Intravitreal triamcinolone staining observation of residual undetached cortical vitreous after posterior vitreous detachment.

AIMS: To study the pattern of residual undetached cortical vitreous (RCV) after posterior vitreous detachment (PVD) in eyes with rhegmatogenous retinal detachment (RRD) and to examine the relationship between RCV and the development of epiretinal membrane (ERM). METHODS: A prospective study was conducted in 33 consecutive patients with clinically evident PVD who underwent pars plana vitrectomy for RRD. During vitrectomy, triamcinolone acetonide (0.2 cm(3), 10 mg/cm(3)) was applied to stain the RCV. The pattern of the staining were recorded. The formation of postoperative ERM was correlated with the staining pattern of RCV. Each case was followed for at least 6 months. RESULTS: In all, 23 of the 33 patients had RCV of variable size, with a single stain patch observed in 13 patients and multiple patches in seven patients. Large circumferential areas of staining at the mid-periphery were noted in three patients. A total of 10 cases had staining over the fovea and five patients had staining over the disc. ERM developed in seven patients during follow-up. None corresponded to RCV. CONCLUSION: RCV is common in eyes with PVD and RRD. The macula and disc area are the most frequent locations for these vitreous islands. The relationship between RCV and ERM remains to be investigated.

Modeling uncertainty reasoning with possibilistic Petri nets.

Manipulation of perceptions is a remarkable human capability in a wide variety of physical and mental tasks under fuzzy or uncertain surroundings. Possibilistic reasoning can be treated as a mechanism that mimics human inference mechanisms with uncertain information. Petri nets are a graphical and mathematical modeling tool with powerful modeling and analytical ability. The focus of this paper is on the integration of Petri nets with possibilistic reasoning to reap the benefits of both formalisms. This integration leads to a possibilistic Petri nets model (PPN) with the following features. A possibilistic token carries information to describe an object and its corresponding possibility and necessity measures. Possibilistic transitions are classified into four types: inference transitions, duplication transitions, aggregation transitions, and aggregation-duplication transitions. A reasoning algorithm, based on possibilistic Petri nets, is also presented to improve the efficiency of possibilistic reasoning and an example related to diagnosis of cracks in reinforced concrete structures is used to illustrate the proposed approach.

A fuzzy Petri net-based expert system and its application to damage assessment of bridges.

In this paper, a fuzzy Petri net approach to modeling fuzzy rule-based reasoning is proposed to bring together the possibilistic entailment and the fuzzy reasoning to handle uncertain and imprecise information. The three key components in our fuzzy rule-based reasoning-fuzzy propositions, truth-qualified fuzzy rules, and truth-qualified fuzzy facts-can be formulated as fuzzy places, uncertain transitions, and uncertain fuzzy tokens, respectively. Four types of uncertain transitions-inference, aggregation, duplication, and aggregation-duplication transitions-are introduced to fulfil the mechanism of fuzzy rule-based reasoning. A framework of integrated expert systems based on our fuzzy Petri net, called fuzzy Petri net-based expert system (FPNES), is implemented in Java. Major features of FPNES include knowledge representation through the use of hierarchical fuzzy Petri nets, a reasoning mechanism based on fuzzy Petri nets, and transformation of modularized fuzzy rule bases into hierarchical fuzzy Petri nets. An application to the damage assessment of the Da-Shi bridge in Taiwan is used as an illustrative example of FPNES.

DCT-based motion estimation.

We propose novel discrete cosine transform (DCT) pseudophase techniques to estimate shift/delay between two one-dimensional(1-D) signals directly from their DCT coefficients by computing the pseudophase shift hidden in DCT and then employing the sinusoidal orthogonal principles, applicable to signal delay estimation remote sensing. Under the two-dimensional (2-D) translational motion model, we further extend the pseudophase techniques to the DCT-based motion estimation (DXT-ME) algorithm for 2-D signals/images. The DXT-ME algorithm has certain advantages over the commonly used full search block-matching approach (BKM-ME) for application to video coding despite certain limitations. In addition to its robustness in a noisy environment and low computational complexity, O(M(2)) for an MxM search range in comparison to the O(N(2) . M(2)) complexity of BKM-ME for an NxN block, its ability to estimate motion completely in DCT domain makes possible the fully DCT-based motion-compensated video coder structure, which has only one major component in the feedback loop instead of three as in the conventional hybrid video coder design, and thus results in a higher system throughput. Furthermore, combination of the DCT and motion estimation units can provide space for further optimization of the overall coder. In addition, the DXT-ME algorithm has solely highly parallel local operations and this property makes feasible parallel implementation suitable for very large scale integration (VLSI) design. Simulation on a number of video sequences is presented with comparison to BKM-ME and other fast block search algorithms for video coding applications even though DXT-ME is completely different from any block search algorithms.

Wavelet-based multiresolution local tomography.

We develop an algorithm to reconstruct the wavelet coefficients of an image from the Radon transform data. The proposed method uses the properties of wavelets to localize the Radon transform and can be used to reconstruct a local region of the cross section of a body, using almost completely local data that significantly reduces the amount of exposure and computations in X-ray tomography. The property that distinguishes our algorithm from the previous algorithms is based on the observation that for some wavelet bases with sufficiently many vanishing moments, the ramp-filtered version of the scaling function as well as the wavelet function has extremely rapid decay. We show that the variance of the elements of the null-space is negligible in the locally reconstructed image. Also, we find an upper bound for the reconstruction error in terms of the amount of data used in the algorithm. To reconstruct a local region 16 pixels in radius in a 256x256 image, we require 22% of full exposure data.

Inhibition of retinal pigment epithelial cell-induced tractional retinal detachment by disintegrins, a group of Arg-Gly-Asp-containing peptides from viper venom.

PURPOSE: Integrin-mediated extracellular matrix (ECM) attachment plays an important role in vitreous contraction of retinal pigment epithelial (RPE) cells. Disintegrins, a group of Arg-Gly-Asp (RGD)-containing peptides from viper venom, are potential anti-adhesion agents that interfere with integrin-ECM binding. This study was performed to determine whether disintegrins were effective in inhibiting RPE cell-induced matrix attachment in vitro and tractional retinal detachment in a rabbit model in vivo. METHODS: Two disintegrins, echistatin from viper Echis carinatus and flavoridin from Trimeresurus flavoviridis, were used. The expression of integrins on the surface of bovine and rabbit RPE cells was examined by indirect immunofluorescent stain with specific anti-integrin monoclonal antibodies. The inhibitory effect of disintegrins on RPE cell-mediated ECM attachment and vitreous contraction was evaluated with cell adhesion and vitreous contraction assays. In the in vivo model, rabbit eyes were injected intravitreously with either homologous rabbit RPE cells alone or together with disintegrins to induce tractional retinal detachment. The cytotoxic effect of disintegrins was examined with a cell proliferation assay using the alamar blue method. Retinal toxicity of disintegrins was evaluated with electroretinograms and histologic examination of the rabbit eyes. RESULTS: Bovine and rabbit RPE cells showed the positive staining for the integrins alpha 2 beta 1 and alpha 5 beta 1 on cell surface. Disintegrins, echistatin, and flavoridin inhibited RPE cell attachment to the ECM. The potency of disintegrins was 150 to 300 times higher than that of Gly-Arg-Gly-Asp-Ser (GRGDS) peptide. The disintegrins also inhibited RPE cell-induced vitreous contraction in a dose-dependent manner, whereas the GRGDS peptide had no effect. In the in vivo experiment, echistatin (50 microgram/ml) or flavoridin (80 microgram/ml) significantly inhibited RPE cell-induced tractional retinal detachment compared with the control group at week 2 (P< 0.05) and week 4 (P< 0.01) after surgery. Disintegrins were nontoxic to RPE cells and rabbit retina as evaluated by cytotoxicity tests, electroretinograms, and histologic examinations. CONCLUSIONS: The disintegrins were effective in inhibiting RPE cell attachment to the ECM and vitreous contraction in vitro. They also were effective in suppressing RPE cell-induced tractional retinal detachment in the rabbit eyes. They were nontoxic. Disintegrins and their analogs might be potential anti-adhesion therapeutic agents in the treatment of proliferative vitreoretinopathy.

Inhibition of cell-induced vitreous contraction by synthetic peptide derived from the collagen receptor binding sequence.

Cell-mediated tractional retinal detachment (TRD) is the end result of various intraocular proliferative disorders. Interactions between cells and extracellular matrix via cellular surface receptors, integrins, play an important role. Anti-adhesion therapy has been suggested as a promising way to treat the integrin-dependent pathological events. We tested three synthetic peptides, Gly-Arg-Gly-Asp-Ser (GRGDS), derived from the fibronectin receptor binding domain; Try-Ile-Gly-Ser-Arg (YIGSR), from the laminin receptor binding domain, and Ala-Asp-Gly-Glu-Ala (ADGEA), from the collagen receptor binding domain, to evaluate their inhibitory effect on cell-mediated matrix attachment and vitreous contraction in vitro, and on cell-induced TRD in rabbit eyes in vivo. Indirect immunofluorescent stain demonstrated both bovine retinal pigment epithelial (RPE) cells and rabbit dermal fibroblasts expressed the alpha 2 beta 1, alpha 5 beta 1 and alpha 6 beta 1 integrins, the collagen, fibronectin, and laminin receptors, respectively. GRGDS exhibited a broad spectrum of inhibitory activity on RPE cell attachment to extracellular matrices. YIGSR specifically inhibited RPE cell attachment to laminin, whereas ADGEA inhibited RPE cell attachment to collagen type I and IV. ADGEA inhibited RPE cell-induced vitreous contraction in a dose-dependent manner, whereas GRGDS and YIGSR had no effect. ADGEA (1250 micrograms/mL) delayed the development of TRD but did not prevent it. ADGEA was nontoxic to cells and retina, as demonstrated by cytotoxicity tests and histological examination. The synthetic peptide, ADGEA, and its analogs may be potential candidates for the treatment of cell-mediated collagenous contraction in the ocular tissues.

Vitreous fluorophotometry in patients with crystalline retinopathy.

Patients with various stages of crystalline retinopathy were examined with vitreous fluorophotometry and the results were compared with those of normal subjects. Two patients with glistening crystals without pigment clumps, together with atrophy of the retinal pigment epithelium in the posterior pole, showed a normal inward permeability of fluorescein. Three patients with a large area of choriocapillaris atrophy in the posterior pole, in addition to atrophy of retinal pigment epithelium, demonstrated an increase in the rate of inward fluorescein penetration. Three patients with extensive areas of choriocapillaris atrophy throughout the fundus also revealed an increased posterior vitreous penetration ratio.

Parental upset associated with participation in induction of anaesthesia in children.

To evaluate the magnitude of parental upset associated with (1) the features of induction most upsetting to parents; (2) the characteristics of parents most likely to become upset; and (3) the accuracy of the anaesthetist's perception of the magnitude of parental upset. The parents (101 mothers and 43 fathers) of 103 children scheduled for elective outpatient surgery requiring general anaesthesia with induction by mask were asked on admission to participate in this study. Parents and children were educated about anaesthesia and surgery according to unit protocols. Immediately after induction of anaesthesia, the parents were asked to complete a demographic information sheet and the Parental Reactions to Anesthesia Induction Questionnaire. Responses were analyzed using descriptive statistics and content analysis. The most upsetting factors for both mothers and fathers in order of significance were: (1) separation from the child after induction of anaesthesia; (2) watching/feeling the child go limp during induction; and (3) seeing the child upset before induction. Characteristics of parents most likely to become upset revealed positive correlations between the amount of upset between mothers and fathers, mothers of an only child, and mothers or fathers who were health care workers (P < 0.05). The anaesthetist's perception of upset correlated with maternal (P < 0.05), but not parental, self-assessment of upset. We conclude that selected factors of parental participation are upsetting for the parents and that recognizing the factors associated with parental upset may enable operating room personnel to minimize these negative consequences.

Indocyanine green videoangiography of choroidal neovascular membrane in age-related macular degeneration.

Fluorescein angiography is the traditional tool for the detection of choroidal neovascularization of age-related macular degeneration. However, some limitations exist which impede its efficacy in the detection of subretinal neovascularization. Indocyanine green videoangiography is a recently developed technique which differs from fluorescein angiography in many ways. We performed indocyanine green videoangiography in 18 eyes with occult choroidal neovascularization, demonstrated by fluorescein angiography. Sixteen of the 18 eyes showed an abnormal vessel loop in the early phase of indocyanine green videoangiography. In the late phase, all 18 eyes had abnormal dye retention around the suspected neovascular area; however, only 12 eyes revealed a distinct border of neovascularization. No side effects, such as nausea, vomiting, or allergic reactions, were noted in our patients. Advantages and drawbacks of indocyanine green videoangiography in comparison with fluorescein angiography are discussed.

Use of high-density vitreous substitutes in the removal of posteriorly dislocated lenses or intraocular lenses.

We successfully used high-density vitreous substitutes to remove four dislocated crystalline lenses and three dislocated intraocular lenses (IOLs) from the vitreous cavity. Fluorosilicone oil (300 cs) was used to remove the four lenses and one of the IOLs. Perfluorophenanthrene (Vitreon) was used to remove the other two dislocated IOLs. The dislocated lenses or IOLs were floated by the high-density vitreous substitutes and removed safely without damaging the retina; there were no intraoperative complications. Postoperative residual fluorosilicone oil droplets were found in one case.

Ocular fundus examination in premature infants.

In order to better acknowledge the ocular fundus picture in premature infants and to determine the incidence and clinical course of retinopathy of prematurity (ROP), from October 1987 to April 1989, 187 cases with a gestational age of less than 38 weeks or a birth weight of less than 2,500 g were enrolled for examination and follow-up study with indirect ophthalmoscope. One hundred and fifty cases (80.21%) were free from ROP bilaterally. Thirty-seven cases (19.79%) had ROP. Except for one case that showed unilateral regressed ROP, all were bilaterally affected. The mean birth weight and gestational age in the nonROP group were 1,824 +/- 426 g and 33.6 +/- 2.9 weeks, respectively, and in the ROP group were 1,395 +/- 490 g and 30.7 +/- 3.9 weeks, respectively. The difference for both factors between the two groups were statistically significant (p less than 0.05). Several specific fundus features were noticed in a high percentage of the nonROP group, these included a small cup to disc (C/D) ratio, pigmented ring around the disc, hypopigmented fundus and a greenish-gray color in the peripheral vascularized retina. In addition, 8.2% of this group had persistent primary vitreous remnant, and 5.6% had retinal hemorrhage. The macular development was subdivided into three stages. In both the ROP and nonROP groups, the difference of gestational age at each advancing stage was statistically significant by the Student t-test. No delay in macular development was noticed in the ROP group.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluorosilicone oil in the treatment of retinal detachment.

We evaluated the use of a heavier-than-water fluorinated silicone oil in the treatment of 30 selected cases of complicated retinal detachment from January 1988 to July 1989. Proliferative vitreoretinopathy grade C-2 or greater accounted for 19 cases, proliferative diabetic retinopathy with traction detachment for two cases, giant retinal tears five, ruptured globe with retinal detachment two, massive choroidal effusion with retinal detachment one, and acute retinal necrosis with retinal detachment one. Initial retinal reattachment was achieved in all cases. Complications included redetachment seven (23%), cataract six (75% of phakic patients), raised intraocular pressure four (13%), hypotony four (13%), keratopathy three (10%), uveitis-synechia formation three (10%), phthisis two (3%), choroidal haemorrhage one (3%), and vitreous haemorrhage one (3%). Postoperative visual acuities with at least six months' follow-up range from no light perception to 20/50, with seven patients (23%) 20/400 or better.

Experimental evaluation of low-viscosity fluorosilicone oil as a temporary vitreous substitute.

Fluorosilicone oil, a high specific gravity fluorinated silicone oil, has been recently reevaluated for temporary use in surgery to repair complicated retinal detachments. We evaluated the toxicity of a low-viscosity (300 centistokes) fluorosilicone oil as a vitreous substitute in vitrectomized eyes of albino rabbits. No toxicities could be demonstrated by histopathologic and electroretinographic examinations 6 weeks following surgery. In vitro experiments also showed no toxic effects on cultured retinoblastoma cells. When fluorosilicone oil was injected into the anterior chamber, endothelial cell damage could be seen 2 weeks following injection. Low-viscosity fluorosilicone oil appears to be a safe vitreous substitute for temporary use; it is easily injected and removed, and it maintains adequate surface tension for intraocular tamponade. Because of its relative low viscosity, 300-cst fluorosilicone oil (FS) may be a better vitreous substitute than perfluorocarbon liquids for both intraoperative manipulation of the retina and short-term intraocular tamponade for complicated retinal detachments.

False positive magnetic resonance imaging of a choroidal nevus simulating choroidal melanoma.

A 68-year-old white male had a pigmented choroidal tumor associated with progressive loss of vision. Clinical studies with fluorescein angiography and magnetic resonance imaging suggested a diagnosis of choroidal melanoma. Specimens obtained by internal eye wall resection revealed a choroidal nevus.

Efficacy of liposome-bound amphotericin B for the treatment of experimental fungal endophthalmitis in rabbits.

The efficacy of intravitreally administered amphotericin B was evaluated. Experimental fungal infections were produced by inoculation of Candida albicans organisms into the vitreous cavities of 46 rabbit eyes. After 72 hr, eight eyes received intravitreal injections of 10 micrograms of free amphotericin B; and ten eyes each received 10 micrograms, 20 micrograms, and 40 micrograms of liposome-bound amphotericin B. The remaining eight eyes served as controls: four eyes received dextrose solution and four eyes received empty liposomes. Histopathologic examination 8 weeks after inoculation showed clear vitreous without retinal damage in groups treated with either 10 micrograms free amphotericin B or 20 micrograms of liposome-bound drug. All eyes in the control group and six eyes (60%) in the group treated with 10 micrograms of liposome-bound amphotericin B developed vitreous abscesses with evidence of fungal infection. In eyes treated with 40 micrograms of liposome-bound amphotericin B, fungal infection was successfully eradicated, but retinal damage was detected in all eyes by light microscopy. It is proposed that a reduced toxicity of intravitreally injected liposome-bound drugs is accompanied by reduced efficacy. In the treatment of fungal endophthalmitis, an increased dosage of liposome-bound amphotericin B (above that dosage of free drug which would be required) is suggested.

Reduced toxicity of intravitreally injected liposome-encapsulated cytarabine.

Cytarabine has been demonstrated to be a more potent inhibitor of fibroblast proliferation than fluorouracil. It is, however, more toxic to the retina. We evaluated the ocular toxicity of liposome-encapsulated cytarabine in vitrectomized and nonvitrectomized rabbit eyes by ophthalmic and histopathologic examination. In the vitrectomized group, doses of up to 26 micrograms were nontoxic to the retina. In nonvitrectomized eyes, doses of up to 55 micrograms were nontoxic. Doses of 85 micrograms resulted in loss of ganglion cells and disorganization of photoreceptor cells. The results obtained in this study demonstrated a substantial reduction in ocular toxicity of liposome-encapsulated cytarabine, as compared with a previous study which employed free drug. By virtue of its reduced toxicity, cytarabine in a liposomal vehicle may be of value in the treatment of ocular proliferative disorders.

Experimental evaluation of perfluorophenanthrene as a high specific gravity vitreous substitute: a preliminary report.

Perfluorophenanthrene, a liquid fluorocarbon with a specific gravity approximately twice that of water, potentially offers certain advantages as a vitreous substitute in vitreoretinal surgery. To determine its efficacy and safety we first purified it by chemical methods used in the preparation of experimental blood substitutes to a level at which it was not at all or only minimally toxic to culture-grown retinoblastoma cells. Nineteen of 22 vitrectomized eyes of white New Zealand rabbits injected with this purified perfluorophenanthrene showed satisfactory clinical tolerance. Light and electron microscopy showed minimal or no toxic effects in the 19 eyes, although uptake of perfluorophenanthrene by some preretinal cells was observed 28 days after implantation. Postoperative light-adapted electroretinography recordings of eight of the injected eyes showed no significant change. Perfluorophenanthrene injected into the anterior chamber of the rabbit eyes had toxic effects on the cornea. If further experimentations confirm our findings, perfluorophenanthrene may be a suitable transparent high-density liquid for temporary use in surgery to repair retinal detachments.