or ocular findings, but the etiology of DVM is probably complex and involves multiple possible origins. Here we report two infants who presented with delayed visual maturation (attention). They were visually unresponsive at birth but were later found to have high myopic errors. Patient 1 had -4 D right eye, -5 D left eye. Patient 2 had -9 D o.u. Upon spectacle correction at 5 and 4 months, respectively, both infants immediately displayed visually-directed behavior, suggesting that a high refractive error was the cause of inattention in these patients. These findings could add to knowledge surrounding DVM and the diagnosis of apparently blind infants. Findings presented here also indicate the importance of prompt refractive error measurement in such cases.

Attention↗