Wolfgang Haigis

Bio: Wolfgang Haigis is an academic researcher from University of Würzburg. The author has contributed to research in topics: Intraocular lens & Photorefractive keratectomy. The author has an hindex of 10, co-authored 22 publications receiving 1020 citations.

Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocular lens calculation according to Haigis

Abstract: Background: The precision of intraocular lens (IOL) calculation is essentially determined by the accuracy of the measurement of axial length. In addition to classical ultrasound biometry, partial coherence interferometry serves as a new optical method for axial length determination. A functional prototype from Carl Zeiss Jena implementing this principle was compared with immersion ultrasound biometry in our laboratory. Patients and methods: In 108 patients attending the biometry laboratory for planning of cataract surgery, axial lengths were additionally measured optically. Whereas surgical decisions were based on ultrasound data, we used postoperative refraction measurements to calculate retrospectively what results would have been obtained if optical axial length data had been used for IOL calculation. For the translation of optical to geometrical lengths, five different conversion formulas were used, among them the relation which is built into the Zeiss IOLMaster. IOL calculation was carried out according to Haigis with and without optimization of constants. Results: On the basis of ultrasound immersion data from our Grieshaber Biometric System (GBS), postoperative refraction after implantation of a Rayner IOL type 755U was predicted correctly within ±1 D in 85.7% and within ±2 D in 99% of all cases. An analogous result was achieved with optical axial length data after suitable transformation of optical path lengths into geometrical distances. Conclusions: Partial coherence interferometry is a non- contact, user- and patient-friendly method for axial length determination and IOL planning with an accuracy comparable to that of high-precision immersion ultrasound.

Corneal power after refractive surgery for myopia: contact lens method☆

Abstract: Purpose To clarify the theoretical background of the rigid contact lens overrefraction (CLO) method to determine corneal power after corneal refractive surgery. Setting University Eye Clinic, University of Wurzburg, Wurzburg, Germany. Methods Using paraxial geometrical optics, the measurement situation for the contact lens method was analyzed and the definitions of corneal refractive power were reviewed. Based on the theoretical Gullstrand eye, model eyes were constructed, representing 1 emmetropic and 2 myopic eyes (primary refraction –5.21 diopters [D] and –10.25 D, respectively) before and after photorefractive keratectomy and laser in situ keratomileusis. In these eyes, the application of the CLO was mathematically simulated using Gaussian thick-lens optics and commercial ray-tracing software. Results The CLO method measured neither the equivalent (total) power nor the vertex (back) power of the cornea but rather the quantity 336/ R 1C ( R 1C = anterior corneal radius). Based on these results and the Gullstrand eye, new formulas are proposed to derive the equivalent power and vertex power of the cornea by the CLO method. Conclusions Depending on whether intraocular lens calculation formulas are based on equivalent (total) corneal power or vertex corneal power, the respective new formulas for the CLO method should be applied in patients after corneal refractive surgery. An increase in prediction accuracy of the refractive outcome is expected.

Difficult lens power calculations

Abstract: Purpose of review Although cataract extraction seems to be feasible without major technical obstacles, the surgical technique has changed completely, and patients are no longer satisfied with good spectacle-corrected vision but anticipate complete visual rehabilitation after cataract surgery, without correction. To fulfill this desire, toric or accommodative intraocular lenses are of increasing popularity, and the intraocular lens power calculation after keratorefractive surgery has been improved. Recent findings In this review article, we provide an overview of different mathematical strategies of calculating the intraocular lens power with standard formulas and with new algorithms, such as paraxial or numeric ray-tracing. These enhanced techniques may improve the validity of lens power calculation due to reduction of the prediction error, especially in cases with high or excessive corneal astigmatism and after refractive laser surgery. Furthermore, a new calculation scheme for the determination of bitoric eikonic intraocular lenses allows a distortion-free imaging in astigmatic eyes. The biometric determinants for the different formulas and calculation schemes are discussed in detail. Summary In difficult cases, standard calculation schemes are overemployed and new mathematical algorithms are necessary to adequately address these problems. Ray-tracing algorithms and other complex mathematical computation schemes are of increasing interest and will more and more replace conventional calculation formulas for determination of intraocular lens power.

Optical Coherence Tomography of the Human Retina

Abstract: Objective: To demonstrate optical coherence tomography for high-resolution, noninvasive imaging of the human retina. Optical coherence tomography is a new imaging technique analogous to ultrasound B scan that can provide cross-sectional images of the retina with micrometer-scale resolution. Design: Survey optical coherence tomographic examination of the retina, including the macula and optic nerve head in normal human subjects. Settings Research laboratory. Participants: Convenience sample of normal human subjects. Main Outcome Measures: Correlation of optical coherence retinal tomographs with known normal retinal anatomy. Results: Optical coherence tomographs can discriminate the cross-sectional morphologic features of the fovea and optic disc, the layered structure of the retina, and normal anatomic variations in retinal and retinal nerve fiber layer thicknesses with 10- μm depth resolution. Conclusion: Optical coherence tomography is a potentially useful technique for high depth resolution, cross-sectional examination of the fundus.

Sources of error in intraocular lens power calculation.

Abstract: Purpose To identify and quantify sources of error in the refractive outcome of cataract surgery. Setting AMO Groningen BV, Groningen, The Netherlands. Methods Means and standard deviations (SDs) of parameters that influence refractive outcomes were taken or derived from the published literature to the extent available. To evaluate their influence on refraction, thick-lens ray tracing that allowed for asphericity was used. The numerical partial derivative of each parameter with respect to spectacle refraction was calculated. The product of the partial derivative and the SD for a parameter equates to its SD, expressed as spectacle diopters, which squared is the variance. The error contribution of a parameter is its variance relative to the sum of the variances of all parameters. Results Preoperative estimation of postoperative intraocular lens (IOL) position, postoperative refraction determination, and preoperative axial length (AL) measurement were the largest contributors of error (35%, 27%, and 17%, respectively), with a mean absolute error (MAE) of 0.6 diopter (D) for an eye of average dimensions. Pupil size variation in the population accounted for 8% of the error, and variability in IOL power, 1%. Conclusions Improvement in refractive outcome requires better methods for predicting the postoperative IOL position. Measuring AL by partial coherence interferometry may be of benefit. Autorefraction increases precision in outcome measurement. Reducing these 3 major error sources with means available today reduces the MAE to 0.4 D. Using IOLs that compensate for the spherical aberration of the cornea would eliminate the influence of pupil size. Further improvement would require measuring the asphericity of the anterior surface and radius of the posterior surface of the cornea.

Calculation of intraocular lens power: a review.

Abstract: This review describes the principles and practices involved in the calculation of intraocular lens (IOL) power The theories behind formulas for calculating IOL power are described, using regression and optical methods employing 'thin lens' and 'thick lens' models, as well as exact ray-tracing methods Numerical examples are included to illustrate the points made The paper emphasizes the importance of establishing an accurate estimation of corneal power as well as an accurate technique for the measurement of axial length and accurate methods of predicting postoperative anterior chamber depth (ACD) It is concluded that current improvements in diagnostic and surgical technology, combined with the latest generation IOL power formulas, make the calculation and selection of appropriate IOL power among the most effective tools in refractive surgery today

Analysis of biometry and prevalence data for corneal astigmatism in 23,239 eyes.

Abstract: Purpose To present and analyze biometry data sets and prevalence data for corneal astigmatism in a large population. Setting High-volume eye surgery center, Castrop-Rauxel, Germany. Methods Axial length (AL), corneal radii, anterior chamber depth (ACD), and horizontal corneal diameter (white-to-white [WTW] distance) were optically measured by partial coherence interferometry (IOLMaster). Patient data sets acquired between 2000 and 2006 were reviewed and analyzed. Results The study evaluated 23 239 data sets of 15 448 patients with a median age of 74 years. The mean values were as follows: AL, 23.43 mm ± 1.51 (SD); corneal radius, 7.69 ± 0.28 mm; WTW distance, 11.82 ± 0.40 mm; and ACD, 3.11 ± 0.43 mm. The ACD and axis of astigmatism were correlated with age. The AL, corneal radius, ACD, and WTW were correlated with one other. Eight percent of eyes had corneal astigmatism greater than 2.00 diopters (D), and 2.6% had more than 3.00 D. Astigmatism was with the rule (WTW) in 46.8% of eyes, against the rule in 34.4%, and oblique in 18.9%. High astigmatism was predominantly WTW. Conclusions The results in this analysis might provide normative data for cataract patients and a useful reference for multiple purposes. The correlation of AL with corneal radius, ACD, and corneal diameter in normal eyes was not present in eyes with extreme myopia or hyperopia. Financial Disclosure Neither author has a financial or proprietary interest in any material or method mentioned.