Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “refractive error”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,315 records · Page 73Linked to original sources
PubMedDate not supplied

Prevalence of astigmatism among students in northern Greece.

PURPOSE: To assess the prevalence of astigmatism in a sample of 1738 students (15-18 years old) from Northern Greece. METHODS: Collection of the sample was based on a questionnaire method. Statistical analysis included estimation of the prevalence of astigmatism and the distribution of students according to their cylindrical values. We also checked whether heredity or sex affected the occurrence of astigmatism. RESULTS: The prevalence of astigmatism was 10.2%. It was mostly at low levels, up to 2 D cyl. Females ran a significantly higher risk of astigmatism than males, and heredity seemed to be an important predisposing factor for this refractive error. CONCLUSIONS: There is considerable variability in the prevalence of astigmatism worldwide, as indicated by different studies. However, this refractive error prevails at low levels in the Greek student population, compared with other countries.

Adolescent↗
PubMed2004

Photorefractive keratectomy for anisometropic amblyopia in children.

PURPOSE: To assess the safety and efficacy of photorefractive keratectomy (PRK) in children with anisometropic amblyopia and to define the characteristics of children who may be candidates for PRK. METHODS: This thesis comprises four parts: (1) a retrospective analysis of risk factors predictive of amblyopia treatment failure in 104 children, (2) a prospective study of pachymetry in 198 eyes of 108 children, (3) development and implementation of a protocol to perform PRK under general anesthesia, and (4) a prospective interventional case-comparison study of PRK in 11 noncompliant children with anisometropic amblyopia to evaluate safety and long-term outcomes. Compliant and noncompliant children with anisometropic amblyopia were analyzed as controls. RESULTS: Factors associated with conventional anisometropic amblyopia treatment failure were poor compliance (P = .004), age 6 years or older (P = .01), astigmatism > or = 1.5 diopters (P = .0002), and initial visual acuity of 20/200 or worse (P = .02). Central and paracentral pachymetry measurements were similar to published adult values. The general anesthesia protocol was efficient, and the laser functioned properly in all cases. All children did well with no anesthesia-related or treatment-related complications. Two years following PRK, the mean reduction in refractive error was 9.7 +/- 2.6 diopters for myopes (P = .0001) and 3.4 +/- 1.3 diopters for hyperopes (P = .001). The cycloplegic refractive error in 9 of 11 treated eyes was within 3 diopters of that in the fellow eye. Uncorrected visual acuity in the amblyopic eye improved by > or = 2 lines in seven of nine children; best-corrected visual acuity improved by > or = 2 lines in six of nine children. Stereopsis improved in five of nine children. The mean visual acuity of the PRK patients at last follow-up was significantly better than that of noncompliant controls (P = .003). The safety and efficacy indices for PRK in this study were 1.24 and 1.12, respectively. CONCLUSIONS: Photorefractive keratectomy can be safely performed in children with anisometropic amblyopia. Visual acuity and stereopsis improved in most eyes, even in older children. Photorefractive keratectomy may have an important role in the management of anisometropic amblyopia in noncompliant children.

Amblyopia↗
PubMed1996

Refractive changes during 72-hour exposure to high altitude after refractive surgery.

PURPOSE: The authors prospectively analyzed refractive and pachymetric parameters during exposure to high altitude after radial keratotomy (RK) and photorefractive keratectomy (PRK). METHODS: The authors measured manifest and cycloplegic refraction, keratometry, computed video keratography, and central and peripheral pachymetry in six subjects who have undergone RK (11 eyes), six who have undergone PRK (12 eyes), and nine with myopia (17 eyes) at sea level and on three consecutive days at 14,100 feet. All measurements were repeated 1 week after subjects returned to sea level. RESULTS: Subjects who have undergone RK demonstrated a significant and progressive increase in spherical equivalence (+0.30 +/- 0.50 diopters on day 1 and +1.52 +/- 1.01 diopters on day 3; P < 0.001) and a decrease in keratometry values during exposure to altitude when compared with control subjects with myopia. Healthy subjects and those who have had PRK demonstrated no significant change in refractive error. Pachymetry measurements demonstrated significant peripheral corneal thickening in all three groups (RK, P < 0.004; PRK, P < 0.007; control subjects, P = 0.0006) by day 3 at high altitude. Refraction, keratometry, and pachymetry returned to baseline (P = 1.000) after return to sea level. CONCLUSIONS: Seventy-two-hour exposure to high altitude in subjects who have had RK induces a significant, progressive, and reversible hyperopic shift in refraction with corresponding video keratographic and keratometric changes. The authors hypothesize that the high-altitude hypoxic environment causes increased corneal hydration in the area of the RK incisions, which may lead to central corneal flattening and a hyperopic shift in refractive error. Subjects who have had PRK and those with myopia are not susceptible to this refractive shift. The authors' RK data suggest that the time since surgery and the amount of surgery are related to the degree of hyperopic shift during altitude exposure.

Adult↗
PubMed1991

Effects of apomorphine, a dopamine receptor agonist, on ocular refraction and axial elongation in a primate model of myopia.

The authors examined the effect of local administration of a dopamine receptor agonist on visual deprivation-induced excessive ocular growth and myopia. Eight rhesus monkeys were monocularly deprived of vision from birth with opaque contact lenses. Four of the monkeys received drops of 1% apomorphine HCl 2-3 times/day in the occluded eye; the four control monkeys received vehicle only. Axial lengths were determined by A-scan ultrasonography at birth and at 5-7 months of age. The authors assessed the axial elongation by comparing the postnatal growth in the axial dimension of the occluded eyes with the postnatal growth in nonoccluded eyes. In three of the four control monkeys, occlusion increased axial growth by an average of 1.3 mm. In contrast, they found that growth of the occluded and nonoccluded eyes of the apomorphine-treated monkeys was equivalent, except in one monkey whose nonoccluded eye did not develop normally and was anomalously small. At 6.5-9.5 months of age, three of four controls had myopic refractive errors (-3 to -7 diopters) in the occluded eyes; three of four of the apomorphine-treated monkeys had hyperopic refractive errors (+1-(+)3 diopters) in their occluded eyes. The occluded eye of the fourth monkey was only -0.5 diopters myopic. The findings suggest that apomorphine administration retards excessive axial elongation and the concomitant development of myopia associated with visual deprivation in primates.

Administration, Topical↗
PubMed1996

Crystalline lens parameters in infancy.

Despite the importance of lens power to ocular development, few data are available regarding infant crystalline lens parameters. Lens and corneal radii of curvature were measured in the horizontal meridian using a video-based keratophakometer, and refractive error was measured by cycloplegic retinoscopy in 19 out of 27 infants ranging in age from 3 to 18 months. The median refractive error was +1.50 D, and the median corneal power was 43.5 D. Using previously reported values for axial ocular dimensions, the median anterior and posterior lens radii of curvature were 8.7 and 5.6 mm, respectively, both substantially flatter than infant schematic eye values. The median equivalent refractive index of the lens was 1.49, considerably higher than previous reported schematic values for infants or children. There was a significant reduction in hyperopia with age (r = -0.47, P = 0.043), but no age-related trends in lens or corneal radii of curvature, suggesting that calculated values for lens power and equivalent index may undergo substantial decline with age during early childhood development as axial length increases. Most of the decrease in lens power (75%) may be due to decreases in equivalent index rather than to flattening of the surface radii of curvature. Videophakometry appears to be a feasible and useful technique for documenting the role of the crystalline lens in infant ocular development.

Anthropometry↗
PubMed1996

Posterior routes of choroidal blood outflow in high myopia.

PURPOSE: A few reports in the ophthalmic literature have described choroidal blood outflow through posterior routes. Most of the patients reported were highly myopic; therefore, a correlation between such posterior routes and high myopia has been suspected. The authors examined highly myopic eyes using indocyanine green (ICG) videoangiography and investigated the prevalence and clinical significance of posterior routes in them. METHODS: The authors examined 255 highly myopic eyes (146 patients) using ICG videoangiography. All had refractive errors greater than--8.25 diopters (D). They also examined a control group consisting of 42 eyes (26 patients) that had refractive errors within +/- 3D. RESULTS: Of 255 highly myopic eyes, 61 (23.9%) had choroidal blood outflow through posterior routes. These routes were classified by type of vein according to its penetration site. One drained into the margin of the optic nerve head, and the other penetrated the sclera near the macula. However, only 1 of the 42 eyes (2.4%) in the control group showed choroidal outflow by a posterior route. The prevalence of posterior routes was significantly higher in the highly myopic eyes than in the control group (P < 0.05). CONCLUSION: Posterior routes of choroidal blood outflow were observed in nearly 25% of highly myopic eyes. These vessels appear to be one of the major routes of posterior choroidal outflow in highly myopic eyes.

Adolescent↗
PubMed1999

The eye in childhood.

Normal visual development is rapid during the first six months of life and continues through the first decade. Young children are uniquely sensitive to conditions that interfere with vision and visual development. Amblyopia, or functionally defective development of the central visual system, may be caused by common vision problems such as strabismus, uncorrected refractive errors and deprivation secondary to occlusion. Prematurity is especially associated with eye pathology, including retinopathy of prematurity, amblyopia, strabismus and refractive errors. When detected early, amblyopia and many other childhood vision abnormalities are treatable, but the potential for correction and normal visual development is inversely related to age. Since many affected children are asymptomatic, early detection of abnormal visual function requires effective screening throughout early childhood. Special considerations apply to screening examinations of children born prematurely.

Age Factors↗
PubMed2000

Clinical analysis of central islands after laser in situ keratomileusis.

PURPOSE: To analyze the incidence and clinical characteristics of central islands after laser in situ keratomileusis (LASIK) and to elucidate factors associated with their formation. SETTING: Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. METHODS: Laser in situ keratomileusis was performed in 103 eyes of 61 patients with myopia ranging from -4.0 to -13.5 diopters (D) using the Hansatome (Chiron) and SVS Apex Plus (version 3.2.1) excimer laser (Summit Technology) in which the anti-central-island program was implemented. After 1 week, corneal topography (Orbscan, Orbtek) was done and manifest refraction and visual acuity were measured. RESULTS: Postoperatively, the mean uncorrected visual acuity (UCVA) and best corrected visual acuity (BCVA) were 0.12 and 0.06 (logMAR scale), respectively, and the mean refractive error (spherical equivalent) was 0.07 D +/- 0.76 (SD). On topographic examination, a central island was defined as an area of higher refractive power of more than 1.5 D and 2.5 mm or more in diameter. Budding or isolated central islands were observed in 12 eyes of 12 patients (11.7%). The peak, height, and area of the islands were 41.5 +/- 3.1 D, 5.6 +/- 1. 9 D, and 3.5 +/- 1.1 mm(2), respectively. In the eyes with central islands, there were statistically significant differences in the postoperative change in UCVA and BCVA (P <.05). There was no significant correlation between the occurrence of a central island and preoperative refractive error, corneal thickness, age, or in sex and correction of astigmatism (P >.05). CONCLUSION: Despite use of the anti-central-island pretreatment program, the occurrence of central islands after LASIK was significant, as in photorefractive keratectomy. Further studies of the effect of central islands on surgical results and clinical progress and measures to prevent the occurrence are needed.

Adult↗
PubMed2006

Asthenopia in schoolchildren, orthoptic and ophthalmological findings and treatment.

The aim of this study was to describe the orthoptic and ophthalmological findings in schoolchildren with asthenopia, to correlate them with asthenopic symptoms and to evaluate the effect of treatment. One hundred and twenty schoolchildren, aged 6-16 years, were included in the study. They were all referred by school nurses, for asthenopic symptoms. An orthoptic and ophthalmological assessment was performed. The main diagnoses were accommodative insufficiency, convergence insufficiency, refractive errors, and latent strabismus. Reading glasses could help 98% of the schoolchildren with reduced accommodation, and 94% of the children with refractive errors and heterophorias were helped with appropriate spherical, cylindrical and prism correction. Convergence exercise reduced the symptoms in all patients with convergence insufficiency. Ninety-three percent of all 120 schoolchildren were symptom free 3-6 month after treatment had started. By an orthoptic and ophthalmological examination abnormalities in schoolchildren with asthenopia related to visual problems can be identified. Most of the children were relieved from their symptoms by giving adequate glasses, convergence exercises and surgery.

Accommodation, Ocular↗
PubMed1985

An animal model of myopia.

Myopia develops in macaque monkeys when their lids are surgically fused at birth and kept closed for one year. This experimental refractive error has many features in common with human myopia: It is caused by progressive axial elongation of the eye, is often accompanied by fundus changes, and can only be induced before eye growth has been completed. Myopia does not develop in animals raised in the dark; thus, it is triggered by an alteration of the visual input and is presumably mediated by the nervous system. In Macaca arctoides, atropine administration prevents abnormal eye elongation, and this suggests that lid-fusion myopia is caused by excessive accommodation. In M. mulatta, atropine is ineffective; furthermore, myopia develops when lids are sutured after interruption of the optic pathways. Thus, in this species accommodation can be ruled out as a determinant of eye elongation, and other neural mechanisms may be responsible for the refractive error. Our experiments suggest that the refractive state is largely programmed on a genetic basis, but that an abnormal visual experience can disrupt the process of postnatal eye growth and induce axial myopia.

Accommodation, Ocular↗
PubMedDate not supplied

Photorefractive keratectomy for myopia: single vs double-zone treatment in 166 eyes.

We studied 58 single-zone and 58 double-zone treatments; attempted correction ranged between 6.50 and 10.00 D. There were no significant differences in the age or sex in the two groups. All the eyes received the same topical corticosteroid therapy. Refractive outcome showed a greater overcorrection in the double-zone than in the single-zone treatments, but the difference was not statistically significant (F = 3.17, p = 0.07). The refractive error shifted toward myopia significantly over time (F = 561.34, p < 0.0001). In the first-, third- and sixth-month follow up, the mean refractive error was +2.39 (+/- SD) +/- 1.94, +0.45 +/- 1.54, and -0.60 +/- 1.50 D in the single-zone treatments, while in the double-zone ones they were +1.95 +/- 2.49, +0.87 +/- 2.85 and +1.34 +/- 2.57 D, respectively. The Student's T test demonstrated a statistically significant difference of refractive outcome between the two groups only at 6 months (T = -3.788, p < 0.0001). Corneal haze decreased during follow up (F = 123.38, p < 0.0001) and was more severe in the single-zone than in the double-zone treatments (F = 9.28, p = 0.002). The Student's T test showed a significant difference at 6 months (T = 2.877, p = 0.006). The double-zone procedure appeared to be safer than the single-zone, but a longer follow up period and a greater number of treatments are required to draw final conclusions.

Adult↗
PubMed1999

Myopia progression in adolescent wearers of soft contact lenses and spectacles.

The purpose of this 3-year, randomized clinical trial was to determine the difference in myopia progression in adolescents wearing soft contact lenses over a control group wearing spectacles. A total of 175 adolescents between the ages of 11 and 14 years were randomized into 2 groups, spectacle wearers and soft contact lens wearers. The main result was that the spherical equivalent change between the groups showed no clinical or statistically significant difference. However, when a power vector analysis was used, which uses all the refractive error data, a small but statistically significant (F test = 4.24, T2 = 17.35, p < 0.01) difference between the groups was found (i.e., the refractive error of the spectacle wearers had a slight increase in astigmatism). It can be concluded that soft contact lens wear does not lead to additional myopia progression in adolescents.

Adolescent↗
PubMed2004

The Children's Overnight Orthokeratology Investigation (COOKI) pilot study.

PURPOSE: Innovations in contact lens materials and designs allow patients to wear contact lenses during sleep to flatten the cornea and temporarily to reduce myopic refractive error and improve unaided visual acuity. We conducted the Children's Overnight Orthokeratology Investigation (COOKI) pilot study, a case series, to describe the refractive error and visual changes, as well as the slitlamp observations associated with overnight orthokeratology in children, over a period of 6 months. METHODS: Twenty-nine 8- to 11-year-old children with myopia between -0.75 and -5.00 D and <-1.50 D corneal toricity were fitted with corneal refractive therapy contact lenses (Paragon Vision Sciences, Mesa, AZ). They were examined within 1 hour of awakening and about 6 hours later at 1 day, 1 week, 2 weeks, 1 month, 3 months, and 6 months after the first night of contact lens wear. At each visit, the logarithm of the minimum angle of resolution (logMAR) visual acuity, manifest refraction, slitlamp examination, and corneal topography were performed. RESULTS: Twenty-three subjects completed the 6-month study. Three subjects decided not to wear contact lenses, two did not achieve acceptable fits, and one moved from the area. At the 6-month afternoon visit, the mean +/- SD uncorrected high-contrast visual acuity was +0.08 +/- 0.15 logMAR (Snellen equivalent, 20/24), and the mean +/- SD spherical equivalent refraction was -0.16 +/- 0.66 D. The corneas of three-fifths of the subjects showed mild staining at the morning visit, and one-third of the patients showed mild corneal staining at the afternoon visit. The most common type of stain was central punctate staining. No subjects experienced lasting adverse visual effects from cornea-reshaping contact lens wear during the study period. CONCLUSIONS: Overnight cornea-reshaping contact lenses are efficacious for young myopic patients, and no children experienced a serious adverse event during the study.

Child↗
PubMed2000

Good visual function in posterior microphthalmos.

Posterior microphthalmos is a rare condition in which the anterior segment is normal in size and configuration, but the posterior segment is reduced in size; this results in axial hyperopia and retinal folding. Patients have decreased vision that is caused by posterior segment abnormalities, high refractive error, and amblyopia. We present a case of posterior microphthalmos in which retinal function was relatively intact and visual loss was believed to be primarily caused by refractive error and amblyopia. After treatment, the child's visual acuity and school performance improved. This case emphasizes the need for careful examination, refraction, and follow-up for these children because their visual potential may be reasonably good.

Amblyopia↗
PubMed2001

Ophthalmology inpatient consultation.

OBJECTIVE: To profile inpatients and eye problems evaluated and managed by the Ophthalmology Consultation Service of a large university teaching hospital. DESIGN: A hospital-based retrospective, cross-sectional study. PARTICIPANTS: One thousand four hundred seventy-two patients admitted to the University of California Los Angeles Medical Center. METHODS: We reviewed the inpatient medical records, discharge summaries, and Ophthalmology Consultation Service notes of every patient evaluated by the Service from July 1990 through January 1997. MAIN OUTCOME MEASURES: We recorded demographic information, hospitalization information, and eye examination information, including reason for consultation, type of consultation (screening examination, new eye problem, or preexisting eye problem), as well as primary and secondary ophthalmologic diagnoses. RESULTS: Internal medicine services requested 39.7% of consultations, surgery services 20.9%, and trauma services 13.5%. There were 92 different reasons why consultations were requested. The most common reason was decreased vision. Eye problems that developed either on the day of admission or some time during hospitalization accounted for 39.6% of consultations, preexisting eye problems accounted for 31.6%, and screening examinations for the remaining 28.7%. We recorded 166 unique primary ophthalmologic diagnoses and 130 unique secondary ophthalmologic diagnoses. The top five common primary ophthalmologic diagnoses were refractive error (88 patients), fungal endophthalmitis ruled out (80 patients), conjunctivitis (56 patients), diabetic retinopathy (52 patients), and corneal abrasion (52 patients). Refractive error was the most common secondary ophthalmologic diagnosis (201 patients). Inpatient diagnostic or surgical procedures were performed 7911 times. There were 947 unique primary and 1391 unique secondary hospital discharge diagnoses. The most common primary discharge diagnosis, human immunodeficiency virus infection, accounted for only 1.6% of all hospitalizations, indicating a considerable diversity of systemic disease in the study population. CONCLUSIONS: This study profiled the typical patients and eye problems an ophthalmologist may expect to encounter when inpatient consultation is requested. The information may be useful for the planning and management of consultation services in residency training programs.

Adolescent↗
PubMed1994

Use of the 193 nm excimer laser for photorefractive keratectomy in low to moderate myopia.

As part of a Phase III clinical trial, photorefractive keratectomy using the VISX 2015 193 nm excimer laser was performed on 91 sighted eyes of 91 patients. Preoperative refractive errors (spherical equivalent) ranged from -1.00 diopters (D) to -7.50 D (mean -4.11 D +/- 1.43 D). At six months, average residual refractive error was 0.02 D +/- 0.64 D (range -2.21 D to +1.38 D). Ninety-three percent of eyes were within 1.00 D of attempted correction, 93% had uncorrected visual acuity of 20/40 or better, and 72% achieved uncorrected visual acuity of 20/25 or better. All patients returned to their best corrected visual acuity within one line of their preoperative best corrected visual acuity. Photorefractive keratectomy with the 193 nm excimer laser appears to be useful in reducing low to moderate myopia.

Adolescent↗
PubMed1997

Detection, prevention, and rehabilitation of amblyopia.

The necessity of visual preschool screening for reducing the prevalence of amblyopia is widely accepted. The beneficial results of large-scale screening programs conducted in Scandinavia are reported. Screening monocular visual acuity at 3.5 to 4 years of age appears to be an excellent basis for detecting and treating amblyopia and an acceptable compromise between the pitfalls encountered in screening younger children and the cost-to-benefit ratio. In this respect, several preschoolers' visual acuity charts have been evaluated. New recently developed small-target random stereotests and binocular suppression tests have also been developed with the aim of correcting the many false negatives (anisometropic amblyopia or bilateral high ametropia) induced by the usual stereotests. Longitudinal studies demonstrate that correction of high refractive errors decreases the risk of amblyopia and does not impede emmetropization. The validity of various photoscreening and videoscreening procedures for detecting refractive errors in infants prior to the onset of strabismus or amblyopia, as well as alternatives to conventional occlusion therapy, is discussed.

Amblyopia↗
PubMed1998

Zinn-Haller arterial ring observed by ICG angiography in high myopia.

AIMS: To delineate the entire Zinn-Haller arterial ring angiographically in vivo. METHODS: 382 highly myopic eyes (210 patients) with refractive errors greater than -8.25 D were examined using indocyanine green (ICG) videoangiography. A control group of 80 eyes (40 patients) had refractive errors within plano +/- 3D. RESULTS: The Zinn-Haller ring was visible in 206 of 382 highly myopic eyes (53.9%) by ICG angiography. Although only a part of the Zinn-Haller ring was visible in 162 of 206 eyes, in the remaining 44 eyes it was observed almost completely around the optic nerve head. No anastomotic channels between lateral and medial short posterior ciliary arteries were filled by ICG angiography. In 22 of the 44 eyes (50.0%) the Zinn-Haller ring was supplied by branches of the lateral and medial short posterior ciliary arteries; in seven eyes, it was supplied only by the lateral short posterior ciliary artery; and in seven eyes, it was supplied only by the medial short posterior ciliary artery. In none of the control subjects was the Zinn-Haller ring visible by ICG angiography. CONCLUSIONS: The Zinn-Haller ring observed by ICG angiography was not a complete collateral circle between lateral and medial posterior ciliary arteries. Also, the patterns in supply vessels to the Zinn-Haller ring varied. ICG angiography made possible the detailed observation of the Zinn-Haller ring in human eyes in vivo.

Adolescent↗