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T Seiler

Publications and source records attributed to T Seiler.

At least 37 records · Page 2Linked to original sources
PubMed2001

[Supportive amblyopia treatment by means of computer games with background stimulation; a placebo controlled pilot study of 10 days].

BACKGROUND: Computer programmes for visual stimulation may give new impulses to the field of amblyopia treatment by offering an option to shift the apparative visual training into the domestic sphere. Regarding this aspect we report on a placebo controlled study on a newly developed vision training consisting of a background stimulation by a drifting sinusoidal grating combined with a foreground game aimed to maintain the attention. MATERIALS AND METHODS: Fourteen amblyopia patients aged from 6 to 13 years participated in the study. Seven were allocated to a placebo and seven to a treatment group. Both groups had to train at the computer for a period of 10 working days by two sessions of about 20 minutes daily. Whilst the placebo group played in front of a neutral background, the treatment group did this with a drifting sinusoidal grating in the background. RESULTS: The treatment condition resulted in a greater increase of visual acuity than the placebo condition. Near vision improved in the treatment group from 0.20 (SD +/- 4.51 steps) to 0.39 (SD +/- 3.06 steps), i.e. by 3.0 steps of visual acuity (SD +/- 1.8 steps), in the placebo group from 0.14 (SD +/- 6.02 steps) to 0.17 (SD +/- 5.85 steps), i.e. by 0.8 steps of visual acuity (SD +/- 1.6 steps). Far vision improved in the treatment group from 0.29 (SD +/- 2.57 steps) to 0.44 (SD +/- 3.16 steps), i.e. by 1.9 steps of visual acuity (SD +/- 1.3 steps), in the placebo group from 0.24 (SD +/- 5.20 steps) to 0.28 (SD +/- 5.51 steps), i.e. by 0.7 steps of visual acuity (SD +/- 1.1 steps). CONCLUSIONS: Stimulation with drifting sinusoidal gratings improves the visual acuity of amblyopic eyes in a specific way. The effect might be accounted for by a synergy of spatial and temporal frequency in form vs. motion channels. A preliminary hypothesis is discussed and will be the subject of ongoing research. The presented method has been developed for the treatment of "delayed" amblyopia in the elder child. It is aimed to support and complement occlusion therapy. However, the reported results obtained over 10 days should be estimated only within the context of evaluation. By no means should the results be interpreted as a renewed pledge for a short-term treatment of amblyopia.

Amblyopia↗
PubMed2001

Ocular optical aberrometer for clinical use.

Higher-order optical errors of the human eye are often responsible for reduced visual acuity in spite of an optimal spherical or cylindrical refraction. These optical aberrations are of natural origin or can result from operations in the eye that involve optical structures. The ocular aberrometer presented is based on Tscherning's aberroscope. A collimated laser beam (532 nm, 10 mW) illuminates a mask with a regular matrix of holes which forms a bundle of thin parallel rays of 0.3 mm diameter. These rays are focused by a lens in front of the eye so that their intraocular focus point is located a certain distance in front of the retina, generating a corresponding pattern of light spots on it. According to the existing ocular optical errors, this spot pattern is more or less distorted in comparison to the mask matrix. For a 6 mm pupil diameter 68 retinal spots are plottable for assessment of the optical aberrations. The retinal spot pattern is imaged onto the sensor of a low-light charge coupled device video camera by indirect ophthalmoscopy. Deviations of all spots from their ideal regular positions are measured by means of a PC, and from these values the intraocular wave front aberration is computed in the form of the sum of Zernike polynomials up to sixth order.

Eye↗
PubMed2001

Erbium: yttrium-aluminum-garnet laser induced vapor bubbles as a function of the quartz fiber tip geometry.

BACKGROUND: The use of modern erbium: yttrium-aluminum-garnet (YAG) laser systems in opthalmic microsurgery requires a precise knowledge of the size and dynamics of the laser induced vapor bubbles. The aim of this work was to clarify the possibilities of controlling the vapor bubble shape and size by using an optimized fiber tip geometry for various ophthalmic applications with the erbium: YAG laser. METHODS: The mid-infrared radiation of free-running erbium: YAG laser was coupled optically into means of different low OH(-) quartz fiber tips to investigate the vapor bubble formation in water by high-speed photography. The core diameter of four fiber tips ranged from 200 up to 940 microm. Fourteen fiber tips were polished at an angle graduated from 10 degrees to 70 degrees over the full core diameter (seven fiber tips) and over the half core diameter (seven fiber tips). Three fiber tips were produced to have a curvature at the distal end with curvature radii of 160, 230, and 420 microm. RESULTS: The shape as well as the size of erbium: YAG laser induced vapor bubbles can be controlled systematically by using adequate fiber tip geometries. In detail, the used different angles and curvatures demonstrate that the propagation direction of the vapor bubbles can be estimated by optical modeling considering Snell's law and the Fresnel laws at a quartz-air boundary. Beside this, the size of a vapor bubble can be predetermined by choosing ideal fiber tip geometries to reduce or increase the radiant exposure at the distal end of the quartz fiber tip. CONCLUSIONS: The good possibility of controlling the shape and size of vapor bubbles offers a wider range of new applications, especially in ophthalmic microsurgery such as erbium YAG laser vitrectomy.

Equipment Design↗
PubMed2000

Ocular optical aberrations after photorefractive keratectomy for myopia and myopic astigmatism.

OBJECTIVES: To study the effects of photorefractive keratectomy on ocular optical aberrations and to establish correlations with glare vision and low-contrast vision. METHODS: Preoperative ocular aberroscopy of 15 eyes undergoing photorefractive keratectomy was compared with aberroscopy at 3 months postoperatively by means of a newly developed automated aberroscope of the Tscherning type. The correlation of the wavefront errors with best spectacle-corrected visual acuity, low-contrast visual acuity, and visual acuity under glare conditions was analyzed. RESULTS: In any individual treated, the total wavefront error increased. On average, the total wavefront error increased by a factor of 17.65; this increase was highly statistically significant (P = .001). Also, the correlation with best-corrected visual acuity, low-contrast visual acuity, and glare visual acuity was statistically significant (P = .02, P = .001, and P = .03, respectively). The increase in ocular aberrations was significantly related with the virtual pupil size. CONCLUSIONS: Photorefractive keratectomy increases the ocular aberrations, impairing the visual performance of the eyes treated. In detail, scotopic visual measures such as low-contrast visual acuity and glare visual acuity suffer most from the myopia correction. Aberroscopy-guided photorefractive keratectomy may avoid such effects.

Adolescent↗
PubMed2000

[Erbium:YAG laser vitrectomy: temperature measurements in different replacement materials].

BACKGROUND: The erbium:YAG laser has the potential of being used routinely for vitrectomy because of the excellent quality of liquefying vitreous structures and the low vacuum forces required. However, the use of silicone oil and perfluorocarbon may lead to unwanted temperature increases in the microsurgery probe. The aim of this work was to investigate this side effect. MATERIALS AND METHODS: Different replacement materials such as water, methocel, silicone oil and perfluorocarbon were used in a simple eye model. The temperature increase during laser application was measured by means of thermocouples. The maximum temperature increase and time decay were derived with and without aspiration from these time-resolved measurements. The average power at the distal end of the microsurgery probe was chosen to be 1 W. RESULTS: The temperature increase with aspiration in water was found to be significantly smaller than all other replacement materials. Interruption of aspiration leads to a critical temperature increase of approximately 14 K; however, this increase occurred very slowly (decay time 200 s). A comparable result could be observed for methocel, which was used to simulate condensed vitreous structures. In perfluorocarbon and silicone oil we measured a far higher increase in temperature of up to 130 K within a few seconds. Furthermore, small remnants of carbonized materials can be seen in the microsurgery probe after laser application. CONCLUSIONS: The temperature increase during erbium:YAG laser vitrectomy in water can be considered to be harmless for other intraocular structures. However, insufficient aspiration or increased vitreous condensation leads to increased temperature in the microsurgery probe. Our results demonstrate that the use of erbium:YAG laser vitrectomy in materials such as silicone oil or perfluorocarbons is contraindicated.

Contraindications↗
PubMed2000

[Studies on the stabilization of the cornea in rabbits].

BACKGROUND: The mechanical stabilization of the cornea in keratoconus may delay progression of this disease. The cross-linking techniques optimized in corneas of enucleated porcine eyes were investigated under in vivo conditions in rabbits to estimate the biocompatibility and duration of the stiffening effect. METHODS: Twenty-eight rabbits were treated monocularly, the fellow eye serving as control. The epithelium was mechanically removed and 19 eyes were treated with riboflavin plus ultraviolet irradiation (365 nm, 2 mW/cm2) for 45 min and 9 eyes with 0.075% glutaraldehyde for 20 min. After treatment, the eyelids were sutured for 3 days. The healing process was controlled by slit-lamp examination and photographically documented. After 1 month, 20 animals and after 3 months 8 animals were sacrificed, the eyes enucleated, and the stress-strain relation of the corneas measured and compared to the fellow eye. RESULTS: The epithelium was closed after 4-5 days. The transparency of the corneas remained clear during follow-up, and there were no signs of inflammatory reaction. Stress for a strain of 6% was higher in the treated corneas by a factor of 1.3 +/- 0.66 (P = 0.319) in the glutaraldehyde group and by a factor of 1.6 +/- 0.75 (P = 0.0408) in the riboflavin group at 1 month, and by 1.3 +/- 0.48 (P = 0.07) at 3 months after treatment. CONCLUSIONS: The cross-linking technique using riboflavin plus UV irradiation is suitable for at least temporarily stiffening the cornea in vivo and seems to be a promising method for conservative treatment of keratectasia.

Animals↗
PubMed2000

[Motion artifacts in the vitreous body during vitrectomy].

BACKGROUND: Movements and vibrations of intraocular structures can be observed during vitrectomy with mechanical cutting systems. We experimentally compared these intraocular motion artifacts between mechanical and erbium:YAG laser vitrectomy. MATERIAL AND METHODS: The intraocular structures were reliably simulated by a 0.9-mm-wide foil (thickness 10 microns) in a water-filled cuvette. The movements caused by commercial mechanical cutter systems were compared with vibration induced by means of laser surgery probes (laser pulse energy 20 mJ). Laser triangulation was used to measure the movement amplitudes at various cutting rates of 2, 5, and 10 Hz and a constant suction force of 50 mmHg. RESULTS: At all cutting rates the amplitude with the laser was less than that with the mechanical system. The ratio of the maximal amplitude between laser surgery probes (AL) and mechanical cutter system (AM) was AL/AM = 0.29 at 10 Hz, AL/AM = 0.33 at 5 Hz, and AL/AM = 0.45 at 2 Hz. CONCLUSION: The reduced intraocular movements with erbium:YAG laser vitrectomy constitutes a potential advantage for the nonpulsatile vitrectomy.

Erbium↗
PubMed2000

Manifest diabetes and keratoconus: a retrospective case-control study.

PURPOSE: To assess the influence of diabetes on the development of keratoconus to show whether biomechanical effects are also reflected in epidemiology. The two diseases have opposite impact on the biomechanics of the corneal stroma: manifest diabetes stiffens the cornea, whereas keratectasia weakens the tensile strength of the stroma. METHODS: The retrospective case-control study included files of 1,142 patients, with 571 patients in the case group (keratoconus patients) and 571 in the control group (clinical population). The groups were well matched with respect to sex and age. We established the number of diabetics in both groups and compared it statistically by means of the odds ratio to determine whether diabetes can be interpreted as having a "protective effect" whether it is a "risk factor" for the development of keratoconus. RESULTS: Two patients of the keratoconus group had manifest diabetes that developed many years after the diagnosis of keratoconus, while nine cases of diabetes were found in the control group. Statistical analysis revealed a strong protective effect of manifest diabetes regarding keratoconus (odds ratio = 0.2195, P = 0.034). This effect was evident only in type II diabetes patients. CONCLUSIONS: The protective effect of manifest diabetes may be explained by the induction of cross-links in the stroma, preventing biomechanical weakening of the cornea. This study shows that different biomechanical changes can be superimposed and assume epidemiological relevance.

Adult↗
PubMed2000

Comparison of erbium:yttrium-aluminum-garnet-laser vitrectomy and mechanical vitrectomy: a clinical study.

OBJECTIVE: To evaluate the clinical usefulness of the erbium:YAG (yttrium-aluminum-garnet) laser for vitrectomy and to compare it with a conventional mechanical vitrectomy system regarding the intraoperative parameters. DESIGN: Prospective, randomized, clinical trial. PARTICIPANTS: Thirty eyes of 30 patients underwent vitrectomy, 15 eyes in each group. METHODS: For mechanical vitrectomy, a commercially available vitrectomy unit was used. The operating parameters, cutting rate (7 Hz = 420 cpm), maximal suction force (300 mmHg), and aspiration flow (20 ml/min), were held constant. A newly developed erbium (Er):YAG laser unit and handpiece was used for laser vitrectomy with predetermined parameters for cutting rate (70 Hz = 4200 cpm), maximal suction force (50 mmHg), and aspiration flow (20 ml/min). Surgery parameters were recorded in real time and the operation was video recorded. The clinical follow-up time was a minimum of 3 months (average, 6.2 months; range, 3-9 months). MAIN OUTCOME MEASUREMENTS: The surgery time was comparable in both groups. During Er:YAG laser vitrectomy, the average suction force was significantly reduced (P< 0.001) compared with that during mechanical vitrectomy. The mean-square variation in suction as a measure to quantify the forces acting on intraocular structures during surgery was significantly smaller in the Er:YAG laser vitrectomy group (P << 0.001). CONCLUSIONS: Erbium:YAG laser vitrectomy may provide a semicontinuous procedure. This technique minimizes periodical intraoperative forces and movements of intraocular structures and may provide, therefore, a safer vitrectomy.

Aged↗
PubMed2000

[Irradiation of cornea with ultraviolet light and riboflavin administration as a new treatment for erosive corneal processes, preliminary results in four patients].

BACKGROUND: Corneal melting is a serious condition and in many cases maybe managed only by surgery. UV-radiation with Riboflavin is a new method that may stop the melting process of the cornea. PATIENTS AND METHOD: Four patients suffering from melting ulcera of the cornea of various origin underwent a single UV-radiation. Two ultraviolet diodes were used emitting light with an wavelength of 370 nm with an energy of 2.5 mW/cm2. The radiation time was 30 minutes. Before he radiation was performed 2-3 drops of 0.11% Riboflavinsolution were applied to the cornea. The treatment area was 6-7 mm in diameter. RESULTS: After the treatment in three of the four patients the melting process of the cornea stopped. At least temporarily, a surgical procedure could be delayed. CONCLUSION: Because of the absence of any side-effects in serious cases the method is recommended prior to surgery.

Adult↗
PubMed2000

Transpupillary laser phototherapy of tumors and vascular anomalies of retina and choroid: theoretical approach and clinical implications.

BACKGROUND: Small retinal and choroidal tumors situated near the optic nerve or macula, such as retinoblastomas and malignant melanomas, as well as various other anomalies, in particular vascular malformations, may successfully be treated by photocoagulation. Model assumptions geared towards maximizing efficiency and minimizing undesirable side effects are forwarded, and the most important parameters subserving photothermal destruction, such as radiation field and thermal energy, analyzed. The influence exerted by physical traits of various tissues involved are also considered. METHODS: The model approximations presented are based on classical radiation and absorption laws, as well as on the scattering properties of the various tissues implicated, these being considered as a function of wavelength and their relevance to the photodestructive task at hand. Particular attention is paid to the rate processes and reaction kinetics of irradiated proteins. CONCLUSIONS: Radiation sources emitting in the near-infrared range of the electromagnetic spectrum, such as the diode (810 nm) and the cw Nd:YAG (1064 nm) lasers, are optimal for the treatment of tumors and large, voluminous entities (such as Hippel-Lindau angiomas), owing to the good tissue penetration properties of their light. Those emitting in the shorter wavelength range, such as the argon ion (488 and 514 nm) and first harmonic--mode Nd:YAG (532 nm) lasers, are not suitable for such tasks, but they are ideal for the destruction of fine sanguinous structures, within which their light is strongly absorbed but through which it penetrates poorly. For the treatment of large anomalous structures, a combined short/long wavelength--strategy should also be considered as a viable alternative. Such a "wavelength mixture" is emitted by the xenon high pressure lamp of the once renowned Meyer-Schwickerath light coagulator. The precision and safety of photothermal destruction methods depend, in the first approximation, upon the details of the pulse energy deposition (wavelength, pulse height and duration, pulse dynamics, mode composition, focussing), the choice of which is determined by the optical and thermal constants of the irradiated tissues. Higher pulse energies will, of course, be more effective in destroying neoplastic cells, but the risk of producing undesired collateral heat damage will also increase concomitantly. Until we can ascertain the physical properties of the pathological tissues treated with certainty, we will hardly be able to achieve more than an approximation of an ideal treatment strategy. But with increasing developments in in vivo-diagnostic techniques, we expect that this goal will be attainable in the not too distant future.

Animals↗
PubMed1999

[Arcus senilis].

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Aged↗
PubMed1999

[Laser in situ keratomileusis (LASIK). Intraoperative and postoperative complications].

PURPOSE: To quantify the incidence and type of complications after LASIK for the correction of myopia with special consideration to the time lapse after surgery and the possible consequences regarding high-contrast sensitivity and other modalities of visual acuity. MATERIAL AND METHODS: Between January 1995 and April 1997, 125 eyes of 88 patients with myopia greater than -6.0 D who could not wear contact lenses were operated on at our institute. In this prospective study the patients were examined consecutively preoperatively as well as postoperatively at day 4 and months 1, 3 and 6. The complications were divided into three groups (intraoperative, early postoperative and late postoperative). RESULTS: Our complication rate was 7.2% (loss of 2 lines of visual acuity)--with cutting artifacts related to the microkeratome, wrinkling of the flap and epthelial ingrowth. CONCLUSIONS: LASIK is a microsurgical procedure that requires adequate experience and the desire by the surgeon for self-evaluation. In spite of the good clinical results in the correction of high myopia the complication rates seems still to be too high. This should be the objective for further improvement primarily related to the microkeratomes.

Cornea↗
PubMed1999

[Photo-ablation of the cornea with the erbium:YAG laser].

BACKGROUND: Ablation experiments and preclinical studies have shown increased thermal damage and surface roughness after photorefractive keratectomy (PRK) with the erbium: YAG laser. MATERIALS AND METHODS: In this study, the thermal damage was investigated on enucleated pig corneas for various laser pulse durations (80 ns to 1 ms) and radiant exposures (0.2-5 J/cm2). The "scanning-spot" method and the fundamental mode photo-ablation were used for spherical corrections. SEM pictures and surface roughness measurements enabled comparison with the morphology after ArF-excimer laser treatment. The surface roughness is one order of magnitude higher compared to the ArF-excimer laser ablation. The surface of the tissue after ablation looks melted. RESULTS: The thermal damage reduces with increased intensity, and at high intensities the thermal damage results in a constant thickness of > 5 microns. CONCLUSIONS: Laser-induced melting processes might be the main reason for the high thermal damage and the increased surface roughness after erbium: YAG laser treatment. This leads to the conclusion that the erbium: YAG laser is not a real alternative to the ArF-excimer laser in PRK.

Animals↗
PubMed1999

Effects of photorefractive keratectomy and cataract surgery on ocular optical errors of higher order.

BACKGROUND: This pilot study was carried out to assess the effects of photorefractive keratectomy (PRK) for myopia and myopic astigmatism and cataract surgery on the ocular optical aberrations of higher degrees. METHODS: The optical aberrations were measured in 12 patients before and after PRK and in 10 patients after cataract surgery with a video aberroscope for clinical use (based on Tscherning's aberroscope) designed by the authors. To characterize the optical performance of the eye the deviation of the wavefront of a foveal image point from its ideal (spherical) shape (wavefront aberration) was determined. The wavefront aberration is represented mathematically in Zernike polynomials. The first 14 Zernike coefficients K(i) were determined and compared with data from normal eyes with full visual acuity. RESULTS: Most Zernike coefficients were considerably greater after PRK than before surgery. These changes differed significantly from the variability of repeated individual measurements. In particular, coefficients corresponding to astigmatism, spherical aberration or coma were highly significantly increased (P<0.001). After cataract surgery, the averaged Zernike coefficients exhibited no significant differences from normal values, except the coefficient K(5) (astigmatism at 0 degrees or 90 degrees ). However, coefficients showed a significant high variability, especially the coefficients for spherical aberration or astigmatism. CONCLUSION: Both PRK and cataract surgery are operations which may considerably increase the ocular optical errors of higher order. These aberrations are not predictable and can affect the visual acuity despite optimal sphero-cylindrical correction, in particular under mesopic conditions.

Adult↗
PubMed1999

Ethical concerns.

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Cataract Extraction↗