Wolfgang Haigis

Intraocular lens calculation after refractive surgery for myopia: Haigis-L formula.

PURPOSE: To describe the Haigis‐L formula for the calculation of intraocular lenses (IOLs) after refractive laser surgery for myopia based on current biometry and keratometry and present clinical results. SETTING: University Eye Hospital, Wuerzburg, Germany, and various clinics and private practices. METHODS: The basic concepts of the new algorithm were described and summarized. The Haigis formula was analyzed with respect to its usability for eyes after laser surgery for myopia and modified accordingly. Correction curves for IOLMaster keratometry were derived from previous studies. The new formula was checked using the postoperative results of 187 cataract procedures in which 32 IOL types were implanted by 57 surgeons. Input data were current IOLMaster biometry as follows: axial length (AL), anterior chamber depth (ACD), and keratometry (corneal radii) measurements. RESULTS: Before IOL surgery, the mean spherical equivalent was −7.60 diopters (D) ± 3.90 (SD) (range −20.00 to −1.25 D); the mean AL, 27.02 ± 2.01 mm (range 23.09 to 35.32 mm); the mean ACD, 3.52 ± 0.36 mm (range 2.43 to 4.39 mm); and the mean of the measured corneal radii, 8.70 ± 0.60 mm (range 7.28 to 10.96 mm). The mean arithmetic refractive prediction error was −0.04 ± 0.70 D (range −2.30 to +2.40 D) and the median absolute error, 0.37 D (range +0.01 to +2.40 D). The percentages of correct refraction predictions within ±2.00, ±1.00, and ±0.50 D were 98.4%, 84.0%, and 61.0%, respectively. CONCLUSIONS: The new formula would produce promising results in eyes without refractive history. Its refractive predictability fulfills the current criteria for normal eyes.

Posterior chamber myopia lenses in phakic eyes

Objective: To determine the best technique for implanting a hypernegative intraocular lens (IOL) in the posterior chamber of phakic eyes to neutralize high myopia and its results. Setting: Robert Koch Hospital, Hannover‐Gehrden, Germany. Methods: We implanted the Chiron‐Adatomed silicone myopia IOL in 69 eyes of 37 patients between June 1992 and August 1994 and followed them prospectively. Results: To avoid marked decentration, the IOL should merely touch the ciliary sulcus. Its best length should equal the horizontal diameter of the cornea (white to white). Iritis from implantation trauma was avoided by intravenous administration of 250 mg prednisone preoperatively. When inserting the Chiron‐Adatomed myopia IOL, we avoided putting pressure on the crystalline lens with the spatula. In 53 eyes, the difference between precalculated postoperative refraction and achieved postoperative refraction at 3 months was +0.07 ± 1.05 diopters (D) (mean ± SD). No eye deviated more than 2.80 D. Eleven of 69 eyes had a follow‐up of fewer than 6 months and 13 had marked preoperative cortical opacities. Eight of the remaining 45 eyes with clear or almost clear cortexes showed a central subcapsular opacity after 1 to 2 years, probably IOL induced. Conclusion: Use of the Chiron‐Adatomed IOL should be confined to older patients with early cataract until its role as the cause of opacities has been clarified by further observation.

Distribution of corneal spherical aberration in a comprehensive ophthalmology practice and whether keratometry can predict aberration values

PURPOSE: To determine the spherical aberration of the cornea in the general population and whether keratometry readings are predictive of corneal spherical aberration values. SETTING: Private comprehensive ophthalmology practice. METHODS: Corneal spherical aberration and keratometry readings were measured in 696 normal eyes of patients presenting for ocular examination to a comprehensive ophthalmologist. The Easygraph (Oculus) was used to measure the corneal topography and keratometry readings in patients with healthy corneas. The analysis was performed using software in the Easygraph to determine the Zernike coefficients for each cornea. The keratometry and spherical aberration (Zernike coefficient Z40) were then statistically analyzed. RESULTS: The corneal spherical aberration, analyzed by the Kolmogorov‐Smirnov test for normality, fit a normal Gaussian distribution. The spherical aberration value was (+0.274 ± 0.089) × 10−3, measured at an optical zone of 6.0 mm. A very weak correlation was found between corneal spherical aberration and central keratometry readings of the cornea: Corneal spherical aberration = {0.017 × (mean keratometry) − 0.457} × 10−3. CONCLUSIONS: The corneal spherical aberration distribution was a normal Gaussian curve. However, the mean value was significantly different when the sex of the patient was considered. Corneal keratometry readings could not be reliably used to predict corneal spherical aberration.

Corneal power after refractive surgery for myopia: Contact lens method

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 Würzburg, Würzburg, 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/R1C (R1C = 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.

Intraocular lens power calculation and optimized constants for highly myopic eyes

PURPOSE: To determine the accuracy of intraocular lens (IOL) power calculations in eyes with high myopia and to suggest adjusted constants for these cases. SETTING: Centre for Ophthalmology, Eberhard‐Karls‐University, Tuebingen, Germany. METHODS: Patients with high myopia having phacoemulsification with implantation of an AcrySof MA60MA IOL (power range +5.00 to −5.00 diopters [D]) were evaluated. Optical biometry (IOLMaster) and IOL calculations were performed before and after IOL implantation. Because of different optic principal planes of negative‐diopter and positive‐diopter IOLs, separate constants were calculated for these groups. RESULTS: Fifty eyes (32 patients) were evaluated. Thirty eyes (mean AL 31.15 mm ± 1.69 [SD]) had implantation of a positive‐diopter IOL (mean power +3.10 ± 1.50 D) and 18 eyes (mean AL 33.20 ± 2.25 mm), a negative‐diopter IOL (mean power −3.20 ± 1.70 D). Postoperatively, the mean spherical equivalent was −1.42 ± 1.33 D and −0.41 ± 1.81 D, respectively. The difference in optimized constants between positive‐ and negative‐diopter IOLs was significant for all formulas. Power calculation with the SRK II formula showed a wide range of deviation of postoperative refraction from target refraction. Calculation with the Haigis, SRK/T, Holladay 1, and Hoffer Q formulas showed a mean deviation of 0.00 D with an SD of 0.88, 0.92, 1.03, and 1.15, respectively. CONCLUSIONS: Results indicate that the SRK II formula cannot be recommended for IOL power calculation in highly myopic patients. With optimized constants, the SRK/T, Haigis, Hoffer Q, and Holladay 1 formulas produced small deviation of postoperative refraction from target refraction.

Difficult lens power calculations.

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.

Intraocular lens calculation in extreme myopia

PURPOSE: To study from a theoretical viewpoint the effects in cases of extreme myopia of the different axial length (AL) behavior of current intraocular lens (IOL) calculation formulas and the problems caused by changes in lens geometry in the transition from plus to minus lenses. SETTING: University Eye Hospital, Wuerzburg, Germany. METHODS: A comparison of the thick‐lens and thin‐lens approach was made with allowance for the role of IOL constants and exemplified in model calculations based on design data of the MA60MA IOL in the power range from +5.0 to −5.0 diopters. Ray tracing was used to define model eyes for the MA60MA IOL, and the IOL constants producing the correct lens powers with the Haigis formula were determined. RESULTS: An equation was derived linking lens geometry represented by the positions of the principal planes with the effective thin‐lens position and thus with the respective IOL constants. Because IOL geometry changes considerably at the transition from plus to minus powers, a corresponding change is obtained in the necessary IOL constants. If no allowance is made for this effect, refractive errors increasing with AL will be associated with minus‐power IOLs. CONCLUSION: Plus IOLs and minus IOLs have to be characterized by different sets of IOL constants.

Protocols for Studies of Intraocular Lens Formula Accuracy

M ANY STUDIES HAVE BEEN PUBLISHED ASSESSING the accuracy of intraocular lens (IOL) power calculation. Since the formation of the IOL Power Club in 2005, errors have been noted in the protocols used in these studies of accuracy in the peerreviewed literature. These errors have been seen in articles in most all of our most respected journals. Unfortunately, no methodology standards for authors for these studies have been published since 1981. Many discussions were held along with statistical consultation to agree on a set of protocols. In an attempt to aid authors, 10 recommendations are offered to make a study statistically valid and completely fair in evaluating the accuracy of tested formulas, methods, and instruments. Firstly, the demographics of the study population (ie, sex, age, and ethnicity) should be clearly described at the beginning of the Methods section. These may well have a relevant influence on eye biometric parameters and, therefore, IOL power calculation performance. Optimization through IOL-specific lens constants may depend on these variables as well. More importantly, before comparing the results of the formulas, the mean error (ME) of the study group for each formula should be made to equal zero by changing the lens factor (constant) individually for each formula. This eliminates the bias of the lens factor chosen and is the only proper way to do this so that all the formulas are the same. This can easily be done using the Excel software’s Data/What If Analysis/Goal Seek function. There are other ways to do this if you have the dataset in a database and are able to do stepwise iterations through the lens constant

Repeatability and agreement in optical biometry of a new swept-source optical coherence tomography–based biometer versus partial coherence interferometry and optical low-coherence reflectometry

Purpose To estimate the repeatability of biometric parameters obtained with a new swept‐source biometer and to compare the agreement with that of partial coherence interferometry (PCI) and optical low‐coherence reflectometry (OLCR). Setting Department of Ophthalmology, Helios Hospital Erfurt, Erfurt, Julius‐Maximilians University, Würzburg, and Philipps University, Marburg, Germany. Design Prospective comparative multicenter clinical study. Methods Biometry was taken with the use of 3 different biometers: the IOLMaster 700 swept‐source biometer, the PCI‐based IOLMaster 500, and the OCLR‐based Lenstar LS 900. Axial length (AL), anterior chamber depth (ACD), and spherical equivalent (SE) were compared between swept‐source and PCI biometry and central corneal thickness (CCT) and lens thickness (LT) between swept‐source and OLCR biometry. The repeatability of swept‐source biometry was evaluated on the basis of 3 measurements captured for each patient. Results One hundred twenty cataract eyes were included in the study. The mean difference between swept‐source and PCI biometry for AL, ACD, and SE measurements was 4 &mgr;m ± 25 (SD), 17 ± 122 &mgr;m, and −0.001 ± 0.19 diopter (D), respectively. The mean difference between swept‐source and OLCR biometry for LT and CCT measurements was 21 ± 122 &mgr;m and 0.15 ± 4.51 &mgr;m, respectively. Differences between swept‐source biometry and the other devices distributed around zero without statistical significance. The standard deviation of repeatability for AL, ACD, LT, CCT, and SE was 8.8 &mgr;m, 9.8 &mgr;m, 2.3 &mgr;m, 19.5 &mgr;m, and 0.1 D, respectively. Conclusions Swept‐source biometry showed high repeatability performance for all biometric parameters. The agreement of AL, ACD, and SE between swept‐source and PCI biometry as well as that of LT and CCT between swept‐source and OLCR biometry was excellent. It remains to be validated whether high repeatability shown by swept‐source biometry will result in better postoperative refractive outcomes. Financial Disclosure Drs. Blum and Sekundo are members of the Scientific Advisory Board of Carl Zeiss Meditec AG. Drs. Peter and Bühren are employees of Carl Zeiss Meditec AG.

Age-related behavior of posterior chamber lenses in myopic phakic eyes during accommodation measured by anterior segment partial coherence interferometry

PURPOSE: To evaluate age‐related position shifts of the crystalline lens and the implantable contact lens (ICL, Staar Surgical) by a new, commercially available, anterior segment partial coherence interferometer, the ACMaster (Carl Zeiss Meditec), during accommodation in myopic eyes. SETTING: ALZ Augenklinik, Munich, Germany. METHODS: Fifty‐three eyes of 29 consecutive patients were measured after myopic ICL implantation before and during subjective accommodation to a stimulus of 3 diopters (D) by anterior segment partial coherence interferometry (PCI). Nine eyes were also measured with a 5.00 diopters (D) stimulus; 14 eyes were measured repeatedly at different visits. The mean patient age was 33 years ± 9 (SD) (range 21 to 59 years). The preoperative mean sphere was −7.6 ± 1.9 D (range −5.0 to −11.5 D) and the cylinder, −1.4 ± 1.1 D (range 0 to −4.25 D). RESULTS: Older patients had a tendency toward smaller vaults on desaccommodation between the ICL and the crystalline lens compared to younger individuals. In younger patients, there was a decrease of the vault on accommodation, whereas it increased in older persons (P = .005). During accommodation, the more the anterior lens surface shifted forward, the more the ICL bulged (P = .005). The change in vaulting was significantly larger at 5.00 D than at 3.00 D accommodation stimulus (P = .012). CONCLUSIONS: The behavior of ICLs in relation to the crystalline lens during accommodation varied with age and could be shown by PCI. The position shift of the ICL depended on the initial vault at desaccommodation and the ability of the anterior lens surface to bulge forward. Even though the crystalline lens stiffened, and therefore accommodation deteriorated with age, there was still a movement of the ICL, pointing to the role of the ciliary muscle movement in accommodation.