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Biomedical subjects

Thomas Kohnen

Publications and source records attributed to Thomas Kohnen.

At least 19 recordsLinked to original sources
PubMed2006

European multicenter study of the AcrySof ReSTOR apodized diffractive intraocular lens.

OBJECTIVE: To report the safety and effectiveness of the AcrySof ReSTOR apodized diffractive intraocular lens (IOL), model MA60D3, when implanted into the capsular bag. DESIGN: Multicenter European study including university clinics, eye hospitals, and private ophthalmic surgical centers. PARTICIPANTS: One hundred twenty-seven subjects implanted in cataractous eyes in an open multicenter study. INTERVENTION: After phacoemulsification, the foldable 3-piece hydrophobic acrylic apodized diffractive IOL was implanted in the capsular bag using a Monarch injector with an A-cartridge. The mean preoperative patient age was 68.4+/-12 years. Intraocular lens implant power ranged from 18.0 to 25.0 diopters (D) in 0.5-D increments. MAIN OUTCOME MEASURES: Distance visual acuity (VA), near VA, spectacle dependence, unwanted visual symptoms, and patient satisfaction. RESULTS: At the 6-month postoperative visit, binocular (both eyes simultaneously) mean uncorrected distance and near logarithm of the minimum angle of resolution VAs for the MA60D3 were 0.04+/-0.14 and 0.09+/-0.12 (n = 118), respectively. In addition, 88.0% and 84.6% of ReSTOR subjects achieved spectacle independence for distance and near vision, respectively. Glare and halos were reported as severe by only 8.5% and 4.2% of patients, respectively. Ninety-two percent of patients stated that they would choose to have the same lens implanted again after the first implant, and 95.7% answered likewise after the second implant. CONCLUSIONS: The AcrySof ReSTOR MA60D3 IOL demonstrated excellent near VA without compromising distance vision. Spectacle independence and patient satisfaction were high, whereas unwanted photic phenomena were clinically acceptable.

Acrylic Resins↗
PubMed2006

Intraindividual comparison of higher-order aberrations after implantation of aspherical and spherical intraocular lenses as a function of pupil diameter.

PURPOSE: To compare intraindividual higher-order wavefront aberrations after implantation of aspherical and spherical intraocular lenses (IOLs) as function of pupil diameter. SETTING: Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. METHODS: In this prospective study, wavefront measurements of 21 patients after implantation of a spherical IOL (AMO AR40e) in 1 eye and an aspherical IOL (AMO Tecnis) in the contralateral eye were analyzed. Third-, 4th-, 5th-, total higher-order aberration (HOA) root-mean-square (RMS), and primary spherical aberration (Z(4)(0)) were compared at different virtual pupil diameters of 3 to 6 mm. RESULTS: For both IOLs and each higher order analyzed, values increased with increasing pupil diameter. Fourth-order RMS and Z(4)(0) in the aspherical IOL group were significantly lower than with the spherical IOL at all analyzed pupil diameters. The total HOA RMS of the aspherical IOL was significantly lower than the spherical IOL only at 6 mm pupil diameter. For 3rd- and 5th-order RMS, no significant difference was found between the tested IOLs at any pupil diameter. CONCLUSION: In comparison to a spherical IOL, the aspherical Tecnis IOL reduced Z(4)(0) and 4th-order RMS significantly for pupil diameters of 3 to 6 mm, whereas total HOA RMS was only significantly reduced for a pupil diameter of 6 mm.

Aged↗
PubMed2006

Factors affecting the change in lower-order and higher-order aberrations after wavefront-guided laser in situ keratomileusis for myopia with the Zyoptix 3.1 system.

PURPOSE: To identify factors that affect the change in lower- and higher-order wavefront aberrations after myopic wavefront-guided laser in situ keratomileusis (wg-LASIK). SETTING: Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. METHODS: Sixty myopic eyes of 32 patients were treated with wg-LASIK (Zyoptix version 3.1, Bausch & Lomb) and had an uneventful follow-up of 12 months. Wavefront errors were measured preoperatively and 12 months after LASIK and were computed for pupil diameters (PDs) of 3.5 mm and 6.0 mm. Multiple stepwise regression analysis was performed to assess the influence of patient age, spherical equivalent (SE), sphere, cylinder, optical zone (OZ) diameter, and the preoperative individual Zernike coefficients on lower- and higher-order aberration (HOA) change. RESULTS: The mean preoperative SE was -5.59 diopters (D) +/- 2.20 (SD) (range -1.00 to -9.50 D); the mean OZ diameter was 6.70 +/- 0.68 mm (range 5.6 to 8.1 mm). Reduction in almost all Zernike coefficients was influenced significantly by the preoperative amount of the individual coefficient. The effect varied among the coefficients and was lower with the 6.0 mm PD. With the 3.5 mm PD, age, SE, sphere, cylinder, and OZ diameter did not have a significant effect on individual Zernike coefficients. With the 6.0 mm PD, SE and OZ diameter had a significant effect on the induction of Z4(0); the OZ diameter also had an effect on the induction of coma root mean square. CONCLUSIONS: Three groups of factors influenced the change in HOAs: The negative correlation with the magnitude of preoperative HOA values reflected the effect of the wavefront-guided algorithm. The SE and OZ diameter affected the inadvertent induction of spherical aberrations. Randomly acting effects such as decentration or flap creation, which were not included in the model, affected the induction of HOAs, particularly coma-like terms.

Adult↗
PubMed2006

Measuring contrast sensitivity under different lighting conditions: comparison of three tests.

PURPOSE: The purpose of this study was to evaluate three psychophysical tests for the measurement of contrast sensitivity (CS) and disability glare (DG) at different luminance levels. METHODS: In 60 eyes of 60 individuals (group 1: 20 healthy eyes of young individuals; group 2: 20 healthy eyes of elderly subjects; group 3: 20 eyes with nuclear cataract), CS with best correction was measured twice with the Frankfurt-Freiburg Contrast and Acuity Test System (FF-CATS) and the Functional Acuity Contrast Test (FACT, 1.5 cycles per degree [cpd]) at 167 cd/m2 and 0.167 cd/m2, and with the Pelli-Robson Chart (PRC) at 100 cd/m2 with and without glare. Repeatability of test and retest, and discriminative ability between the different subgroups, were assessed for CS values. RESULTS: Maximum CS values varied across tests. In all groups, highest CS values were obtained with the photopic FF-CATS. For FACT scores at 1.5 cpd, there was a ceiling effect for young subjects. CS scores obtained with the PRC were the lowest. The PRC had the best test-retest repeatability of all tests. Under mesopic conditions with glare, reliability was generally lower; the FF-CATS had the highest repeatability of the mesopic tests. The FF-CATS discriminated best between the different groups for all conditions. CONCLUSIONS: There are large discrepancies in the test results between CS testing methods, especially under different lighting conditions. Results from different CS tests are not interchangeable.

Adult↗
PubMed2006

A standardized drawing scheme to document corneal changes following refractive corneal surgery.

PURPOSE: To present a systematic and standardized drawing scheme for unambiguous and reproducible documentation of corneal changes after incisional techniques, coagulative procedures, and lamellar and surface ablation excimer surgery. METHODS: Standardized symbols in five colors representing specific corneal conditions after incisional surgery (eg, radial keratotomy, astigmatic keratotomy), coagulative procedures (eg, laser thermokeratoplasty, conductive keratoplasty), surface ablation (eg, photorefractive keratectomy, laser subepithelial keratomileusis, epi-LASIK), and LASIK are used to record corneal changes in frontal and sectional views. RESULTS: Corneal changes following refractive corneal surgery were documented. CONCLUSIONS: The drawing scheme permits specific features to be followed in the clinic in a clear and unambiguous manner.

Cornea↗
PubMed2005

Incidence of posterior vitreous detachment after laser in situ keratomileusis.

BACKGROUND: Vitreoretinal complications are rare in laser in situ keratomileusis (LASIK). Increase in intraocular pressure caused by intraoperative suction with subsequent deforming of the ocular globe and excimer laser shock during the ablation have been discussed as possible causes. The purpose of this study was to determine the effect of LASIK on the vitreous body. PATIENTS AND METHODS: In a prospective study we performed ocular ultrasonography (B scan) immediately before and 1 week after LASIK procedure in 103 myopic or myopic-astigmatic eyes (53 patients, mean age 36.3 years, 32 women, 21 men). In particular, the prevalence, localization, and extent of posterior vitreous detachment (PVD) were determined. RESULTS: The mean spherical equivalent was -4.85 D (range -1.25 to -8.38) and the mean anteroposterior ocular globe length was 25.13 mm (range 23.31-27.65). Ninety-five eyes (92.2%) had no PVD preoperatively. Nine eyes out of this group (seven patients, 9.5%) developed incomplete PVD as assessed 1 week postoperatively. Eight eyes (7.8%) had a partial PVD preoperatively and in only one eye was an extension of vitreous detachment observed after the surgery. None of the preoperatively measured parameters could predict the occurrence of PVD by LASIK. CONCLUSIONS: LASIK may in rare cases lead to new occurrence of PVD or extension of a previously existing partial PVD.

Adult↗
PubMed2005

Tilt and decentration of three-piece foldable high-refractive silicone and hydrophobic acrylic intraocular lenses with 6-mm optics in an intraindividual comparison.

PURPOSE: Intraindividual comparison of tilt and decentration of three-piece foldable intraocular lenses (IOLs) with 6-mm optics and different edge design and material. DESIGN: Prospective randomized study. METHODS: Twenty-five patients with senile cataract (group I) received a foldable silicone, sharp optic edge IOL in one eye and a silicone, rounded optic edge IOL in the other eye. Group II (n = 28) received the foldable silicone, sharp optic edge IOL in one eye and an acrylate, sharp optic edge IOL in the other eye. Scheimpflug photography was performed after the procedure with an anterior eye segment analysis system. Tilt and decentration of the IOL optic were measured 1 week, 6 months, and 12 months after the procedure. RESULTS: In group I, the foldable silicone, sharp optic edge IOL showed a mean optic tilt of 3.03 +/- 1.79 degrees and an optic decentration of 0.24 +/- 0.13 mm; the silicone, rounded optic edge IOL showed a tilt of 3.26 +/- 1.69 degrees and a decentration of 0.23 +/- 0.13 mm. In group II, the foldable silicone, sharp optic edge IOL showed an average tilt of 2.34 +/- 1.81 degrees and a decentration of 0.29 +/- 0.21 mm after 12 months; the acrylate, sharp optic edge IOL had a tilt of 2.32 +/- 1.41 degrees and a decentration of 0.24 +/- 0.10 mm. There were no significant differences in either group. CONCLUSION: The examined IOLs showed a stable position regarding tilt and decentration in the first 12 postoperative months, independent of material and edge design. Slight deviations from the optical axis might affect the outcome in aspheric or multifocal IOLs.

Acrylic Resins↗
PubMed2005

Corneal first-surface aberration analysis of the biomechanical effects of astigmatic keratotomy and a microkeratome cut after penetrating keratoplasty.

Astigmatic keratotomy (AK) was performed in a patient after penetrating keratoplasty (PKP) for keratoconus to reduce high post-PKP astigmatism. The procedure led to a significant decrease in astigmatism, but corneal higher-order aberrations (HOAs) increased. After PKP, the patient was scheduled for 2-step laser in situ keratomileusis (LASIK) to correct myopia and astigmatism. One day after the microkeratome cut, a decrease of -2.75 diopters in the spherical equivalent (SE) was noted. Although subjective manifest cylinder and corneal spherical aberrations were marginally affected, a marked decrease in coma and other HOAs could be observed. One month after the cut, the SE was unchanged. Excimer laser ablation was not performed as the patient was satisfied with the result and refused further treatment. This case shows that AK cuts can induce HOAs and a single microkeratome cut performed in corneal grafts can have strong biomechanical effects on lower-order aberrations and HOAs. If LASIK is planned after PKP, a 2-step approach is recommended to anticipate biomechanical effects and avoid overcorrection or undercorrection.

Adult↗
PubMed2005

Intermittent myopic shift of 4.0 diopters after implantation of an Artisan iris-supported phakic intraocular lens.

A 45-year-old man with bilateral high myopia and myopic astigmatism had uneventful implantation of a -10.5 diopters (D) Artisan iris-fixated anterior chamber phakic intraocular lens (PIOL) (Ophtec) in both eyes. In the first days after surgery, uncorrected visual acuity (UCVA) was 20/16 in the right eye and 20/16 in the left; the position of the PIOL was stable. Ten days after surgery, the left eye developed a myopic shift of 4.0 D. Further examination showed that the myopia disappeared when the pupil was medically dilated. After the pupil returned to a natural position, the myopic shift reappeared. Because there were no changes in the subsequent 4 months, we decided to exclavate the IOL, rotate it by 10 degrees, and reenclavate it with less tissue. The myopic shift did not return over the following 20 months, and the UCVA was 20/20. In rare cases, iris-fixated anterior chamber IOLs may induce refractive changes related to effects on the surrounding anatomic structures. This may be corrected by phakic IOL rotation or reenclavation of the phakic IOL with less tissue.

Astigmatism↗
PubMed2005

Late in-the-bag intraocular lens dislocation: incidence, prevention, and management.

Dislocation of an intraocular lens (IOL) with the capsular bag is a late complication of cataract surgery, reported with increasing frequency in recent years. Pseudoexfoliation, uveitis, myopia, and other diseases associated with progressive zonular weakening and capsular contraction are the predisposing conditions. Capsular tension rings probably help but do not prevent this complication. Management includes IOL exchange, replacement with an anterior or a sutured posterior chamber IOL, or suturing the IOL through the bag to the iris or the sclera.

Foreign-Body Migration↗