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Biomedical subjects

J Krohn

Publications and source records attributed to J Krohn.

At least 19 recordsLinked to original sources
PubMed2001

Dosimetric verification of a dedicated 3D treatment planning system for episcleral plaque therapy.

PURPOSE: Episcleral plaque therapy (EPT) is applied in the management of some malignant ocular tumors. A customized configuration of typically 4 to 20 radioactive seeds is fixed in a gold plaque, and the plaque is sutured to the scleral surface corresponding to the basis of the intraocular tumor, allowing for a localized radiation dose delivery to the tumor. Minimum target doses as high as 100 Gy are directed at malignant tumor sites close to critical normal tissues (e.g., optic disc and macula). Precise dosimetry is therefore fundamental for judging both the risk for normal tissue toxicity and tumor dose prescription. This paper describes the dosimetric verification of a commercially available dedicated treatment planning system (TPS) for EPT when realistic multiple-seed configurations are applied. MATERIALS AND METHODS: The TPS Bebig Plaque Simulator is used to plan EPT at our institution. Relative dose distributions in a water phantom, including central axis depth dose and off-axis dose profiles for three different plaques, the University of Southern California (USC) #9 and the Collaborative Ocular Melanoma Study (COMS) 12-mm and 20-mm plaques, were measured with a diode detector. Each plaque was arranged with realistic multiple 125I seed configurations. The measured dose distributions were compared to the corresponding dose profiles calculated with the TPS. All measurements were corrected for the angular sensitivity variation of the diode. RESULTS: Single-seed dose distributions measured with our dosimetry setup agreed with previously published data within 3%. For the three multiple-seed plaque configurations, the measured and calculated dose distributions were in good agreement. For the central axis depth doses, the agreement was within 4%, whereas deviations up to 11% were observed in single points far off-axis. CONCLUSIONS: The Bebig Plaque Simulator is a reliable TPS for calculating relative dose distributions around realistic multiple 125I seed configurations in EPT.

Brachytherapy↗
PubMed2001

Transillumination for accurate placement of radioactive plaques in brachytherapy of choroidal melanoma.

PURPOSE: To present a technique for accurate plaque placement in episcleral brachytherapy of choroidal melanoma. METHODS: The tumor margins are marked on the scleral surface, and a dummy plaque is temporarily sutured to the globe. A fiber optic light pipe is then wedged into the space between the sclera and the plaque. Because of the reflecting inner surface of the plaque, the perimeter of the plaque can easily be observed during indirect ophthalmoscopy as a circle of light surrounding the tumor. By this method, it is possible to determine the exact position of the entire plaque in relation to the tumor and make the necessary adjustments. When the correct position is found, the dummy plaque is replaced by a radioactive plaque. RESULTS: Since 1993, we have routinely used this procedure in episcleral brachytherapy. CONCLUSION: This modified transillumination technique facilitates a correct positioning of episcleral plaques.

Brachytherapy↗
PubMed2001

Salvage intravesical therapy with interferon-alpha 2b plus low dose bacillus Calmette-Guerin is effective in patients with superficial bladder cancer in whom bacillus Calmette-Guerin alone previously failed.

PURPOSE: We determined whether combining low dose bacillus Calmette-Guerin (BCG) interferon-alpha 2B would be effective for patients in whom previous BCG failed. MATERIALS AND METHODS: A total of 40 patients in whom 1 (19) or more (21) previous induction courses of BCG failed received 6 to 8 weekly treatments of 1/3 dose (27 mg.) BCG plus 50 million units interferon-alpha 2B. Additional 3 week miniseries of further decreased BCG (1/10, 1/30 or 1/100) titrated to symptoms without changing the interferon-alpha 2B dose were given at 5, 11 and 17 months. In 12 patients a second induction course was given with 1/10 BCG plus 100 million units interferon-alpha 2B. There was multifocal disease in 39 patients, previous BCG had failed within 6 months in 34, disease was aggressive (stage T1, grade 3 or carcinoma in situ in 31, there had been 2 or more previous recurrences in 25 and disease history was greater than 4 years in 13. RESULTS: At a median followup of 30 months 63% and 53% of patients were disease-free at 12 and 24 months, respectively. Patients in whom 2 or more previous BCG courses had failed fared as well as those with 1 failure. Of the 18 failures 14 occurred at the initial cystoscopy evaluation. Of 22 patients initially counseled to undergo cystectomy 12 (55%) are disease-free with a functioning bladder. Combination therapy was well tolerated. CONCLUSIONS: While longer followup and larger multicenter studies are required to validate these encouraging findings, intravesical low dose BCG plus interferon-alpha 2B appears to be effective in many cases of high risk disease previously deemed BCG refractory. However, early failure while on this regimen should be aggressively pursued with more radical treatment options.

Adjuvants, Immunologic↗
PubMed2001

Effect of endothelin and BQ123 on ocular blood flow parameters in healthy subjects.

PURPOSE: To characterize the role of the endothelin system in the blood flow control of the optic nerve head and of the choroid in humans. METHODS: Two studies were performed in healthy subjects. Study 1 was a randomized, placebo-controlled, double-masked, balanced, two-way crossover design and study 2 a three way-way crossover design. In study 1 twelve healthy male subjects received endothelin (ET)-1 in stepwise increasing doses of 1.25, 2.5, and 5 ng/kg x min (each infusion step occurred over 20 minutes) coinfused with BQ123 (60 microg/kg x min) or placebo on two different study days. In study 2 twelve healthy male subjects received two doses of BQ123 (60 or 120 microg/kg x min over 60 minutes) or placebo on three different study days. Measurements of optic nerve head blood flow (ONHBF) and choroidal blood flow (ChBF) were performed with laser Doppler flowmetry in both studies. In study 2 mean flow velocity (MFV) of the ophthalmic artery was assessed with Doppler sonography. RESULTS: In study 1, ET-1 significantly decreased ONHBF (-22.8% +/- 4.3% at 5 ng/kg x min, P = 0.003 versus baseline) and ChBF (-21.7% +/- 3.2% at 5 ng/kg x min, P = 0.0001 versus baseline). The effect of the highest administered dose of exogenous ET-1 on ONHBF was significantly attenuated (P = 0.04, ANOVA) by coinfusion of BQ123. Effects of exogenous ET-1 on blood flow (2.5 ng/kg x min ET-1 or higher) also were attenuated in the choroid by coinfusion of BQ123 (ChBF: P = 0.03, ANOVA). In study 2, both dosages of BQ123 significantly increased MFV in the ophthalmic artery (60 microg/kg x min, 12.5% +/- 7.3%; 120 microg/kg x min, 17.2% +/- 9.2%, versus baseline; P = 0.001), but did not change blood flow in the ONH or the choroid. CONCLUSIONS: BQ123 antagonizes the effects of exogenously administered ET-1 on blood flow in the ONH and the choroid. The data indicate, however, that ET-1 does not substantially contribute to the regulation of basal vascular tone in these tissues.

Adult↗
PubMed2000

Simultaneous, bilateral rhegmatogenous retinal detachment.

PURPOSE: To examine the incidence, the preoperative findings and the surgical outcome of patients presenting with simultaneous, bilateral retinal detachment. METHODS: A retrospective analysis of the medical records of patients undergoing surgery for rhegmatogenous retinal detachment between 1990 and 1998. RESULTS: During this period a total of 827 operations for rhegmatogenous retinal detachment were done in 791 consecutive patients. Eighteen patients (2.3%) had simultaneous, bilateral retinal detachment, giving an annual incidence of 0.35 patients per 100,000 population. They all presented with unilateral symptoms. Compared with the group of unilateral or consecutive, bilateral retinal detachments, patients suffering from simultaneous, bilateral retinal detachments were significantly younger, with a mean age of 40.3 years. Thirteen patients had multiple, round retinal holes associated with lattice degeneration. Sixteen patients were myopic, ranging from -3 to -9.25 diopters. The retina was reattached in 35 (97%) of the 36 eyes operated on during the study period. CONCLUSION: Simultaneous, bilateral retinal detachment is usually found in relatively young, myopic patients with round, atrophic retinal holes, presenting with unilateral visual symptoms.

Adolescent↗
PubMed1999

Iris cyst associated with topical administration of latanoprost.

PURPOSE: To report an adverse side effect associated with topical latanoprost usage. METHOD: Case report. A 76-year-old woman with primary open-angle glaucoma developed an iris cyst 5 weeks after beginning treatment with latanoprost. Clinical examinations and slit-lamp photographs were performed. RESULTS: Latanoprost was discontinued. Periodic examinations disclosed that the iris cyst gradually diminished and finally disappeared within 3 weeks. CONCLUSION: The formation of an iris cyst is a possible complication of topical latanoprost therapy.

Administration, Topical↗
PubMed1999

Expression of factor VIII-related antigen in human aqueous drainage channels.

PURPOSE: Previous studies have indicated that there are preformed channels at the inner aspect of the anterior sclera, capable of draining fluid from the suprachoroidal space into scleral veins. The aim of this study was to characterize the cellular lining of these channels, and to compare it with the endothelium of Schlemm's canal, the collector channels and the scleral blood vessels. METHODS: Histological sections from the angular region of human eyes were prepared by an immunoperoxidase method to evaluate the expression of factor VIII-related antigen in different aqueous drainage channels. RESULTS: The cellular lining of the scleral channels showed a weak immunostaining to factor VIII-related antigen. Factor VIII-related antigen was also detected in the endothelium of the collector channels and Schlemm's canal. CONCLUSION: The positive immunoreaction to factor VIII-related antigen indicates that the previously described scleral channels, the collector channels and Schlemm's canal are all lined by an endothelium derived from a vascular origin.

Aqueous Humor↗
PubMed1998

Exudative retinal detachment in nanophthalmos.

PURPOSE: To report the treatment of exudative retinal detachment in a patient with nanophthalmos. METHODS: A 46-year-old man with bilateral nanophthalmos suffered from acute angle-closure glaucoma in his left eye. The first day after a peripheral iridectomy an exudative retinal detachment was observed. Two months later a partial thickness sclerectomy with a central sclerostomy, covered by a thin film of absorbable gelatine, was performed in each quadrant of the left eye. RESULTS: The retinal detachment gradually resolved and after eight months the retina was completely reattached. Vision, which had been limited to hand movements, improved to 6/18 with correction. CONCLUSION: Scleral resections are effective in the treatment of nanophthalmic retinal detachment. The use of absorbable gelatine film to cover the sclerectomized area may prevent regeneration of scleral tissue and recurrence of the exudative retinal detachment.

Acute Disease↗
PubMed1998

Light microscopy of uveoscleral drainage routes after gelatine injections into the suprachoroidal space.

PURPOSE: To visualize the suprachoroidal space and to study the morphology of possible uveoscleral drainage routes in the human eye. METHODS: Indian ink stained gelatine was injected directly into the suprachoroidal space of 7 human donor eyes. Those quadrants where gelatine appeared in the episcleral venous network were cut in their entirety in consecutive sections and examined by light microscopy. RESULTS: Gelatine was observed in the connective tissue surrounding scleral vessels and nerves. Gelatine was also traceable in fine, endothelium-lined channels at the inner aspect of the anterior sclera. These channels seemed to originate at the inner surface of the sclera, close behind the scleral spur, and communicate with the intrascleral venous plexus. CONCLUSION: Fluid is drained from the suprachoroidal space through the perivascular and perineural spaces of scleral blood vessels and nerves. In addition, this study indicates that there are preformed channels at the inner aspect of the anterior sclera, capable of draining fluid directly into scleral veins.

Aged↗
PubMed1997

Corrosion casts of the suprachoroidal space and uveoscleral drainage routes in the pig eye.

Eyes from pigs were studied by corrosion casting technique. Batson's mixture No. 17 (methyl methacrylate) was injected through a sclerotomy into the suprachoroidal space. Following polymerisation of the injected mixture the surrounding tissue was dissolved with 10% natrium hydroxide. Macroscopic and scanning electron microscopic findings in casts of the suprachoroidal space are presented. The outer (scleral) surface of the casts was rough, with a fish-scale-like appearance caused by fine lamellas between the sclera and choroid, running from the inner layers of the sclera traversing the space anteriorly to the choroid. Frequently, irregular, Y-shaped branches deriving from the outer surface of the casts were observed. They corresponded to the perivascular space of the vortex veins and represent a possible uveoscleral drainage route for aqueous humour.

Animals↗
PubMed1997

Corrosion casts of the suprachoroidal space and uveoscleral drainage routes in the human eye.

Human cadaver eyes were studied by corrosion casting technique. Batson's mixture No. 17 (methyl methacrylate) was injected through a sclerotomy into the suprachoroidal space. Following polymerisation of the injected mixture the surrounding tissue was dissolved with 10% natrium hydroxide. Macroscopic and scanning electron microscopic findings in casts of the suprachoroidal space are presented. Due to transscleral drainage of resin from the suprachoroidal space, different types of branches deriving from the outer (scleral) surface of the casts were found. Some of these branches corresponded to the perivascular spaces of both ciliary vessels and vortex veins. In addition, we found branches probably representing channels deriving directly from the suprachoroidal space, communicating with the intrascleral venous plexus. Such channel systems have previously not been described, and their possible relation to the uveoscleral drainage of aqueous humour is discussed.

Aged↗
PubMed1997

Cryotherapy in the treatment of cyclodialysis cleft induced hypotony.

A 26-year-old man with juvenile glaucoma developed persisting hypotonic retinopathy after trabeculotomy ab externo. An unintended cyclodialysis cleft at the site of the trabeculotomy was suspected, but visualization of the chamber angle was impossible due to a shallow anterior chamber. Seven months after the trabeculotomy the patient was treated with transconjunctival cryotherapy at the presumed localization of a cyclodialysis cleft. Eight days later an episode of acute ocular hypertension occurred, otherwise the postoperative course was uneventful with reversal of the hypotony and complete normalization of the visual acuity. The diagnostic and therapeutic problems of a hypotonous cyclodialysis cleft combined with a shallow anterior chamber are discussed.

Adult↗
PubMed1995

Retrobulbar anesthesia with and without adrenaline in extracapsular cataract surgery. A prospective, randomized, double-blind study.

Seventy-five patients with senile cataract underwent a planned extracapsular cataract extraction. They were randomly divided into two groups, receiving retrobulbar anesthesia (4 ml lidocaine 2% and 250 IU hyaluronidase) with or without adrenaline. Patients in the adrenaline group had the lowest mean intraocular pressure after the retrobulbar injection (p < 0.02) and they required a shorter time of digital bulbar massage to reduce tension before surgery (p < 0.01). They also appeared to have a deeper anterior chamber during the first part of surgery, although the difference was not statistically significant. The duration of postoperative analgesia was significantly prolonged in patients receiving adrenaline. Different mechanisms explaining the effects of adrenaline in retrobulbar anesthesia are discussed.

Adult↗
PubMed1994

[Primary intraocular lymphoma].

Primary intraocular lymphoma can arise as an isolated clinical entity or in combination with lymphomas in the central nervous system. The symptoms are usually floaters in the visual field and reduced visual acuity. The condition is commonly misdiagnosed as chronic uveitis in spite of unresponsiveness to corticosteroids. The authors discuss a case of primary intraocular lymphoma diagnosed in a 65 year old male patient. He had bilateral intraocular lesions in addition to two brain tumours. He went into complete remission after radiation therapy, but experienced later a recurrence in one eye. A course of chemotherapy using cytarabin (cytosine arabinoside) intravenously has kept the patient in remission for four months. The authors also discuss the diagnostic and therapeutic problems connected with this rare condition.

Aged↗
PubMed1993

Retrobulbar anesthesia with and without hyaluronidase in extracapsular cataract surgery. A prospective, randomized, double-blind study.

Eighty patients with senile cataract were subjected to a planned extracapsular cataract extraction (ECCE) with implantation of a posterior chamber intraocular lens. Retrobulbar anesthesia was administered by injection of 4 mg lidocaine 2% with adrenalin. In 40 patients 150 I.U. hyaluronidase (Kinetin) was added to the anesthesia. The hyaluronidase group had a significantly lower frequency of iris prolapse, and deeper anterior chamber, both before and after expression of the lens nucleus. Possible mechanisms explaining the beneficial effect of hyaluronidase in extracapsular cataract surgery are discussed.

Aged↗
PubMed1990

Repair of a cerebral artery aneurysm in a patient with persistent truncus arteriosus.

We describe the anesthetic management of a 19-year-old woman with persistent truncus arteriosus who presented for cerebral artery aneurysm clipping. The anatomy and pathophysiology of persistent truncus arteriosus are reviewed to provide a basis for the choice of anesthetic agents and monitoring devices in this patient. The hazards of induced hypotension in the patient with truncus arteriosus are also discussed.

Journal Article↗