SEARCH · PubMed Health
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Data from 166 eyes with iridocapsular implants were analyzed and different prediction methods were compared. A new formula was derived which predicted implant power better than any other method. The theoretic formulas and correction factors of Fyodorov, Colenbrander, and others were examined in detail and compared to the more accurate, simpler linear regression formula derived in this study.
A simple lens power calculation formula of the form: Predicted implant power = A + B X axial length + C X keratometry, can be produced with different constants (A, B, and C) for each type of lens implant and each manufacturer. We have determined the constants for iris-fixated, anterior chamber and posterior chamber lens implants, based on data from 923 cases. The results have been more accurate than those from presently available theoretical formulas, and the well-known phenomenon of predicting too much dioptric power in eyes with short axial lengths has been avoided. Only 1% of the cases had a predicted lens power more than 3 diopters in error.
I describe a case of anterior capsule contraction after implantation of piggyback acrylic intraocular lenses (IOLs). Treatment by neodymium:YAG capsulotomy resulted in anterior chamber deepening despite a myopic shift. With acrylic IOLs, refractive changes may be due to optical deformation rather than axial shifts.
Matrix calculations are applied to Gaussian optics in the study of myopic correction by photorefractive keratectomy. The Colliac matrix formula determines the postoperative anterior curvature radius of the treated cornea. It also calculates the maximal depth of the removed corneal tissue and the ablation zone diameter needed to achieve emmetropia.
Explore the source record for details and available documents.
A new formula, the Hoffer Q, was developed to predict the pseudophakic anterior chamber depth (ACD) for theoretic intraocular lens (IOL) power formulas. It relies on a personalized ACD, axial length, and corneal curvature. In 180 eyes, the Q formula proved more accurate than those using a constant ACD (P < .0001) and equal (P = .63) to those using the actual postoperative measured ACD (which is not possible clinically). In 450 eyes of one style IOL implanted by one surgeon, the Hoffer Q formula was equal to the Holladay (P = .65) and SRK/T (P = .63) and more accurate than the SRK (P < .0001) and SRK II (P = .004) regression formulas using optimized personalization constants. The Hoffer Q formula may be clinically more accurate than the Holladay and SRK/T formulas in eyes shorter than 22.0 mm. Even the original nonpersonalized constant ACD Hoffer formula compared with SRK I (using the most valid possible optimized personal A-constant) has a better mean absolute error (0.56 versus 0.59) and a significantly better range of IOL prediction error (3.44 diopters [D] versus 7.31 D). The range of error of the Hoffer Q formula (3.59 D) was half that of SRK I (7.31 D). The highest IOL power errors in the 450 eyes were in the SRK II (3.14 D) and SRK I (6.14 D); the power error was 2.08 D using the Hoffer Q formula. The series using overall personalized ACD was more accurate than using an axial length subgroup personalized ACD in each axial length subgroup. The results strongly support replacing regression formulas with third-generation personalized theoretic formulas and carefully evaluating the Holladay, SRK/T, and Hoffer Q formulas.
A method of in vitro optical performance evaluation of intraocular lenses (IOLs) is discussed. The IOLs are tested in the eye cell, which is designed to be optically equivalent to the theoretical eye model. The eye cell is a combination of a wet cell and the optical element (the "conjugation lens") that converges a beam of light, similar to the action of the cornea in the theoretical eye model. The eye cell is designed so the spatial frequency scale (modulation transfer frequency [MTF] testing), expressed in terms of line pairs per millimeter (linear scale), equals the scale produced by the theoretical eye model. The most common way to express spatial frequencies in visual science is in line pairs per degree or cycles per degree (angular scale). The problem with in vitro testing is that the corresponding angular scale varies with the dioptric power of the conjugation lens. This paper provides a simple method of mapping the angular scale of the eye cell onto the theoretical eye model, allowing a comparison with clinical results as well as with MTFs measured in different eye cells. All corresponding formula for calculating the eye cell optical characteristics are provided.
Five methods for predicting pseudophakic anterior chamber depth (ACD) by five previously described intraocular lens power calculation formulas (Binkhorst II, Lepper and Trier, Holladay et al., Sanders-Retzlaff-Kraff (SRK/T), Olsen et al.) were evaluated in a series of 640 patients with a posterior chamber lens implant. Significant differences in formula performance were found in unusually short and long eyes. High errors were found in long eyes with the Lepper and Trier formula, the Holladay formula, and the SRK/T method. The highest accuracy was found with the Binkhorst formula and our previously described linear regression formula which expresses the pseudophakic ACD as a function of the average pseudophakic ACD for a given lens style, the preoperative ACD, and the axial length. The use of the preoperative ACD in combination with the axial length for the prediction of the pseudophakic ACD can therefore be expected to improve the accuracy of IOL power calculation.
By applying Gaussian optics we propose a new matrix formula model for intraocular lens (IOL) calculation that yields not only IOL optical power for a particular eye but also an evaluation of the bending factor of different IOL optical designs. This option improves IOL selection and results in the best possible optical image, a function dependent on the IOL's bending factor. This formula is a new approach to IOL calculation and may be useful in designing IOLs for abnormally hyperopic or myopic eyes. Optimal IOL power and design should both be considered in IOL calculation, which may improve the optical and clinical results of IOL implantation in the aphakic patient. The radius of the cornea is assumed to be spherical, and aspherical curves of the cornea may influence the optimal "bending" or shape factor of a lens.
Explore the source record for details and available documents.
A simple modification of the SRK formula was developed for use with extreme axial length cases (short and long eyes) to maximize prediction accuracy in these groups. For "average" eyes (over 75% of all cases), SRK needed no modifications to maintain maximum predictive accuracy. The new, modified SRK formula (SRK II) was compared with current second generation formulas and the Binkhorst formula. The SRK II formula, while maintaining the simplicity and ease of the SRK, was comparable to and in some cases superior to the other formulas. Overall, 80.0% of 2,068 posterior chamber intraocular lenses from seven different manufacturers demonstrated less than one diopter of prediction error and only 0.5% had three or more diopters of error. In short eyes (less than 22 mm), 74.0% were corrected to within one diopter and less than 2.0% had three or more diopters of error. In long eyes (greater than or equal to 24.5 mm), 78.0% of cases demonstrated less than one diopter of error and less than 1.0% had three or more diopters of error. Although the SRK II formula is incorporated in most new A-scan units, the modifications are so simple that surgeons can take the standard SRK predictions and mentally calculate the modifications for extreme cases.
PURPOSE: To calculate retinal magnification and visual acuity in highly myopic phakic eyes corrected with anterior chamber intraocular lenses (IOLs) versus correction by other methods. SETTING: Laboratory of Optics, University of Alicante, Alicante, Spain. METHODS: Relative retinal magnification (RRM) was used to study changes in retinal image size induced by different correcting systems. Relative spectacle magnification (RSM) was used to compare these systems with the emmetropic eye. The matrix method was used to calculate RRM, RSM, and visual acuity in 12 theoretical cases of myopia in eyes with axial lengths from 27.0 to 33.0 mm and corneal powers from 42.00 to 48.00 diopters. RESULTS: The RRM, RSM, and visual acuity increased as corneal power increased for a myopic eye of fixed length. Changing the plane of correction from the spectacle or cornea to the intraocular increased retinal magnification, which increased visual acuity. CONCLUSION: Visual acuity in myopic eyes corrected with an IOL will be better than that in myopic eyes corrected by other means because of the retinal magnification induced by the IOL, which increases visual acuity one line or more.
The progesterone concentration in blood samples can be utilised as a marker for the diagnosis of early pregnancy, endocrinopathy and virilism. Here, we describe a method for progesterone detection and measurement in whole blood samples by a surface sensitive biosensor used in conjunction with an integrated optical grating coupler. This device determines refractive index changes near the biosensor's surface. Hence, biological species bound to a surface layer can be measured in real-time without any label. For the measurements, we have modified the indirect competitive immunoassay principle. The concentration of the progesterone antibody was kept at 1 microg/ml. Progesterone concentration was determined in buffer solution and whole blood in a range between 0.005 and 10 ng/ml. The detection limit was determined to be 3 pM. The relative standard deviation was calculated to be 3.5%.
BACKGROUND: Optical penalization (OP) has previously been shown to successfully maintain vision in amblyopic eyes of older children when patching compliance is poor and when vision decreases once patching is discontinued. This study shows that the final vision in optically penalized eyes is often better than the vision obtained after patching alone. SUBJECTS AND METHODS: During the 5-year period from January 1992 to February 1997, 28 children aged between 3.7 and 8.2 years (average age, 6.5+/-1.1 years) were optically penalized for an average of 1.5+/-0.75 years. The maximum length of penalization was 3.3 years, whereas the minimum time was 6 months. There were 21 children with strabismic amblyopia and 7 children with anisometropic amblyopia. All 28 children had worn a patch to achieve their best visual levels and then had shown a loss of best vision when occlusion was stopped. Patching was usually resumed and continued until the previous best vision was obtained; at this point OP was started to "maintain" vision. Eighteen of the 28 children have discontinued penalization and have been followed up an average of 1(1/2) years. RESULTS: Twenty-six (93%) of the 28 patients showed an increase in best vision from that found at the conclusion of patching, and 2 patients maintained their vision at the initial level. The average visual acuity at the start of penalization was 20/50 (0.42+/-0.11 logarithm of the minimum angle of resolution [log MAR]). Final average visual acuity was 20/27 (0.15+/-0.12 log MAR). The average increase in vision was nearly 3 lines or 0.27+/-0.12 log MAR. CONCLUSION: OP alone (without the use of pharmacologic agents such as atropine) not only maintains vision after patching therapy, but also appears to improve the final visual outcome.
Explore the source record for details and available documents.
One hundred and fifty-one eyes with anterior chamber implants and a best corrected visual acuity of at least 6/12 were studied to compare the predictive accuracies of the newer generation intraocular lens power calculation formulae. There was no statistically significant difference between the predictive accuracies of the SRK (Sanders-Retzlaff-Kraff), SRK II, SRK/Theoretical (SRK/T) and Holladay formulae. All these four formulae were more accurate than the Binkhorst II formula.
An understanding of the physical basis of corneal transparency has been a subject of interest amongst physicists, basic scientists and ophthalmologists. Impairment of corneal clarity is a significant cause of visual morbidity worldwide. Several highly mathematical treatises have been presented in support of different theories of corneal transparency in the normal cornea relating structure to function, particularly in the years since the advent of the electron microscope, which has brought about a much greater understanding of corneal ultrastructure. This review presents the concepts that underpin the theories of corneal transparency.
PURPOSE: This study evaluates the agreement between the calculations performed by IOLMaster and as performed according to the published methods, for three formulas, Holladay I, Hoffer Q, and SRK-T. METHOD: Hypothetical and identical data were used as input variables for calculations by IOLMaster and by a computer program written in visual basic to perform calculations with the three formulas. Results were compared and statistical significance carried out. RESULTS: Significant disagreement was found using Hoffer-Q formula between the results shown by the study program and IOLMaster, while identical results were obtained using Holladay I and SRK-T formulas. For an average eye (AL 23.45 mm and K 45D, ACD constant 6.15, vertex 12 mm), the mean difference in the predicted postoperative (postop) SE between the study-set and IOLMaster dataset was 0.13 D (+/-0.03 D), which is a measure for the systematic error (relative bias). In such eyes, the mean predicted postop ACD in IOLMaster dataset was 0.11 mm (+/-0.04 mm) less than in the study-set, and the data spread of the predicted postop ACD was much higher (+/-0.042 mm) indicating more discrepancy in predicting ACD with IOLMaster. CONCLUSION: When using Hoffer-Q formula, the mean predicted postop SE with IOLMaster was 0.13 D less than the computation in this study, that is, IOLMaster was showing a consistently myopic overestimation, or, a mean undercorrection of necessary intraocular lens power by 0.13 D, or, a residual hyperopic error of 0.13 D. This translates to a consistently more anterior estimation (0.11 mm mean) of predicted postop ACD by IOLMaster, as compared with theoretical analysis.