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At least 811 records · Page 45Linked to original sources
PubMed2003

The efficacy of photoscreening for amblyopiagenic factors in a high risk population.

BACKGROUND: Amblyopia is the leading cause of monocular "legal" blindness in children and young adults, affecting 3% to 5% of the population. Factors producing amblyopia can be detected through a complete eye examination. Although it is important to treat children at risk for amblyopia as early as possible, appropriate screening methods for severely impaired individuals are lacking. The purpose of this study was to assess the ability of a photoscreening camera to detect amblyopiagenic factors (strabismus, unequal refractive error, and media opacities) in a group of disabled children, who were currently unscreenable with standard methodology. METHODS: Fifty-four high risk individuals, 6-20 years in age, were evaluated for amblyopiagenic factors using the MTI photoscreening camera, pre- and post-cycloplegia. The "gold standard" for comparison was a concurrent complete eye examination, including ocular health, visual acuity estimation, motility, ophthalmoscopy and clinical cycloplegic refractive error determination. Criteria for a "failure" on the clinical examination included myopia greater than -1.00 diopters (D), hyperopia greater than +3.00 D (2-6 years) and greater than +2 D (over 6 years), astigmatism greater than 1.5 D, unequal refractive error greater than 1.5 D, any strabismus, or any media opacity. RESULTS: Fifty- four individuals with disabilities, deemed untestable by standard vision screenings, were evaluated. The number of children with amblyopiagenic factors by complete cycloplegic ophthalmologic examination was 30 (55%) and by photoscreening was 25 (46%). Using the MTI photoscreener, the sensitivity was determined to be 83% with a specificity of 79%. The positive and negative predictive values of photoscreening were 83% and 79% respectively. CONCLUSIONS: The MTI photoscreener can detect such amblyopiagenic factors as high refractive error, strabismus, unequal refractive error, and significant media opacity. Photoscreening is an excellent way of obtaining valid vision screening with limited patient cooperation. Using photoscreening data, proper referrals can be made and prioritized for disabled individuals.

Adolescent↗
PubMed1999

Does overcorrecting minus lens therapy for intermittent exotropia cause myopia?

BACKGROUND: Overcorrecting minus lens therapy has been used as a treatment for intermittent exotropia. It is based on the principle that an exotropic deviation will be decreased by stimulating accommodative convergence with additional minus power in spectacles. Because excessive accommodation has been implicated as a cause of myopia, there is theoretical concern that overcorrecting minus lens therapy for exotropia may cause myopia. OBJECTIVE: To investigate the effect of overcorrecting minus lens therapy for exotropia on the progression of myopia. DESIGN: A retrospective chart review. SUBJECTS AND METHODS: Seventy-four patients with intermittent exotropia were treated with overcorrecting minus lens therapy for at least 6 months (6-month treatment group), and a 34-patient subset of them received overcorrecting minus lens therapy for 5 years (5-year treatment group). The mean change in refractive error (spherical equivalent of the fixing eye) of these 2 groups 5 years after initial examination was compared with the mean change in refractive error of a control group of 45 patients with intermittent exotropia who did not receive overcorrecting minus lens therapy. RESULTS: At the time of initial examination, the mean (+/-SD) refractive error was 0.00 +/- 1.40 diopters (D) in the control group, 0.00 +/- 1.50 D in the study group, and -0.10 +/- 1.50 D in the 5-year study group, all of which were essentially identical. Five years after initial examination, the mean change in refractive error was -1.40 +/- 2.80 D in the control group, -1.52 +/- 1.80 D in the 6-month treatment group, and -1.54 +/- 1.80 D in the 5-year treatment group. These differences in the change in refractive error (myopic shift) were not statistically significant (t test), and the differences are clinically unimportant. CONCLUSION: Overcorrecting minus lens therapy for intermittent exotropia does not appear to cause myopia.

Accommodation, Ocular↗
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↗
PubMed2001

The effect of reading and near-work on the development of myopia in emmetropic boys: a prospective, controlled, three-year follow-up study.

This study aimed to investigate the effect of reading and near work on myopic development in emmetropic boys in school age. It involved totally 114 children in two groups. Right eyes of 67 randomly selected students (mean age=12.93) with mean 6 h of reading and near work (Group 1) were compared with the right eyes of 47 apprentices (mean age=12.96) working as skilled laborers (Group 2). Cycloplegic refraction, keratometric readings and biometric measurements including anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD) and axial length (AL) were performed for 3 years at 18 month intervals. Two analyses were conducted: (1) for subjects in both groups with baseline refractive error from +0.50 to -0.50 D; (2) for all subjects in both groups with baseline refractive error from +1.00 to -1.00 D. For subjects with baseline refractive error of +/-0.50 D, myopic shift was present in 20 of 41 (48.8%) in group 1 and in seven of 37 (18.9%) in group 2 at the end of the study. The magnitude of the myopic shift was 0.56 and 0.07 D in group 1 and 2, respectively. For subjects with a baseline refractive error of +/-1.00 D, myopic progression was present in 40 of 67 (59.7%) in group 1 and in 10 of 47 (21.3%) in group 2 at the last readings. In this larger refractive range, the magnitude of the myopic shift was 0.61 and 0.12 D in group 1 and 2, respectively. The mean ACD, VCD and AL were significantly higher in the last readings after 36 months than in the first readings (for each, P=0.0001) in group 1. There was no statistically significant difference between two measurements of these parameters in group 2. The final keratometric dioptric readings were lower than the first values (for each, P=0.0001) in both groups at the end of the study. This prospective and controlled study suggested that reading and near work, important environmental factors, might cause refractive myopic shifts in emmetropic students. The myopic shift was primarily related to significant increases in ACD, VCD and AL in this young age group.

Anterior Chamber↗
PubMed2003

Repeatability and validity of the PowerRefractor and the Nidek AR600-A in an adult population with healthy eyes.

We assessed the repeatability and validity of the PowerRefractor and the Nidek AR-600A autorefractor. This is the first independent study conducted on adults to evaluate the performance of these instruments in a laboratory setting. Fifty subjects (23 males and 27 females) aged 16 to 61 years (mean, 37 +/- 12) participated in the study. The validity of the PowerRefractor and the Nidek autorefractor readings were determined by comparing them to subjective refraction. Measurements of refractive error were obtained from the two instruments on two separate occasions to assess their repeatability. The measured refractive error was converted into a dioptric power matrix for data analysis. No significant difference was found between the measurements obtained with the two instruments and the subjective refraction. The estimate of refractive error given by the two instruments was also found to be repeatable. In addition to measuring the refractive error, the PowerRefractor also offers the facility to measure eye position, pupil size, and dynamics of accommodation. We suggest some improvements to the PowerRefractor measurement technique to standardize its clinical use and to improve accuracy.

Adolescent↗
PubMedDate not supplied

Polaroid photorefractive screening of infants.

We modified a Polaroid SE camera for use as a photoretinoscope. A total of 187 infants between 2 and 18 months of age were photographed using this device. About half of these infants (97) participated in a double blind study in which the results of photorefraction were compared with those of standard cycloplegic retinoscopy. Eighty-three infants were photographed without cycloplegia. Thirty-four infants were photographed while cyclopleged. Photographs were evaluated for significant refractive errors and other ocular abnormalities. The effectiveness of the camera system to screen for significant refractive errors without the use of cycloplegia was assessed. Infants were identified to be at risk by photorefraction if, in any photograph, a hyperopic bright crescent calculated to be greater than or equal to +1.25 D was present in the pupil. Clinically significant refractive errors were defined by the results of cycloplegic retinoscopy: "at-risk" infants had either 3.5 D or more hyperopia in either eye, or astigmatism in either eye greater than or equal to 2.5 D, or anisometropia greater than or equal to 1.5 D. With these clinical criteria and the above photographic screening criterion, the camera's sensitivity and specificity were 83% and 69%, respectively. The present system compares favorably with earlier, more sophisticated units in alerting practitioners to potentially significant refractive errors in infants. Additionally, as a screening tool, this device offers the benefits of being inexpensive and easy to use, and of providing immediate feedback.

Calibration↗
PubMed1982

Aphakic ultrasonographic refraction in adults. Comparison with retinoscopy and subjective refraction.

A simple method of aphakic refraction using ultrasonographic axial length measurement and keratometry was tried on 97 eyes of adult aphakic patients. The refractive errors determined by this method and by retinoscopy were compared to the subjective refraction of the same eyes. The ultrasonographically determined refractive errors were significantly nearer the subjective refraction than were the retinoscopically determined refractive errors.

Aged↗
PubMedDate not supplied

Recurrent esotropia following early successful surgical correction of congenital esotropia.

A study was conducted using a group of congenital esotropes who had an adequate surgical alignment prior to 18 months of age, to determine how many of them would redevelop esotropia. In the group that redeveloped the condition, a high percentage of the esotropia was accommodative in nature and was therefore able to be corrected with spectacles. Both the initial refractive error and changes in refractive error were noted to be significant. This study emphasizes the importance of monitoring the refractive state continuously, especially in children with subnormal fusion.

Accommodation, Ocular↗
PubMedDate not supplied

Three year results of the Prospective Evaluation of Radial Keratotomy (PERK) study.

The Prospective Evaluation of Radial Keratotomy (PERK) study is a nine-center clinical trial of a standardized technique of radial keratotomy in 435 patients who had simple myopia with a preoperative refractive error between -2.00 and -8.00 diopters (D). We report results for one eye of each patient. The surgical technique consisted of eight incisions using a diamond micrometer knife with the blade length determined by intraoperative ultrasonic pachymetry and the diameter of the central clear zone determined by the preoperative refractive error. At three years after surgery, 58% of eyes had refractive error within one diopter of emmetropia; 26% were undercorrected, and 16% were overcorrected by more than one diopter. Uncorrected visual acuity was 20/40 or better in 76% of eyes. The operation was more effective in eyes with a preoperative refractive error between -2.00 and -4.37 diopters. Between one and three years after surgery, the refractive error changed by 1.00 diopter or more in 12% of eyes, indicating a lack of stability in some eyes.

Astigmatism↗
PubMed1987

Three-year results of the Prospective Evaluation of Radial Keratotomy (PERK) Study.

The Prospective Evaluation of Radial Keratotomy (PERK) study is a nine-center clinical trial of a standardized technique of radial keratotomy in 435 patients who had simple myopia with a preoperative refractive error between -2.00 and -8.00 diopters (D). The authors report results for one eye of each patient. The surgical technique consisted of eight incisions using a diamond micrometer knife with the blade length determined by intraoperative ultrasonic pachymetry and the diameter of the central clear zone determined by the preoperative refractive error. At 3 years after surgery, 58% of eyes had refractive error within 1.00 D of emmetropia; 26% were undercorrected and 16% were overcorrected by more than 1.00 D. Uncorrected visual acuity was 20/40 or better in 76% of eyes. The operation was more effective in eyes with a preoperative refractive error between -2.00 and -4.37 D. Between 1 and 3 years after surgery, the refractive error changed by 1.00 D or more in 12% of eyes, indicating a lack of stability in some eyes. In the 435 eyes, there was a small number of complications including six eyes that lost two or three lines of best-corrected acuity, 16 that experienced vascularization of the incisions, 2 that had delayed bacterial keratitis, and 4 that had recurrent epithelial erosions.

Follow-Up Studies↗
PubMed1996

Atropine versus cyclopentolate plus tropicamide in esodeviations.

BACKGROUND AND OBJECTIVE: The correction of the total hypermetropic refractive error in the management of esodeviations is well accepted. The choice of the appropriate cycloplegic agent is still not settled. Despite evidence that atropine will more effectively uncover the total refractive error, cyclopentolate in combination with other cycloplegic agents continues to be recommended. This study evaluates the use of atropine compared with a combination of cyclopentolate and tropicamide and analyzes age, size of the refractive error, and size of the esodeviation as possible contributing variables in the response. PATIENTS AND METHODS: The records of 74 patients who underwent refraction with atropine 1% on one occasion and a combination of 1% cyclopentolate and 1% tropicamide on another occasion were reviewed. The mean and range of refractive errors for each eye for each group were determined. Comparisons were made for groups depending on age, size of the refractive error, and size of the esodeviation. RESULTS: The amount of hypermetropia determined with atropine was significantly higher than the amount determined with the combination of cyclopentolate and tropicamide. This difference was significant for three age groups of three groups with increasing amounts of hypermetropia, and two groups with differing amounts of esodeviations. In addition, 11% of right eyes and 19% of left eyes showed 1.25 D or more of hypermetropia with atropine. CONCLUSION: Refraction with 1% atropine ointment yields a significantly larger amount of hypermetropia than does refraction with a combination of cyclopentolate and tropicamide. This difference is statistically significant regardless of age, amount of hypermetropia, or size of the esotropia.

Administration, Topical↗
PubMed1992

Development of accommodation and convergence in infancy.

Paraxial photorefraction was used to assess the development of accommodation and convergence in a large sample of infants under 1 year of age. The infants viewed small dolls placed at various distances (200-25 cm). The majority of infants at all ages demonstrated appropriate convergence for target distance, regardless of manifest refractive error. However, accommodation lagged behind convergence in development. Infants under 2 months tended to demonstrate either flat accommodation responses with a fixed plane of focus at around 30 cm, or accommodated appropriately for near targets, but failed to relax their accommodation sufficiently for the more distant targets. Thus, the focussing error increased with increasing target distance. Since the manifest refractive error was estimated by extrapolating the accommodation function to 0 diopters demand, these infants demonstrated spuriously myopic behavior. After 2 months, the majority of infants showing emmetropic behavior had accommodation responses that changed appropriately with target distance. However, infants with myopic or hyperopic manifest refractive errors displayed a variety of accommodative styles.

Accommodation, Ocular↗
PubMed2004

Compensation for experimentally induced hyperopic anisometropia in adolescent monkeys.

PURPOSE: Early in life, the optical demand associated with the eye's effective refractive state regulates emmetropization in many species, including primates. However, the potential role of optical demand and/or defocus in the genesis of common refractive errors, like myopia, that normally develop much later in life is not known. The purpose of this study was to determine whether chronic optical defocus alters refractive development in monkeys at ages corresponding to when myopia typically develops in children. METHODS: A hyperopic anisometropia was produced in seven adolescent rhesus monkeys by photorefractive keratectomy (PRK) with an excimer laser. Standard treatment algorithms for correcting myopia in humans were used to selectively flatten the central cornea of one eye thereby producing relative hyperopic refractive errors in the treated eyes. The laser ablation zones were 5.0 mm in diameter and centered on the monkeys' pupils. The laser procedures were performed when the monkeys were 2 to 2.5 years old, which corresponded to onset ages between approximately 8 and 10 human years. The ocular effects of the induced anisometropia were assessed by corneal topography, retinoscopy, and A-scan ultrasonography. RESULTS: By approximately 30 days after PRK, the experimentally induced refractive errors had stabilized and the treated eyes were between +0.75 and +2.25 D more hyperopic than their fellow eyes. Subsequently, over the next 300 to 400 days, six of the seven monkeys showed systematic reductions in the degree of anisometropia. Although some regression in corneal power occurred, the compensating refractive changes were primarily due to relative interocular differences in vitreous chamber growth. CONCLUSIONS: Vision-dependent mechanisms that are sensitive to refractive error are still active in adolescent primates and probably play a role in maintaining stable refractive errors in the two eyes. Consequently, conditions that result in consistent hyperopic defocus could potentially contribute to the development of juvenile onset myopia in children.

Animals↗
PubMed1997

Cryotherapy and laser treatment for acute retinopathy of prematurity: refractive outcomes, a longitudinal study.

BACKGROUND: Infants who require treatment for threshold retinopathy of prematurity are at increased risk of developing refractive errors. Following the introduction of laser treatment for threshold disease, the clinical impression was that the degree of myopia was reduced compared with cryotherapy. METHODS: A longitudinal study was carried out of refractive error at 3 and 12 months in 19 patients undergoing cryotherapy and 15 patients undergoing laser treatment. RESULTS: At 3 months the median spherical equivalent refractive error in the right eye was -3.25 dioptres after cryotherapy and +0.25 dioptres after laser therapy (similar results left eye). The median spherical equivalent refractive error in the right eye at 12 months was -5.25 dioptres following cryotherapy and -0.50 dioptres after laser (similar results left eye). There was a statistically significant difference in median spherical refractive error between the therapies at 3 months and 12 months (p < 0.05 Wilcoxon rank sum) in both eyes. CONCLUSION: Laser therapy is associated with lower degrees of myopia during the first year of life, which is clinically significant in terms of visual performance and development.

Acute Disease↗
PubMed2000

Normal emmetropization in infants with spectacle correction for hyperopia.

PURPOSE: The development of emmetropic refraction is known to be under visual control. Does partial spectacle correction of infants' refractive errors, which has been shown to have beneficial effects in reducing strabismus and amblyopia, impede emmetropization? The purpose of the present study was to perform the first longitudinal controlled trial to investigate this question in human subjects. METHODS: Children identified as having significant hyperopia in a population screening program at age 8 to 9 months were assigned to treated (partial spectacle correction) or untreated groups. A control group of infants with no significant refractive errors at screening was also recruited. Measurements of retinoscopic refraction under cycloplegia were taken at 4- to 6-month intervals up to the age of 36 months, and changes in refraction of 148 subjects were analyzed longitudinally. RESULTS: Refractive error decreased toward low hyperopic values between 9 and 36 months in both hyperopic groups. By 36 months, this reduction of hyperopia showed no overall difference between children who were treated with partial spectacle correction and those who were not. Despite the improvement, both hyperopic groups' mean refractive error at 36 months remained higher than that of the control group. When infants in all three groups were considered together, the rate of reduction of refractive error was, on average, a linear function of the initial level of hyperopia. CONCLUSIONS: The benefits of spectacle correction for infants with hyperopia can be achieved without impairing the normal developmental regulation of refraction.

Accommodation, Ocular↗
PubMed1981

Regression curves for the optical parameters of the eye.

Based on the data collected by Stenstrom (1948), the regression curves involving refractive error and axial length are examined. The regression of refractive error on axial length is shown to be nonlinear; it curves upward at low axial lengths and downward at high axial lengths. It is shown that this curve can be partially accounted for by the lack of compensating corneal changes for extreme values of the axial length. On the other hand, the regression of axial length on refractive error, is shown to be approximately linear. The slope of this regression is related to a formula derived from geometrical optics.

Cornea↗
PubMed1984

Visually related headache in a preschooler.

A female patient, age 4, presented with the chief complaint of severe headaches. Onset was within the past year. A neurological evaluation was conducted with negative results. Our testing revealed a moderate hyperopic refractive error, a marked lag of accommodation, and reduced stereopsis. The refractive error was corrected and a 6 week follow-up evaluation was performed. Correction of the refractive error resulted in abatement of the headache complaint, improved visual function, and improved preschool performance.

Accommodation, Ocular↗
PubMed1985

A statistical analysis of radial keratotomy results.

Radial keratotomy surgery was begun in a private ophthalmologic practice in July 1980. A statistical analysis of the first 557 cases is presented. The mean postoperative refractive error was -4.00 diopters. One year after surgery, 95% of the patients with a preoperative refractive error of -3.00 diopters or less had a visual acuity of 20/40 or better, and 79% of those with a refractive error of -3.25 to -6.00 diopters had a visual acuity of 20/40 or better. The mean decrease in keratotomy readings at six months postoperatively was 2.95 diopters. Of the patients with a preoperative refractive error of less than 6 diopters, 85% wore glasses rarely or not at all, whereas 15% wore a refractive correction full time.

Adolescent↗