Evaluation of optic neuropathy in multiple sclerosis using low-contrast visual evoked potentials.

BACKGROUND: Contrast acuity (identification of low-contrast letters on a white background) is frequently reduced in patients with demyelinating optic neuropathy associated with multiple sclerosis (MS), even when high-contrast (Snellen) visual acuity is normal. Since visual evoked potentials (VEPs) induced with high-contrast pattern-reversal stimuli are typically increased in latency in demyelinating optic neuropathy, we asked if VEPs induced with low-contrast stimuli would be more prolonged and thus helpful in identifying demyelinating optic neuropathy in MS. METHODS: We studied 15 patients with clinically definite MS and 15 age-matched normal controls. All subjects underwent a neuro-ophthalmologic assessment, including measurement of high-contrast visual acuity and low-contrast acuities with 25%, 10%, 5%, 2.5%, and 1.25% contrast Sloan charts. In patients with MS, peripapillary retinal nerve fiber layer (RNFL) thickness was determined using optical coherence tomography. Monocular VEPs were induced using pattern-reversal checkerboard stimuli with 100% and 10% contrast between checks, at 5 spatial frequencies (8-130 minutes of arc). RESULTS: VEP latencies were significantly increased in response to low- compared with high-contrast stimuli in both groups. VEP latencies were significantly greater in patients with MS than controls for both high- and low-contrast stimuli. VEP latencies correlated with high- and low-contrast visual acuities and RNFL thickness. VEPs were less likely to be induced with low- than with high-contrast stimuli in eyes with severe residual visual loss. CONCLUSIONS: Visual evoked potentials obtained in patients with multiple sclerosis using low-contrast stimuli are increased in latency or absent when compared with those obtained using high-contrast stimuli and, thus, may prove to be helpful in identifying demyelinating optic neuropathy.

Treatment of abnormal eye movements that impair vision: strategies based on current concepts of physiology and pharmacology.

Certain abnormal eye movements, especially pathological nystagmus, degrade vision and cause illusory motion of the seen environment. These symptoms are due to excessive movement of images of stationary objects on the retina. Recently, the pathophysiology underlying several types of nystagmus and saccadic oscillations was better defined by the development of animal models and by experimental pharmacological studies. Despite this, few reliable therapies are currently available for these abnormal eye movements. In clinical studies, a number of drugs reportedly helped individual patients, but few drugs have been subjected to double-blind trials. An alternative approach to pharmacological suppression of abnormal eye movements is optical stabilization of images on the retina, which is helpful in selected patients. Weakening of the extraocular muscles, using botulinum toxin or surgery, is prone to cause diplopia and may induce plastic-adaptive changes that render the effect temporary. In some patients, treatment of an underlying condition, such as the Arnold-Chiari malformation, reduces nystagmus and improves vision. There is a need for multicenter trials to evaluate systematically potential treatments of abnormal eye movements that impair vision.

An optometric quality assurance program.

BACKGROUND: To be accredited by the Joint Commission on Accreditation of Health Care Organizations (JCAHO), a health care facility must have an ongoing quality assurance program. METHODS: In accordance with JCAHO Guidelines the Optometry Section at the Cleveland Veterans Administration Medical Center developed such a program as part of the Medical Center's hospital-wide ongoing quality assurance plan. RESULTS: The methodology used to develop a quality assurance program is outlined. A discussion of how specific clinical indicators are used to monitor performance and/or patient outcomes is presented. CONCLUSIONS: After the quality assurance monitoring period is completed the data is analyzed; if the outcome is unacceptable action must be taken to improve care. This dynamic process involves patient outcomes and enhances overall care.

Effectiveness of botulinum toxin administered to abolish acquired nystagmus.

We injected botulinum toxin into the horizontal rectus muscles of the right eyes of 2 patients who had acquired pendular nystagmus with horizontal, vertical, and torsional components. This treatment successfully abolished the horizontal component of the nystagmus in the injected eye in both patients for approximately 2 months. Both patients showed a small but measurable improvement of vision in the injected eye that may have been limited by coexistent disease of the visual pathways. The vertical and torsional components of the nystagmus persisted in both patients. In 1 patient, the horizontal component of nystagmus in the noninjected eye increased; we ascribe this finding to plastic-adaptive changes in response to paresis caused by the botulinum toxin. Such plastic-adaptive changes and direct side effects of the injections--such as diplopia and ptosis--may limit the effectiveness of botulinum toxin in the treatment of acquired nystagmus. Neither patient elected to repeat the botulinum treatment.

Refinement of an optical device that stabilizes vision in patients with nystagmus.

An optical device that produces partial stabilization of retinal images has been described. It consists of a high-plus spectacle lens used in combination with a large, high-minus, polymethyl methacrylate (PMMA) contact lens. This device is designed to provide more clear and stable vision in patients with acquired nystagmus due to neurological disease. We report success in using a smaller, rigid, gas permeable (RGP) contact lens that achieves the required degree of stabilization, but is more comfortable for patients than the PMMA contact lens originally described. We have confirmed that the degree of retinal image stabilization is similar to that achieved with the PMMA lens. We present a case report to illustrate its use.

Oscillopsia, retinal image stabilization and congenital nystagmus.

Most individuals with congenital nystagmus (CN) do not complain of oscillopsia (visual inconstancy) even though the amount of retinal image slip varies considerably according to gaze angle and CN waveform. We induced oscillopsia in four subjects with CN by artificially stabilizing images upon the retina under several conditions. Every subject reported oscillopsia during retinal image stabilization, but the condition of stabilization varied from one individual to another. Our results indicate that a variety of mechanisms operate to maintain spatial constancy in congenital nystagmus; some individuals appear to use one mechanism more than another. Possible mechanisms include use of extra-retinal signals, elevated threshold for motion detection and "suppression" of visual input except during foveation periods.

Effects of retinal image stabilization in acquired nystagmus due to neurologic disease.

We studied the effects of variable amounts of artificial retinal image stabilization (RIS) upon oscillopsia and visual acuity in eight patients with acquired nystagmus due to neurologic disease. We measured horizontal and vertical eye movements with the magnetic search coil technique and used these electronic signals to control the position of a visual stimulus on a screen in front of the patient. We also used an optical device to stabilize images of the real world upon the retina. During electronic stabilization, RIS was progressively increased until oscillopsia was abolished; this was achieved in all eight patients and corresponded to retinal image drift of 5 degrees/sec or less. In five patients with downbeat nystagmus, further increases in RIS caused the oscillopsia to reappear, but in the opposite direction. Electronic stabilization also improved visual acuity in four of five patients; the limitation of improvement could be related to coexistent visual system defects. Using electronic feedback, we could measure the range of RIS that any individual required to abolish oscillopsia; from this measurement, the components of the optical device that were best suited to provide a stable field of vision could be calculated.