Faculty Bibliography

PURPOSE/OBJECTIVE:To report 2 interventional cases of dedifferentiated chondrosarcoma with orbital involvement after radiotherapy performed in childhood and to review the literature on chondrosarcoma in the orbit following radiation treatment. METHODS:Retrospective analysis of medical records of 2 patients with chondrosarcoma of the orbits with review of the literature. RESULTS:The first patient developed chondrosarcoma of the orbital and maxillary sinus 36 years after external beam radiation therapy to the OS to treat retinoblastoma. The second patient developed a large orbital chondrosarcoma 35 years after external beam radiation therapy in the treatment of craniofacial fibrous dysplasia. CONCLUSIONS:These cases highlight the risk of secondary chondrosarcoma in patients following radiotherapy and the importance of lifetime monitoring.

Ocular imaging technologies continue to evolve and play increasingly important roles in both the diagnosis and management of corneal pathology. In addition to improved documentation of exam findings using increasingly better resolution photographs, newer modalities, including specular and confocal microscopy, can facilitate diagnosis by imaging single cell layers within the cornea. Anterior segment optical coherence tomography (OCT) and ultrasound biomicroscopy (UBM) can image structures in the cornea and anterior segment which may not otherwise be visible. This is particularly useful in patients with opaque corneas. The ability to topographically map the cornea allows for more accurate pre- and post-operative planning, especially in patients with corneal ectasia. As these technologies develop, their use in specific patient populations, such as children, must be optimized. In this report, we provide an updated analysis of selected imaging modalities used in the diagnosis and management of pediatric corneal pathology.

Nonarteritic anterior ischemic optic neuropathy (NAION) causes sudden profound loss of vision with no known cause or cure. Various treatment modalities, both surgical and pharmacologic, have been tried without success. The purpose of our retrospective study was to evaluate the effect of intravitreal bevacizumab (Avastin) as a treatment option for NAION. We evaluated demographics of 5 patients and compared visual acuity and automated visual fields prior to and following intravitreal bevacizumab injection. Visual acuity at presentation was 20/20 in 4 of 5 patients and 20/150 in 1. Visual acuity improved to 20/40 in the patient who presented with decreased acuity and decreased slowly in 3 patients and rapidly in 1. All patients presented with variable visual field defects: 1 improved slightly, 3 progressed, and 1 remained stable. One patient subsequently developed NAION in the fellow eye. These results are consistent with the natural course of the disease, and bevacizumab did not appear to have a dramatic effect on the clinical outcome in this small series of patients with NAION.

Glutamate is the predominant excitatory neurotransmitter in the central nervous system. The receptors that bind glutamate, including N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor subtypes, are strongly implicated in higher cognitive processes, especially learning and memory. Loss of glutamate receptor function impairs the ability to acquire and retain information in some patients subsequent to stroke or brain injury, and positive allosteric modulators of glutamate receptors can restore learning and memory in some of these patients. Here we demonstrate that kynurenic acid (KYNA), an endogenous tryptophan metabolite, acts upon heterologous AMPA receptors via two distinct mechanisms. Low (nanomolar to micromolar) concentrations of KYNA facilitate AMPA receptor responses, whereas high (millimolar) concentrations of KYNA competitively antagonize glutamate receptors. Low concentrations of KYNA appear to increase current responses through allosteric modulation of desensitization of AMPA receptors. These findings suggest the possibility that low concentrations of endogenous KYNA acting at AMPA receptors may be a positive modulator of excitatory synaptic transmission.