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Thomas Kohnen

Publications and source records attributed to Thomas Kohnen.

At least 37 records · Page 2Linked to original sources
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↗
PubMed2005

Influence of pupil and optical zone diameter on higher-order aberrations after wavefront-guided myopic LASIK.

PURPOSE: To investigate the influence of pupil and optical zone (OZ) diameter on higher-order aberrations (HOAs) after myopic wavefront-guided laser in situ keratomileusis (LASIK). METHODS: Twenty-seven myopic eyes of 19 patients were included. The mean preoperative spherical equivalent was -6.86 diopters (D) +/- 1.24 (SD) (range -4.25 to -9.5 D); the mean planned OZ diameter was 6.26 +/- 0.45 mm (range 5.7 to 7.1 mm). All patients had uneventful wavefront-guided LASIK (Zyoptix version 3.1, Bausch & Lomb) and an uncomplicated follow-up of 12 months. Wavefront measurements were performed with a Hartmann-Shack sensor in maximum mydriasis preoperatively and 12 months after LASIK. Wavefront errors were computed for pupil diameters (PDs) of 3.0, 3.5, 4.0, 5.0, 6.0, and 7.0 mm for the individual OZ diameter and for the individual mydriatic PD (7.93 +/- 0.46 mm). The impact of the relationship between pupil diameter and OZ diameter (fractional clearance [FC]) on HOA was described and quantified using curvilinear regression with a 4th-order polynomial fit. RESULTS: There was a reproducible relationship between FC and the amount of induced HOA. The change in HOA root mean square and primary spherical aberration (Z(4)0) was significantly correlated with FC. If the OZ was 16.5% larger than the pupil (FC = 1.17), only half the amount of HOA was expected to be induced than if the OZ equaled the pupil. In contrast, an OZ that was 9% smaller than the pupil (FC = 0.91) resulted in an HOA induction 50% higher than at FC = 1. CONCLUSION: The OZ zone to pupil ratio (fractional clearance) had a significant impact on HOA induction after wavefront-guided LASIK.

Adult↗
PubMed2005

Incision sizes before and after implantation of 6-mm optic foldable intraocular lenses using Monarch and Unfolder injector systems.

PURPOSE: To determine incision sizes for 6-mm optic foldable intraocular lenses (IOLs) implanted with injector systems. DESIGN: Nonrandomized, prospective clinical study. PARTICIPANTS: One hundred fifty eyes of 150 patients with cataract and without other anterior segment pathological features or previous eye surgeries. INTERVENTION: We performed implantation of foldable IOLs with sharp optic edges and 6-mm total optic diameter with their recommended injector systems and cartridges: (1) Alcon MA60BM with Monarch II/cartridge A, (2) Alcon SA60AT with Monarch II/cartridge B, (3) Alcon SA60AT with Monarch II/cartridge C, (4) AMO AR40e with Unfolder Sapphire, (5) AMO AR40e with Unfolder Emerald, and (6) AMO Clariflex with Unfolder Silver. With every combination, 25 IOLs were implanted. MAIN OUTCOME MEASURES: We measured incision width before and after phacoemulsification as well as before and after IOL implantation using a Kohnen caliper. RESULTS: The tunnel width (in millimeters; +/- standard deviation) for each combination before and after IOL implantation, respectively, was (1) 3.61 (+/-0.12) and 3.74 (+/-0.15), (2) 3.31 (+/-0.12) and 3.44 (+/-0.16), (3) 2.88 (+/-0.11) and 2.96 (+/-0.11), (4) 3.37 (+/-0.12) and 3.52 (+/-0.09), (5) 2.99 (+/-0.16) and 3.11 (+/-0.14), and (6) 3.06 (+/-0.12) and 3.15 (+/-0.11). The incision sizes before and after implantation for (3) were significantly smaller than all other combinations. Combinations (2) and (4) were not statistically significantly different, but were statistically significantly smaller in preimplantation and postimplantation incision size compared with combination (1) and were larger compared with combinations (5) and (6). However, the relationship of incision size and effective IOL optical zone differed: AR40e (Unfolder Sapphire) < MA60BM < Clariflex < AR40e (Unfolder Emerald) < SA60AT with both Monarch II B and C cartridge (greater means better relationship). CONCLUSIONS: Postimplantation incisions sizes of 2.96 to 3.74 mm were determined with 6-mm total optic foldable IOLs using Monarch and Unfolder injector systems. Because the effective optical zone size is different for some of these IOLs, the incision size alone may not be the only relevant factor for optical outcome.

Adult↗
PubMed2005

Effect of microkeratome suction during LASIK on ocular structures.

PURPOSE: To study the effect of microkeratome suction on ocular structures during LASIK. DESIGN: Observational, prospective case series. PARTICIPANTS: Twenty-one eyes of 11 patients with myopia or astigmatic myopia (8 females, 3 males) were included. The mean patient age was 36.3 years (median, 37 years; range, 24-48 years), and the mean spherical equivalent was -5.03 diopters (D) (median, -4.63 D; range, -2.38 to -8.38 D). METHODS: We performed preoperative and intraoperative A-scan ultrasonography during application of suction using the Hansatome microkeratome (Bausch & Lomb Surgical, Munich, Germany) to create corneal flaps during LASIK. We also performed preoperative and postoperative B-scan ultrasonography of the posterior ocular segment with special attention to the presence and size of posterior vitreous detachment (PVD). MAIN OUTCOME MEASURES: We measured changes in the axial length, anterior chamber depth, lens thickness, and vitreous distance (distance from the posterior lens capsule to the posterior pole) during application of the microkeratome suction ring and recorded new occurrences of or increases in the size of the PVD after surgery. RESULTS: The lens thickness decreased (mean change, -0.20 mm; P = 0.001; 95% confidence interval [CI], -0.11 to -0.30) in 18 eyes during application of the suction ring. The vitreous distance increased (mean change, 0.20 mm; P = 0.004; 95% CI, 0.08-0.32) in 16 eyes. No statistically significant changes were found in the anterior chamber depth (P = 0.75) or axial length (P = 0.51). After surgery, 3 of 14 eyes (21.4%) experienced PVD that did not have echographic signs of PVD before surgery. Of 7 eyes with preoperative PVD, the PVD enlarged in 1 eye (14.3%). CONCLUSIONS: During application of microkeratome suction, the lens thickness decreases, whereas the vitreous distance increases, suggesting anterior traction on the posterior segment. The relationship between the observed PVD and LASIK merits further investigation.

Adult↗
PubMed2005

Comparison of corneal higher-order aberrations induced by myopic and hyperopic LASIK.

OBJECTIVE: To compare the change in anterior corneal higher-order (third- to fifth-order) aberrations (HOAs) induced by myopic and hyperopic LASIK. DESIGN: Retrospective comparative case series. PARTICIPANTS: One hundred eyes (50 myopes and 50 hyperopes) of 59 patients were included. The mean preoperative spherical equivalent (SE) was -4.22+/-1.78 diopters (D; range, -1.25 to -8.00 D) in the myopic group (group A) and +2.72+/-1.25 D (range, +0.25 to +5.00 D) in the hyperopic group (group B). INTERVENTION: LASIK was performed using a conventional spherocylindrical laser algorithm (Planoscan V2.9992, Bausch & Lomb/Technolas, Munich, Germany). Optical zone diameter was 6.70+/-0.32 mm (range, 6-7 mm) in group A and 6.59+/-0.19 mm (range, 6.5 to 7 mm) in group B. Third to fifth corneal HOA were computed for a pupil diameter of 6 mm from corneal topographic examinations before and 1 month after surgery. MAIN OUTCOME MEASURES: Change in corneal HOAs, derived from corneal topography. RESULTS: Total HOA root mean square (RMS) changed in group A by 0.167+/-0.180 microm (factor 1.53) and in group B by 0.341+/-0.341 microm (factor 1.89). The mean induction of coma RMS was significantly different in both groups (myopes, 0.092+/-0.195 microm; hyperopes, 0.252+/-0.305 microm; P<0.05). For spherical aberration (Z 4,0), the myopic group showed a significant increase (0.130+/-0.120 microm; factor 1.6; P<0.001), whereas the hyperopic group showed a significant decrease (-0.317+/-0.158 microm; factor 0.76; P<0.001). Fifth-order aberrations showed an increase in both groups, which was higher in group B (0.069+/-0.120 microm; factor 2.46) than in group A (0.005+/-0.065 microm; factor 1.49). CONCLUSIONS: Myopic and hyperopic LASIK had different patterns of HOA induction. Myopic LASIK induced positive spherical aberrations and positive secondary astigmatism, whereas hyperopic LASIK induced negative spherical aberrations and negative secondary astigmatism. Hyperopic LASIK induced more third- and fifth-order comalike aberrations than myopic LASIK.

Adult↗
PubMed2004

Scleral and corneal laceration with iris prolapse caused by an eagle claw.

BACKGROUND: To describe the visual rehabilitation after surgical treatment of an ocular injury sustained during an attack by a bird of prey. METHODS: A 51-year-old woman who was attacked by an eagle in a cage had a laceration of cornea and sclera at 9 o' clock, an iris prolapse that was jammed into the scleral wound, and a flat anterior chamber with hyphema. The uncorrected visual acuity was hand movements. Surgical treatment was performed immediately and included iris repositioning and suturing, scleral and conjunctival suturing, and transscleral cryotherapy to the retina. RESULTS: Eight months later, the best corrected visual acuity was 20/20. The anterior segment showed a posterior synechia in the area of the iris repair and an almost round pupil; the crystalline lens showed only a localized opacification. CONCLUSIONS: A bird of prey, even though caged, can injure an eye in humans. With immediate surgical treatment, good visual rehabilitation was achieved in this case. It should be reiterated that spectacles offer no protection against ocular trauma in these cases.

Animals↗
PubMed2004

Position of angle-supported, iris-fixated, and ciliary sulcus-implanted myopic phakic intraocular lenses evaluated by Scheimpflug photography.

PURPOSE: To examine postoperative positional stability of myopic phakic intraocular lenses (IOLs). DESIGN: Prospective, nonrandomized clinical study. METHODS: The study included 46 eyes which received an anterior chamber angle-supported (Bausch & Lomb NuVita; 10 eyes), anterior chamber iris-fixated (Ophtec Artisan; 20 eyes) or ciliary sulcus-implanted phakic IOL (Staar ICL; 16 eyes). The distance between the phakic IOL and the crystalline lens and the cornea as well as rotation around the optical axis was evaluated using Scheimpflug photography at 1, 3 to 6, and 12 months postsurgery. RESULTS: The anterior chamber phakic IOLs showed no significant movement in anteroposterior direction. The posterior chamber phakic IOL showed a significant movement toward the crystalline lens between postoperative months 3 and 12. The median amount of rotation around the optical axis between the 3- and the 12-month evaluation was 1.9 degrees (range = 0.0-33.5 degrees) for the NuVita, 0.6 degrees (range = 0.0-3.5 degrees) for the Artisan, and 0.9 degrees (range = 0.2-2.3 degrees) for the ICL. Four NuVita IOLs rotated more than 10 degrees. CONCLUSIONS: The angle-supported anterior chamber phakic IOLs showed a generally stable position regarding distance to cornea and natural lens, but rotation was observed in four IOLs. The iris-fixated phakic IOL showed the highest overall stability. The posterior chamber phakic IOL was stable in terms of rotation but had a tendency to decrease in distance toward the crystalline lens. Intraocular lenses implanted in phakic eyes followed for 12 months demonstrate stable IOL position overall.

Adult↗
PubMed2004

Comparison of manual and automated methods to determine horizontal corneal diameter.

PURPOSE: To compare 2 manual methods and 2 automated devices for measuring the horizontal corneal diameter (white-to-white [WTW] distance). SETTING: Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. METHODS: In 100 eyes of 61 patients, the WTW distance was measured independently by 2 examiners using the following techniques: the Holladay-Godwin gauge, a measuring caliper, Zeiss IOLMaster, and Orbscan II topography system (Bausch & Lomb). The results were compared with measurements on magnified slitlamp photographs of the anterior eye segment. Statistical evaluation was performed using the Bland-Altman method for comparison of measurement techniques. RESULTS: The mean horizontal corneal diameter was 11.91 mm +/- 0.71 (SD) with the measuring caliper, 11.8 +/- 0.60 mm with the Holladay-Godwin gauge, 11.78 +/- 0.43 mm with the Orbscan II, and 12.02 +/- 0.38 mm with the IOLMaster. The coefficient of inter-rater repeatability was 1.30 for the caliper, 0.92 for the Holladay-Godwin gauge, 0.76 for the Orbscan II, 0.50 for the IOLMaster, and 1.16 for the manual measurement in anterior segment images. The results obtained with the caliper were statistically significantly different between the 2 examiners (P<.001). The measurements of examiner 2 using the caliper were significantly different from the measurements of the same examiner using the Holladay-Godwin gauge. This was not the case with the 2 automated devices. CONCLUSIONS: Automated measurement of the WTW distance provides more precise results than measurements using manual methods. The Zeiss IOLMaster had the highest reliability in measuring corneal diameter.

Adult↗
PubMed2004

Posterior capsule opacification after implantation of CeeOn Edge 911A, PhacoFlex SI-40NB, and AcrySof MA60BM lenses: one-year results of an intraindividual comparison multicenter study.

PURPOSE: To perform an intraindividual comparison of posterior capsule opacification (PCO) with 2 foldable intraocular lenses (IOLs) and a foldable acrylic IOL 1 year after in-the-bag implantation. SETTINGS: Seven German ophthalmology centers. METHODS: In an open prospective randomized multicenter study, each center intraindividually compared a high-refractive-index, sharp-edged optic silicone IOL (CeeOn Edge 911A, Pharmacia) with a high-refractive-index, round-edged optic silicone IOL (PhacoFlex SI-40NB, Allergan) or a sharp-edged optic acrylic IOL (AcrySof MA60BM, Alcon). Of 288 randomized patients, 247 had standard phacoemulsification with in-the-bag IOL implantation in both eyes by the same surgeon. One eye of each patient received a CeeOn Edge IOL and the fellow eye, an AcrySof or PhacoFlex IOL. A morphologic evaluation of PCO was performed using the Evaluation of Posterior Capsule Opacification (EPCO) system 1 to 2 weeks and 11 to 14 months after surgery. The digital pictures were evaluated by an independent investigator who was blind to the type of IOL. Intraindividual differences in EPCO scores were statistically evaluated by a 1-sided binomial test at an alpha-level of 5%. RESULTS: One year after surgery, 127 patients with the AcrySof IOL and 102 patients with the PhacoFlex IOL in the control eye were reexamined. Functional results, safety, and handling were not significantly different between the 3 IOLs. All reexamined eyes had a very low PCO grade. The EPCO values revealed less PCO in eyes with the CeeOn Edge IOL than in eyes with the AcrySof or PhacoFlex IOL, but the difference was not statistically significant. A neodymium:YAG laser capsulotomy was performed in 1 eye with a CeeOn Edge IOL, 1 eye with an AcrySof IOL, and 2 eyes with a PhacoFlex IOL. CONCLUSIONS: The EPCO PCO grade was low 1 year after implantation of CeeOn Edge 911A, PhacoFlex SI-40NB, and AcrySof MA60BM IOLs; there was no statistically significant difference between the IOLs. The impact of IOL material and edge design on PCO development might be relevant in a long-term follow-up of this study.

Acrylic Resins↗
PubMed2004

Clinical course of severe central epithelial defects in laser in situ keratomileusis.

PURPOSE: To report the clinical outcome of laser in situ keratomileusis (LASIK) cases complicated by severe central intraoperative epithelial defects (EDs) caused by the microkeratome cut. SETTING: Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. METHODS: In a retrospective study of 1650 LASIK cases at 1 center, the preoperative data, surgical procedures, and postoperative course in 22 eyes of 14 patients who experienced severe central EDs during the LASIK procedure (1.3%) were reviewed. The surgery was performed using a Technolas C-LASIK 217 excimer laser (Bausch & Lomb) and a Hansatome microkeratome (Bausch & Lomb). A follow-up of at least 12 months was available in all but 1 case. The median follow-up was 13.5 months (range 12 to 25 months). In the postoperative period, the following parameters were reviewed: course of refraction, best spectacle-corrected visual acuity (BSCVA), slitlamp findings, and corneal topography. RESULTS: The mean patient age was 42 years (range 27 to 61 years). Eight patients were affected bilaterally. Fifteen eyes (68%) had moderate to severe dry-eye symptoms preoperatively. Almost all eyes lost BSCVA in the postoperative period, and visual acuity improved slowly. By the last follow-up visit, no eye had lost more than 1 line of BSCVA. Diffuse lamellar keratitis (DLK) was observed in 20 eyes (91%), irregular astigmatism in 17 (77%), and microfolds in 12 (55%). In unilaterally affected patients, the refractive outcome was better in the nonaffected eye. CONCLUSIONS: A large central ED is a severe intraoperative complication of LASIK that may lead to DLK, irregular astigmatism, flap microfolds, clearly prolonged visual rehabilitation, and temporary loss of BSCVA. The improvement in BSCVA may take several months.

Adult↗
PubMed2004

Ten-year follow-up of a ciliary sulcus-fixated silicone phakic posterior chamber intraocular lens.

In 1992, a ciliary sulcus-fixated, silicone, phakic posterior chamber intraocular lens (PPC IOL) (Adatomed, Fyodorov type) was implanted in both eyes of a 42-year-old white woman to correct high myopia (right eye, -17.0 diopters [D]; left eye, -11.5 D). In the right eye, localized cortical opacification was present in the anterior part of the natural lens preoperatively but did not progress during a 10-year follow-up period. With Scheimpflug photography, it was possible to detect a space between the natural lens and the IOL that was not evident on slitlamp examination. Maintenance of space between an IOL and the natural lens appears to be an important factor in preventing cataract formation after PPC IOL implantation.

Cataract↗