Biomedical subjects

G Geerling

Publications and source records attributed to G Geerling.

42 records · Page 3Linked to original sources

PubMed1998

Initial clinical experience with the picosecond Nd:YLF laser for intraocular therapeutic applications.

AIMS/BACKGROUND: Compared with nanosecond (ns) pulses of conventional Nd-YAG lasers, picosecond (ps) laser pulses allow intraocular surgery at considerably lower pulse energy. The authors report initial clinical experiences using a Nd:YLF ps laser for the treatment of various indications for photodisruption. METHODS: A Nd:YLF laser system (ISL 2001, wavelength 1053 nm) was used to apply pulse series of 100-400 microJ single pulse energy at a repetition rate of 0.12-1.0 kHz. Computer controlled patterns were used to perform iridectomies (n = 53), capsulotomies (n = 9), synechiolysis (n = 3), and pupilloplasties (n = 2). Other procedures were vitreoretinal strand incision (n = 2) and peripheral retinotomy (n = 1). For comparison, 10 capsulotomies and 20 iridotomies were performed with a Nd:YAG ns laser. The ps laser cut of an anterior capsule was assessed by scanning electron microscopy (SEM). RESULTS: Open, well defined iridectomies (mean total energy 4028 mJ, mean diameter 724 microns), were achieved at first attempt in 92% of the cases. In 64% an iris bleeding and in 21% an IOP increase of > 10 mm Hg occurred. All capsulotomies were performed successfully (mean energy 690 mJ/mm cutting length) but with a high incidence of intraocular lens damage. The attempted vitreoretinal applications remained unsuccessful as a result of optical aberrations of the eye and contact lens. Although ps laser capsulotomies and iridectomies required much higher total energy than ns procedures, the resulting tissue effects of the ps pulses were more clearly defined. SEM examination of a ps incision of the anterior lens capsule demonstrated, nevertheless, that the cut was more irregular than the edge of a continuous curvilinear capsulorhexis. CONCLUSION: Series of ps pulses applied in computer controlled patterns can be used effectively for laser surgery in the anterior segment and are considerably less disruptive than ns pulses. The ps laser is well suited for laser iridectomies while the ns laser is preferable for posterior capsulotomies. As vitreoretinal applications remained unsuccessful, the range of indications for intraocular photodisruption could not be extended by the ps laser.

Humans↗

PubMed1997

[Comparative studies with various corneal topography measurement devices].

PURPOSE: It is difficult to measure the topography of the cornea with high resolution and visualize it on a map displaying refraction. This is demonstrated by the ongoing improvement and further development of different methods and by the fact that users of these techniques are not always satisfied. MATERIALS AND METHODS: Five different ring projectors were compared. Spherical and aspherical ball standards were used to measure the standard deviation of the refraction of the system. A patient group of eight people with healthy eyes was used to compare the measurement accuracy and operational errors. Some patients were also measured after cataract surgery. The lateral and axial range of the devices was determined. RESULTS: The measurement accuracy for ball standards for the five devices was below 1/8 D. For the in vivo case in the control group it was below 1/4 D for four devices. Furthermore, the reproducibility of the results, the accuracy of angle determination and the influence of mechanical and optical design will be discussed. The study demonstrates applications and limits of this measurement method.

Cataract Extraction↗

PubMed1997

Patient expectations and recollection of information about photorefractive keratectomy.

PURPOSE: To assess the expectations of surgical result and recollection of a standardized information briefing by patients having photorefractive keratectomy (PRK). SETTING: Department of Ophthalmology, Medical University of Lübeck, Germany. METHODS: Thirty-two patients were asked to complete a multiple-choice questionnaire immediately after standardized information briefings and 1 month after PRK to establish their comprehension of the information briefing, what they remembered of it, and what they expected from the refractive procedure. RESULTS: Although the estimated intelligence quotient of the patients was above average (115 +/- 7.23) and almost all rated the information briefings as being comprehensible, only simple, basic facts about PRK were remembered immediately after the briefing as well as 1 month postoperatively. Of 12 possible undesired consequences, 6.4 were remembered before surgery and 3.9 after surgery. The latter were mainly side effects the patients experienced themselves. CONCLUSION: As most patients rejected the possibility of serious complications, for medicolegal reasons, careful, accurate documentation of the contents of and patients' satisfaction with the information briefing is necessary.

Adult↗

PubMedDate not supplied

Scintigraphic evaluation of lacrimal glands using a rabbit experimental model.

The aim of this study was to establish an experimental model to evaluate functional changes in lacrimal gland parenchyma using gamma scintigraphy. Although the lacrimal glands of the rabbit have frequently been used for ophthalmological research, scintigraphic evaluation of these glands has received far less attention and we could not find any reports concerning this topic in the literature. Ten rabbits were used for the study; in 4 of them, the orbital region was dissected to provide the topographic anatomy of the lacrimal glands. Four rabbits underwent a static scintigraphy after excision of a unilateral lacrimal gland. Changes in the pattern of tracer uptake indicated the exact position of the gland on the scintiscan. One rabbit served as a control, and another one was used to prove the surgical accessibility of the gland. Using a frontal projection of the head the (99m)TcO(-)(4) uptake of the rabbit lacrimal glands could be identified and evaluated in the upper lateral region of the scintiscan. In conclusion, the lacrimal glands of the rabbit provide an appropriate experimental model to study quantitative disturbances of lacrimal secretion using scintigraphy and enable the assignment of functional impairment to morphological changes of the lacrimal parenchyma.

Animals↗

PubMedDate not supplied

Relative mydriasis after photorefractive keratectomy.

PURPOSE: To report the incidence of anisocoria after unilateral excimer laser photorefractive keratectomy (PRK) for myopia and subsequent corticosteroid therapy in a retrospective and prospective study and to explore possible etiologies. METHODS: The horizontal pupil diameter was determined in 6 patients (6 eyes) at 21.8 +/- 12.6 months after unilateral wide-field excimer laser PRK (retrospective group) as well as in 8 consecutive patients (8 eyes) before and 3.4 +/- 2.9 months after unilateral PRK (prospective group). The Schwind-Keratom wide-field excimer laser was used. Measurements were done in an examination room using Rosenbaum card comparison pupillometry and with a Goldmann perimeter at 31.5 asb. In the prospective group, the effect of fitting a hard contact lens of zero diopter power and the application of 0.1% pilocarpine were evaluated. RESULTS: Relative mydriasis was present in all treated eyes and the difference in pupil diameter between the two eyes measured 0.25 to 1.75 mm (retrospective group: +0.56 +/- 0.82 mm; prospective group: +0.72 +/- 0.29 mm). At the time of pupil measurement, the retrospective group had a significantly longer mean postoperative follow-up (21 mo) than the prospective group (3.4 mo) and significantly more eyes still received topical corticosteroid treatment (retrospective group, 1 of 6 eyes; prospective group, 7 of 8 eyes). The amount of anisocoria did not correlate with the applied laser energy, ablation depth, or refractive change, but showed a negative correlation with increasing time after PRK. Neither hard contact lens fitting nor pilocarpine 0.1% reduced the amount of anisocoria significantly. CONCLUSION: Unilateral PRK with wide-field excimer laser ablation and subsequent application of topical corticosteroids regularly resulted in a relative pupillary mydriasis. Neither an altered corneal profile nor parasympathetic denervation is responsible for this. Weakening of the pupillary sphincter of the treated eye may cause this phenomenon.

Administration, Topical↗

PubMedDate not supplied

Corneal endothelial cell damage after experimental diode laser thermal keratoplasty.

PURPOSE: To evaluate the safety of diode laser thermal keratoplasty (LTK) with respect to corneal endothelial cell damage. METHODS: In an in vitro animal model system, porcine eyes were irradiated with a continuously emitting laser diode at wavelengths (lambda) of 1.85 or 1.87 microm, corresponding to an absorption coefficient (micro(a)) of 1.1 or 2.0 mm(-1). Different irradiation and application parameters were tested serially. To determine the temperature threshold for endothelial damage, corneal buttons were analyzed separately in a waterbath experiment. The endothelial damage was assessed after trypan blue and alizarin red supravital staining under light microscopy. RESULTS: The thresholds for the 50% probability of thermal damage (ED50) were determined at corneal temperatures of 65 degrees C for a 10-second water-bath immersion, and 59 degrees C for 60 seconds. Coagulations that reached the deeper stromal layers revealed severe endothelial cellular alterations and areas of exposed Descemet's membrane. The thermally induced changes were dependent on laser power and the absorption coefficient (wavelength). Mean diameter of total endothelial cell damage was 245 +/- 154 microm (range, 0 to 594 microm) for an absorption coefficient of 1.1 mm(-1). The maximal lateral extent of endothelial cell damage induced by the laser exposure was 594 microm in diameter. Increasing the absorption coefficient decreased the penetration depth of the laser irradiation, creating a greater temperature rise within the corneal stroma and significantly less endothelial damage (P < .01), when the same laser power was applied. The calculated total area of damage for the paracentral human corneal endothelium ranged from 1.8% to 13.6%. CONCLUSION: Data obtained in this in vitro study were transferred to an endothelial cell damage nomogram, demonstrating that appropriate parameter improvements can minimize the adverse effects to the corneal endothelium. However, model adjustment to the human cornea indicates the potential for endothelial cell damage after diode laser thermal keratoplasty, and should be considered when performing this elective procedure.

Animals↗