Evaluation of correlated studies using liquid cell and cryo-transmission electron microscopy: Hydration of calcium sulphate and the phase transformation pathways of bassanite to gypsum.

Insight into the nucleation, growth and phase transformations of calcium sulphate could improve the performance of construction materials, reduce scaling in industrial processes and aid understanding of its formation in the natural environment. Recent studies have suggested that the calcium sulphate pseudo polymorph, gypsum (CaSO4 ·2H2 O) can form in aqueous solution via a bassanite (CaSO4 ·0.5H2 O) intermediate. Some in situ experimental work has also suggested that the transformation of bassanite to gypsum can occur through an oriented assembly mechanism. In this work, we have exploited liquid cell transmission electron microscopy (LCTEM) to study the transformation of bassanite to gypsum in an undersaturated aqueous solution of calcium sulphate. This was benchmarked against cryogenic TEM (cryo-TEM) studies to validate internally the data obtained from the two microscopy techniques. When coupled with Raman spectroscopy, the real-time data generated by LCTEM, and structural data obtained from cryo-TEM show that bassanite can transform to gypsum via more than one pathway, the predominant one being dissolution/reprecipitation. Comparisons between LCTEM and cryo-TEM also show that the transformation is slower within the confined region of the liquid cell as compared to a bulk solution. This work highlights the important role of a correlated microscopy approach for the study of dynamic processes such as crystallisation from solution if we are to extract true mechanistic understanding.

Beam-induced oxidation of mixed-valent Fe (oxyhydr)oxides (green rust) monitored by STEM-EELS.

Analytical transmission electron microscopy (TEM) is often used to investigate morphologies, crystal structures, chemical compositions and oxidation states of highly reactive mixed-valent mineral phases. Of prime interest, due to its potential role in toxic metal remediation, is green rust sulphate (GRSO4) an FeII-FeIII layered double hydroxide. In this study, we quantified the effects that TEM analysis has on GRSO4 in order to ensure the measured material properties are a result of synthesis and reaction kinetics, and not due to sample preparation and analysis technique. To do this, we compared two sample preparation techniques (anoxic drop-cast with drying, and frozen-hydrated cryogenic) and exposed samples to the electron beam for several minutes, acquiring fluence series between ca. 40 e- Å-2 and 10,000 e- Å-2. TEM imaging and electron diffraction showed that the hexagonal plate-like morphology and crystal structure of GRSO4 were largely unaffected by sample preparation and analysis technique. However, quantitative analysis of a series of monochromated Fe L3,2-edge electron energy loss spectra (EELS) showed that electron irradiation induces oxidation. We measured an Fe(II)/Fe(III) ratio of 1.94 (as expected for GRSO4) at 50 e- Å-2. However, above this fluence, the ratio logarithmically decreased and dropped to ca. 0.5 after 1000 e- Å-2. This trend was approximately the same for both sample preparation techniques implying that it is the beam alone which causes valence state changes, and not exposure to oxygen during transfer into the TEM or the vacuum of the TEM column. Ultimately this work demonstrates that GR valence can be quantified by EELS provided that the sample is not over exposed to electrons. This also opens the possibility of quantifying the effect of redox-sensitive toxic metals (e.g., As, Cr, Se) on Fe oxidation state in GR phases (relevant to the treatment of contaminated soils and water) with a higher spatial resolution than other techniques (e.g., Mössbauer spectroscopy).

Anterior proliferative vitreoretinopathy in the silicone study. Silicone Study Report Number 10.

BACKGROUND: As part of the design of the Silicone Study, a new classification of proliferative vitreoretinopathy (PVR) was developed that distinguishes the different types of contraction found in PVR. In contrast to the original Retina Society system that emphasized the post-equatorial retinal pathology (posterior PVR), the Silicone Study classification system included the characteristic types of contraction found in both the equatorial region and the pre-equatorial retina and vitreous base (anterior PVR). METHODS: The authors contrast (1) preoperative and intraoperative findings and (2) vision and anatomic outcomes in the cohort of anterior PVR eyes with the cohort of posterior-only PVR eyes. For the cohort of eyes randomized to perfluoropropane gas (C3F8) or silicone oil, the authors carry out univariate and multivariate analyses to assess the predictive value of baseline and intraoperative parameters on vision and anatomic outcome. RESULTS: Anterior PVR was present in 321 eyes (79%) and was more prevalent in eyes that had undergone an unsuccessful vitrectomy before study entry than in eyes that underwent a primary vitrectomy for PVR (88% versus 73%; P < 0.001). Compared with eyes that had posterior PVR at the preoperative examination, eyes that had anterior PVR tended to (1) be graded (Retina Society classification system) as D-1 or worse (86% versus 49%; P < 0.0001), (2) have worse (< 2/200) visual acuity (93% versus 86%; P = 0.003), (3) have more hypotony (24% versus 11%; P = 0.03), more edema (8% versus 2%; P = 0.04), more aqueous flare (P = 0.02), more macular pucker (69% versus 52%; P = 0.005), and more intravitreal contraction (21% versus 6%; P = 0.002). When compared with eyes that had anterior PVR, eyes with posterior PVR had a better outcome at the 6-month postoperative examination: complete attachment of the retina (76% versus 62%; P = 0.04), visual acuity of 5/200 or better (64% versus 45%; P = 0.006), and normal intraocular pressure (86% versus 71%; P = 0.04). For eyes with anterior PVR, significant predictors of poor (< 5/200) visual acuity were a preoperative PVR grade D-1 or worse and the use of C3F8 gas as the intraocular tamponade. CONCLUSION: The Silicone Study classification of anterior PVR permits greater specificity in characterizing PVR and is prognostic of anatomic and vision outcome. Eyes with anterior PVR and clinically significant posterior PVR changes had a better visual prognosis if silicone oil was used. With the current understanding of the pathoanatomy of anterior PVR and the recent development of new surgical techniques, the incidence of anterior PVR in eyes that previously underwent vitrectomy may decline, and the prognosis in eyes with anterior PVR may improve.

The complications of perfluoropropane gas use in complex retinal detachments.

BACKGROUND: Perfluoropropane (C3F8) is a valuable adjunct in the management of complex rhegmatogenous retinal detachments, and it has become the most commonly used perfluorocarbon gas. However, there have been few large reports about its complications. This retrospective study was undertaken to evaluate the complications of the use of perfluoropropane gas. METHODS: Perfluoropropane gas was used in the repair of a complex retinal detachment in 157 consecutive eyes. Only eyes that had a follow-up of 6 months or greater were included. Any eyes that had undergone previous vitrectomy and vitreous substitution with gas or silicone oil were excluded. RESULTS: Gas-induced lens opacities developed in 26 (67%) phakic eyes; transient increased intraocular pressure developed postoperatively in 50 (32%) eyes; a transient fibrinous, pupillary membrane developed in 20 (13%) eyes; and a flat anterior chamber developed in 10 (6%) eyes. CONCLUSIONS: Scleral buckle placement and increased gas concentration were found to be risk factors for the development of increased intraocular pressure. Proliferative diabetic retinopathy was associated with a higher development of lens opacities and pupillary membranes. No major complications were associated with the use of C3F8.

Macular pucker after successful surgery for proliferative vitreoretinopathy. Silicone Study Report 8.

BACKGROUND: The prevalence of postoperative macular pucker and the factors associated with its development after successful surgery for proliferative vitreoretinopathy (PVR) using silicone oil or gas tamponade are unknown. METHODS: The postoperative status of the macula was determined by reviewing the photographs of 336 eyes taken 6 months after randomization. Two hundred eleven eyes with attached maculas were identified and analyzed to determine the prevalence of macular pucker after silicone oil and gas tamponades in eyes without (group 1) and with (group 2) previous vitrectomy surgery. Data obtained at baseline, from the primary study surgery, and from subsequent examinations and repeat surgeries during a follow-up period of 6 months were analyzed for factors associated with postoperative macular pucker. RESULTS: The 6-month-point prevalence rate of postoperative macular pucker was 15% (32 of 211 eyes). Ten of the 32 eyes were new cases of macular pucker. The authors were unable to document a difference in the 6-month-point prevalence of postoperative macular pucker between group 1 and group 2 eyes (13% versus 18%) or between eyes randomized to gas versus silicone oil (19% versus 12%). Postoperative pucker was three times as likely to develop in aphakic/pseudophakic eyes compared with phakic eyes (P = 0.02). Focal contraction posteriorly causing starfolds, and intravitreal contraction involving the vitreous base or vitreous cavity, were significantly less prevalent in eyes with postoperative macular pucker (P < 0.05). Large (> or = 2 disc diameters) retinal breaks (P = 0.04) were associated significantly with postoperative macular pucker (P = 0.04). The authors were unable to document an association between postoperative macular pucker and the type of adhesive modality used or the extent of its application. Postoperative visual acuity was significantly better if the macula was not puckered (P < 0.01). CONCLUSIONS: The occurrence of macular pucker after successful surgery for retinal detachments complicated by severe PVR is not influenced by the choice of intraocular tamponade. Certain preoperative factors may be associated with postoperative macular pucker.

An updated classification of retinal detachment with proliferative vitreoretinopathy.

The Retinal Society classification on proliferative vitreoretinopathy of 1983 has been updated to accommodate major progress in understanding of this disease. There are three grades describing increasing severity of the disease. Posterior and anterior location of the proliferations have been emphasized. A more detailed description of posterior and anterior contractions has been made possible by adding contraction types such as focal, diffuse, subretinal, circumferential contraction, and anterior displacement. The extent of the abnormality has been detailed by using clock hours instead of quadrants.

Anterior proliferative vitreoretinopathy. Clinicopathologic, light microscopic, and ultrastructural findings.

Proliferative vitreoretinopathy (PVR) involving the posterior and equatorial retina is an established clinicopathologic entity. Clinically, a similar process, anterior PVR (APVR), results in anterior dragging of the peripheral retina by membranes which connect to the ciliary body or iris and cause circumferentially and radially fixed retinal folds. The pathology of APVR, however, has not been reported. The authors describe pathologic findings in 28 cases of APVR and ultrastructural pathologic findings in 6 surgical APVR specimens. Anterior PVR was frequently associated with retinal detachment (RD) repair (96%) and trauma (38%). Residual vitreous at the vitreous base virtually always provided a scaffold for membranes containing proliferating cells and deposited extracellular matrix. Major components of APVR membranes were fibrovascular tissue (71%), pigment epithelial cells (43%), fibrous and corneal stromal ingrowth (32%), and glial proliferation (18%). Because of its anterior location, APVR membranes also incorporated ciliary epithelium and corneal endothelium. Contraction of APVR membranes caused anterior retinal displacement and detachment in anatomic configurations corresponding to narrow and wide peripheral troughs. The authors' findings indicate that APVR is a distinctive clinicopathologic entity which may complicate rhegmatogenous RD and its repair.

Collateral circulation in hemicentral retinal vein occlusion.

The perchance occurrence of a hemicentral retinal vein occlusion in an eye with a lightly pigmented fundus allowed us the opportunity to observe the development and flow dynamics of collateral circulation. We are able to demonstrate an optic disc collateral draining into a choroidal vein, a finding which to our knowledge had previously only been documented histologically. The collateral circulation developed slowly over many months and was not rapid enough to prevent chronic microcystic macular changes.

Bilateral acute retinal necrosis. Clinical and ultrastructural study.

In a 28-year-old man with bilateral acute retinal necrosis, a severe, bilateral panuveitis, necrotizing retinitis, and retinal vasculitis developed. Severe vitreous traction on atrophic retina resulted in bilateral giant retinal tears with an inoperable retinal detachment in the right eye. A retinal detachment developed in the left eye that was reattached after a pars plana vitrectomy and two scleral buckling procedures, but ultimately became inoperable. Large numbers of lymphocytes in the vitreous aspirate and depressed serum complement levels may indicate that an immune mechanism was involved in the necrotizing retinitis. We present the first electron microscopic evidence, to our knowledge, that preretinal membranes occurring in rhegmatogenous retinal detachment due to bilateral acute retinal necrosis arise from retinal pigment epithelium.

Asteroid hyalosis. Biomicroscopy, ultrastructure, and composition.

The vitreous in 16 patients (average age, 65 years) with asteroid hyalosis was studied and photographed using a preset lens (El Bayadi-Kajiura) and slitlamp. Asteroid hyalosis was bilateral in one patient (6%) and unilateral in 15 patients (94%). The gel was biomicroscopically normal in 13 patients (81%) and showed moderate liquefaction in three patients (19%). In ten (63%) of the 16 patients, there was no posterior vitreous detachment, in four patients (25%), there was partial vitreous detachment, and in two patients (12%), there was complete vitreous detachment. The preponderance of complete vitreous detachment was lower than expected for patients in this age group, probably because of a reduced preponderance of vitreous liquefaction in patients with asteroid hyalosis. A vitreous aspirate from one of these patients was studied using phase-contrast microscopy and scanning and transmission electron microscopy. Asteroid bodies were enmeshed within normal vitreous collagen fibrils and some were attended by macrophages or multinucleated epithelioid cells. Transmission electron microscopy disclosed irregular calcific material and complex lipids within the asteroid bodies. X-ray spectroscopy demonstrated calcium and phosphorus.

Fellow eyes of eyes with macular holes.

We studied the fellow eyes of eyes with macular holes by fundus photography, fluorescein angiography, and central visual field testing. Eight of 37 fellow eyes (22%) observed for a minimum of 36 months developed macular holes. Fellow eyes initially classified as normal developed fewer macular holes than fellow eyes with initial pigment epithelial defects or cystic formation.

Bilateral multifocal intraocular cysticercosis.

A 47-year-old male from India was treated for the rare condition of bilateral multifocal intraocular infestation with Cysticercus cellulosae, the larval form of Taenia solium. The intravitreous parasite in the left eye was removed via pars plana vitrectomy. A subretinal cysticercus in the right eye, which caused a rhegmatogenous retinal detachment, was removed via sclerotomy during the scleral buckling procedure. An additional peripapillary subretinal cyst could not be removed. A subconjunctival cysticercus was incidentally found and removed at the time of surgery. The patient returned to India six weeks after surgery and is doing well.

Vitreous cinematography in the study of vitreoretinal diseases.

A new technique of vitreous cinematography involves scanning of the vitreous cavity using optical sections to provide objective, reproducible information on the dynamics of the posterior vitreous and vitreoretinal relationships. Using a newly developed preset lens (El Bayadi-Kajiura lens), this technique makes it possible to document an entire optical section of the posterior vitreous. This is done by mechanically displacing the vitreous so that maximum reflectivity can be obtained from the vitreous gel. This article describes the technique and presents clinical examples documenting complete and incomplete vitreous detachment in normal eyes, Cloquet's canal associated with an optic disc pit, vitreous traction associated with a lamellar hole in an area of preretinal macular fibrosis, and vitreous traction at the anterior flap of a retinal break.

Current management of giant retinal breaks: results with vitrectomy and total air fluid exchange in 95 cases.

These results indicate that vitrectomy is a valuable adjunct in the management of giant retinal breaks with a partial or complete inversion of the posterior retinal flap. Removal of the vitreous gel makes possible the injection of a large bubble of air to more optimally unfold the posterior retinal flap. In addition, vitrectomy severs the equatorial membrane that can cause postoperative circumferential extension of the giant retinal break or the formation of new retinal tears. A 360 degree scleral buckle is mandatory in giant retinal breaks with a partial or complete inversion of the posterior retinal flap. Unless there are medical contraindications, the air fluid exchange should be carried out in the prone position.

Closed vitrectomy in the management of diabetic traction retinal detachment.

One hundred and seventy-four instances of diabetic traction retinal detachment in which the patient underwent closed vitrectomy during the period of January 1970 to December 1978 and had adequate follow-up ranging from six months to five years are reported. As a rule, eyes with vision better than 20/200, or with inaccurate light projection, or with no response to electrophysiologic tests were excluded. The surgical technique avoided stripping of vitreous membranes. Closed vitrectomy was combined with scleral buckling in eyes with retinal breaks, and with scleral resection in eyes with incomplete section of traction membranes. Anatomic improvement was noted in 75.3% of the eyes; vision improved in 64.9% of the eyes; new or recurrent vitreous hemorrhage was observed in 43.1%; corneal decompensation in 51.8%, rubeosis iridis in 23.0%, phthisis bulbi in 9.2%, iatrogenic retinal break in 8.6%, postoperative rhegmatogenous retinal detachment in 5.2%, and iatrogenic cataract in 4.6%.