Ulrik Christensen

Enhancing the signal-to-noise ratio in ophthalmic optical coherence tomography by image registration—method and clinical examples

Optical coherence tomography (OCT) has already proven an important clinical tool for imaging and diagnosing retinal diseases. Concerning the standard commercial ophthalmic OCT systems, speckle noise is a limiting factor with respect to resolving relevant retinal features. We demonstrate successful suppression of speckle noise from mutually aligning a series of in vivo OCT recordings obtained from the same retinal target using the Stratus system from Humphrey-Zeiss. Our registration technique is able to account for the axial movements experienced during recording as well as small transverse movements of the scan line from one scan to the next. The algorithm is based on a regularized shortest path formulation for a directed graph on a map formed by interimage (B-scan) correlations. The resulting image enhancement typically increases the contrast-to-noise ratio (CNR) with a factor of three or more and facilitates segmentation and quantitative characterization of pathologies. The method is currently successfully being applied by medical doctors in a number of specific retinal case studies.

Microsimulators in medical education: an overview

Four types of educational simulators are available for medical education: simple (part task) and complex microsimulators, and simple and complex macrosimulators (full-scale simulators). There has been a tendency to see full-scale simulators as the ideal solution for all educational simulation needs. However, each of the above groups has different strengths and weaknesses in achieving educational goals. Microsimulators are a complementary tool to full-scale macrosimulators. Their role in medical education will become increasingly important because it is now possible to make intelligent, autonomous microsimulators. Using a combination of microsimulators and macrosimulators will allow a wide range of cognitive and behavioral skills to be addressed. The development of microsimulators should—as soon as the realism is sufficient—focus on the intelligent, educational feedback in the debriefing. This challenge for microsimulators may become their greatest asset in medical education.

Prognosis of pseudophakic retinal detachment

Purpose: To compare preoperative and postoperative findings in phakic and pseudophakic patients operated on for rhegmatogenous retinal detachment (RD). Setting: Herlev University Hospital, Copenhagen, Denmark. Methods: This retrospective review comprised 120 pseudophakic patients and 280 phakic patients who had RD surgery during a 4‐year period. An identical scleral buckling procedure was used for primary surgery in both groups. Cataract surgery had been performed using extracapsular cataract extraction (ECCE) in most eyes; phacoemulsification was used in 67.5% of the pseudophakic eyes. The mean follow‐up was 13.5 months. Results: Pseudophakic patients with RDs presented with significantly worse preoperative visual acuity than phakic patients due to a higher frequency of total RDs and macula‐off RDs. Retinal breaks were found significantly less frequently and reoperations were performed with a higher frequency in pseudophakic patients than in phakic patients. At 6 months, no differences between pseudophakic and phakic patients were found. The overall anatomic reattachment rate was 94% and 96% in the 2 groups, and the visual outcome was also identical, with a visual acuity better than 0.4 in about 60% of patients. Conclusions: Pseudophakic patients presented with more extended RDs and with the macula detached more frequently. Retinal breaks were found less frequently. Despite these findings, the anatomic and visual prognosis of pseudophakic detachments was identical to that of phakic detachments.

The Sophus anaesthesia simulator v. 2.0. A Windows 95 control-center of a full-scale simulator.

The Sophus group was founded in Denmark in 1992 with the aims of doing research into human error in anaesthesiology. Development of a simulation-environment was seen as one of the tools for research and training. This article describes the PC user interface of the SOPHUS anaesthesia simulator, SOPHUS v. 2.0 for Windows 95, and the script language, SASL v. 1.2. The script language provides possibilities of making scenarios, which develop in different directions according to the treatment of the patient by means of IF/THEN-statements, loops etc.

Quantification of Metamorphopsia in Patients with Macular Hole

PURPOSE To describe a novel method for the evaluation of metamorphopsia within the central 10 degrees of the visual field in 55 patients with idiopathic macular hole. The test evaluates the interocular disparity between the two eyes in metamorphopsia. METHODS Semicircular test and reference stimuli of variable diameters were used in a binocular test that measured interocular size disparity between perceptually iseikonic stimuli in subjects with a unilateral macular hole. A group of 11 healthy subjects was used as the reference. RESULTS In 55 patients with a macular hole, interocular disparity demonstrated a mean value of 0.71 degrees with stimuli in the range 1.0 degrees to 2.5 degrees in diameter. This number declined to 0.41 degrees with stimuli in the range of 9.0 degrees to 10.0 degrees in diameter. Both hole diameter and eccentricity had a significant effect on mean disparity (P < 0.001). CONCLUSIONS The level of metamorphopsia declined as a function of eccentricity and affected the central 10 degrees of visual field. Macular hole size had an independent effect on interocular disparity. These results confirm reports that visuospatial distortion in the presence of macular hole is primarily the result of radial displacement of photoreceptors. (ClinicalTrials.gov number, NCT00302328.).

ResusSim 98—a PC advanced life support trainer

Advanced life support (ALS) requires several different skills and the recall of complex information. The personal computer is an ideal tool for the teaching of factual information. We have developed a computer programme that simulates a variety of cardiac arrest scenarios. Its aim is to communicate specialist knowledge to junior staff in a challenging and entertaining way. Each scenario has a real time ECG, clinical signs of the simulated patient, blood pressure, oxygen saturation and temperature. Arterial blood samples can be analysed and the medical record can be reviewed. Interventions available include defibrillation, intubation, fluid and drug therapy. Built-in variation means that repeating a scenario may lead to different patient behaviour. An important part of the programme is the intelligent debriefing of the user after each patient. Each action elicits a comment that is based upon the current European Resuscitation Council guidelines. This is then hyperlinked to an extensive help file that includes the text of the guidelines, diagrams, pictures and algorithms that aid the user in the learning of ALS skills in association with existing teaching programmes. ResusSim 98 runs under Windows 3.1, Windows 95/98 and Windows NT 4.0.

Reoperation for rhegmatogenous retinal detachment as quality indicator for disease management: a register study

To establish a quality indicator that could be used in optimizing treatment for rhegmatogenous retinal detachment (RRD).

Metamorphopsia Assessment before and after Vitrectomy for Macular Hole

PURPOSE To evaluate the degree of metamorphopsia in 42 patients before and 6 months after vitrectomy for idiopathic unilateral macular hole. METHODS Semicircular test and reference stimuli of variable diameters were applied in a binocular test that measured interocular size disparity in patients with unilateral macular hole. The test was applied 1 day before surgery and repeated after 6 months. RESULTS Before surgery, mean disparity was 0.34 degrees at 1 degrees visual field eccentricity declining to a plateau value of approximately 0.2 degrees between 3 degrees and 5 degrees of eccentricity. Six months after successful hole closure, interocular disparity was practically constant, with a median disparity below 0.1 and no significant effect of eccentricity. Baseline interocular disparities lower than 0.35 degrees at 1 degrees eccentricity were associated with nine EDTRS letters of better visual outcome compared with higher disparities (P < 0.001). CONCLUSIONS Metamorphopsia was consistently reduced after macular hole surgery, supporting that the intervention was successful in repositioning displaced photoreceptors toward their original location. Final best corrected visual acuity was related to the degree of preoperative disparity in spatial projection between receptive units with a shared perceptual projection in visual space in the two eyes. (ClinicalTrials.gov number, NCT00302328.).

Retinal thickening after successful surgery for macula-off retinal detachment.

Purpose: To study changes in retinal thickness after reattachment of the retina after scleral buckling surgery for rhegmatogenous retinal detachment. Methods: In this retrospective study, patients were classified into three subgroups according to preoperative macular status. Retinal thickness within 3 mm of the center was measured with optical coherence tomography. Results: Foveal retinal thickness at a mean of 2 years postoperatively was significantly increased in patients with preoperatively detached macula. Additionally retinal thickness in the fovea and postoperative visual acuity was positively correlated. Conclusions: Successful surgery for macula-off retinal detachment is associated with significant thickening of the neurosensory retina when examined with optical coherence tomography 6 months postoperatively.