PubMed Health⌕ Search

Biomedical subjects

W Konen

Publications and source records attributed to W Konen.

At least 19 recordsLinked to original sources
PubMed2006

An optical evaluation of the phenomenon of red out in neuroendoscopic surgery: what is the physical background?

BACKGROUND: The loss of visualization in neuroendoscopy due to intraoperative bleeding is called "red out". Although red out is a well-known problem during endoscopy, clear physical descriptions of this phenomenon are lacking. OBJECTIVE: The aim of this study was to investigate the optical properties of red out. In particular, the attenuation coefficient, comprising scattering, and absorption, of various blood/Ringer solutions was quantified and measured spectrally resolved. Small amounts of blood virtually preclude neuroendoscopic visualization. In blood/Ringer solutions with a dilution of 1:101, it was not possible to distinguish characters (font size 10, Arial) at a distance of 5 mm. We have concluded, from our physical investigations, that the problem of red out is dominated by scattering rather than by absorption. Accordingly, technical developments aimed at increasing information acquisition under red out conditions should be based on optical measurement concepts for scattering media.

Blood↗
PubMed2005

Application of a newly developed visual navigation system in humans. First results.

A visual navigation system (VN) was developed which uses intraoperatively stored endoscopic images together with their specific 3D-address. A special calibration enables one to recalculate the distortion of the endoscopic images. Several modules (e. g., landmark tracking, virtual back-movement) are offered to the neurosurgeon. The system was tested in 12 human subjects during neuroendoscopic interventions and worked without problems in nearly all cases. The possibilities of digital image navigation can be used especially for control of instrument movement in case of red-out situations or blurred vision. Many further developments of the VN system are possible in order to increase the safety of neuroendoscopic interventions.

Adolescent↗
PubMed2005

Consideration of ergonomic aspects in the development of a new endoscopic navigation system.

During the development of new navigation systems, the ergonomic aspects of the accompanying software are seldom taken into account. The VN system is a navigation system working with real and previously stored neuroendoscopic images. The latter enable the module to execute virtual back movement, e.g. in case of bleeding. Several other modules are offered. The aim of the study was the ergonomic analysis of different modules and their learning curves in cadaveric heads. The endoscope was navigated by the neurosurgeon while another person operated the computer. A total of 128 experiments were performed with two software versions. When the landmark tracking module was used, a real learning curve could be observed. By contrast, testing the measurement module did not produce a learning curve. A significant reduction of the time required by the three modules investigated could be observed with software version 2. The module for virtual back movement works best with a minimum time of 20 s for image storage. During machine-human interactions ergonomic software use is important, especially if operative procedures are performed.

Clinical Competence↗
PubMed2004

[Implant exposure after viscocanalostomy with reticulated hyaluronic acid (SK-GEL)].

BACKGROUND: Lately, the application of intrascleral implants has been increasingly discussed to improve success rates of nonpenetrating surgery for the treatment of open-angle glaucoma. PATIENTS AND METHODS: A 36-year-old male patient with medically uncontrolled pigmentary glaucoma underwent viscocanalostomy with intrascleral implantation of reticulated hyaluronic acid (SK-GEL) in his right eye. RESULTS: The immediate postoperative course was unremarkable with control of intraocular pressure without additional glaucoma medications. At first follow-up, 2 weeks post surgery, conjunctival dehiscence with partial extrusion and exposure of the reticulated hyaluronic acid implant was observed. Under topical tobramycin ointment a gradual limbal readaptation of the conjunctiva over the surface of the exposed parts of the implant with formation of a filtration bleb was noted. Therefore, surgical revision remained unnecessary. CONCLUSIONS: Implant exposure following nonpenetrating antiglaucomatous surgery is a specific complication, which can appear whenever intrascleral implants are used. Depending on the local situation nonsurgical treatment may be successful.

Adult↗
PubMed2003

[Combined deep sclerectomy and trabeculotomy in congenital glaucoma with complications].

BACKGROUND: Lately there has been growing interest in deep sclerectomy as a therapeutic approach for the management of congenital glaucoma.In theory, its pressure-lowering effect is independent of external filtration, which minimizes the risk of failure due to conjunctival or episcleral scarring. In patients who have failed to benefit from previous filtering procedures and have refractory congenital glaucoma,deep sclerectomy could become an alternative. PATIENTS AND METHODS: A 3-year-old girl with refractory congenital glaucoma underwent deep sclerectomy in her left eye. Intraoperatively, percolation through the trabeculodescemetic window was weak, so that the procedure was supplemented by a trabeculotomy. RESULTS: By now, throughout a follow-up period of 20 months, stabilisation of disc cupping and ocular axial length has been achieved without additional glaucoma surgery or medications. CONCLUSIONS: In patients with congenital glaucoma,the combination of deep sclerectomy with trabeculotomy may provide an additional therapeutic approach whenever the prospect of success appears to be limited with deep sclerectomy alone.

Child, Preschool↗
PubMed2003

A prospective randomised trial of viscocanalostomy with and without implantation of a reticulated hyaluronic acid implant (SKGEL) in open angle glaucoma.

AIM: To prospectively assess the efficacy and complications of viscocanalostomy with a reticulated hyaluronic acid implant (VSRHAI) versus standard viscocanalostomy in patients with medically uncontrolled open angle glaucoma. METHODS: A consecutive series of 40 patients (40 eyes) with uncontrolled open angle glaucoma underwent non-penetrating antiglaucomatous surgery. After the excision of the deep scleral flap they were randomly assigned to either a standard viscocanalostomy or additional implantation of a reticulated hyaluronic acid implant. Follow up visits were over a period of 12 months after surgery. RESULTS: The mean preoperative intraocular pressure (IOP) was 26.5 (SD 6.1) mm Hg for all patients enrolled. The mean IOP was 8.1 (SD 5.6) mm Hg 1 day after surgery for the viscocanalostomy group (p<0.001) and 12.0 (SD 5.2) mm Hg for the VSRHAI group (p<0.001). The postoperative IOP difference between the two groups was statistically significant (p = 0.03). The success rate, defined as an IOP lower than 22 mm Hg without medication, was 40% in both groups at 12 months postoperatively (p = 0.90). The number of postoperative complications was equally low for both groups. CONCLUSIONS: Both surgical procedures, viscocanalostomy and VSRHAI, provide comparable success rates over a 1 year follow up period. The specific intraoperative and postoperative complications of non-penetrating surgery were seen in our series, although the overall rate of postoperative complications proved equally low for both techniques.

Aged↗
PubMed2002

Ultrasound biomicroscopy and its value in predicting the long term outcome of viscocanalostomy.

AIMS: To examine whether the early postoperative morphology at the site of sclerectomy, as visualised by ultrasound biomicroscopy (UBM), is an indicator of the mechanisms that lower intraocular pressure (IOP) and/or predictors of the long term outcome of viscocanalostomy. METHODS: 15 eyes of 14 patients with medically uncontrolled open angle glaucoma and no history of surgery underwent viscocanalostomy according to Stegmann's technique. Ultrasound biomicroscopy was performed during the first month after surgery. The following parameters were assessed: dimensions of the intrascleral "lake," presence of a filtering bleb, presence of a subconjunctival cavity or a suprachoroidal hypoechoic area, and the thickness of the residual trabeculocorneal membrane. A complete ophthalmological examination was performed the day before and the day after surgery. Follow up visits were scheduled 1 week, 4 weeks, 6 months, and 12 months after surgery. RESULTS: At 1 year successful control of IOP (<20 mm Hg) was achieved without further manipulation or medication in six of 15 eyes. The size of the intrascleral "lake" (average 0.62 mm(3)) did not correlate with later IOP; however, a visible route under the scleral flap and accidental perforation of the trabeculocorneal membrane were associated with long term lowering of IOP. Normal thickness of the trabeculocorneal membrane (0.10-0.15 mm) was indicative of IOP control with and without medication. When UBM showed an early collapse of the intrascleral cavity, control of IOP was not achieved. Other UBM findings did not predict long term function. CONCLUSION: In accordance with previous studies, the authors found that UBM examination is a useful method to evaluate outflow mechanisms after glaucoma surgery. This study shows that UBM imaging of external filtration during the early postoperative period can be used to predict the success of viscocanalostomy. However, to establish conclusively what parameters of UBM predict successful viscocanalostomy a larger number of patients must be studied.

Adult↗
PubMed2001

Primary viscocanalostomy versus trabeculectomy in white patients with open-angle glaucoma: A randomized clinical trial.

PURPOSE: To compare viscocanalostomy, a nonpenetrating procedure for glaucoma treatment, with trabeculectomy. DESIGN: Randomized controlled trial. PARTICIPANTS: Twenty white subjects (20 eyes) with open-angle glaucoma with no history of surgery were enrolled. METHODS: Ten subjects were randomly assigned to viscocanalostomy according to Stegmann's technique and 10 subjects to a modified Cairns trabeculectomy. A complete ophthalmologic examination was performed the day before surgery and postoperatively. Further visits were scheduled monthly for 6 to 8 months after surgery. MAIN OUTCOME MEASURES: Success was defined as intraocular pressure (IOP) between 7 and 20 mmHg, with no medication. RESULTS: After a mean follow-up of 6 months (range, 6-8 months), success was obtained in 5 of 10 cases in the trabeculectomy group and in no case in the viscocanalostomy group. With Kaplan-Meier's method, subjects with viscocanalostomy showed shorter postoperative IOP-reduction periods than subjects undergoing trabeculectomy. CONCLUSIONS: According to the results of this short-term study, trabeculectomy was more effective than viscocanalostomy in lowering IOP in glaucomatous eyes of white patients.

Adult↗
PubMed2001

Multifocal intraocular lens implantation in pediatric cataract surgery.

OBJECTIVE: To evaluate implantation of a zonal-progressive multifocal intraocular lens (IOL) in children. STUDY DESIGN: Prospective, noncomparative, interventional case series. PARTICIPANTS: Thirty-five eyes of 26 pediatric patients aged 2 to 14 years with multifocal IOL implantation at one institution with more than 1 year of follow-up. INTERVENTIONS: Standard surgical procedure comprised an anterior capsulorrhexis, lens material aspiration via two side-port incisions, temporal tunnel incision, and multifocal IOL (SA40-N; Allergan, Irvine, CA) implantation in all eyes. In 24 eyes (68%), a 5-mm posterior capsulorrhexis was created with forceps, followed by an anterior vitrectomy in 19 of those eyes (54%). RESULTS: Twenty-six patients (35 eyes) had an average follow-up of 27.4 +/- 12.7 months (range, 12-58 months). At last follow-up, best-corrected distance visual acuity improved significantly (P = 0.001), 71% of eyes with a visual acuity of 20/40 or better and 31% of eyes with a visual acuity of 20/25 or better. In the 9 bilateral cases, spectacle dependency was moderate, with only 2 children (22%) reporting the permanent use of an additional near correction. The remaining children were either using distance-correction only (4 patients; 44%) or no glasses at all (3 patients; 33%). Stereopsis also improved significantly after multifocal IOL implantation (P = 0.01). Sixteen eyes (46%) experienced obscuration of the entrance pupil that required intervention, with 10 requiring a second intraocular surgery. Four eyes required an anterior membranectomy for persistent fibrinous membrane. Intraocular lens decentration requiring surgical intervention developed in six eyes. CONCLUSIONS: Multifocal IOL implantation is a viable alternative to monofocal pseudophakia in this age group.

Adolescent↗
PubMed2001

Massive anterior capsule shrinkage after plate-haptic silicone lens implantation in uveitis.

Two patients, both with bilateral uveitis, had synechiolysis, continuous curvilinear capsulorhexis (CCC), phacoemulsification, and in-the-bag implantation of a foldable single-piece plate-haptic silicone intraocular lens (IOL) in 1 eye. Several weeks postoperatively, massive anterior capsule shrinkage with obstruction of the visual axis occurred in both patients. Surgical revision was performed in both eyes. Both patients had CCC and phacoemulsification and confirmed in-the-bag acrylic IOL implantation in the second eye months after surgery in the first eye. Follow-up examinations showed no significant shrinkage of the anterior capsule opening in any eye. In patients with uveitis, intraoperative lens epithelial cell removal, creation of a large CCC, and careful selection of IOL style and material may prevent occlusion of the anterior capsule opening.

Aged↗
PubMed2001

[Does the dissection depth and thickness of the deep scleral flap affect intraocular pressure after viscocanalostomy? A clinico-pathologic correlation].

BACKGROUND: Non-perforating glaucoma surgery preserves the integrity of the trabecular meshwork in order to avoid postoperative hypotony. The purpose of our study was to investigate whether the morphologic variability of the excised deep scleral flap influences the postoperative intraocular pressure (IOP) after viscocanalostomy. METHODS: Light-microscopy of the deep scleral flap was performed in 17 patients who had undergone viscocanalstomy. Morphologic parameters (thickness and dissection level of the deep scleral flap) were correlated with the postoperative IOP. RESULTS: The mean thickness of the deep scleral flap was 309 +/- 95 microns; the dissection level was too deep in 5 cases (trabecular tissue excised) and too high in 6 cases (no signs of Schlemm's canal). The max. preop. IOP was 36.2 +/- 8.5 mmHg and came down to 10.6 +/- 5.7 mmHg at day 1 postop. and 12.4 +/- 4.9 mmHg at day 3/4 postop. At a median follow-up of 6 months IOP was 21.7 +/- 5.5 mmHg. A significant correlation between postop. IOP and the morphology of the deep scleral flap could not be demonstrated. CONCLUSIONS: Variations of the thickness and depth of the deep scleral flap showed little influence on the initial IOP level following viscocanalostomy. Other factors, f.e. the suturing of the external flap or invisible microruptures of the trabecular meshwork, could be of importance for the early postoperative IOP.

Adult↗
PubMed2001

[Painless acanthamoeba keratitis].

BACKGROUND: Acanthamoeba keratitis is a severe, painful corneal infection found in contact lens wearers. The entity can easily be confused with herpetic or fungal keratitis, especially if no ocular pain is reported. HISTORY AND SIGNS: A 32-year old myopic female presented a unilateral keratitis of unknown etiology since 3 weeks. Administration of topical antiviral substances and corticosteroids led only to temporary improvement of the condition. The patient complained of photophobia but not of ocular pain. The affected eye showed corneal edema, central stromal thickening, descemet's striae as well as fibrin deposits on the corneal endothelium and in the anterior chamber. DIAGNOSIS: An aqueous specimen was negative for a viral infection. A culture for bacteria was negative. Staphylococci were cultured from corneal scrapings and Enterococci from the contact lens solution. Another corneal scraping revealed Acanthamoeba class II (6 weeks after the onset of symptoms). CLINICAL COURSE: Under treatment with propamidine, polymyxin b, neomycin, gramicidin and polyhexidine (topical) as well as fluconazole/ketoconazole (systemic) the diameter of the annular infiltrate, which had developed decreased, but the infiltrate persisted. In the further course, the infiltrate persisted while the amount of fibrin in the anterior chamber increased. Penetrating keratoplasty was performed. Histologic examination of the host corneal tissue revealed massive infiltration with Acanthamoeba. CONCLUSIONS: Severe pain and history of wearing contact lenses are features suggestive of Acanthamoeba keratitis. The patient presented here had a history of contact lens wear, but no ocular pain was reported. The characteristic annular infiltrate had a late onset. Bacterial superinfection could not be ruled out. Therapeutic penetrating keratoplasty had to be performed as the condition deteriorated inspite of intensive chemotherapy. With penetrating keratoplasty a good visual acuity could be regained.

Acanthamoeba Keratitis↗
PubMed2000

Variability of dissection depth in deep sclerectomy: morphological analysis of the deep scleral flap.

BACKGROUND: Deep sclerectomy and similar procedures including a deroofing of Schlemm's canal are meeting with increasing interest owing to the limited risk profile of non-perforating glaucoma surgery. The aim of our study was to investigate how often the outer wall of Schlemm's canal or parts of the trabecular meshwork were incorporated in the excised tissue on deep scleral flap dissection by an experienced glaucoma surgeon. METHODS: The excised deep scleral flap was prepared for light microscopy after performing deep sclerectomy in 7 children and 22 adult patients suffering from glaucoma. Meridional serial sections were checked for the presence of fragments of trabecular beams and collector channels and parts of the endothelial wall of Schlemm's canal. Morphology was compared with the intraoperative appearance of the operated tissue. RESULTS: In 15 patients (52%) the deep scleral flap contained at least some tissue from the outer wall of Schlemm's canal; in 5 of these 15 patients noticeable remnants of the juxtacanalicular trabecular meshwork were also found, although only in one patient was this obvious during surgery. In 14 patients (48%) no evidence of the deroofing of Schlemm's canal was found within the excised deep scleral flap, although intraoperatively the dissection seemed to have been too superficial in only 5 patients. CONCLUSION: Even when performed by an experienced glaucoma surgeon, deep sclerectomy produces biopsy material of remarkable morphological variability that does not always correspond to the intraoperative appearance of the site of operation. More than in conventional trabeculectomy this variability may be of importance for the outcome of surgery.

Adult↗
PubMed2000

Complications of endocapsular tension ring implantation in a child with Marfan's syndrome.

A 4-year-old boy with Marfan's syndrome had severe visual impairment after subluxation of the crystalline lens with bisection of the pupil. In the first eye, a capsular tension ring and an intraocular lens (IOL) were uneventfully placed in the capsular bag after phacoemulsification. During implantation of the endocapsular tension ring in the second eye, an inadvertent tear of the anterior capsule occurred, and the posterior chamber IOL was placed in the sulcus. In both eyes, severe lens epithelial proliferation with secondary IOL decentration developed postoperatively. Several surgical revisions were necessary to keep the IOL within the optical axis. In the eye with the sulcus-implanted IOL, the endocapsular tension ring was markedly decentered.

Capsulorhexis↗
PubMed2000

Intracorneal inclusion of high-molecular-weight sodium hyaluronate following detachment of Descemet's membrane during viscocanalostomy.

PURPOSE: Viscocanalostomy in accordance with Stegmann's technique is a new surgical option in the treatment of glaucoma. There are few reports available describing the specific complications of viscocanalostomy. We report a case of intracorneal inclusion of high-molecular-weight sodium hyaluronate following viscocanalostomy. CASE REPORT: A 66-year-old man with uncontrolled primary open angle glaucoma of his right eye and a history of argon laser trabeculoplasty underwent viscocanalostomy in accordance with Stegmann's technique. During the filling of Schlemm's canal, a limited lysis of Descemet's membrane advanced centrally in the clear cornea adjacent to the site of canalostomy forming an intracorneal bubble of high-molecular-weight sodium hyaluronate. Postsurgical slit-lamp biomicroscopy showed an intracorneal clear bubble within the corneal periphery without evidence of adjacent corneal edema and with no contact between the corneal endothelium and the iris. Follow-up examinations determined that the appearance of the corneal inclusion, essentially, was unchanged, with only a slight tendency of resorption. No signs of corneal scarring or endothelial decompensation could be noted. CONCLUSION: To date, we could not determine a significant corneal damage in conjunction with the described complication. However, it is difficult to predict the long-term clinical course of our patient. Corneal decompensation as a result of possible endothelial toxicity of high-molecular weight sodium hyaluronate as well as spontaneous absorption seem possible.

Aged↗
PubMed2000

Virtual image navigation: a new method to control intraoperative bleeding in neuroendoscopic surgery. Technical note.

In this neuroendoscopic study the authors tested the newly developed "red-out module" of their visual navigation system that enables the neurosurgeon to achieve hemostasis if total visualization is lost due to hemorrhage ("red out") within the visual field. An optical position measurement system connected to the endoscope guarantees that digitized endoscopic images are coupled with the accurate endoscopic position. Computerized images are simultaneously stored with their respective position data, and this creates a virtual anatomical landscape. The system was tested in in vivo bleeding conditions in a rat model. Artificial endoscopic cavities were created in the inguinal, pelvic, and jugular regions in rats to imitate the conditions of the human ventricular system. Two experimental settings were tested: Technique I, in which a computer landmark has been previously determined at the point where the vessel will be lesioned; and Technique II, in which a landmark has been previously set in the surrounding area of the vessel. Immediately after hemorrhage obscures the visual field (red out), the computer automatically displays the virtual images on a separate monitor. The previously set landmarks and the graphic overlay of the coagulation fiber enable the surgeon to navigate within the operative field based on the virtual images and to perform coagulation at the site of the lesion. A total of 175 vessels were coagulated: 43 arteries and 132 veins. In using Technique I, 130 (90.9%) of 143 vessels and in using Technique II, 26 (81.2%) of 32 arteries were successfully coagulated. The authors' data revealed that virtual image guidance has the potential to be a helpful tool in neuroendoscopy.

Animals↗