PubMed Health⌕ Search

Biomedical subjects

T Seiler

Publications and source records attributed to T Seiler.

At least 19 recordsLinked to original sources
PubMed2006

[Nomograms for the improvement of refractive outcomes].

BACKGROUND: Nomograms are efficient tools to improve the predictability of refractive procedures by using statistical methods to analyze pre- and postoperative refractive data. The purpose of this work was to analyze the clinical relevance and limitations of nomograms in a case series. METHODS: Computer simulations based on the known unpredictability for refractive outcomes were performed for three different distribution functions of the preoperative refractions. In addition, the clinical applicability was investigated in three different cohorts that underwent laser in situ keratomileusis (LASIK). RESULTS: The use of individual nomograms significantly improves the predictability of the refractive outcome. However, theoretical investigation demonstrates that a homogeneous data distribution within cohorts is a key factor for predictable nomogram calculations. Outliers within the cohorts are not integrated into the nomogram calculation due to the mathematical model used. CONCLUSIONS: Nomograms are helpful for improving refractive outcomes. However, they are currently limited to approximately 90% within +/-0.5 D.

Adolescent↗
PubMed2006

[Ablation profiles in corneal laser surgery. Current and future concepts].

The predictability and quality of results in corneal refractive laser surgery are determined by a number of factors. Here, the calculation and choice of the ablation profile represent central elements. Our growing knowledge about the physical and optical properties of the eye in recent years has led to the development of different strategies in the generation of ablation profiles. This review describes the currently used ablation profiles with their advantages and disadvantages and provides an outlook on future methods for the calculation of ablation profiles.

Cornea↗
PubMed2006

[Reoperations after LASIK].

BACKGROUND: Repeat operations after refractive surgery have increased in frequency during the past 10 years. The spectrum of the indications for repeat LASIK may have changed. METHODS: All cases of repeat operations after refractive surgery performed between May 1, 2004 and April 30, 2005 at the Institute of Refractive and Ophthalmic Surgery (IROC) were retrospectively investigated regarding indication for repeat surgery and visual and refractive results. The 1-month results were used to estimate the refractive and visual success rate. RESULTS: Of the 76 reoperations, 69 were performed as re-lifts, 3 eyes had new lamellae cut, and 3 cases needed keratoplasties. The reoperations took place 7.5 +/- 13 months after the primary operation (range 0.5 to 60 months). The most frequent indication was residual astigmatism of 0.5 D and more. Visual loss of more than 1 decimal line did not occur and unaided visual acuity increased from 0.64 to 1.05. No complications were reported, however, 3 eyes needed additional enhancement. CONCLUSIONS: Reoperations after LASIK performed as re-lifts appear to be effective and reasonably safe when using the technique described and respecting a residual stromal thickness of 280 microns.

Comorbidity↗
PubMed2005

[Asphericity of the cornea and astigmatism].

BACKGROUND: Regarding astigmatism of the cornea, curvature as well as asphericity depend on the meridional axis. Their functional dependence and relation to the quality of the retinal image are still unclear. METHODS: The astigmatic eye was modelled using a biconoid anterior corneal surface by means of a commercially available optical designer programme (Zemax EE, Zemax). The influence of asphericity and astigmatism on the quality of the retinal image was determined by means of ray tracing. Thirty eyes with astigmatism of up to 5.3 D underwent corneal topography (Keratograph C, Oculus) which allowed a numerical evaluation of the cylindric power as well as the asphericity in the main meridians. RESULTS: The quality of the retinal image of an eye with corneal astigmatism can be improved by a factor of 2.28 if the asphericity is optimised. Correction of the central astigmatism only (without considering asphericity) yields only a rather marginal improvement. The average difference of the asphericity in the main meridians is close to zero, however, the individual difference ranges from - 0.372 to + 0.444 which is definitely clinically relevant. CONCLUSIONS: Anisotropic asphericity of the cornea may significantly enhance or compensate central corneal astigmatism. Clinically manifest astigmatism is an individually variable combination of asphericity and curvature difference in the two main meridians and is dependent on the pupil size. Laser correction of corneal astigmatism must take meridional asphericity into account.

Astigmatism↗
PubMed2004

Keratocyte cytotoxicity of riboflavin/UVA-treatment in vitro.

PURPOSE: Collagen crosslinking using ultraviolet- A (UVA) -irradiation combined with the photosensitizer riboflavin is a new technique for treating progressive keratoconus. It has been shown to increase effectively the biomechanical strength of the cornea and to stop or even reverse the progression of keratoconus. As part of a safety evaluation, the present study was undertaken to investigate in vitro the possible cytotoxic effect of combined riboflavin/UVA-treatment on corneal keratocytes and to compare it to UVA-irradiation alone. METHODS: Cell cultures established from porcine keratocytes were treated with 0.025% riboflavin solution and various UVA (370 nm)-irradiances ranging from 0.4 to 1.0 mW/cm2 and with UVA alone between 2 and 9 mW/cm2 for 30 min. The cell cultures were evaluated for cell death 24 h after irradiation using trypan-blue and Yopro-fluorescence staining. RESULTS: An abrupt cytotoxic irradiance level was found at 0.5 mW/cm2 for keratocytes after UVA-irradiation combined with the photosensitizer riboflavin, which is 10-fold lower than the cytotoxic irradiance of 5 mW/cm2 after UVA-irradiation alone. CONCLUSIONS: A cytotoxic effect of combined riboflavin/UVA-treatment on keratocytes is to be expected at 0.5 mW/cm2, which is reached in the clinical setting in human corneas down to a depth of 300 microm using the standard surface UVA-irradiance of 3 mW/cm2.

Animals↗
PubMed2003

[Treatment of keratoconus by collagen cross linking].

BACKGROUND: We were able to show a significant increase in corneal stiffness of rabbit and porcine eyes after combined riboflavin/UVA-induced collagen cross-linking. In this study,we tried to treat keratoconus patients with this method to stop the progression of corneal ectasia. PATIENTS AND METHODS: We treated 16 eyes of 15 patients with progressive keratoconus and mostly moderate keratectasia (48-56 dpt). After removal of the epithelium (7 mm X), riboflavin solution was applied on the cornea, which was irradiated with UVA (370 nm,3 mW/cm(2)) at a distance of 1 cm for 30 min.Post-operative follow-up controls were conducted every 3 months in the first year and then every 6 months, always including visual acuity testing, corneal topography and measurements of endothelial cell density. The follow-up time was between 1 and 3 years. RESULTS: Progression of keratectasia was stopped in all patients. Best corrected visual acuity and the maximal keratometry values improved slightly in about 50% of the cases. In all patients corneal transparency, the degree of keratectasia registered by corneal topography and the density of endothelial cells remained unchanged within the follow-up time. No negative side-effects were observed. CONCLUSIONS: Our results show that collagen cross linking might be a useful conservative treatment modality to stop the progression of keratoconus. By this means the need for keratoplasty might be significantly reduced. Given the simplicity of the technique and minimal costs of the treatment it might also be well suited for developing countries.Further studies are envisaged to exclude long-term side effects and to evaluate the long term durability of the mechanical stiffness effect.

Adolescent↗
PubMed2003

[Asymptomatic cor triatriatum in a 2 1/4 year old patient].

We report on an asymptomatic 2 1/4 year old girl. Echocardiography revealed cor triatriatum with a membrane separating the left atrium. Transesophageal echocardiography demonstrated 3 large perforations of the intraatrial membrane. Using Doppler sonography, no pressure gradients across these orifices were identified. Obstruction of the intraatrial membrane and pulmonary hypertension were excluded by cardiac catheterization. We therefore decided against surgical resection of the membrane and to follow the patient noninvasively by echocardiography. Follow-up over 18 months revealed no development of an obstruction across the intraatrial membrane. Our case shows that immediate surgical correction is not necessary in all patients with cor triatriatum. Conservative management of these patients requires full evaluation of the hemodynamics and careful follow-up examinations by echocardiography.

Child, Preschool↗
PubMed2001

[Does refractive surgery really make eyeglasses superfluous?].

Spectacles have become a problem of life-style in some societies. In the USA, in 1999 approximately 1 million LASIK operations have been performed to correct myopia and astigmatism and in Europe the frequency of refractive surgery stead by increases. However, only 3 to 5% of these operations are medically indicated. Refractive surgery is evaluated regarding safety and efficacy. Modern laser techniques demonstrate excellent refractive results: photorefractive keratectomy (PRK) achieved refractive success rates of 90% and more with complication rates of 0.5% and less. PRK is, therefore, a valuable technique for corrections of myopia up to -6.0 D. Similar efficacy is obtained with LASIK (laser in situ keratomileusis) in corrections up to -10 D, however, the complication rate is somewhat higher. Laser correction of hyperopia is equally successful regarding the refractive success but shows an even higher complication rate and the patient satisfaction is lower. Modern refractive laser surgery may replace spectacles in the majority of the cases, however, none of the techniques is free of complications. Therefore, we understand refractive surgery still to be inferior to the correction of ametropia by means of spectacles and any such operation should be attempted only after thorough discussion.

Astigmatism↗
PubMed2001

[Fundamentals of wavefront-guided refractive corneal surgery].

The clinical introduction of aberration-sensing and wavefront-guided refractive surgery opens new ways in diagnostic and therapy of high order optical aberrations of the human eye. The main application is the optimization of current treatment methods such as LASIK or PRK. The aim of wavefront-guided treatments is to omit the deterioration of the optical performance under mesopic conditions of the eye by the refractive treatment and, if possible, to increase contrast sensitivity by correcting the higher order aberrations. First clinical trails on wavefront-guided corneal laser surgery demonstrate the possibility of improving the optical quality of the eye by LASIK or PRK and to correct irregular astigmatism.

Contrast Sensitivity↗
PubMed2001

[Ultrasound biomicroscopy diagnosis of traumatic choroid effusion without cyclodialysis].

BACKGROUND: Chamber angle changes due to trauma represent a diagnostic challenge in modern ophthalmology and two examination techniques are compared: gonioscopy which has been used in ophthalmology for almost a century and is still undergoing continuous improvements and ultrasound biomicroscopy (UBM) which was introduced into clinical ophthalmology in 1991. CASE REPORT: We report the case of a 14-year-old boy with ocular trauma caused by a soft gun projectile. Gonioscopy showed a large goniosynechia in the presence of ocular hypotension, therefore, cyclodialysis was suspected. However, a control investigation using UBM showed an intact and circularly attached but anteverted ciliary body behind the synechia, a circular choroidal effusion and an anterior displacement of the iris-lens diaphragm. CONCLUSION: In ocular trauma, UBM may under certain conditions clearly be of a higher diagnostic value than gonioscopy. Therefore, UBM should not only be considered as an additional examination technique in the evaluation of traumatic ocular pathologies but rather as the technique of choice.

Adolescent↗
PubMed2001

[Cavitation bubble formation during Erbium:YAG laser vitrectomy].

BACKGROUND: Clinical and experimental studies demonstrated the potential advantages of Erbium:YAG laser vitrectomy for posterior segment surgery. However, a detailed knowledge on the laser-tissue interaction is needed for an optimization of new ophthalmic applications. The aim of this experimental work was to investigate the cavitation bubble formation during Erbium:YAG laser vitrectomy and to find optimized laser parameters and the best geometry of the aspiration port of the microsurgical probe. MATERIALS AND METHODS: We investigated the formation of cavitation bubbles in water by high-speed photography. The output energy at the quartz tip reached up to 50 mJ and the laser pulse duration ranged from 50 to 300 microseconds. Various commercially available microsurgery probes were investigated regarding the extent of the cavitation bubbles. RESULTS: The threshold for laser-induced cavitation bubble formation was found to be 0.32 +/- 0.1 mJ for a laser pulse duration of 130 microseconds and a core diameter of 320 microns of the quartz fiber tip. The length of the cavitation bubbles increases with the laser pulse energy up to a length of 1.6 mm at a pulse energy of 10 mJ. In contrast, the size of the vapor bubbles decreases with an increase of the laser pulse duration. A slit-shaped aspiration port led to a 50% smaller volume of the cavitation bubble exiting the port compared with a circular aspiration port. CONCLUSIONS: The optimized laser parameters and microsurgery probe geometry may significantly decrease the risk of intraoperative ocular damages during Erbium:YAG laser vitrectomy.

Animals↗
PubMed2001

Understanding refraction and accommodation through "retinal imaging" aberrometry: a case report.

PURPOSE: A new form of aberrometry based on Tscherning optics has been proposed that captures the refraction and high-order aberrations of the eye with and without accommodation. DESIGN: Experimental clinical optics study. METHOD: A green neodymium:yttrium-aluminum-garnet laser grid pattern is projected into the eye and viewed on the retina through a narrow, collimated aperture of 1 mm. The resulting aberrated pattern is photographically recorded in a normal eye in the unaccommodated and accommodated state through a pharmacologically dilated pupil without cycloplegia. MAIN OUTCOME MEASURES: Detection of pupil-dependent refraction and high-order optical aberration with and without accommodation. RESULTS: Subtle pupil-dependent errors in refraction and high-order aberrations (spherical aberrations and coma) are demonstrated in the unaccommodated normal eye. Accommodation reveals slightly more spherical power through the central 3-mm zone than through a 6.5-mm pupil without significant increase in aberration. CONCLUSIONS: Tscherning aberrometry based on 'retinal imaging' is useful in defining the refraction and optical aberrations in a normal eye. Accommodation increases spherical refractive power with only small aberration changes, including negative asphericity.

Accommodation, Ocular↗
PubMed2001

Stress wave amplitudes during laser surgery of the cornea.

PURPOSE: To determine the stress wave amplitudes generated during photoablation of the cornea using an argon fluoride excimer laser. DESIGN: Experimental study using porcine eyes. METHODS: Profiles of the stress wave amplitudes and enucleated human eyes along the axis of symmetry of porcine eyes and enucleated human eyes were measured using a miniature piezoelectric transducer. The ablation parameters, fluence, and ablation diameters were varied within the range of clinical application. MAIN OUTCOME MEASURES: Stress wave amplitudes generated during photoablation. RESULTS: The stress waves pass through a pressure focus located in the posterior lens and anterior vitreous, where amplitudes of up to 100 atm were measured with a 6-mm or larger ablation zone. Posterior to this focus, the stress wave amplitudes rapidly decrease to less than 10 atm at the retinal site. Small diameter excimer laser spots (< or =1.5 mm) produce a declining stress wave with no pressure focus at the lens and anterior vitreous. CONCLUSIONS: Stress waves may be potentially hazardous to anterior structures of the human eye, including the corneal endothelium, lens and anterior vitreous face. They peak at the lens and vitreous with a broad beam, but not with small spot laser ablation. At posterior retinal and subretinal structures, they may be considered harmless.

Animals↗
PubMed2001

Increased higher-order optical aberrations after laser refractive surgery: a problem of subclinical decentration.

PURPOSE: To study the clinical and theoretical effects of subclinical decentrations on the optical performance of the eye after photorefractive laser surgery. SETTING: Department of Ophthalmology, University of Dresden, Dresden, Germany. METHODS: Ocular aberrations were determined before and 1 month after uneventful photorefractive keratectomy (PRK) with the Multiscan laser (Schwind) in 10 eyes of 8 patients. The corrections ranged from -2.5 to -6.0 diopters, and ablation zones of 6.0 mm and larger were used. The measured wavefront errors were compared to numerical simulations using the individually determined decentrations and currently used ablation profiles. RESULTS: The PRK-induced aberrations were significantly greater than the preoperative aberrations. The numerically calculated increase in the higher-order optical aberrations correlated with the clinical results, demonstrating a major increase in coma- and spherical-like aberrations. Subclinical decentration (less than 1.0 mm) was found to be a major factor in increased coma-like and spherical-like aberrations after corneal laser surgery. CONCLUSION: To minimize higher-order optical errors, special efforts to center the ablation zone are necessary; for example, by eye-tracking systems that consider the visual axis.

Astigmatism↗
PubMed2001

Clinical results of wavefront-guided laser in situ keratomileusis 3 months after surgery.

PURPOSE: To investigate the visual and refractive outcome of wavefront-guided laser in situ keratomileusis (LASIK) to correct myopic astigmatism. SETTING: Departments of Ophthalmology of the Universities of Dresden, Dresden, Germany, and Zurich, Zurich, Switzerland. METHODS: This prospective study comprised 35 eyes of 28 patients who had a mean preoperative spherical refraction of -4.8 diopters (D) +/- 2.3 (SD) and a cylinder of -1.1 +/- 0.9 D. Preoperative and postoperative wavefront analysis was performed with a Tscherning aberrometer. A scanning-spot laser with a 1.0 mm spot size and a 200 Hz repetition rate was used. The eye-tracking system had a response time of less than 6 milliseconds. The treatment area diameter ranged from 6.0 to 7.0 mm with a transition zone of 1.0 mm. RESULTS: At 3 months, 68.0% of the eyes were within +/-0.5 D of emmetropia and 93.5% were within +/-1.0 D. Uncorrected visual acuity was 20/20 or better in 93.5% of eyes. No eye lost more than 1 line of low-contrast, glare, and best spectacle-corrected visual acuity (BSCVA). Supernormal vision (BSCVA of 20/10 or better) was achieved in 16.0% of eyes. The correction of higher-order aberrations (spherical aberration, coma) was insufficient, with an increase factor of the overall root-mean-square wavefront error of 1.44 +/- 0.74. Coma was better corrected than spherical aberration. CONCLUSIONS: Wavefront-guided LASIK is a promising technique that offers the potential to correct refractive errors, to improve visual acuity, and to increase the quality of vision, especially under mesopic conditions. Studies that include selective overcorrection of different Zernike components are needed to achieve better correction of the aberrations. Prospective controlled clinical studies must clarify the major benefits of wavefront-guided LASIK.

Adult↗
PubMed2001

Improvement in photorefractive corneal laser surgery results using an active eye-tracking system.

PURPOSE: To study the advantage of modern eye-tracking systems for photorefractive surgery. SETTING: Department of Ophthalmology, University of Zurich, Zurich, Switzerland. METHODS: Photorefractive surgery (photorefractive keratectomy and laser in situ keratomileusis) for myopia and myopic astigmatism was performed in 40 eyes with a commercially available medical excimer laser system. The eyes were selected retrospectively from a larger group of patients treated at 1 clinic. In 20 eyes, the ablation was centered on the entrance pupil using the active, video-based, eye-tracking system (sampling frequency 50 Hz) of the laser. During laser treatment in the nontracker group (20 eyes), the active eye-tracking system was switched off and centration was done manually by the surgeon. Preoperatively and 1 and 3 months after surgery, the patients had a standard ophthalmic examination as well as wavefront analysis by means of a custom-designed wavefront analyzer. RESULTS: After surgery, the visual acuity was significantly better (P <.05) in patients treated with the eye tracker. The increase in coma-like (relative increase factor 0.4) and spherical aberrations (relative increase factor 1.1) was significantly smaller in these patients than in those in the nontracker group (spherical equivalents of 3.9 and 5.1, respectively; P <.05). The refractive outcome, however, was not significantly different in sphere and cylinder. CONCLUSION: The use of active eye tracking appeared to improve the optical and visual outcomes but did not affect the refractive outcome after photorefractive laser surgery.

Adult↗