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Results for “refractive error”

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At least 1,603 records · Page 89Linked to original sources
PubMed1980

Astigmatism in visually immature child with strabismus.

Astigmatic refractive errors may develop late in the visual maturity period of strabismic children. Seventeen strabismic children who had surgery and ten strabismic children who did not have surgery are discussed; none had astigmatic error at the initial refraction. Significant astigmatism developed in both groups at age 4 years and two years after the initial refraction. The ophthalmologist should be aware that late-developing astigmatism can cause a recurrence or deterioration of strabismus. The best response is serial refractions and appropriate correction of all strabismus patients during the visual maturity period.

Aging↗
PubMed1992

Steady-state accommodation and ocular biometry in late-onset myopia.

The steady-state accommodative responses of emmetropes and late-onset myopes was measured for an array of numbers located at -1, -3 and -5 dioptres using an objective infra-red optometer. Responses were compared for passive (reading numbers) and active (adding numbers) conditions. For the passive condition, the late-onset myopes showed a significantly lower accommodative response than the emmetropic group. No significant differences were found between the two groups for the active condition. Ocular biometric characteristics were also measured in emmetropes, late-onset myopes and early-onset myopes using keratometry and ultrasonography. No significant differences in corneal curvature, anterior chamber depth and crystalline lens thickness were found between the groups. Late-onset myopes exhibited significantly deeper vitreous chambers than emmetropes, which more than accounted for the difference in refractive error between the two refractive groups. We conclude that, while significant differences exist in the accommodative responses of late-onset myopes and emmetropes, late-onset myopia is due predominantly to elongation of the vitreous chamber.

Accommodation, Ocular↗
PubMed1990

Study of gene-environment effects on development of hyperopia: a study of 191 adult twin pairs from the Finnish Twin Cohort Study.

The Finnish Twin Cohort material was used to estimate genetic and environmental effects in the etiology of hyperopia (farsightedness). All twin pairs in the cohort born before year 1927 (age 60 years and over at the time of the study), with both members alive, were sent a questionnaire. The questionnaire included questions of past and present eye diseases, visits to ophthalmologists, use of glasses and other vision-related questions. The hyperopia was assessed by asking the patients to send their last prescription for glasses to the authors. Twins with any eye disease affecting refraction (cataract, corneal damage), operation or trauma to their eyes were discarded from the present study. In 191 pairs (80 monozygotic and 111 dizygotic pairs) one or both members of the pair had a hyperopic refractive error. The correlations of refraction between right and left eyes of both MZ and DZ pairs were high (Spearman Rank Correlations of 0.86-0.89). The intrapair correlations among MZ pairs were higher (0.44 for right and 0.45 for left eyes) than intrapair correlations among DZ pairs (0.24 for right and 0.15 for left eyes). The variances were not significantly different among MZ and DZ pairs. The classical analysis of heritability gave an estimate of 0.75 for hyperopia. The result suggests that genetic factors are important in hyperopia and especially in hyperopia of higher degree.

Adult↗
PubMed2000

Confocal microscopy of a patient with irregular astigmatism after LASIK reoperations and relaxation incisions.

PURPOSE: Laser-assisted in situ keratomileusis (LASIK) is widely used for correcting refractive errors. If the predicted refractive result is not achieved after the first operation, a re-operation can be performed by ablating more stromal tissue after reopening the flap. The goal of this study was to analyze, by using in vivo confocal microscopy, the morphologic changes associated with repeated LASIKs. METHODS: Clinical examination, computed corneal topography, and real-time in vivo confocal microscopy were performed on both eyes of a 50-year-old patient with induced irregular astigmatism leading to decreased best-corrected vision in the left eye after LASIK. The left cornea had been operated on 5 times (LASIK with two reoperations followed by two relaxing incisions), and the right cornea twice (LASIK with one reoperation). RESULTS: Microfolds at the level of the Bowman's layer and highly reflective particles at the flap interface were observed in both corneas. The subbasal nerve plexus was severed in the left eye. In addition, we identified epithelial material in the flap margin and inside one of the two relaxing incisions placed inferotemporally. CONCLUSION: Repeated LASIKs may stretch the flap and result in microfolding at the Bowman's layer. This and deposition of particles in the flap interface may increase with the number of reoperations, challenging the healing response. Microfolding and occurrence of foreign material in the interface may add to the irregular astigmatism and poor visual outcome after LASIK. Clinical in vivo confocal microscopy offers new possibilities for the assessment of ultrastructural changes after corneal refractive surgery.

Astigmatism↗
PubMedDate not supplied

Treating myopia with acoustic biofeedback: a prospective study on the evolution of visual acuity and psychological distress.

OBJECTIVE: The effects of a visual training technique on changes in myopia, visual acuity, and psychological distress were studied in a controlled prospective study. METHOD: A group of 33 female students with myopia < or = 3.50 diopters (D) underwent visual training using an acoustic biofeedback technique. A group of 22 female students with myopia and a group of 27 students with emmetropia formed the two control groups, matched for school, age, sex, and refractive error. Manifest and cycloplegic refraction, visual acuity, personality profile (CPI), and psychological distress (SCL-90) were measured at the baseline (T0), at 10 weeks (T1), and after 12 months (T2). RESULTS: At T2, myopia significantly progressed both in the treated and in the untreated students with myopia. Visual acuity improved only in the treated myopia group (despite refraction objectively being worse). No differences were found among the personality profiles in the three groups. All items indicative of psychological suffering improved in the group treated for myopia whose visual acuity was ameliorated. CONCLUSIONS: The visual training technique led to no improvement in objective measures of visual acuity, but did lead to an improvement in one relatively subjective measure of visual acuity and a parallel improvement in psychological conditions. The students with myopia who were treated consequently had a greater sense of general well-being.

Accommodation, Ocular↗
PubMedDate not supplied

Clinical evaluation of patient tolerance to autorefractor prescriptions.

BACKGROUND: In clinical optometric practice, autorefractors are used as an objective measure of refractive error prior to subjective refraction. We evaluate the clinical efficacy of autorefractor measurements by determining whether spectacles can be prescribed from autorefractor results. METHODS: Forty-seven subjects were randomly allocated spectacles using prescriptions determined either by an optometrist or from an autorefractor in a double-blind protocol. Subjects wore each prescription for two weeks and completed an oral questionnaire following each period of wear. The questionnaire assessed both pairs of spectacle lenses in terms of visual performance and ocular comfort. RESULTS: The level of negative responses to all questions was higher for spectacles based on the autorefractor findings than for those based on the optometrist's prescriptions. Having reported initial discomfort, many subjects indicated that they had adapted to the spectacle lenses over a two-week period. CONCLUSIONS: Our results suggest that, in a clinical environment, subjective refraction produces a more accurate and acceptable spectacle prescription than an autorefractor.

Journal Article↗
PubMed2002

Immediately sequential phacoemulsification performed under topical anaesthesia as day case procedures.

AIMS: To evaluate the visual outcome, safety, and economic benefits of immediately sequential phacoemulsification performed under topical anaesthesia as a day case procedure. METHODS: Immediately sequential phacoemulsification under topical anaesthesia was performed as a day case procedure on 218 eyes of 109 patients over 21 months by a single senior surgeon using intracameral antibiotics. Case notes were retrospectively analysed. RESULTS: The final best corrected visual acuity (BCVA) was 6/9 or better in 86% of eyes with 47% achieving 6/6 or better. The incidence of intraoperative complications was 0.45%. Postoperative complications occurred in 13.8% of eyes and included refractive error >1.00D from refractive aim (6.9%). Bilateral complications occurred in 5.5% of the patients. There were no cases of endophthalmitis. The mean time from surgery to discharge was 24 days. CONCLUSION: Immediately sequential phacoemulsification under topical anaesthesia performed as a day case procedure is not associated with an increased number of complications when compared to unilateral phacoemulsification. Under strict surgical protocol with the use of intracameral antibiotics and performed by an experienced surgeon with a good track record this procedure is safe.

Aged↗
PubMed2006

Prescribing spectacles: reasons for failure of spectacle lens acceptance.

The objective of this descriptive study was to determine the frequency with which patients return for re-examination due to a failure of spectacle lens acceptance and to quantify the reasons for the failure. A random sample of patient records was reviewed to determine the rate of spectacle lens prescription. Spectacles reassessment records, completed after dispensing problems were dealt with were reviewed to determine the primary reason for the failure. Spectacles were prescribed for 58% of the 44 341 patients seen over 6 years. Of the 25 718 prescriptions written, 400 patients (1.6%) returned for reassessment. The most common problem was incorrect refractive error measurement (59%), followed by inability of the patient to adapt to an accurate refractive correction (10.3%), inadequate patient education regarding lens design (9.5%), pathology (9.3%), appliance problem (5.8%), transcription errors (1.6%) and other (4.5%). The frequency of failure to adapt to spectacle prescriptions is quite low and the most common reason for this failure is inaccuracy in the measurement of the refractive error.

Accommodation, Ocular↗
PubMed1989

Effectiveness of intraocular lens calculation in high ametropia.

The error in prediction of emmetropic intraocular lens power or postoperative refractive error after lens implantation was analyzed in three groups of eyes after posterior chamber lens implantation. Regression line calculation with the SRK equation or with a group-specific regression was compared with theoretical calculations in unselected, long myopic and short hyperopic eyes. The cut-off length was below 22.0 mm for the short eyes and above 25.9 mm for the long eyes. In the unselected and hyperopic group, there was only a small difference in mean error and error variance when the three calculation methods were compared. In the high myopic group, the range of error increased in all methods. The worst results were obtained with the standard SRK equation because the slope of the regression line in myopic eyes differs from the classical regression line calculated on an average population of implants. Lens calculation in high myopic eyes should therefore be performed with a specific regression line or by theoretical calculation.

Humans↗
PubMed1997

Choice of lens and dioptric power in pediatric pseudophakia.

PURPOSE: To evaluate lens choice and dioptric power in pediatric eyes having posterior chamber intraocular lens (IOL) implantation. SETTING: Oxford Eye Center and the St. John Eye Hospital, Johannesburg, South Africa. METHODS: This retrospective study evaluated the refractive development in 156 pseudophakic eyes of 99 children aged 1 month to 8 years who had surgery between June 1983 and April 1994. The children were divided into three groups based on age at time of IOL implantation: Group A (68 eyes), 1 to 18 months; Group B (32 eyes), 19 to 36 months; Group C (48 eyes), 3 to 8 years. Poly(methyl methacrylate) posterior chamber IOLs with an overall diameter between 10.5 and 12.0 mm were used. The dioptric power was 3.00 to 6.00 diopters (D) less than that needed to achieve emmetropia. RESULTS: In Group A, the mean growth in axial length was 3.59 mm +/- 1.80 (SD) and the mean change in refraction was 6.39 +/- 3.68 D. In Group B, the respective means were 0.75 +/- 0.85 mm and 2.73 +/- 1.40 D and in Group C, 0.76 +/- 0.69 mm and 2.60 +/- 1.84 D. CONCLUSIONS: The younger the child at time of implantation, the greater the myopic shift. To reduce the necessity of IOL exchange, these eyes should be undercorrected, with the residual refractive error corrected by spectacles that are adjusted throughout life according to refractive development. This leads to initial hypermetropia that gradually moves to emmetropia or moderate myopia in adulthood.

Cataract↗
PubMed1980

The Coleman theory of accommodation and its relevance to myopia.

The Coleman theory of accommodation is reviewed in this paper, with the inclusion of subsequent experimental evidence to support the theory. Implications on the developmental characteristics of refractive error are presented. The scleral structure is hypothesized as an important refractive determinant, consistent with Coleman's accommodation theory. Additional concepts of refractive development are also explored.

Accommodation, Ocular↗
PubMed2003

Holographic multivergence target for subjective measurement of the spherical power error of the human eye.

We have fabricated a single hologram with which to determine the spherical refractive error of the human eye in the range 5 to -2.5 diopters (D) with an accuracy of +/-0.25 D in a single step. The amplitude of accommodation is determined at the same time. The hologram is a record of 16 targets, each of which has a different image vergence in the range 5 to -2.5 D in steps of 0.5 D. This idea can be applied readily to any dioptric range. The measurement method is simple, fast, and reliable.

Computer Simulation↗
PubMed1995

[Myelin fibers in Zairian patients].

PURPOSE: to determinate the characteristics of myelinated nerve fibres in Zairian blacks patients. METHODS: a review of records of patients with myelinated nerve fibers seen from 1962 to 1994. RESULTS: the relative incidence of myelinated nerve fibers was 0.02%. There were 13 (76%) male patients and 4 (24%) female patients. The average age at the moment of diagnosis was 32 years (range, 7 to 61 years). Myelinated nerve fibers were bilateral in 8 (47%) patients (16 of 25 eyes, 64%) and unilateral nerve fibers, 21 (84%) eyes contained a single lesion and 4 (16%) eyes contained multiple separate and distinct patches of myelinated fibers. Continuous lesions were present in 21 (84%) eyes and discontinuous lesions in 4 (16%) eyes. The 25 affected eyes varied in refractive error from a spherical equivalent of + 1.5 to - 16.00. The distribution of refraction was: emmetropia in 2 (12%) patients (2 eyes, 8%), simple myopia in 4 (24%) patients (5 eyes, 20%), myopia over 6 D with amblyopia in 6 (35%) patients (10 eyes, 40%), hypermetropia in 5 (29%) patients (8 eyes, 32%). CONCLUSION: this study showed a low relative incidence of myelinated nerve fibers and the bilaterality of lesions was frequent.

Adolescent↗
PubMed1992

Retinoscopic measurement of the refractive state of the rat.

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

Albinism, Ocular↗
PubMedDate not supplied

Objective measurement of wavefront aberrations with and without accommodation.

PURPOSE: The measurement of the refractive error profile is more useful than corneal topography in understanding the complexities of refractive surgery. We report on experimental studies of the spatially resolved refractometer Tracey-1, developed in Ukraine by IBME in medical cooperation with VEIC, Greece. METHODS: Ten eyes were subjected to dynamic measurement of accommodation, in order to test the effectiveness of Tracey refractometry. Measurements were performed in zones 0 to 6 mm. The refractive aberrations were calculated and accommodation was evaluated. RESULTS: Evaluation of data shows that the instrument can effectively follow the dynamic change of refractive aberrations through the accommodation process. CONCLUSION: Clinical tests of Tracey technology demonstrated the ability to investigate accommodation using this instrument.

Accommodation, Ocular↗
PubMed2003

Acute psychotic reaction caused by topical cyclopentolate use for cycloplegic refraction before refractive surgery: case report and review of the literature.

A 56-year-old woman was evaluated for the surgical correction of hyperopia (+3.0 diopters). Two drops of cyclopentolate 1% were instilled in both eyes for measurement of the cycloplegic refraction and wavefront analysis. Immediately after the second instillation, the patient reported drowsiness, dizziness, nausea, and fatigue. Ten minutes later, stimulatory central nervous system symptoms in the form of restlessness, cheerfulness, and a 20-minute-long roar of laughter were observed, interrupted by a new sedative phase. Basic medical and neurologic examinations were unremarkable except for gait ataxia. Four hours later, the examination was continued uneventfully. As surgical treatment of refractive errors and measurement of cycloplegic refraction using cyclopentolate become more frequent, ophthalmologists should be aware of this unusual acute event.

Acute Disease↗
PubMed1997

Comparison of portable automated keratometry and manual keratometry for IOL calculation.

PURPOSE: To compare the accuracy of portable automated keratometry (PAK) with that of manual keratometry (MK) in measuring corneal power for intraocular lens calculations. SETTING: Wilford Hall Medical Center, San Antonio, Texas, USA. METHODS: In Part 1 of the study, five ophthalmic technicians performed keratometric analysis in 20 eyes in 10 volunteers using both manual and automated methods to determine the relative accuracy and reproducibility of each instrument. In Part 2, both MK and PAK were prospectively performed in 11 patients having cataract surgery to compare the accuracy of each instrument in predicting postoperative refractive outcome. RESULTS: The difference between instruments in determining the average corneal power in all eyes was less than 0.10 diopter (D) (MK = 43.84 D, PAK = 43.93 D). Portable keratometry demonstrated less variability in measurements in each eye (average standard deviation, MK = 0.30 D, PAK = 0.11 D; average range, MK = 1.08 D, PAK = 0.44 D). The mean absolute refractive error (difference between the actual refractive outcome and predicted refractive outcome) was 0.37 D +/- 0.30 (SD) using MK values and 0.45 +/- 0.19 D using PAK values. CONCLUSIONS: Portable automated keratometry is a simple keratometric technique that appeared to be as accurate as but with less variability than manual keratometry in determining corneal power for cataract surgery.

Algorithms↗