Calibration of histological retina specimens after fixation in Margo's solution and paraffin embedding to in-vivo dimensions, using photography and optical coherence tomography.

BACKGROUND: The extent of retinal tissue deformation by histological processing needs to be separately measured for every workup protocol. This work presents a simple approach for its quantitative assessment, and shows lateral and axial scaling factors for a common protocol. We calibrated histological measurements by in-vivo photographic and optical coherence tomographic (OCT) measurements, using retinal photocoagulation lesions as calibration markers. METHODS: We evaluated four rabbit eyes that were examined histologically after fixation in Margo's solution (1 % paraformaldehyde:1.25 % glutaraldehyde), isopropanol dehydration, paraffin embedding and hematoxylin and eosin staining. Distances between 51 pairs of laser lesions were compared in photographs and on histological slides. Retinal thickness measurements were performed at 15 anatomically defined sites in these eyes, and related to anatomically matched OCT thickness measurements of six different rabbit eyes. RESULTS: We found that the ratio of histological over photographic lesion distances was 1.17 (95 % CI 1.13-1.22), indicating 17 % lateral retinal stretching or expansion by the processing. Thickness measurements in histology were 65.6 % of the in-vivo thickness as measured in OCT, indicating 1/3 axial tissue compression or shrinkage. CONCLUSIONS: We provide an analysis of retinal tissue deformation after fixation in Margo's solution and paraffin embedding. In spite of protocol optimization for reduced tissue deformation, the workup caused 1/3 axial compression/shrinkage and 17 % lateral elongation, which was unexpected. We show a simple way how to calibrate retina specimens by fundus photography and OCT, two methods that are readily available to most ophthalmologists. Our findings underline the necessity to calibrate specimens prior to morphometry.

Photocoagulation in rabbits: optical coherence tomographic lesion classification, wound healing reaction, and retinal temperatures.

BACKGROUND AND OBJECTIVE: The rabbit is the most common animal model to study retinal photocoagulation lesions. We present a classification of retinal lesions from rabbits, that is based on optical coherence tomographic (OCT) findings, temperature data, and OCT-follow-up data over 3 months. MATERIALS AND METHODS: Four hundred eighty-six photocoagulation lesions (modified Zeiss Visulas® 532 nm CW laser, lesion diameter 133 µm, exposure duration 200 milliseconds or variable, power variable) were analyzed from six eyes of three chinchilla gray rabbits. During the irradiation of each lesion, we used an optoacoustics-based method to measure the retinal temperature profile. Two hours, 1 week, 1 month, and 3 months after the treatment, we obtained fundus color and OCT (Spectralis®) images of each lesion. We classified the lesions according to their OCT morphology and correlated the findings to ophthalmoscopic and OCT lesion diameters, and temperatures. RESULTS: Besides an undetectable lesion class 0, we discerned subthreshold lesions that were invisible on the fundus but detectable in OCT (classes 1 and 2), very mild lesions that were partly visible on the fundus (class 3), and 3 classes of suprathreshold lesions. OCT greatest linear diameters (GLDs) were larger than ophthalmoscopic lesion diameters, both increased for increasing classes, and GLDs decreased over 3 months within each class. Mean peak end temperatures for 200 milliseconds lesions ranged from 61°C in class 2 to 80°C in class 6. CONCLUSION: The seven step rabbit lesion classifier is distinct from a previously published human lesion classifier. Threshold lesions are generated at comparable temperatures in rabbits and humans, while more intense lesions are created at lower temperatures in rabbits. The OCT lesion classifier could replace routine histology in some studies, and the presented data may be used to estimate lesion end temperatures from OCT images.

First experience with the BioSTAR-device for various applications in pediatric patients with congenital heart disease.

BACKGROUND: Interventional closure of atrial septal defects (ASD) and surgical tunnel fenestrations in Fontan patients has become the procedure of choice for many years. Recently, the BioSTAR Occluder, a modification of the Starflex device with a resorbable matrix has become available. PATIENTS: Ten Biostar devices were implanted in nine children with interatrial septal defects, one within a fontan baffle, eight with secundum atrial septal defects. The age of the patients ranged from 11 months to 17 years, the body weight ranged from 12.9-78 kg. RESULTS: 10 BioSTAR devices were implanted in nine patients. In one patient, two BioSTAR devices were used to occlude multiple defects within the oval fossa. All defects were successfully and uneventfully occluded. Mean procedure time was 56 (range 28-125). Mean fluoroscopy time was 4.8 (range 1.1 to 13.0) min. None of the nine patients showed residual shunts after device implantation. After 30 days no shunt was seen in the control transthoracic echocardiography. No adverse effects like allergic reactions, tachyarrhythmia or thrombembolic events occurred in any of the patients. CONCLUSION: The BioSTAR closure device is a safe and effective device for the closure of a variety of interatrial shunts in children including multifenestrated interatrial defects and fontan fenestrations, however, possible long term consequences (e.g., fractures, recurrent shunts after scaffold degradation) remain to be studied.

Long-term biocompatibility of a corrodible peripheral iron stent in the porcine descending aorta.

Currently there are no biodegradable stents available for treatment of vascular obstructions in patients with congenital heart defects. This study was performed to evaluate the safety of a corrodible stent produced from pure iron in a peripheral stent design (6-12mm diameter) in a slotted tube design similar to a commercially available 316-L stent which served as control. Both stents were implanted into the descending aorta of 29 minipigs with an overstretch injury without technical problems. Two animals died after the implantation not related to the iron stent. The remaining 27 minipigs were followed for 1-360 days. Histomorphometry and quantitative angiography showed no difference with regard to the amount of neointimal proliferation between 316-L and iron stents. Histopathological examination of heart, lung, spleen, liver, kidney and para-aortic lymphatic nodes demonstrated no signs of iron overload or iron-related organ toxicity. Adjacent to the iron stent struts, there was no evidence for local toxicity due to corrosion products. We conclude that iron is a suitable metal for the production of a large-size degradable stent with no local or systemic toxicity. A faster degradation rate, however, is desirable and further studies have to focus on the modification of the composition and design of the stent to expedite the degradation process.

Temperature-Controlled Retinal Photocoagulation Reliably Generates Uniform Subvisible, Mild, or Moderate Lesions.

PURPOSE: Conventional retinal photocoagulation produces irregular lesions and does not allow reliable control of ophthalmoscopically invisible lesions. We applied automatically controlled retinal photocoagulation, which allows to apply uniform lesions without titration, and aimed at five different predictable lesion intensities in a study on rabbit eyes. METHODS: A conventional 532-nm photocoagulation laser was used in combination with a pulsed probe laser. They facilitated real-time fundus temperature measurements and automatic exposure time control for different predefined time/temperature dependent characteristics (TTC). We applied 225 control lesions (exposure time 200 ms) and 794 TTC lesions (5 intensities, exposure times 7-800 ms) in six rabbit eyes with variable laser power (20-66.4 mW). Starting after 2 hours, we examined fundus color and optical coherence tomographic (OCT) images over 3 months and classified lesion morphologies according to a seven-stage OCT classifier. RESULTS: Visibility rates in funduscopy (OCT) after 2 hours were 17% (68%) for TTC intensity group 1, 38% (90%) for TTC group 2 and greater than 94% (>98%) for all consecutive groups. TTC groups 1 through 4 correlated to increasing morphological lesion intensities and increasing median funduscopic and OCT diameters. Group 5 lesions were as large as, but more intense than group 4 lesions. CONCLUSIONS: Automatic, temperature controlled photocoagulation allows to apply predictable subvisible, mild, or moderate lesions without manual power titration. TRANSLATIONAL RELEVANCE: The technique will facilitate standardized, automatically controlled low and early treatment of diabetic retinopathy study (ETDRS) intensity photocoagulation independently of the treating physician, the treated eye and lesion location.

Correlation with OCT and histology of photocoagulation lesions in patients and rabbits.

PURPOSE: To examine spectral domain optical coherence tomographic (OCT) and histological images from comparable retinal photocoagulation lesions in rabbits, and to correlate these images with comparable OCT images from patients. METHODS: 508 rabbit lesions were examined by HE-stained paraffin histology. 1019 rabbit lesions versus 236 patient lesions were examined by OCT, all at the time-points 1 hr, 1 week and 4 weeks after photocoagulation. We analysed 100 µm lesions (in humans) and 133 µm lesions (in rabbits) of 200 ms exposures at powers titrated from the histological threshold up to intense damage. Lesions were matched according to morphological criteria. RESULTS: Dome-shaped layer alterations, retinal infiltration by round, pigmented cells, outer nuclear layer interruption, and eventually full thickness retinal coagulation are detectable in histology and OCT. Horizontal damage extensions are found 1½ times larger in OCT. More intense irradiation was necessary to induce comparable layer affection in rabbit OCT as in histology. Restoration of the inner retinal layers is only shown in the OCT images. Comparable primary lesions caused more pronounced OCT changes in patients than in rabbits during healing. CONCLUSIONS: Optical coherence tomographic images indicate different tissue changes than histologic images. After photocoagulation, they show wider horizontal damage diameters, but underestimate axial damage particularly during healing. Conclusions on retinal restoration should not be drawn from OCT findings alone. Retinal recovery after comparable initial lesions appears to be more complete in rabbit than in patient OCTs.

Open heart surgery for a very-low-weight (660 g) premature infant.

An intracardiac calcified thrombus in a premature infant weighing only 660 was successfully removed using normothermic caval inflow occlusion. This technique avoids the use of a heart-lung machine with its deleterious effects for this specific group of patients. In addition, closure of the persistent ductus arteriosus by ligation was accomplished. Because the authors see increasing numbers of preterm neonates who need intensive care management, their experience may be helpful for those dealing with this group of patients.

Implantation of stents for treatment of recurrent and native coarctation in children weighing less than 20 kilograms.

We report our experience with implantation of stents for treatment of recurrent and native aortic coarctation in children weighing less than 20 kilograms. We treated 9 such patients between March, 2003, and January, 2006. In 2 patients, the coarctation had not previously been treated, while in 7 it had recurred after surgery. The patients had a median weight of 14 kilograms, with a range from 5.5 to 19 kilograms. Balloon dilation was needed in 1 patient before the stent was implanted. We used Palmaz Genesis XD stents in 7 patients, these having lengths from 19 to 29 millimetres, 1 Palmaz Genesis 124P stent, and 1 peripheral JoStent with a diameter of 6 to 12 millimetres. Implantation was effective in all patients. Immediately after implantation, the mean peak systolic gradient decreased from 30 millimetres of mercury, the range having been 15 to 50 mm, to 3 millimetres of mercury, with the final range from zero to 10 mm. There were no complications, with no observations of aneurysms, dissections, or dislocated stents. In 1 patient, the peripheral pulse was weak secondary to arterial access, but treatment with Heparin led to complete resolution. It was necessary to re-dilate the stent in another patient, while 2 others are scheduled for redilation because of growth-related restenosis. Our findings suggest that implantation of stents can produce excellent relief of the gradient produced by recurrent or native coarctation. The process is safe and effective in patients weighing less than 20 kilograms.