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 1,387 records · Page 77Linked to original sources
PubMed1982

Control of astigmatism after surgery and trauma.

Since the introduction of microsurgical accuracy in the closure of corneal wounds, there have been fewer complications due to imperfect wound closure. As a result the eye is much safer after intraocular surgery or trauma. There may, however, be an undesirable and irregular refractive error. Much thought has been given to the prevention of this by attention to other details during closure of wounds. Interest has been revived in surgery for the correction of inherent refractive errors. The methods used for such conditions may also be applied to residual distortion after surgery or trauma. The possibility of adjustment during the early postoperative period has escaped detailed consideration. This neglected approach to the control of astigmatism is discussed in this paper.

Astigmatism↗
PubMedDate not supplied

Changes in intraocular pressure after laser in situ keratomileusis for myopia, hyperopia, and astigmatism.

PURPOSE: Reports have shown that photorefractive keratectomy changes intraocular pressure (IOP) in myopic eyes by changing the thickness and curvature of the cornea. Changes in intraocular pressure after laser in situ keratomileusis (LASIK) for hyperopia led the authors to evaluate IOP after LASIK for various refractive errors. METHODS: The measurement of intraocular pressure with a Goldman applanometer in the central cornea was evaluated before and 3 months after LASIK in 100 eyes of 55 patients with various refractive errors. Corneal thickness (pachymetry) and corneal topography were evaluated. RESULTS: After LASIK, a significant decrease of intraocular pressure was observed in most eyes: mean 11.9 +/- 3.2 mmHg before and 9.8 +/- 2.6 mmHg at 3 months after surgery (P < .001). Mean decrease in IOP was 2.75 +/- 3.3 mmHg (P < .0001) for myopic eyes, 2.28 +/- 2.43 mmHg (P < .001) for hyperopic eyes, and 1.47 +/- 2.5 mmHg (P < .0012) for astigmatic eyes. IOP reduction was not significantly correlated to the amount of ablation (r = 0.05) or to corneal thickness. CONCLUSION: Intraocular pressure decreased in myopic, hyperopic, and astigmatic eyes after LASIK. The reduction was not correlated to the amount of tissue removed or to flattening or steepening of the central cornea.

Adolescent↗
PubMed1993

Decreased uncorrected vision after a period of distance fixation with spectacle wear.

Myopes of low degree commonly report that their vision seems poorer upon removal of their spectacles compared to that after a period without spectacle wear. Notably, this difference in vision can be appreciated after distance fixation. In this paper, we propose and test several alternative hypotheses to explain the phenomenon: an accommodative response to spectacles, sensory adaptation, or altered criteria for blur of psychological origin. We measured visual acuity (VA), refractive error, and lens thickness on 10 subjects with less than 2.00 D of myopia. Testing was performed after two 90-min sessions viewing at distance. At one session, the subjects wore their current spectacle correction and, at the other session, no correction was worn. VA underwent a slight but significant decrease (0.4 of a line) after the session in which spectacles were worn, but no difference in refractive error or lens thickness was found. The change in acuity in the absence of a refractive shift suggests sensory adaptation to blur. However, the demonstrated change in VA appears to be less than that which is subjectively reported; accordingly, psychological input cannot be ruled out.

Accommodation, Ocular↗
PubMed1998

Effect of parental myopia on the development of myopia in Hong Kong Chinese.

A representative sample of Hong Kong Chinese children was followed from 7 to 12 years of age. Refractive error was measured every year (n = 123 at age 7 years and n = 83 at age 12 years), the axial length of the eye was measured at age 12 years (n = 81) and the refractive status of the parents was also determined. Thirty-one percent of the parents in the sample were myopic and at the age of 12 years 53% of the children were myopic. There was no association between the refractive status of the parents and whether or not a child had myopia. The probability of a 12-year-old child with early-onset myopia having at least one myopic parent was 0.55 and the probability of myopic parents having a myopic child was 0.6. There was no difference in the refractive error or the axial length of 12-year-old children according to whether neither, one or both parents were myopic. The genetic influence on myopia may be different in Caucasian and Chinese children, although it is also possible that non-expression of the genotype in the parents may have confounded the determination of the inheritance pattern of myopia in Hong Kong Chinese children.

Adolescent↗
PubMed2006

Comparison of the IntraLase femtosecond laser and mechanical microkeratome for laser in situ keratomileusis.

PURPOSE: To compare clinical outcomes between the IntraLase femtosecond laser and the mechanical microkeratome for creating flaps during laser in situ keratomileusis. DESIGN: Nonrandomized clinical trial. METHODS: The study involved a total of 55 eyes of 30 patients, with 27 eyes of 16 patients comprising the microkeratome group and 28 eyes of 14 patients comprising the IntraLase group. Refractive errors, visual acuity, higher-order aberrations, contrast sensitivity, and corneal sensitivity were compared between the two groups. RESULTS: There were no statistically significant differences between the two groups in terms of refractive errors and postoperative uncorrected visual acuity. There was no loss of best-corrected visual acuity in either group. The higher-order aberrations were similar in both groups (P > .05), except for spherical aberration, which was greater in the microkeratome group (P < .05). In the IntraLase group, the contrast sensitivity value at 12 and 18 cycles per degree under mesopic conditions was significantly improved at three months postoperatively (P < .05). The IntraLase group showed faster corneal sensitivity recovery compared with the microkeratome group, and corneal sensitivity in the peripheral area was nearly normalized at three months postoperatively in the IntraLase group. CONCLUSIONS: The femtosecond laser may have advantages over the microkeratome in the flap-making procedure. However, the IntraLase femtosecond laser failed to have significant superiority over the mechanical microkeratome in clinical outcomes, except for faster recovery of corneal sensation, lesser degree of spherical aberration, and some contrast sensitivity value.

Adult↗
PubMedDate not supplied

Model for deriving the optical performance of the myopic eye corrected with an intracorneal ring.

BACKGROUND: The intracorneal ring has been advanced as a mechanical device for the correction of myopia. The device may reduce refractive error, but the effect on the overall optical performance of the eye has been neglected. This paper addresses this issue by presenting mathematical models that will predict the effect of the intracorneal ring on refractive error, corneal asphericity, and the spherical aberration of the eye. MATERIALS AND METHODS: Algorithms are derived for predicting the corneal apical radius, asphericity, and the change in myopia after inserting intracorneal rings of any thickness and diameter. RESULTS: The model predicts that the magnitude of myopia reduction is a function of both ring thickness and diameter. The large diameter (9 to 10 mm), thin (0.1 to 0.2 mm) intracorneal ring is less likely to adversely affect corneal asphericity and therefore not significantly enhance the spherical aberration of the eye. CONCLUSIONS: An intracorneal ring cannot correct more than 4.00 diopters (D) of myopia without significantly increasing ocular spherical aberration, which, in turn, will compromise the final visual outcome.

Algorithms↗
PubMed2005

Pachymetric evaluation prior to laser in situ keratomileusis.

PURPOSE: To determine whether deviations in the localization of the cornea's thinnest point or the magnitude and localization of posterior corneal ectasia is associated with deviations in the spherical equivalent, the astigmatism, or the magnitude of an anterior corneal ectasia and whether corneas at risk for iatrogenic keratectasia can be identified without a pachymetry map of the cornea. SETTING: University hospital eye clinic. METHODS: Three hundred eight eyes of 156 healthy volunteers with various refractive errors were examined with Orbscan II and autorefractometer-keratometer. The corneal thickness was registered at the fixation point, at the geometrical center, and at the thinnest point of the cornea. Keratometry and refraction were determined for all subjects. RESULTS: The thinnest point of the cornea was predominantly located in the inferotemporal quadrant, and was significantly thinner than the fixation point (539.6 +/- 35.8 microm and 548.0 +/- 35.4 microm, respectively, P<.001). Interestingly, the larger this difference was, the longer the distance between these points. No relationship was found between the refractive or external surface measurements and the internal surface measurements. CONCLUSIONS: The absence of a clear relationship between the shape of the anterior corneal surface or the refractive error, and the shape of the posterior corneal surface, necessitates a thorough pachymetric evaluation of the cornea before a laser in situ keratomileusis procedure, with special attention to the inferotemporal area.

Adult↗
PubMed1996

Corneal aberrations increase with the magnitude of radial keratotomy refractive correction.

BACKGROUND: Refractive surgery induces optically abrupt changes in shape in the midperiphery of the cornea. The abruptness of this change is in part dependent on the magnitude of the surgically induced refractive change. Therefore, the optical aberrations of the cornea, as quantified by wavefront variance (WFV), may be expected to increase as the surgically induced change in the refraction increases. PURPOSE: It is the purpose of this study to test the hypothesis that as the surgery-induced change in refraction increases, so does the WFV of the cornea. METHODS: Fourteen radial keratotomy (RK) patients and seven normal patients served as subjects. Measurements were made before and 2 years after RK surgery. To quantify the WFV of the cornea, we used corneal topography measurements to calculate the surgically induced change in corneal WFV with respect to two different reference surfaces, a sphere and the presurgical cornea. To quantify the surgically induced change in the equivalent spherical correction (ESC), cycloplegic refractions were performed. The measurements were summarized by regressing the surgically induced change in the WFV against the surgically induced change in the ESC. RESULTS: For large pupils (7 mm diameter), the correlation between the change in the WFV referenced to a sphere and the change in the ESC was significant (p < 0.0001, r2 = 0.745) and dominated by fourth order aberrations. Similar results were found for the surgical lens. For small pupils (3 mm diameter), the effects were markedly reduced. CONCLUSIONS: (1) As the magnitude of the surgically induced refractive change increases so does the WFV of the cornea, particularly for large pupils. (2) The increase in corneal WFV for large pupils is dominated by fourth order aberrations. (3) The increase in corneal WFV is consistent with reported decreases in visual function (contrast sensitivity and low contrast visual acuity), particularly for large pupil diameters in combination with large surgically induced changes in refractive error.

Cornea↗
PubMed2002

[Corneal asphericity in myopes].

PURPOSE: To study the variations of corneal asphericity in a population of myopic patients. METHODS: One hundred consecutive myopic patients were included in this study. The EyeSys videokeratoscope was used to assess the corneal topography of these patients seeking refractive surgery. We compared the results of cycloplegic refractions with the values of the corneal asphericity and mean central keratometry. RESULTS: Mean corneal asphericity was -0.09. Eighty per cent of the myopic patients had a prolate corneal contour, whereas 20% had an oblate corneal contour. No significant relationship was found between the corneal asphericity value and the mean keratometry value or the mean refractive error. CONCLUSION: The mean corneal asphericity in our myopic population was -0.09. This is slightly more than previously reported data in similar studies. No statistically significant relationship was found between corneal asphericity, mean refractive error, and mean keratometry.

Adult↗
PubMed1994

Prader-Willi syndrome.

BACKGROUND: First described in 1956, Prader-Willi syndrome is a neurogenetic condition characterized by infantile hypotonia, hypogonadism and obesity. Mental deficiency, behavioral abnormalities, and obvious dysmorphic features are frequently found as well. It is a relatively common condition, with an incidence estimated to be between 1 in 10,000 to 25,000 live births. Few studies have been published that investigated the ocular defects associated with this syndrome. METHODS: This case report discusses the systemic and oculo-visual abnormalities of a 34-year-old white male enrolled in the Easter Seal Society of Metropolitan Chicago/Illinois College of Optometry Eye Care and Treatment Program. Examination techniques commonly used for patients with cognitive/developmental dysfunctions were utilized. RESULTS: Our findings include ocular hypopigmentation with reduced visual acuity, a myopic refractive error, exotropia, corneal abnormalities, glaucoma, and other ocular and systemic health abnormalities. CONCLUSIONS: Reported ocular findings for patients with Prader-Willi syndrome include iris hypopigmentation with depressed visual acuity, moderate to high refractive error, and strabismus. Individual patients with this syndrome have also been reported with cataracts, congenital ocular fibrosis syndrome, diabetic retinopathy, and congenital ectropion uveal. The numerous ocular, systemic, and functional abnormalities of patients with Prader-Willi syndrome make it mandatory that all routinely receive primary optometric vision care.

Adult↗
PubMed2003

Highly precise eye length measurements in children aged 3 through 12 years.

OBJECTIVE: To determine the feasibility, reliability, and validity of using partial coherence interferometry, a noncontact method that detects interference patterns from various layers of the eye, to measure axial length in young children. METHODS: The right eye of 64 subjects (mean age, 8.4 y; age range, 3.4-12.9 y; best-corrected visual acuity >or=20/30) was measured. Subjects fixated monocularly on the collimated light pattern from a laser diode (the alignment beam) and the operator used a video monitor to align the corneal reflection in the optical path. Axial length was measured during an 0.8-second scan using interference patterns from a collimated short coherence superluminescence diode aligned coaxially with the laser diode. Five series of 16 readings each were obtained. The average axial length for each of the 5 series of readings was calculated. Main Outcome Measure Axial length. RESULTS: Within-subject precision of axial length measurements was high, with an overall SE of measurement of 8 micro m for individual subjects across the 5 sessions (95% confidence interval, +/-16 micro m). Subgroup analysis showed that sex, age, spherical equivalent, and refractive error exerted statistically significant effects on precision, but all of the differences among subgroups were 3 micro m or less and likely to be insignificant clinically. Axial length measured by partial coherence interferometry varied systematically, with factors known to influence eye length (ie, age and refractive error), further validating the measurement method. CONCLUSION: The partial coherence interferometry technique provides reproducible, extraordinarily precise eye length measurements in young children and should enable novel approaches to study eye growth and refractive development.

Body Weights and Measures↗
PubMedDate not supplied

Standardized analyses of correction of astigmatism by laser systems that reshape the cornea.

PURPOSE: To develop a minimum set of analyses and a format for presentation of outcomes of astigmatism correction by laser systems that reshape the cornea. METHODS: An Astigmatism Project group was created under the auspices of the American National Standards Institute (ANSI) Z80.11 Working Group on Laser Systems for Corneal Reshaping. The Astigmatism Project Group was made up of experts in astigmatism analyses from academia, government, and industry. An extensive literature review was conducted to identify all currently available methodologies for the evaluation of astigmatic outcomes. Project Group members discussed the utility of each method and its specific parameters for evaluating the effectiveness of astigmatism-correcting devices. They gave consideration to unique terminology and analyses required for evaluation of correction of astigmatism by laser systems that reshape the comea. RESULTS: The Project Group defined a comprehensive list of analysis variables needed for the evaluation of astigmatism-correcting devices and generated a mathematical definition for each term. They developed a minimum set of analyses needed for evaluation of astigmatism treatments by laser systems that reshape the cornea. They established methods for calculating the refractive error analysis variables and constructed recommended table and graph formats for data presentation. CONCLUSIONS: This article contains the recommendations of the Astigmatism Project Group of the American National Standards Institute. We propose it as a standard reference for astigmatic refractive error analyses for the evaluation of safety and effectiveness of laser systems that reshape the cornea.

Astigmatism↗
PubMed2002

Retinoscleral control of scleral remodelling in refractive development: a role for endogenous FGF-2?

AIMS: Studies in avian models of myopia have shown that refractive error development can be influenced by exogenously delivered fibroblast growth factor (FGF)-2. The present study sought to determine whether endogenous FGF-2 was associated with retinoscleral signalling or scleral remodelling during changes in refractive error in a mammalian model of myopia. METHODS: Myopia was induced in tree shrews over a 5-day period. One group of animals was then allowed 3 days of recovery from the induced myopia. Endogenous levels of FGF-2 were measured in scleral and retinal homogenates using ELISA. Real-time PCR was used to investigate scleral FGF-2 and FGF receptor (FGFR)-1 mRNA expression. RESULTS: No difference in FGF-2 content was found in posterior scleral or retinal extracts of myopic eyes (scleral -4+/-9%, retinal +23+/-17%) or recovering eyes (scleral -10+/-18%, retinal +1+/-13%), when compared with contralateral control eyes. In addition, no significant changes were found in scleral FGF-2 mRNA expression in myopic or recovering eyes (+106+/-56% and +14+/-12% respectively, P=0.21). However, FGF-2 concentration was significantly higher in anterior, relative to posterior, scleral regions in all animals (1602+/-105 vs 1030+/-50pg/mg respectively P<0.001). Expression of scleral FGFR-1 mRNA was upregulated in myopic eyes (+186+/-32%, P=0.01) but returned to control eye levels during recovery (+63+/-20%). CONCLUSIONS: The findings indicate that alterations in endogenous retinal or scleral FGF-2 levels are not associated with changes in scleral remodelling in this mammalian model of myopia. However, the reversible changes found in FGFR-1 expression in the sclera of myopic eyes mean that an indirect role for FGF-2 in the control of scleral remodelling is implicated. The anteroposterior difference found in scleral FGF-2 concentration indicates a role for this cytokine in the control of normal scleral growth and development and, presumably, eye size.

Animals↗
PubMed1997

Laser photocoagulation repair of macula-sparing cytomegalovirus-related retinal detachment.

OBJECTIVE: The purpose of the study is to investigate the role of laser photocoagulation in the treatment of macula-sparing cytomegalovirus (CMV)-related retinal detachment (CMVRD) in patients with acquired immune deficiency syndrome (AIDS). DESIGN: Seven macula-sparing CMVRD identified between July 1995 and February 1997 were managed with laser photocoagulation and observed prospectively (group I). Seven CMVRD reattached with pars plana vitrectomy (PPV) and silicone oil injection (group II) between January 1992 and June 1996 were analyzed retrospectively. PARTICIPANTS: Patients with AIDS with macula-sparing rhegmatogenous CMVRD with no proliferative vitreoretinopathy and visual acuity better than 20/30 were studied. INTERVENTION: Demarcation laser photocoagulation (group I) or PPV with silicone oil injection (group II) was performed. MAIN OUTCOME MEASURES: Postoperative best-corrected visual acuity (BCVA), temporary or permanent visual loss, CMVRD progression or recurrence, and cataract were measured. RESULTS: Follow-up ranged from 2 to 19 months (mean, 9 months) in group I. Post-treatment BCVA was unchanged in all eyes after laser. One retina redetached 9 months after laser treatment. Final visual acuity was less than 20/40 in one eye because of progressive CMV retinitis. Follow-up ranged from 2 to 24 months (mean, 10.4 months) in group II. All group II RDs were reattached successfully with PPV and silicone oil injection. Best-corrected visual acuity was an average of 1.6 lines worse after vitrectomy. Silicone-induced hyperopic shift caused temporary visual loss in all eyes (mean duration, 5.6 weeks). Delayed visual loss due to cataract formation occurred in five eyes. Three eyes had cataract extraction within 6 months. Two partial redetachments developed. One was repaired with repeat vitrectomy. Final visual acuity was less than 20/40 in five of seven eyes because of progressive CMV retinitis (1), dense cataract (2), uncorrected refractive error (2), and uncertain cause (1). CONCLUSIONS: Demarcation laser photocoagulation appears to be an effective treatment for many macula-sparing CMVRD. Loss of BCVA, temporary postoperative visual loss due to silicone-induced refractive error, and delayed visual loss due to cataract after vitrectomy with silicone oil injection may be avoided. Demarcation laser photocoagulation may be an effective alternative to vitrectomy in macula-sparing CMVRD.

AIDS-Related Opportunistic Infections↗
PubMed2005

The effect of parental history of myopia on eye size of pre-school children: a pilot study.

PURPOSE: To evaluate parental history of myopia as a predictor of refractive error and eye size in Chinese pre-school children. METHODS: A total of 514 pre-school children (aged 2.3--6.4 years) were examined. Parental history of myopia, amount of near work performed, refractive status and ocular biometry were recorded. RESULTS: There was no significant difference in spherical equivalent refraction (SER) among children with no myopic parents (mean+0.94+/-0.05 D), one myopic parent (mean+0.77+- 0.07 D) and two myopic parents (mean+0.79+/- 0.12 D) (p=0.102) after controlling for age and amount of near work. Further, children with more myopic parents did not have longer eyeballs (p=0.335). CONCLUSIONS: In this study in Chinese pre-school children, parental history of myopia was not found to be associated with a myopic refractive error or increased eyeball length. Further studies with larger sample sizes would help to confirm these results.

Asian People↗
PubMed1993

Corneal asphericity and visual function after radial keratotomy.

Corneal asphericity was measured before and after surgery in 81 radial keratotomy eyes. Asphericity was calculated between keratoscope rings 2 and 9, representing corneal diameters of 2.3 mm and 7.6 mm. Statistical methods were used to assess the relationship between postoperative asphericity and undilated, uncorrected visual acuity. Smaller radial keratotomy clear zones resulted in greater negative asphericity after surgery (R = 0.74, p < 0.0001). For eyes with smaller clear zones of < 4.0 mm, postoperative negative asphericity was high (mean -6.44). Eyes in this smaller clear zone range had better uncorrected visual acuity if they possessed higher levels of negative asphericity (Mann-Whitney U test, p < 0.0001). The study suggests that eyes with smaller clear zones gain a beneficial increase in depth of field as the degree of negative asphericity increases. The study offers this as one reason that radial keratotomy patients with residual refractive error often have better uncorrected visual acuity than expected.

Adult↗
PubMed2001

The association between nonstrabismic anisometropia, amblyopia, and subnormal binocularity.

PURPOSE: To determine if thresholds exist for the development of amblyopia and subnormal binocularity with various types of anisometropia and to compare these with existing guidelines for the treatment or observation of anisometropia. DESIGN: The records of all previously untreated patients evaluated for isolated refractive error during a 42-month period were reviewed to assess the association between anisometropia, amblyopia, and subnormal binocularity. PARTICIPANTS: Three hundred sixty-one (361) patients with anisometropia and 50 nonanisometropic control participants, examined over a 42-month period, with no history of treatment for refractive error, amblyopia, or other ocular pathologic characteristics were evaluated. METHODS: Uncorrected visual acuity in each eye, monofixation response, and degree of stereopsis were recorded for each patient. Patients with unequal or subnormal uncorrected visual acuity were retested with cycloplegic refraction. If the visual acuity was still abnormal, patients were retested while wearing spectacles. MAIN OUTCOME MEASURES: Degree and type of anisometropia were compared with incidence and severity of amblyopia and subnormal binocularity. RESULTS: Spherical myopic anisometropia (SMA) of more than 2 diopters (D) or spherical hypermetropic anisometropia (SHA) of more than 1 D results in a significant increase in the incidence of amblyopia and decrease in binocular function when compared with nonanisometropic patients (P = 0.05). Increasing levels of SMA and SHA beyond these thresholds result in increased incidence and severity of amblyopia. Cylindrical myopic anisometropia (CMA) or cylindrical hyperopic anisometropia (CHA) of more than 1.5 D results in a significant increase in amblyopia and a decrease in binocular function (P = 0.05). Levels of CMA and CHA more than 1.5 D result in an increased incidence and severity of amblyopia. CONCLUSIONS: This study supports existing guidelines for the treatment or observation of anisometropia and characterizes the association between the type and degree of anisometropia and the incidence and severity of amblyopia and subnormal binocularity.

Adolescent↗
PubMed1983

Case-control study of ocular hypertension.

A retrospective case-control study compared 100 ocular hypertensive patients with 100 ocular normotensive patients matched for sex and age. Interviews were conducted and charts were reviewed to explore demographic, personal, and environmental factors, as well as medical history and refractive error. Multiple logistic regression analyses assessed which factors were independently related to the presence or absence of ocular hypertension. The variables significantly associated with the presence of ocular hypertension were family history of glaucoma, myopic refractive error, absence of liquor intake, history of nonocular surgery, high income, and history of high BP.

Aged↗