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Biomedical subjects

N Pfeiffer

Publications and source records attributed to N Pfeiffer.

At least 91 records · Page 5Linked to original sources
PubMed1995

Therapeutic range in transscleral contact cyclophotocoagulation.

Laser contact cyclophotocoagulation (CP) increasingly replaces noncontact CP and cryotherapy as it produces less damage to the conjunctiva and sclera. However, the optimal wavelength and protocol for treatment have not yet been firmly established. We used a contact continuous-wave (cw)-Nd:YAG laser at 1064 nm (Meridian-Microruptor III) with a bare fiber. A total of 30 freshly enucleated porcine eyes with brown irides were treated within 12 h of enucleation. The intraocular pressure was kept at 35-40 mmHg with an infusion system. The fiber was placed at a 1.5-mm distance from the limbus perpendicularly to the scleral surface, and applications were made using power levels ranging from 1.0 to 10.0 W for exposure periods of 0.5, 0.7, 1.0, 1.5, 2.0, 3.0, and 4.0 s. A just-visible whitening of the ciliary body was defined as a minimal effect, a complete whitening without loss of ciliary structures was defined as a medium effect, and a complete whitening with loss of ciliary structures was defined as a maximal effect. Supramaximal "pop" effects could be identified by the typical sound and the destruction of the ciliary body. Pop effects originate from a sudden overheating, which leads to the formation of small gas bubbles. Using an exposure duration of 0.5 s, no pop effect or maximal effect was observed. For longer exposure periods the therapeutic range decreased continuously (3.7 +/- 2.7 W for 0.5 s, 0.3 +/- 0.3 W for 4.0 s).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Prophylactic Nd:YAG-laser iridotomy versus surgical iridectomy: a randomized, prospective study.

Both surgical iridectomy and YAG-laser iridotomy have been shown to prevent angle-closure glaucoma. However, it remains unknown as to which procedure is superior. We therefore conducted a prospective randomized study, which compared the effect of the two methods on visual acuity, intraocular pressure, endothelial cell density, depth of the anterior chamber, and iris configuration as well as acceptance by the patients. A total of 30 patients, who were treated for acute angle-closure glaucoma in one eye, were subjected to either surgical iridectomy or Nd:YAG-laser iridotomy in the other eye according to a randomized protocol. All patients were followed for 12 months by examination at the 1st, 6th, and 12th month post treatment. No significant difference between the two treatments was found regarding visual acuity or intraocular pressure. The peripheral anterior chamber increased in depth following both methods, whereas the central depth of the anterior chamber was unaffected. A better gonioscopic visibility of the trabecular meshwork resulted from the increased width of the chamber angle. Whereas the number of endothelial cells remained constant in the patients treated with laser iridotomy, a small decrease was observed in the group of patients who underwent iridectomy (-7.2% after 12 months; difference not significant). The subjective acceptance by the patients was better in the group treated with laser iridotomy. We conclude that the two methods are equivalent with regard to intraocular pressure and visual acuity. The constant number of endothelial cells and the better acceptance by the patients suggest Nd:YAG-laser iridotomy to be the preferable method for prophylaxis of acute angle-closure glaucoma.

Acute Disease↗
PubMed1994

Evaluation of swinepox virus as a vaccine vector in pigs using an Aujeszky's disease (pseudorabies) virus gene insert coding for glycoproteins gp50 and gp63.

Pigs were vaccinated by scarification or intramuscular injection with a swinepox virus-Aujeszky's disease (pseudorabies) recombinant (rSPV-AD) constructed by inserting the linked Aujeszky's disease virus genes coding for glycoproteins gp50 and gp63, attached to a vaccinia virus p7.5 promoter, into the thymidine kinase gene of swinepox virus. By 21 days after vaccination, 90 and 100 per cent of the animals vaccinated by scarification or intramuscular injection, respectively, had developed serum neutralising antibodies to Aujeszky's disease virus. Upon challenge with virulent virus, significantly fewer vaccinated pigs developed clinical Aujeszky's disease, nasal shedding of challenge virus was markedly reduced, and the vaccinated groups of pigs maintained or gained weight during the week after challenge whereas the unvaccinated control group lost weight. No transmission of rSPV-AD to in-contact controls was detected during the three weeks before challenge. In a second experiment, serum neutralising antibodies to Aujeszky's disease virus persisted for 150 days after the pigs were vaccinated with rSPV-AD by scarification or intramuscular injection and all the pigs showed an anamnestic response when they were revaccinated.

Animals↗
PubMed1994

[Increased threshold for detection of phase differences in pattern-induced color flicker fusion in patients with glaucoma].

BACKGROUND: Pattern-induced flicker-colors are subjective colors produced by rotating disks with black-and-white arcs. Changing the direction of rotation results in a different color. Small variations in the temporal sequence (phase differences) of the black-and-white pattern cause the colors to vary and can be perceived as color differences. PATIENTS AND METHODS: We investigated the thresholds for such phase differences in healthy (n = 11) and in glaucomatous (n = 19) eyes. Acuity and color vision were tested and in patients static visual field perimetry (Octopus G1) was carried out. The disks used for producing the pattern-induced flicker-colors were viewed from a distance of 2 m and had a luminance of 35 cd/m2. The phase difference thresholds were determined using a double staircase procedure. RESULTS: In glaucomatous eyes the thresholds were significantly higher (33.9 +/- 4.8 for clockwise rotation) than in normal eyes (18.2 +/- 1.4), p < 0.005 and this was the case for anticlockwise as well as clockwise rotation. The difference between the two groups remained significant (p < 0.025) when the data for glaucomatous eyes was corrected for acuity losses. CONCLUSIONS: In the glaucomatous eyes the increase in phase difference threshold was correlated with raised visual field MD (r = 0.87 for clockwise rotation). The higher thresholds in glaucomatous eyes point to a loss in blue-yellow-sensitive, parvocellular retinal ganglion cells, which play an important part in the perception of pattern-induced flicker-colors. Pattern-induced flicker-colors are a new method for the clinical investigation of retinal function in the center of the visual field and have the advantage that fixation is unnecessary and the yellow filter properties of the refractive media and the macula are of no importance.

Adolescent↗
PubMed1994

Concentration recovery for SPECT CNS dopamine-receptor studies for monkeys.

Most commercial SPECT scanners do not properly compensate for scattering and partial volume effects, which severely impacts the quantitation of clinical and research SPECT studies, especially in CNS dopamine studies. Hence, in this paper, a brain phantom containing a monkey skull was used to calibrate a Picker Prism 3000 SPECT camera for quantitative studies of 123I and 99mTc-labeled radiopharmaceuticals. In the calibration study, two small vials representing basal ganglia were inserted into a skull phantom. A series of images were taken with different concentration ratios between the basal ganglia and the other brain compartments to simulate the dynamic imaging study of the dopamine D2 receptor in a monkey brain. Based on this calibration, a simple method is proposed for count correction in the region of interest (ROI). This technique is superior to using a single calibration factor from a cylindrical uniform activity phantom since it can compensate for both the partial volume effect and the dynamically changing effect of scattering. A significant difference between the true and measured values was observed in the correction factors (by a factor as much as 3). Furthermore, a cylindrical phantom, approximately the size of a monkey's head and containing the same basal ganglia inserts, was used to investigate the feasibility of using a cylindrical phantom with the proposed correction method. The results indicate that it is feasible to use a cylindrical phantom for the case where the activity inside the brain cavity and the activity in the surrounding tissue are similar.

Animals↗
PubMed1994

[Single dose administration in therapy of glaucoma. Comparison of costs with multiple dose].

Preservatives in antiglaucomatous agents can irritate the conjunctiva and may lead to allergic reactions. Preservative-free single-dose applications of glaucoma medications have increasingly become available. We analysed the therapy costs for single-dose containers per eye and per year and compared them with those for multidose containers. The data were calculated from prices taken from the German pharmacy index, applications per day and number of drops in the container. The drop volume ranged from 34.3 microliters to 48.0 microliters for single-dose containers and from 29.2 microliters to 40.0 microliters for multidose containers. The annual cost of therapy with beta-adrenergic antagonist preparations was DM 42.59-DM 80.78 for multidose containers and DM 162.73-DM 242.42 for single-dose containers. The cost of therapy with philocarpine was DM 21.55 but DM 233.92 for single-dose containers. The cost of combination therapy with beta-adrenergic antagonist preparations and pilocarpine ranged from DM 67.92 to DM 214.33 for multidose containers and from DM 408.15 to DM 428.95 using single-dose containers. Therapy with preparations in single-dose containers is more expensive than with multidose containers (+161 to +1169%). Preparations in single-dose containers without preservatives can have advantages, but the higher costs necessitate careful selection of the patients.

Adrenergic beta-Antagonists↗
PubMed1994

Intraocular thymoxamine or acetylcholine for the reversal of mydriasis.

In a placebo-controlled prospective study, thymoxamine 0.02% or acetylcholine 1.0% or thymoxamine 0.01% plus acetylcholine 0.5% were used intraocularly to reverse mydriasis during cataract surgery. Prior to surgery, pupils were dilated with scopolamine 0.25%, tropicamide 1%, and phenylephrine 10%. At the end of surgery, 228 eyes were randomly assigned to 1 of 4 different treatments: 57 eyes each received intracamerally thymoxamine 0.02%, acetylcholine 1%, a combination of both drugs, or placebo. At 5 min posttreatment, there was a significant mean pupillary constriction of 1.86 +/- 0.67 mm following acetylcholine administration and 1.53 +/- 0.80 mm following thymoxamine application as compared with the placebo group, in which the pupillary diameter remained almost constant. For the combination of acetylcholine plus thymoxamine the effect was fully additive, with a pupillary constriction of 3.42 +/- 0.98 and 4.04 +/- 1.02 mm being observed at 5 and 10 min posttreatment, respectively. No drug-related side effect was detected. We conclude that thymoxamine can be useful during surgery as an intraocular miotic to reverse mydriasis and can considerably enhance miosis when given in combination with acetylcholine.

Acetylcholine↗
PubMed1993

A simplified method for quantitation of iodine-123 iodobenzamide in human plasma: a technical note.

To establish a quantitative single-photon emission tomography (SPET) procedure for imaging CNS D2 dopamine receptors, measurement of unchanged iodine-123 iodobenzamide (123I-IBZM) (a selective D2 ligand) in human plasma was investigated. There are three possible radioactive components in human plasma: hydrophilic compounds (iodide ion, etc.), lipophilic metabolites, and unchanged IBZM. Based on the difference in lipophilicity of IBZM and its lipophilic metabolites (LM), a new quantitative method of analysis of 123I-IBZM using a simple solvent extraction was developed. The selective extraction was achieved with n-octane/phosphate buffer (0.1 M, pH 7.4). Extraction efficiency was 93.2% +/- 0.3% (n = 15) for IBZM from plasma, while 99.3% +/- 0.2% (n = 12) of LM remained in the aqueous plasma fraction. Twenty-one confirmation tests with plasma containing known ratios of IBZM/LM, ranging between 0.39 and 7.60, were performed. The experimental results were very close to the values of the true ratios over the wide range (accuracy approximately 99%, relative standard error 6.6%). The data from this simplified method are comparable to those obtained by the high-performance liquid chromatography method. This improved method provides an easy and accurate way to quantify unchanged IBZM in human plasma. With appropriate kinetic modeling and in conjunction with a dedicated SPET imaging device for measuring quantitative information, it may be possible to develop a practical method for measuring D2 receptor density in vivo.

Benzamides↗
PubMed1993

[Review of glaucoma research].

This paper reviews publications in the field of glaucoma research from 1991 and 1992. The role of elevated intraocular pressure (IOP) is redefined. Raised IOP is not the only, but probably the most important risk factor in the development of glaucomatous optic nerve damage. The IOP threshold of 20-22 mm Hg may be too high for many patients to avoid progressive damage. Early surgical treatment is more successful than medical or laser treatment and is gaining importance. New techniques have made trabeculectomy safer. In patients with poor surgical prognosis antimetabolites such as 5-fluorouracil or mitomycin C may improve results considerably. However, these treatments need to be defined in their side effects as far as long-term results are concerned. Lasersclerostomy ab interno and ab externo minimize surgical trauma and promise better results in eyes with previous surgery. Contact-cyclo-photocoagulation renders results comparable to cyclo-cryo-coagulation with less perioperative side-effects. However, long-term results must be obtained before it can replace the older technique. Medical treatment on the step to clinical introduction (in Germany) are apraclonidine with less side effects than clonidin, topical carbonic anhydrase inhibitors (dorzolamide) and possibly prostaglandin F2alpha-ester such as PhXA34. Galenic modifications are gelrite, a heteropolymer and betaxolol suspension. Which patients with ocular hypertension to treat and which not to treat still is a therapeutic dilemma. Methods such as colour contrast, investigation of scotopic low-contrast vision and the pattern-electroretinogram promise earlier detection of glaucomatous damage than conventional computer perimetry or morphological methods.

Adrenergic alpha-Agonists↗
PubMed1993

[5-fluorouracil in goniotrepanation with poor prognosis. Results of 1-year follow-up].

14 eyes of 14 patients with medically untreatable glaucoma and extremely bad surgical prognosis because of young age, secondary glaucomas or following previous surgery were treated by means of goniotrephination with a scleral flap and a fornix-based conjunctival flap. Postoperatively, all eyes received 5 mg 5-fluorouracil in 0.5 ml NaCl 0.9% subconjunctivally daily for 7 days and weekly for another 6 weeks. IOP was lowered in all eyes from 33.9 +/- 5.0 mmHg preoperatively to 15.6 +/- 8.4 mmHg 1 year postoperatively. 71% of eyes were IOP controlled without further therapy. Results were unfavourable in eyes with irido-corneo-endothelial syndrome. Local side effects were less frequent than described previously, possible due to the reduced but prolonged administration of 5-fluorouracil. Also, all eyes received corneal supportive therapy with hyaluronic acid and polyvinyl alcohol.

Adult↗
PubMed1993

Predictive value of the pattern electroretinogram in high-risk ocular hypertension.

PURPOSE: The pattern electroretinogram (PERG) is reduced in early glaucoma and in some eyes with ocular hypertension (OHT). This study was designed to test the ability of the PERG to predict the development of visual field loss in OHT eyes. METHODS: In 29 eyes of 18 patients with high-risk OHT, the visual fields were tested, and the PERG was recorded using counterphasing checkerboard patterns at check sizes of 0.8 degrees and 15 degrees at 16 reversals/sec. The visual fields were retested 11-31 mo later. Initially, 12 eyes had pathologic PERG recordings. RESULTS: During the observation period, visual field loss developed in five eyes. All these eyes had a pathologic PERG recorded during the first visit. Of the eyes that had a normal PERG, none had field changes. CONCLUSIONS: Within the reservations of the limited sample size and follow-up interval, these findings suggest that the PERG can be used to discriminate between patients with OHT who will develop visual field loss and those who will not.

Adult↗
PubMed1993

[In incipient glaucoma the pattern electroretinogram displays diffuse, retinal damage].

The pattern electroretinogram (PERG), a noninvasive tool to measure the activity of retinal ganglion cells, shows changes in early glaucoma. We wanted to investigate whether or not the PERG is preferentially affected when the Bjerrum area is stimulated. We recorded the PERG from 17 eyes in 17 patients with initial stages of visual field defects due to open-angle glaucoma and from 10 eyes in 10 normal subjects. Counter-phasing checkerboard patterns were used as visual stimuli with a check size of 0.8 degrees at 16 reversals/s and 98% contrast. Three visual field extents were stimulated: (1) full screen (31 degrees x 27 degrees), (2) central stimulation with a diameter of 14 degrees, (3) peripheral stimulation = full screen with central mask of 14 degrees in diameter. The latter stimulus covers the regions where traditionally glaucomatous defects are expected early. In glaucoma patients, there was a significant decrease in the PERG amplitude compared to normals. This reduction was very similar for all three stimuli (42%, 52% and 47%, respectively). Thus, the PERG amplitude is reduced to a similar degree both in regions of the visual field where early damage is found (Bjerrum area) and in the central area. This result suggests that in early glaucoma there is focal as well as diffuse retinal damage.

Adult↗