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Results for “refractive error”

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At least 721 records · Page 40Linked to original sources
PubMed2002

Between-eye asymmetry in keratoconus.

PURPOSE: To report baseline differences between eyes on key variables in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study cohort compared with a retrospectively assembled group of myopic contact lens wearers without ocular disease. METHODS: A total of 1,079 keratoconus patients who had not undergone a penetrating keratoplasty in either eye before their baseline visit were enrolled and examined at baseline. Records from 330 contact lens-wearing myopes were reviewed. Corneal curvature (keratometry), visual acuity, refractive error (manifest refraction), and corneal scarring were measured. RESULTS: The mean differences between keratoconic eyes are as follows (better eye-worse eye for each variable, separately). Flat keratometry: -3.59 +/-4.46 D and steep keratometry: -4.35 +/-4.41 D; high-contrast best-corrected visual acuity: 7.30 +/-6.83 letters; low-contrast best-corrected visual acuity: 8.53 +/-7.51 letters; high-contrast entrance visual acuity: 9.03 +/-8.40 letters; low-contrast entrance visual acuity: 9.43 +/-7.88 letters; spherical equivalent refractive error: 3.15 +/-3.84 D; and refractive cylinder power 1.55 +/-1.42 D. Twenty-one percent of the keratoconus patients had corneal scarring in only one eye. There is an association between patient-reported unilateral eye rubbing and greater asymmetry in corneal curvature, and between a history of unilateral eye trauma and greater asymmetry in corneal curvature and refractive error, with the rubbed/traumatized eye being the steeper eye most of the time. CONCLUSIONS: Keratoconus is asymmetric in the CLEK Study sample.

Adult↗
PubMed1995

The influence of refractive correction upon disorders of vergence and accommodation.

Clinical care routinely includes prescription of lenses that compensate for the distance refractive error. Indeed, refractive correction is so commonly prescribed that we often neglect its potential effects on disorders of binocular vision. We report improvement of binocular function that resulted 1 or more months after prescription of an initial spectacle correction for 143 nonstrabismic patients who had a refractive error and either a vergence anomaly (28%), an accommodative anomaly (8%), or both (64%). Refractive correction was estimated objectively with an autorefractor and subjectively refined without cycloplegia. Most corrections were low to moderate in power, essentially following Orinda Study guidelines. Recovery of normal vergence and accommodative function varied according to refractive error type (79% of hyperopic astigmats recovered; 20% of myopes recovered), direction of astigmatic axes (67% recovered who had against-the-rule; 45% with with-the-rule recovered), age (63% below age 12 years recovered; 41% older than age 13 years recovered), and vergence anomaly (67% of patients with fusional vergence dysfunction recovered; 38% of those with basic exophoria recovered). These results suggest that improvement in acuity is not the only reason for prescription of a refractive correction--prescription of even small corrections should be considered as these can dramatically improve vergence and accommodative function for many patients.

Accommodation, Ocular↗
PubMed1997

Is myopia related to amplitude of accommodation?

PURPOSE: To report the association between amplitude of accommodation and refractive error. METHODS: Refractive error and amplitudes of accommodation were measured in 1,148 eyes of 696 patients as part of the Early Treatment Diabetic Retinopathy Study. RESULTS: Eyes with myopia, defined as those with a refractive error of -0.75 diopter or more, have lower accommodative amplitudes (P = .005). After multivariate logistic regression analysis adjusting for age, occupation, and white race, lower amplitudes of accommodation remained associated with myopia (P = .03). CONCLUSIONS: Eyes with lower amplitudes of accommodation must use more of their accommodative reserve for near work. Myopia may be an adaptation that develops in eyes with reduced accommodative amplitudes.

Accommodation, Ocular↗
PubMed2003

Reliability and validity of refractive error-specific quality-of-life instruments.

OBJECTIVE: To evaluate the reliability and validity of the National Eye Institute Refractive Error Quality of Life Instrument (NEI-RQL-42) and the Refractive Status and Vision Profile survey (RSVP). METHODS: Eighty-one participants with good visual acuity (better than 20/30 best-corrected acuity in each eye) completed the NEI-RQL-42 and RSVP on 2 occasions. Noncycloplegic, subjective refractions and high-contrast visual acuity assessments were also performed. Statistical analyses addressed internal consistency, test-retest reliability, and validity (ie, concurrent and construct validity) of the 2 instruments. OUTCOME MEASURES: The NEI-RQL-42, RSVP survey, subjective refraction, and visual acuity. RESULTS: The internal consistency for the overall NEI-RQL-42 was excellent (Cronbach alpha = 0.91); and for the overall RSVP, good (Cronbach alpha = 0.81). Likewise, the test-retest reliability for the overall NEI-RQL-42 was excellent (intraclass correlation coefficient [ICC], 0.91; 95% limits of agreement, -9.1 to 10.1); and for the RSVP, fair (ICC, 0.76; 95% limits of agreement, -12.1 to 12.5). The NEI-RQL-42 overall score showed good concurrent validity as it correlated significantly with subjective refraction, whereas the RSVP overall score did not. The NEI-RQL-42 and RSVP showed similar construct validity in terms of refractive error discrimination, but the NEI-RQL-42 showed better construct validity when discriminating by the type of refractive correction used by patients. Between-instrument convergent and divergent validity was good. CONCLUSIONS: The NEI-RQL-42 and RSVP generally have good reliability and validity in this sample of patients with refractive error. However, other factors such as content should be considered in choosing 1 of these instruments for studies of refractive error correction.

Adult↗
PubMed2005

Risk of strabismus and ambylopia in children with hydrocephalus.

OBJECTIVES: The present study was undertaken to determine the risk of strabismus and ambylopia in children who underwent operation for hydrocephalus and to compare our results with those in previous studies. METHODS: Full orthoptic and ophthalmological examinations, including cycloplegic refraction, were performed in all subjects. RESULTS: Ten of 25 patients (40%) were found to have manifest squint. Four of these had esotropia and six had exotropia. No paretic squint or alphabetic pattern strabismus was determined. Refraction measurements revealed amblyogenic refractive errors (significant refractive errors that cause amblyopia) in five of the 25 (20%) patients in this study. Strabismus and the risk of amblyopia were found to be significantly higher in patients who experienced shunt revision than those who had not (P<0.05). CONCLUSION: Amblyopia, strabismus, and other acquired defects in the visual system related to hydrocephalus should be closely monitored and treated when indicated. Regular ophthalmic supervision will provide and help to maintain the best possible standard of vision in children with hydrocephalus.

Adolescent↗
PubMed2005

Incidence of corneal pigmented arc and factors associated with its appearance in orthokeratology.

PURPOSE: To determine the incidence of the corneal pigmented arc in orthokeratology (ortho-k) lens wearers over 12 months of lens wear and the factors associated with its appearance. METHOD: Thirty-five ortho-k subjects were recruited; refractive and corneal changes after lens wear (single-lens protocol) were monitored over 12 months. The incidence of the pigmented arc after 3, 6 and 12 months of lens wear was determined. RESULTS: The incidence of corneal pigmented arc was 17% (27%), 49% (49%) and 90% (93%) after 3, 6 and 12 months lens wear respectively in the left and right eyes. For subjects with arcs observed in the left eye within the first 6 months of lens wear, the mean +/- S.D. period of lens wear before initial detection of the arc was 14 +/- 7.4 weeks, and no correlation was found between this factor and the baseline spherical and cylindrical refractive errors (i.e. refractive sphere and cylinder, respectively), spherical equivalent refractive error (SERE), the target myopia reduction, the amount of refractive sphere (or SERE) reduction and changes in central and peripheral corneal curvatures after 6 months of lens wear. Baseline refractive sphere, baseline SERE, target, amount of myopia reduction, and change in central corneal curvature were significantly larger (p < 0.05) in those subjects with pigmented arcs after about 6 months of lens wear. The intensity of the observed pigmented arcs after about 6 months of lens wear was significantly related to the time when it was first observed (p = 0.003). Significant correlation was also found between the intensity of the arcs and the following parameters: baseline refractive sphere and SERE, target, change in central corneal curvature, and amount of myopia reduction (p < 0.006). After about 12 months of lens wear, the intensity of observed arcs was significantly related to the baseline refractive sphere, SERE and the target (p < 0.006). CONCLUSION: The incidence of ortho-k-associated pigmented arc increases from 17% after 3 months of lens wear to over 90% after 12 months of lens wear. The intensity of the arc is related to the time when the arc first appeared. Both the incidence and the intensity of the arc are related to the period of lens wear, baseline refractive sphere, SERE and the target.

Adolescent↗
PubMed1995

[The relations of corneal, lenticular and total astigmatism].

PURPOSE: To determine the relations of corneal, lenticular and total astigmatism and the changes of the astigmatism with age. METHOD: Out-patients with refractive errors were refracted with retinoscope after using cycloplegic drops and measured the radii of anterior corneal curvature. RESULT: One hundred and ninety-four cases (382 eyes) with refractive errors were studied. Of the eyes 67.9% had regular corneal astigmatism, 68.1% irregular lenticular astigmatism and 60.7% regular total astigmatism, 88.5% of the corneal astigmatism has the same quality as the total astigmatism. The total astigmatism in 46% of the eyes included the summation of corneal and lenticular astigmatism, but in 41.3% of the eyes irregular lenticular astigmatism corrected the regular corneal astigmatism. The astigmatism of cornea, lens and total astigmatism changed from regular to irregular with the increase of age. The linear correlation analysis showed a positive correlation between the power of horizontal corneal refraction and age, and a negative corrlation between the power of vertical corneal refraction and age. CONCLUSION: The shape of cornea was the major cause of total astigmatism. The influence of lens on the total astigmatism was different. The reasons for the change of the total astigmatism from regular to irregular with the increase of age were the changes of the power of corneal refraction, particularly the increase of the power of horizontal corneal refraction and lenticular irregular astigmatism.

Adolescent↗
PubMed2001

Familial clustering and myopia progression in Singapore school children.

BACKGROUND: Familial factors may be related to the progression of myopia in children. A cohort study was conducted to determine the relationship between familial factors and myopia progression in children. METHODS: From a larger clinical trial (n = 311), 153 Singapore children aged 6--12 years were recruited to participate in a cohort study of the risk factors for myopia progression. An in-person interview was conducted whereby information on the history of myopia in first-degree relatives was obtained. Other information collected included housing type, parental education and income. Cycloplegic refractive error as measured by subjective refraction and autorefraction were ascertained every six months. The average length of follow-up was 28 months. RESULTS: The adjusted mean rate of progression of myopia was -0.60 (95% confidence interval -0.66, -0.55) diopters per year. The average rate of progression of myopia for children with a parental history of myopia was -0.63 (95% confidence interval -0.69, -0.56) diopters per year compared to -0.42 (95% confidence interval -0.57, -0.27) diopters per year for children whose parents were not myopic. The different measures of family history of myopia were related to rate of change in refractive error and refractive error in the final visit. There was no association between close work and myopia progression. CONCLUSIONS: A positive family history is related to the progression of myopia and final refractive error in Singapore children, thus supporting evidence that hereditary factors may play an important role in myopia progression.

Child↗
PubMed2005

A comparison of 2 methods for estimating residual stromal bed thickness before repeat LASIK.

PURPOSE: To compare 2 methods of calculating residual stromal bed (RSB) thickness after repeat LASIK, to determine which method generates more conservative RSB thickness estimates, and to determine any factors related to the discrepancy between these 2 calculation methods. DESIGN: Retrospective nonrandomized comparative trial. PARTICIPANTS: Seventy-nine patients (one eye per patient) undergoing primary LASIK and 2 repeat procedures (second and third LASIK) from 1998 to 2002. METHODS: We compared calculated RSB thickness after second and third LASIK using either original corneal thickness (CT) minus flap thickness and all ablations (original CT method) or pre-enhancement CT minus flap thickness and enhancement ablation (repeat CT method). MAIN OUTCOMES MEASURES: Differences in calculated RSB thickness after second and third LASIK by each method. RESULTS: Calculated RSB thickness averaged 329 microm by the repeat CT method compared with 305 microm by the original CT method after second LASIK (mean difference, 24 microm; P<0.0001) and 320 microm by the repeat CT method compared with 289 microm by the original CT method after third LASIK (mean difference, 31 microm; P<0.0001). After second LASIK, for 54% of eyes the repeat CT method was greater by >or=20 microm, and for 19% of eyes it was greater by >or=40 microm. After third LASIK, for 67% of eyes the repeat CT method was greater by >or=20 microm, and for 26% of eyes it was greater by >or=40 microm. The repeat CT method gave greater RSB thickness values than the original CT method in 73 of 79 eyes (92%) after second LASIK and in 72 of 79 eyes (91%) after third LASIK. The difference between the 2 methods was not associated with age, gender, initial preoperative refractive error, or refractive error before repeat LASIK. CONCLUSION: Using original preoperative CT measurements provides a more conservative and thus safer approach than using CT measurements obtained before repeat LASIK to calculate RSB thickness after repeat LASIK.

Adult↗