Explaining Cold-Pulse Dynamics in Tokamak Plasmas Using Local Turbulent Transport Models.

A long-standing enigma in plasma transport has been resolved by modeling of cold-pulse experiments conducted on the Alcator C-Mod tokamak. Controlled edge cooling of fusion plasmas triggers core electron heating on time scales faster than an energy confinement time, which has long been interpreted as strong evidence of nonlocal transport. This Letter shows that the steady-state profiles, the cold-pulse rise time, and disappearance at higher density as measured in these experiments are successfully captured by a recent local quasilinear turbulent transport model, demonstrating that the existence of nonlocal transport phenomena is not necessary for explaining the behavior and time scales of cold-pulse experiments in tokamak plasmas.

Effects of magnetic shear on toroidal rotation in tokamak plasmas with lower hybrid current drive.

Application of lower hybrid (LH) current drive in tokamak plasmas can induce both co- and countercurrent directed changes in toroidal rotation, depending on the core q profile. For discharges with q(0) <1, rotation increments in the countercurrent direction are observed. If the LH-driven current is sufficient to suppress sawteeth and increase q(0) above unity, the core toroidal rotation change is in the cocurrent direction. This change in sign of the rotation increment is consistent with a change in sign of the residual stress (the divergence of which constitutes an intrinsic torque that drives the flow) through its dependence on magnetic shear.

Edge temperature gradient as intrinsic rotation drive in Alcator C-Mod tokamak plasmas.

Intrinsic rotation has been observed in I-mode plasmas from the C-Mod tokamak, and is found to be similar to that in H mode, both in its edge origin and in the scaling with global pressure. Since both plasmas have similar edge ∇T, but completely different edge ∇n, it may be concluded that the drive of the intrinsic rotation is the edge ∇T rather than ∇P. Evidence suggests that the connection between gradients and rotation is the residual stress, and a scaling for the rotation from conversion of free energy to macroscopic flow is calculated.

Rotation reversal bifurcation and energy confinement saturation in tokamak Ohmic L-mode plasmas.

Direction reversals of intrinsic toroidal rotation have been observed in diverted Alcator C-Mod Ohmic L-mode plasmas following electron density ramps. For low density discharges, the core rotation is directed cocurrent, and reverses to countercurrent following an increase in the density above a certain threshold. Such reversals occur together with a decrease in density fluctuations with 2 cm(-1)≤k(θ)≤11 cm(-1) and frequencies above 70 kHz. There is a strong correlation between the reversal density and the density at which the Ohmic L-mode energy confinement changes from the linear to the saturated regime.

Efficient design and verification of diagnostics for impurity transport experiments.

Recent attempts to measure impurity transport in Alcator C-Mod using an x-ray imaging crystal spectrometer and laser blow-off impurity injector have failed to yield unique reconstructions of the transport coefficient profiles. This paper presents a fast, linearized model which was constructed to estimate diagnostic requirements for impurity transport experiments. The analysis shows that the spectroscopic diagnostics on Alcator C-Mod should be capable of inferring simple profiles of impurity diffusion DZ and convection VZ accurate to better than ±10% uncertainty, suggesting that the failure to infer unique DZ and VZ from experimental data is attributable to an inadequate analysis procedure rather than the result of insufficient diagnostics. Furthermore, the analysis reveals that even a modest spatial resolution can overcome a low time resolution. This approach can be adapted to design and verify diagnostics for transport experiments on any magnetic confinement device.

Clinical suppression and amblyopia.

In individuals with abnormal binocular vision, such as strabismics and anisometropes, it is common for all or part of one eye's view to be suppressed so binocular confusion and diplopia are eliminated. We examined the relation between the depth of suppression (the amount by which the monocular contrast increment threshold for an eye was elevated by stimulation in the contralateral eye) and the degree of amblyopia (difference in monocular contrast thresholds for the two eyes). There was a significant negative correlation between suppression and amblyopia, so that clinical suppressors with no amblyopia exhibited deep suppression (ie, large threshold elevation) while observers with amblyopia exhibited weaker or no suppression. This negative correlation was found when the two eyes viewed orthogonally oriented contours as well as identically oriented contours. These results suggest that when an eye is amblyopic there is no longer a need for strong suppression of that eye by the contralateral eye.

Acne rosacea with keratitis in childhood.

We present three cases of acne rosacea keratitis that developed in childhood. All three children were prepubescent and demonstrated characteristic dermatologic findings involving the nose, cheeks, and/or chin. The patients had complained of ocular irritation for at least 6 months, and in one case symptoms were reported by the family to have occurred intermittently since age 4 years. All three children showed evidence of meibomian gland inflammation; two patients demonstrated bilateral keratitis, the third had only unilateral involvement. In each case, oral tetracycline hydrochloride or doxycycline hyclate was necessary to relieve symptoms. Rosacea keratitis should be considered in the differential diagnosis of chronic keratoconjunctivitis during childhood.

Metastatic bacterial endophthalmitis: a contemporary reappraisal.

Metastatic bacterial endophthalmitis remains a challenge to the clinician despite the success of antibiotics in reducing its frequency and severity. Controversy currently surrounds the management of this condition because of uncertainty about the value of and indications for vitreous surgery. We review 72 cases of metastatic endophthalmitis from the past decade, including five not previously published. The spectrum of causative bacteria changed significantly during this period, with displacement of meningococcus by Bacillus cereus as the most frequently reported agent and an increasing incidence of infection by organisms of low pathogenicity in immunologically compromised hosts. We propose a new classification scheme for metastatic endophthalmitis based on the location (anterior or posterior segment) and extent (focal or diffuse) of the primary intraocular infection. Focal and anterior cases appear to have a good prognosis, while posterior diffuse disease nearly always leads to blindness. Our analysis of outcomes suggests that systemic antibiotics are more valuable in metastatic than in postoperative or traumatic endophthalmitis and that intraocular antibiotic injection and vitrectomy make only a limited contribution to successful treatment in metastatic infection. We recommend a clinical approach to metastatic endophthalmitis that minimizes exposure of patients to the risks of invasive procedures.

Scleritis and Wegener's granulomatosis in children.

We treated two children with scleritis (one unilateral, one bilateral), in whom Wegener's granulomatosis was diagnosed on the basis of pathologic changes in respiratory tract mucosa. Both patients were girls, 13 and 14 years of age, respectively. One patient had otitis media and a nodular scleritis. Laboratory test results demonstrated an increased erythrocyte sedimentation rate and microscopic hematuria. A biopsy of the sinus confirmed the diagnosis of Wegener's granulomatosis. The second patient had fever, arthralgias, a nonproductive cough, and bilateral scleritis. Laboratory test results demonstrated an increased erythrocyte sedimentation rate, positive test results for rheumatoid factor, and bilateral pulmonary nodules on chest x-ray. Open-lung biopsy confirmed the diagnosis of Wegener's granulomatosis. Both patients responded well to treatment with a combination of prednisone and cyclophosphamide.

Retinoblastoma and simulating lesions: role of CT and MR imaging.

Diagnosis of retinoblastoma is one of the most challenging problems of pediatric ophthalmology and radiology. It must be differentiated from numerous simulating lesions. Accurate diagnosis by means of ultrasonography, CT, and MR is essential for prompt treatment and prevention of metastasis. The CT and MR findings in 45 patients are presented in this article in order to evaluate and compare the usefulness of these two imaging techniques in the diagnosis of retinoblastoma.

Iridocorneal adhesions in patients with the Marfan syndrome.

Marfan syndrome is an autosomal dominant connective tissue disorder characterized by skeletal, cardiovascular, and ocular anomalies. Ectopia lentis is the most common ocular manifestation. We report an ocular sign not previously described in Marfan syndrome, iridocorneal adhesions secondary to anterior lens subluxation. Three patients with the Marfan syndrome had iridocorneal adhesions on slit-lamp examination. One patient developed adhesions following treatment with pilocarpine. She underwent pars plana vitrectomy and lensectomy in both eyes due to progression of the iridocorneal adhesions. Treatment with miotics rotates the lens-iris diaphragm anteriorly and may contribute to the formation of such adhesions. The two other patients remained stable and did not received lensectomy or vitrectomy. Careful slit-lamp examination of the anterior segment should be conducted in patients with dislocated lenses.

Selective losses in binocular vision in anisometropic amblyopes.

Human anisometropic amblyopes typically exhibit reduced contrast sensitivity in the amblyopic eye, especially at higher spatial frequencies. We determined whether this spatial frequency selective loss in contrast sensitivity is accompanied by selective losses in binocular function. Binocular summation (the improvement in one eye's detection performance produced by a subthreshold pattern presented to the fellow eye) was measured at several spatial frequencies. Normal observers exhibited equivalent binouclar summation at all spatial frequencies, whereas all anisometropic amblyopes exhibited normal summation at low spatial frequencies but none at high spatial frequencies. Stereoacuity (minimum resolvable disparity) was also measured as a function of spatial frequency. For normal observers, stereoacuity was best at the highest spatial frequency; for anisometropes stereoacuity was normal at low spatial frequencies, subnormal at intermediate spatial frequencies, and unmeasurable at higher spatial frequencies. Anisometropia may represent a form of selective binocular deprivation that affects neural mechanisms underlying binocular summation and stereopsis.

Mucolipidosis IV in an African American patient with new findings on electron microscopy.

PURPOSE: We report an unusual case of mucolipidosis IV in a patient of African ancestry, with intracytoplasmic inclusions of the corneal endothelium found on electron microscopy. METHOD: Clinical description with light and electron microscopy. RESULTS: We describe a case of mucolipidosis IV diagnosed in a patient of African ancestry after penetrating keratoplasty. Electron microscopic evaluation revealed intracytoplasmic inclusions in both the corneal epithelium and endothelium. CONCLUSION: The diagnosis of mucolipidosis in a patient of African ancestry is unusual, as this genetic disorder is found predominantly in individuals of Jewish descent. Corneal endothelial involvement in mucolipidosis IV has not previously been reported.

Ocular and dermatologic manifestation of neurocutaneous syndromes.

The dermatologic and ophthalmologic manifestations of neurocutaneous syndromes are numerous and varied, but familiarity with them is essential to the clinician from any specialty who may have to deal with these disorders. Although many of their complications are unfortunately still difficult or impossible to treat effectively, there may be significant benefit to the patient from prompt detection of optic glioma in NF, retinal angiomas in VHL disease, and glaucoma in SWS. Recognition of characteristic lesions of skin and eye in individuals with mild expressions of NF and TS is essential for genetic counseling. For affected children and their parents, early diagnosis (based on sometimes subtle findings) and formulation of a complete and accurate prognosis can considerably ease the burden imposed by any of these conditions.

Visual development in infancy and childhood.

This article considers the development of vision in normal children, emphasizing new evaluative techniques that may eventually play an important role in clinical practice, and follows with a discussion of abnormal development, where recent discoveries in the laboratory and in clinical observation have already led to significant advances in the treatment of children with ophthalmologic problems.

Orbital roof fractures in the pediatric population.

Twenty-three patients aged 3.3 +/- 1.6 years (mean +/- SD) presented between January of 1984 and September of 1987 with fronto-orbital trauma resulting in fractures of one (N = 20) or both (N = 3) orbital roofs. All patients had computed tomography (CT) with axial and coronal sections that revealed three fracture patterns of the orbital roof (nondisplaced, superiorly displaced, and inferiorly displaced fractures). Orbital dystopia was exhibited in 35 percent (N = 8) of the patients. Exophthalmos was noted in 61 percent (N = 14) of the patients. Only 30 percent of the patients (N = 7) sustained associated maxillofacial fractures. Eight percent of fractures exhibited orbital encephaloceles. All patients lacked frontal sinus pneumatization. The majority of children with orbital roof fractures do not exhibit concomitant facial fractures. CT utilizing both axial and coronal sections is valuable in defining the extent and pattern of the fracture as well as in identifying associated neurologic injuries. Large, displaced orbital roof fractures, which occurred in 3 of 13 patients with displaced fractures in our series, should undergo early reduction to avoid late development of encephalocele.

Visual outcomes after surgery for unilateral cataract in children more than two years old: posterior chamber intraocular lens implantation versus contact lens correction of aphakia.

PURPOSE: We sought to determine whether posterior chamber intraocular lens implantation yields better visual acuity and binocular vision than does conventional contact lens correction of aphakia in similar groups of pediatric cataract patients. METHODS: We reviewed the medical records of children aged 2 to 16 years who had unilateral cataract surgery by a single pediatric ophthalmologist between 1986 and 1996. Before 1992 all patients underwent standard lensectomy with vitrectomy. Beginning in 1992 posterior chamber intraocular lens (IOL) implantation was offered as a choice to families and was performed on most patients. RESULTS: Monocular vision outcomes were not significantly different in 20 IOL and 31 lensectomy-vitrectomy patients, with 85% of the IOL group and 77% of the lensectomy-vitrectomy group showing better than 20/100 final acuity. Binocularity, however, was much better in the IOL group, with 90% demonstrating at least 400 seconds of arc stereopsis, as opposed to 39% in the lensectomy-vitrectomy group (p = 0.003). Subgroups of patients with traumatic or nontraumatic cataract origin, age at surgery less than 7 years, and preoperative visual acuity less than 20/100 compared very similarly. CONCLUSION: Posterior chamber IOL implantation appears to provide significantly better binocular function than conventional management of unilateral cataract in childhood but does not substantially improve visual acuity results.

Hypobaric ocular trauma from a Popper.

We have observed 3 cases of ocular trauma in children that were caused by an atypical, hypobaric mechanism induced by a toy called a Popper. When we initially notified the United States Consumer Product Safety Commission in 1990, Poppers disappeared from store shelves. We are concerned that this potentially harmful toy is making a comeback in 1998 (Smilemakers Inc, Spartanburg, SC; June-July 1998 catalog, p. 57). In 1990, packaged poppers cautioned against applying to face or skin; we are not sure that such warnings accompany current Poppers.

In-the-bag secondary intraocular lens implantation in children.

BACKGROUND: Surgery for congenital cataracts in early infancy usually includes a primary posterior capsulectomy and an anterior vitrectomy. Initially, most of these infants have aphakia after surgery. Over time, remaining equatorial lens epithelial cells produce new cortical fibers, resulting in a ring of cortex trapped between the lens equator and the fused anterior and posterior capsulectomy edges. A potential space is maintained between the anterior and posterior capsular leaflets. We describe a technique for placing a secondary intraocular lens (IOL) within the capsular bag. PATIENTS AND METHODS: Eight children, ranging in age from 11 months to 14 years, who originally had aphakia after cataract extraction were operated on with the intent to reopen the capsular bag and place an IOL in the bag. RESULTS: Secondary in-the-bag IOL implantation was successfully completed in 7 of 8 children. This was accomplished by reopening the capsular bag 360 degrees at the edge of the fused anterior and posterior capsulectomy remnants, using the previously published vitrectorhexis technique. Residual cortical material was aspirated, and an IOL was placed within the capsular bag. In 1 child, aged 14 years, the capsular bag was reopened, but the lens was placed in the ciliary sulcus because the new anterior capsule edge could not be visualized for 360 degrees . CONCLUSION: Placement of secondary IOLs within the capsular bag can be accomplished successfully for selected patients in the pediatric population. Surgeons operating on infantile cataracts without primary IOL placement can facilitate capsular IOL sequestration later by limiting the anterior and posterior capsulectomy to 4 to 5 mm and performing a generous anterior vitrectomy to help prevent secondary closure of the smaller capsulectomy.

Afferent pupillary defects in amblyopia.

We detected mild afferent pupillary defects with the "swinging flashlight" test in 4 out of 45 amblyopic patients. Our study was designed to minimize the effect of observer bias and to control for the difficulty of testing the pupils in young children. We found afferent defects in both strabismic and anisometropic amblyopes. There was no apparent relationship between pupillary response and visual acuity: afferent defects were noted in association with better than 20/100 vision in three cases but were absent in a majority of patients with profound visual loss. Vision was improved by occlusion therapy in two amblyopes with pupillary abnormalities. We regard the occurrence of afferent pupillary defects as evidence for a physiological disturbance at the retinal level in at least some cases of amblyopia. Our findings suggest that the extent of retinal involvement in amblyopic eyes is independent of reduction in acuity, to which primary cortical abnormalities may contribute as well.