red or pink due to uptake of eosin) cytoplasm with plump and elongated nuclei composed of granulated (i.e. having many small, distinct parts) chromatin. The most pathognomonic (i.e. indicative of a particular disease) feature of these cells is the presence of cytoplasmic perinuclear inclusion bodies which usually are small, round, pale pink bodies on hematoxylin and eosin staining that often indent their parent cells nuclei. These inclusions are composed of densely packed vimentin and actin filaments. Newer tumors show relatively abundant inclusion bodies and scarce collagen fibers while older tumors show few or no detectable inclusion bodies and abundant collagen fibers. Immunohistochemical analyses show that the spindle-shaped cells typically express α-smooth muscle actin, calponin, desmin, and CD99 proteins but not S100 protein or glial fibrillary acidic protein. Diagnosis
The diagnosis of IDF is usually based on its presentation in newborn or young infants and biopsy or fine needle aspirate analyses of the tumors pathology. These analyses should show the presence of spindle-shaped cells bearing eosinophilic paranuclear inclusions consisting of actin and vimentin filaments, which, if necessary, can be confirmed by immunofluorescence staining of the filaments. Inclusions may not be evident in older lesions stained with hematoxylin and eosin but may be apparent when stained with other reagents such as the Massons trichrome stain, phosphotungstic acid-haematoxylin stain, elastic Van Giesons stain, or Lendrums phloxine-tartrazine stain. Demonstration of these filaments is not necessary for a diagnosis of IMF if the clinical picture and other histological findings are consistent with the disorder.
These descriptive names can be misleading, however, as many were assigned historically, solely on the basis of subjective clinical examination, which is not sufficient to determine the eyes true trajectory. Optokinetic (syn. opticokinetic) nystagmus: a nystagmus induced by looking at moving visual stimuli, such as moving horizontal or vertical lines, and/or stripes. For example, if one fixates on a stripe of a rotating drum with alternating black and white, the gaze retreats to fixate on a new stripe as the drum moves. This is first a rotation with the same angular velocity, then returns in a saccade in the opposite direction. The process proceeds indefinitely. This is optokinetic nystagmus, and is a source for understanding the fixation reflex. Postrotatory nystagmus: if one spins in a chair continuously and stops suddenly, the fast phase of nystagmus is in the opposite direction of rotation, known as the "post-rotatory nystagmus", while slow phase is in the direction of rotation. Treatment
Congenital nystagmus has long been viewed as untreatable, but medications have been discovered in recent years that show promise in some patients. In 1980, researchers discovered that a drug called baclofen could stop periodic alternating nystagmus. Subsequently, gabapentin, an anticonvulsant, led to improvement in about half the patients who took it. Other drugs found to be effective against nystagmus in some patients include memantine, levetiracetam, 3,4-diaminopyridine (available in the US to eligible patients with downbeat nystagmus at no cost under an expanded access program), 4-aminopyridine, and acetazolamide.