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Results for “refractive error”

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At least 649 records · Page 36Linked to original sources
PubMed1994

The surgical correction of refractive errors of the eye.

Authors review the available surgical methods, the radial keratotomy, the keratophakia, the keratomileusis, the epikeratophakia and the excimer laser technique which are available presently in order to change the refractive power of the eye. The newest excimer technique is discussed in detail. During the past one and a half year period authors performed and closely followed 37 photorefractive keratectomies with the use of Aesculap Meditec MEL 60 excimer laser. They present the postoperative results, according to their experiences, the method is highly effective and predictable in treating myopic refractive failures. The side effects were of no clinical importance.

Adult↗
PubMedDate not supplied

Electroretinogram responses and refractive errors in patients with a history of retinopathy prematurity.

Ametropias, particularly myopia, and mild retinal dysfunction are found in eyes with a history of retinopathy of prematurity. The retina is an important controller of refractive development. The aims of this study were to find out whether altered measures of retinal function and ametropias are associated and to consider mechanisms by which the retina might control refractive development. Nine infants and children with a history of stage 1, 2 or 3 retinopathy of prematurity and known courses of refractive development were studied. Spherical equivalents at the time of the electroretinogram ranged from +5.50 to -9.00 diopters. Rod photoresponse characteristics were derived from the a-wave, and postreceptoral components were also analyzed with calculation of the sensitivity and saturated amplitude of the b-wave, the sensitivity of oscillatory wavelet OP2, and average amplitudes of OP3 and OP4. In hyperopic and myopic patients alike, the saturated amplitude and gain of the rod cell response were attenuated. In all patients, b-wave sensitivity was low, but in most there was little effect on saturated b-wave amplitude. In patients with courses toward myopia, the amplitude of OP4, an 'OFF' signal, is relatively more attenuated than that of OP3, an 'ON' signal. OP4 is relatively larger in patients with courses toward hyperopia. The OP results suggest that an imbalance of 'ON' and 'OFF' activity in the retina is associated with development of ametropias in retinopathy of prematurity.

Child↗
PubMed2004

Surgery for 4 refractive errors in 1 patient.

We report a case of cataract extraction with implantation of a multifocal intraocular lens (IOL) after photorefractive keratectomy for myopia and astigmatism and subsequent laser thermal keratoplasty for surgically induced hyperopia. Good refractive results were obtained using standard biometry techniques for calculation of the IOL power.

Cornea↗
PubMed2006

Implantation of verisyse phakic intraocular lens to correct myopic refractive error after penetrating keratoplasty in pseudophakic eyes.

PURPOSE: We report 2 cases in which a Verisyse phakic intraocular lens (PIOL) was used to successfully treat high myopia after penetrating keratoplasty (PK) in pseudophakic patients. METHODS: Case 1 involved a 69-year-old pseudophakic man with a manifest refraction (MR) of -6.50 + 1.75 x 048 and a best spectacle corrected visual acuity (BSCVA) of 20/40 approximately 16 months after PK in the right eye. Case 2 was a 78-year-old pseudophakic man who had an MR of -9.00 + 5.75 x 132 with a BSCVA of 20/100 approximately 24 months after PK in the left eye. RESULTS: In case 1, 10 months after Verisyse PIOL implantation, the MR was pl +2.00 x 135 with a BSCVA of 20/30. Endothelial cell density (ECD) in this patient decreased from 1926.1 to 815.3 cells/mm over 17 months. In case 2, 24 months after Verisyse PIOL implantation, the MR was -3.25 + 3.50 x 105 with a BSCVA of 20/60. ECD in this patient decreased from 2108.4 to 753.8 cells/mm in 30 months. CONCLUSION: The Verisyse PIOL may provide an alternative method to correct high myopia for anisometropia in pseudophakic patients after PK. In this report, PIOL implantation was associated with a decrease in ECD. Further studies are required to determine the long-term effects and ultimate safety of PIOL placement on the integrity of the cornea endothelium after corneal transplant in pseudophakic patients.

Aged↗
PubMed1999

Screening for refractive errors in children: accuracy of the hand held refractor Retinomax to screen for astigmatism.

AIMS: To assess the reliability of the hand held automated refractor Retinomax in measuring astigmatism in non-cycloplegic conditions. To assess the accuracy of Retinomax in diagnosing abnormal astigmatism in non-cycloplegic refractive screening of children between 9 and 36 months. METHODS: Among 1205 children undergoing a non-cycloplegic refractive screening with Retinomax, 299 (25%) had repeated non-cycloplegic measurements, 302 (25%) were refracted under cycloplegia using the same refractor, and 88 (7%) using retinoscopy or an automated on table refractor. The reproducibility of non-cycloplegic cylinder measurement was assessed by comparing the cylindrical power and axis values in the 299 repeated measurements without cycloplegia. The influence of the quick mode on cylinder measurement was analysed by comparing the cylinder and axis value in 93 repeated measurements without cycloplegia where normal mode was used in one measurement and quick mode in the other. Predictive values of the refractive screening were calculated for three different thresholds of manifest astigmatism (> or = 1.5, > or = 1.75, and > or = 2 D) considering as a true positive case an astigmatism > or = 2 D under cycloplegic condition (measured by retinoscopy, on table, or hand held refractor). RESULTS: The 95% limits of agreement between two repeated manifest cylinder measurements with Retinomax attained levels slightly less than plus or minus 1 D. The 95% limits of agreement for the axis were plus or minus 46 degrees. The comparison of non-cycloplegic measurements in the quick and normal mode showed no significant difference and 95% limits of agreement plus or minus 0.75 D. The mean difference between non-cycloplegic and cycloplegic cylinder values measured by Retinomax reached 0.17 D and was statistically significant. Manifest thresholds of > or = 1.5 D, > or = 1.75 D, > or = 2 D cylinder value diagnosed 2 D of astigmatism under cyclplegia respectively with 71-84%, 59-80%, 51-54% of sensitivity (right eye-left eye) and 90-92%, 95%, 98% of specificity. CONCLUSION: Without cycloplegia, Retinomax is able to measure cylinder power with the same reproducibility as cycloplegic retinoscopy. No significant difference was found in the cylinder values obtained with the quick and the normal modes. Therefore, the quick mode of measurement is recommended as it is more feasible in children. No difference, which is significant from a screening point of view, exists between the non-cycloplegic and the cycloplegic cylinder value (< 0.25 D). Retinomax diagnoses abnormal astigmatism (> or = 2 D) in a non-cycloplegic refractive screening at preschool ages with 51-84% sensitivity rates and 98-90% specificity rates, depending on the chosen threshold of manifest astigmatism. If 2 D of manifest astigmatism is chosen as a positive test, the positive predictive value of the screening reaches 81-84% and the negative predictive value 91-90% (right eye-left eye).

Age Distribution↗
PubMed1999

Mechanism of binocular interaction in refraction errors: study using pattern-reversal visual evoked potentials.

In this study we sought to determine whether a natural condition involving fine discrimination, for example moderately severe myopia, might yield interesting information regarding the binocular interaction expressed by visual evoked potentials (VEPs). We studied ten normal subjects with a mild refraction deficits. Transient VEPs were elicited by monocular and binocular stimulation under conditions of natural and lens-corrected vision. The visual stimulus was a pattern-reversal checkerboard consisting of 15' and 40' checks. VEPs in response to binocular stimulation were compared with monocular VEPs. We plotted the monocular 'better-VEP' and 'worse-VEP' response, since significant differences between individual eye stimulations were present. We found no significant difference between the mean N75 and P100 latencies of the binocular VEP and the better monocular VEP, regardless of the check size used and of natural or corrected vision. Under all stimulus conditions, the mean amplitude of the N75-P100 of the binocular VEPs was also larger than the better monocular VEP response. The difference proved more significant when we stimulated our subjects with smaller squares and left vision uncorrected. The mean P100-N145 amplitude obtained with binocular stimulation was larger than the better monocular VEP response only when using small checks (15') and uncorrected vision. Overlapping latencies are consistent with an earlier hypothesis that monocular and binocular VEPs originate postsynaptically from the binocular neurons in the primary visual cortex. The gain in amplitude achieved by binocular stimulation may depend upon the removal of 'tonic interocular inhibition' and/or on a cortical modulatory mechanism.

Adult↗