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Thomas Kohnen

Publications and source records attributed to Thomas Kohnen.

At least 55 records · Page 3Linked to original sources
PubMed2004

Correlation of infrared pupillometers and CCD-camera imaging from aberrometry and videokeratography for determining scotopic pupil size.

PURPOSE: To compare 2 infrared pupillometers with a videokeratographer and 2 aberrometers for the determination of scotopic pupil size. SETTING: Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. METHODS: The pupil diameter was measured in 100 eyes of 51 patients after 2 minutes of dark adaptation using the following devices: digital infrared pupillometer (Procyon Instruments Ltd.), handheld infrared pupillometer (Colvard) (Oasis Medical), Zywave aberrometer (Bausch & Lomb), Wasca aberrometer (Asclepion-Meditec-Zeiss), and Orbscan II topography system (Bausch & Lomb Surgical). Measurements taken with the Procyon pupillometer were considered reference values for comparison with the other devices. Statistical evaluation was performed using the Bland-Altmann method for comparison of measurement techniques. RESULTS: The mean pupil size was 6.10 mm +/- 0.86 (SD) with the Procyon pupillometer, 5.68 +/- 1.07 mm with the Colvard pupillometer, 5.91 +/- 1.01 mm with the Zywave aberrometer with the fixating target turned off, 5.09 +/- 1.14 mm with the Zywave aberrometer with the fixating target turned on, 5.59 +/- 0.99 mm with the Wasca aberrometer, and 3.75 +/- 0.67 mm with the Orbscan topographer. The limits of agreement were smallest for measurements between Procyon and Colvard and largest for measurements between Procyon and Orbscan. The sign test revealed statistically significant differences for all devices compared with the Procyon pupillometer (P<.001 in all cases) except the Zywave aberrometer with the fixating target turned off (P=.13). CONCLUSIONS: The Zywave wavefront sensor with the fixating target turned off using the study settings and light conditions provided measurements of scotopic pupil diameter that were closest to the reference values (Procyon). With the other devices (Colvard pupillometer, Zywave aberrometer with the fixating target switched on, Wasca aberrometer, and Orbscan topographer), the difference was statistically significant.

Adult↗
PubMed2004

Wavefront-guided LASIK with the Zyoptix 3.1 system for the correction of myopia and compound myopic astigmatism with 1-year follow-up: clinical outcome and change in higher order aberrations.

OBJECTIVE: To assess safety, efficacy, predictability, stability, and change in aberrations after wavefront-guided LASIK for myopia and myopic astigmatism. DESIGN: Prospective, nonrandomized, self-controlled trial. PARTICIPANTS: Wavefront-guided LASIK was performed in 97 eyes in a 1-year trial. Treated eyes had a mean subjective manifest spherical equivalent (SE) of -5.22+/-2.07 diopters (D), with a range of -0.25 to -9.00 D of myopia and 0 to -3.25 D of astigmatism. INTERVENTION: After a microkeratome cut, a wavefront-based excimer ablation (Zyoptix 3.1) was performed. The full treatment to achieve emmetropia of an early nomogram provided by the system manufacturer was used in all procedures. MAIN OUTCOME MEASURES: Safety, efficacy, predictability, and stability were evaluated at 1, 3, and 12 months postoperatively. Wavefront changes of higher order aberrations (HOAs) at 1 year were determined for pupil sizes of 3.5 and 6 mm. RESULTS: At 1 year postoperatively, uncorrected visual acuity (VA) was 20/20 or better in 83% of the eyes, and 20/40 or better in 98%. The mean subjective manifest SE at 1 year was -0.25+/-0.43 D; it was within 0.50 D in 77% and within 1.0 D in 95%. No eye lost > or =2 lines of best spectacle-corrected VA (BSCVA) at 1 year postoperatively; 40 eyes gained 1 line of BSCVA, and 5 eyes gained 2 lines. The total HOA root mean square (RMS) increased on average by a factor of 1.23+/-0.57 with a 3.5-mm pupil; for the 6 mm pupil, the increase factor was 1.52+/-0.36. No change or reduction in the total HOA RMS was observed in 45.5% of the eyes for a 3.5-mm pupil and in 20.6% for a 6-mm pupil. There was a significant increase of primary spherical aberration (Z 4,0) by a factor of 4.11+/-10.17 for 3.5-mm pupils and 4.31+/-6.76 for 6-mm pupils. CONCLUSIONS: Wavefront-guided LASIK using Zyoptix 3.1 is an effective and safe procedure for the treatment of myopia and myopic astigmatism. Although in close to half of the eyes HOAs could be reduced, there was still undercorrection and induction of HOAs with the algorithm employed.

Adult↗
PubMed2004

Intraindividual comparison of epithelial defects during laser in situ keratomileusis using standard and zero-compression Hansatome microkeratome heads.

PURPOSE: To determine the difference between the standard and a modified (zero-compression) Hansatome microkeratome head (Bausch & Lomb) in the incidence of epithelial defects. SETTING: Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. METHODS: Ninety-three patients (186 eyes) with a mean age of 39.1 years +/- 9.5 (SD) having laser in situ keratomileusis (LASIK) in both eyes were enrolled in a prospective randomized study using intraindividual comparison. In 1 eye, the flaps were created with the Hansatome microkeratome using the standard Hansatome head and in the other eye, the flaps were created with a microkeratome head with a modified design (zero-compression head). Intraoperative evaluation of epithelial defects was done using a standardized protocol. Statistical evaluation was performed with McNemar and Bowker tests. RESULTS: Epithelial defects occurred in 21 eyes (22.6%) in which the standard head was used and in 2 eyes (2.1%) in which the zero-compression head was used. In the former group, 15 (16.1%) of the epithelial defects were larger than 1.5 mm(2); the remaining 6 (6.4%) were smaller than 1.5 mm(2). In the latter group, both epithelial defects were smaller than 1.5 mm(2); both patients also had an epithelial defect in the eye in which the standard Hansatome head was used. The difference between the 2 Hansatome heads in the incidence (P<.001, McNemar) and size (P<.001, Bowker) of the epithelial defects was statistically significant. CONCLUSIONS: The Hansatome microkeratome with a zero-compression head significantly reduced the occurrence of intraoperative epithelial defects. The change in the construction of the Hansatome head is a useful improvement in LASIK technology.

Adolescent↗
PubMed2004

[Heparin Surface-Modified Poly(methylmethacrylate) and Foldable Hydrophobic Acrylic Intraocular Lenses in Cataract Patients with Acquired Immune Deficiency Syndrome and CMV-Retinitis].

BACKGROUND: In HIV-positive patients with necrotising retinitis, well-tolerated lens material as well as minimal invasive surgery to avoid postoperative complications are imperative. Heparin surface-modified PMMA-IOLs as well as acrylic IOLs are associated with less postoperative inflammation than conventional intraocular lenses. METHODS: In this randomised prospective clinical trial 18 patients received 7 HSM-IOLs through a self-sealing scleral tunnel and 11 foldable Acrysof-IOLs through a self-sealing limbal tunnel incision by the same surgeon. 7 of the 18 eyes were silicone oil-filled before cataract surgery, one eye received oil after the IOL implantation. Visual acuity, intraocular pressure, contrast sensitivity, intraocular inflammation and posterior capsule opacification were assessed. The follow-up period was 1 year. RESULTS: Eyes with Acrysof-IOLs were associated with lower, but not statistically significant, laser flare photometry values (photon counts/ms) than those with HSM-IOLs pre- (90.18 +/- 54.7 vs. 73.92 +/- 6.44) and 3 months post-surgery (69.06 +/- 8.27 vs. 55.03 +/- 7.75). 6 of the 7 eyes with HSM-IOL and 3 eyes of the Acrysof-group developed a dense posterior capsule opacification (PCO), 2 eyes had no and 6 eyes only a distinct PCO. YAG capsulotomy did not improve visual acuity in any case but retinal examination was again possible. Eyes with Acryl-IOL showed pre- and postoperatively a better visual acuity than eyes with HSM-IOL ("hand movement" - 0.4 vs. "no light perception" - 0.1 pre- and 0.05 - 0.6 vs. "no light perception" - 0.1 3 months postoperatively. Contrast sensitivity testing (Vistech method) could be performed in the PMMA-group preoperatively only in 1 eye (A1), in the Acryl-group in 2 eyes (A4, B4, C2, D2) and revealed postoperatively "no contrast vision" - A1, B2, C1 vs. "no contrast vision" - A2, B2, C3, D1, E1. The intraocular pressure was preoperatively 13.86 mm Hg (PMMA) vs. 14.82 mm Hg (Acrysof) and 14.4 mm Hg vs. 12.89 mm Hg 3 months post surgery. CONCLUSION: In the parameters we observed there was no statistical significant difference between heparin-surface modified (Pharmacia 811 C) and hydrophobic acrylic IOLs (Alcon Acrysof MA60BM) in patients with AIDS. As foldable Acrysof-IOLs can be implanted through a self-sealing bloodless tunnel incision and are associated with less posterior capsule opacification we prefer this IOL type in cataract surgery of AIDS patients.

AIDS-Related Opportunistic Infections↗
PubMed2003

Scotopic pupil size in a normal pediatric population using infrared pupillometry.

PURPOSE: To determine scotopic pupil diameter in a normal pediatric population. METHODS: Scotopic pupil size was measured in 166 eyes of 83 children with a mean age of 6.01+/-4.11 years (range 0.51-14.26 years) using the light and hand-held Colvard infrared pupillometer. Measurements were performed under dim illumination after 2 min of dark adaptation. The Colvard infrared pupillometer utilizes light amplification technology to determine scotopic pupil size. RESULT: The mean scotopic pupil diameter was 6.06+/-0.95 mm (range 4.0-8.5 mm) in the right eyes (OD) and 6.11+/-1.02 mm (range 4.0-8.5 mm) in the left eyes (OS), and 6.09+/-0.98 mm (range 4.0-8.5 mm) for both eyes (OU). An increase in mean scotopic pupil size with age was detected, with a peak of 7.28+/-0.42 mm at the age of 10-11 years. The correlation coefficient for age and scotopic pupil diameter was 0.51 OU (OD 0.52, OS 0.51), and the correlation coefficient for objective refraction (spherical equivalent) and scotopic pupil diameter was 0.05 OU (OD 0.01, OS 0.08). CONCLUSIONS: The scotopic pupil diameter in a pediatric population increases with age until the age of 11 years and then decreases again.

Adolescent↗
PubMed2003

Scheimpflug imaging of bilateral foldable in-the-bag intraocular lens implantation assisted by a scleral-sutured capsular tension ring in Marfan's syndrome.

A 35-year-old white man with bilateral high myopia, astigmatism, subluxated crystalline lenses, and incipient cataract had phacoemulsification and implantation of a hydrophobic acrylic intraocular lens (IOL) (Alcon MA60BM) in both eyes. The subluxated capsular bag was stabilized and recentered using a scleral-fixated capsular tension ring (CTR) (type 1L, Morcher). Measured with Scheimpflug photography, the capsular bag and IOL were in a stable intraocular position during the 18-month follow-up. There were no major changes in refraction. Despite the sharp-edged IOL design, both eyes had posterior capsule opacification (PCO) 18 months after surgery that in 1 eye caused a decrease in visual acuity of more than 2 lines. High myopia and subluxated lenses may be treatable long-term with a scleral-fixated CTR and foldable IOL implantation; further evaluation of PCO is necessary.

Acrylic Resins↗
PubMed2003

Acute psychotic reaction caused by topical cyclopentolate use for cycloplegic refraction before refractive surgery: case report and review of the literature.

A 56-year-old woman was evaluated for the surgical correction of hyperopia (+3.0 diopters). Two drops of cyclopentolate 1% were instilled in both eyes for measurement of the cycloplegic refraction and wavefront analysis. Immediately after the second instillation, the patient reported drowsiness, dizziness, nausea, and fatigue. Ten minutes later, stimulatory central nervous system symptoms in the form of restlessness, cheerfulness, and a 20-minute-long roar of laughter were observed, interrupted by a new sedative phase. Basic medical and neurologic examinations were unremarkable except for gait ataxia. Four hours later, the examination was continued uneventfully. As surgical treatment of refractive errors and measurement of cycloplegic refraction using cyclopentolate become more frequent, ophthalmologists should be aware of this unusual acute event.

Acute Disease↗
PubMed2003

Comparison of a digital and a handheld infrared pupillometer for determining scotopic pupil diameter.

To compare a digital infrared pupillometer with a handheld infrared pupillometer for determining scotopic pupil size. Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. In 100 eyes of 50 healthy individuals (mean age 38.8 years +/- 10.7 [SD]), the scotopic pupil size was measured with a digital (Procyon) and a handheld (Colvard) infrared pupillometer. After dark adaptation of 1 minute, measurements were performed with both devices by 2 examiners (E1 and E2). Agreement and repeatability were analyzed using a comparison method described by Bland and Altman. The mean scotopic pupil diameter was 5.90 +/- 0.97 mm (range 3.24 to 7.91 mm) with the Procyon and 5.78 +/- 0.98 mm (range 3.00 to 7.30 mm) with the Colvard pupillometer. The mean difference between the 2 devices was -0.01 mm (E1) and -0.24 mm (E2). The limits of agreement ranged from 2.84 (E1) to 3.24 (E2). The coefficients of repeatability were 0.64 (Procyon) and 1.16 (Colvard). The mean difference between E1 and E2 was -0.10 for the Procyon and 0.13 for the Colvard pupillometer. The limits of agreement ranged from 1.28 (Procyon) to 2.32 (Colvard). The digital infrared pupillometer (Procyon) demonstrated better repeatability and agreement in measuring scotopic pupil size than a handheld device (Colvard).

Adult↗
PubMed2003

Stromal haze after laser in situ keratomileusis: clinical and confocal microscopy findings.

PURPOSE: To report clinical and confocal microscopy characteristics of haze-like opacities in corneas after laser in situ keratomileusis (LASIK). SETTING: Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. METHODS: Eighteen eyes of 11 patients with clinically apparent corneal clouding were examined by slitlamp and confocal microscopy (Confoscan P4, Tomey) 1 to 9 months after primary LASIK or LASIK retreatment. RESULTS: Postoperative slitlamp examination showed faint, white, snowflake-like clouding at the interface level in all patients. One patient had folds and rather diffuse haze-like opacities. Confocal microscopy revealed highly reflective structures in the flap stroma and at the interface level in all patients, probably due to numerous activated keratocytes and their processes. The confocal microscopy appearance was similar to that of photorefractive keratectomy haze. CONCLUSION: Focal wound-healing reactions in the central flap stroma and interface resulting in significant keratocyte activation could be observed after LASIK.

Adult↗
PubMed2003

Corneal wound healing after laser in situ keratomileusis flap lift and epithelial abrasion.

We report the clinical and confocal microscopic findings of wound-healing reactions after epithelium debridement and flap lift for the treatment of folds in a thin laser in situ keratomileusis (LASIK) flap. A 30-year-old woman had a flap lift with deepithelialization because of persistent striae after LASIK. The patient developed stage 2 diffuse lamellar keratitis (DLK) and dense haze. Confocal microscopy showed a loss of the most anterior keratocytes 6 days after flap relifting and deepithelialization. Subsequently, stromal repopulation with the appearance of spindle-shaped fibroblasts and activated keratocytes was detectable. Two months postoperatively, a maximum of haze tissue was found at the interface level and a myopic shift of -2.00 diopters was observed. Under treatment with topical steroids, the haze resolved and the spherical equivalent returned to baseline within 12 months.

Adult↗
PubMed2003

In vivo and in vitro repeatability of Hartmann-Shack aberrometry.

PURPOSE: To assess the in vivo and in vitro repeatability of objective refraction and higher-order aberrations (HOAs) measured by a commercially available Hartmann-Shack wavefront sensor. SETTING: Department of Ophthalmology, Johann-Wolfgang-Goethe University, Frankfurt am Main, Germany. METHODS: After pupil dilation of 40 myopic or myopic, astigmatic eyes of 20 patients, wavefront measurements were performed 6 times in each eye and in a test object provided by the manufacturer by 2 experienced examiners using a Hartmann-Shack wavefront sensor (Zywave, software version 3.21, Bausch & Lomb). The mean standard deviation (SD) and the coefficient of variation (CV) for sphere, cylinder, and each Zernike polynomial were computed for a 7.0 mm pupil diameter. Vector analysis was performed for the astigmatism. After the data were subdivided into 2 groups with 3 measurements in each, one measurement that best matched the subjective manifest refraction was chosen in each group and the difference between them was calculated. RESULTS: The mean SD (CV) was 0.15 diopter (D) (7%) for the sphere value of the predicted phoropter refraction and 0.16 D (22%) for astigmatism. Thirty-two eyes had an axis deviation of at least 10 degrees. Vector analysis revealed a mean SD of 0.24@109.8. Other results for mean SD and mean CV were as follows: total in vivo higher-order RMS, 0.097 microm, 13.4%; sphere in myopic test device, 0.034 D, 0.65%; sphere in hyperopic test object, 0.035 D, 0.72%. The difference between the 2 best-matched refractions was significantly different from zero (0.11 D, P<.001). The CV was significantly higher for HOAs than for the 2nd-order aberrations (defocus and astigmatism). CONCLUSIONS: Repeatability of Hartmann-Shack aberrometry by the Zywave wavefront sensor was not satisfactory, particularly for small amounts of HOAs. Under these conditions, aberrometry measurements should be repeated several times and outliers should be excluded in calculating the means.

Adult↗
PubMed2003

[Flap Amputation in Mycobacterium chelonae Keratitis after Laser-in-situ Keratomileusis (LASIK)].

BACKGROUND: Keratitis due to Mycobacterium chelonae after laser-in-situ keratomileusis (LASIK) is a rare, but severe complication. In the following report, we present clinical findings, microbiological investigation, treatment and outcome of the first case of Mycobacterium chelonae reported in Europe. PATIENT AND METHODS: A 52-year old woman presented with atypical unilateral keratitis after LASIK. Mycobacterium chelonae keratitis was diagnosed by microbiological investigation. Interface irrigation and treatment with topical and oral antibiotics was performed. RESULTS: Despite intensive treatment, flap removal was necessary to control the infection. Best-corrected visual acuity dropped from preoperatively 1.0 to postoperatively 0.2. CONCLUSION: The diagnosis of mycobacterial keratitis after laser-in-situ keratomileusis is often delayed due to atypical clinical appearance. Therefore consideration of atypical pathogens and rapid microbiological diagnosis is necessary to provide adequate treatment.

Anti-Bacterial Agents↗
PubMed2002

Effect of temporal and nasal unsutured limbal tunnel incisions on induced astigmatism after phacoemulsification.

PURPOSE: To compare the surgically induced corneal astigmatism after unsutured temporal and nasal unsutured limbal tunnel incisions. SETTING: Departments of Ophthalmology, Marienhospital, Aachen, and Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. METHODS: In a prospective clinical study, 42 eyes of 21 patients with a mean age of 75.1 years had phacoemulsification and implantation of a foldable hydrophobic acrylic intraocular lens using a 3.6 to 3.8 mm unsutured limbal tunnel incision. The right eye always received a temporal incision and the left eye, a nasal incision. Computerized videokeratography was performed preoperatively and 2 weeks and 6 months postoperatively. Surgically induced astigmatism was calculated by vector analysis using the Holladay-Cravy-Koch formula. The 2 groups were compared using a paired Wilcoxon test. RESULTS: The mean surgically induced corneal astigmatism in the temporal incision group was 0.62 diopters (D) +/- 0.48 (SD) 2 weeks postoperatively and 0.47 +/- 0.32 D at 6 months and in the nasal incision group, 1.55 +/- 0.84 D and 1.05 +/- 0.57 D, respectively. The difference between the groups was statistically significant (P <.05). CONCLUSIONS: There was a highly statistically significant difference in surgically induced corneal astigmatism after temporal and nasal unsutured limbal tunnel incisions. The degree of induced astigmatism and the difference between the temporal and the nasal incisions decreased over time. A nasal tunnel incision is not appropriate for astigmatism-neutral surgery.

Adult↗
PubMed2002

Scanning electron microscopic evaluation of the surface characteristics of 4 microkeratome systems in human corneas.

PURPOSE: To evaluate the surface characteristics of keratectomy specimens created with 4 microkeratomes by scanning electron microscopy (SEM). SETTING: Two university institutions. METHODS: Keratectomies were performed in 10 fresh, unfrozen human eyes with 1 of 4 microkeratomes: the Draeger rotary microkeratome (Storz Instruments), the Universalkeratome (Phoenix), the Automated Corneal Shaper (Bausch & Lomb), or the Hansatome (Bausch & Lomb). The beds and edges of the keratectomy specimens were then examined by SEM. Standardized photographs were taken, and the surface and cut-edge characteristics of the keratectomies were compared. RESULTS: Irregularities were noted in the cut edges of Bowman's membrane and the surface of the keratectomy beds with all instruments. The irregularities were most prominent in corneas cut with the Draeger instrument and least prominent in those cut with the Universalkeratome. The serrations in Bowman's membrane and the irregularities in the keratectomy bed appeared to be related to the blade movement in oscillating blade instruments. CONCLUSIONS: All 4 microkeratomes caused some degree of surface irregularity. The Draeger microkeratome, which uses a continuously rotating blade, resulted in the greatest number of Bowman's membrane serrations and irregularities in the keratectomy bed. The tissue irregularities may be related to the development of pressure ridges ahead of the blade. In instruments that use an oscillating blade, chatter marks appear to be related to the reciprocating movement of the blade as it travels across the corneal stroma.

Cornea↗