High-resolution spatio-temporal mapping of visual pathways using multi-electrode arrays.

The parallel processing of visual information was studied with penetrating microelectrode arrays. We studied the high-resolution visuotopic organization of cat primary visual cortex, and the encoding of simple visual stimuli by ensembles of ganglion cells in the isolated turtle retina. The high-resolution visuotopic organization of visual cortex is non-conformal. Regions of visual cortex separated by 400 mu may have receptive field centers that are separated by as much as 3 degrees, or they may superimpose. Ganglion cells are 'generalists', and are poor specifiers of the color of full field visual stimuli. Groups of 'luminosity' type ganglion cells can assist in the specification of stimulus color, but even individual 'chromatic' ganglion cells are not capable of quality color specification. These basic studies have relevance to the development of visual neuroprostheses based upon electrical stimulation of the retina and cortex.

Identification of intranasal cerebrospinal fluid leaks by topical application with fluorescein dye.

The purpose of this paper is to describe a safe new technique for intraoperative identification of the site of cerebrospinal fluid rhinorrhea. Cerebrospinal fluid (CSF) rhinorrhea after intracranial or intranasal surgery is a known potential complication with significant morbidity and mortality. It is currently accepted that endoscopic intranasal management of CSF rhinorrhea is the preferred method of surgical repair, with higher success rates and less morbidity than intracranial surgical repair in selected cases. Accurate identification of the site of CSF leakage is necessary for a successful endoscopic surgical repair. Computer tomography (CT) with or without intrathecal contrast and preoperative nasal endoscopy are frequently used to preoperatively localize the site of the leak. Intrathecal fluorescein administered immediately before surgery has aided in the intraoperative identification of the site of CSF leak in 25-64% of patients undergoing endoscopic repair of CSF rhinorrhea in whom preoperative CT scanning and nasal endoscopy had not identified the site of CSF leak. Intrathecal fluorescein, however, has been associated with severe complications, such as lower extremity weakness, numbness, generalized seizures, opisthotonus, and cranial nerve deficits. We present three cases of CSF rhinorrhea in which fluorescein was applied intranasally during the endoscopic surgical repair. Ten percent fluorescein was applied to the nose with a cotton swab. Under endoscopic visualization the fluorescein changed its fluorescent color from amber/yellow to a dark green and was found streaming from high in the nasal cavity, which led to accurate identification of the site of the CSF leak.

Infectious ocular complications in orthotopic liver transplant patients.

We report the frequency and type of infectious ocular complications following orthotopic liver transplantation (OLT) and review diagnostic and therapeutic strategies. During the period September 1988 through November 1994, 684 patients underwent OLT at Mount Sinai Hospital (New York). Nine orthotopic liver transplant patients (1.3%) developed ocular infections: Candida albicans endophthalmitis (2), Aspergillus fumigatus endophthalmitis (1), cytomegalovirus retinitis (4), herpes simplex virus keratitis (1), and varicella-zoster virus panophthalmitis (1). The mean time from OLT to ocular symptoms was 42 days for patients with fungal infections and 128 days for patients with viral infections. Blurred vision was the commonest symptom (five of nine cases). The mean duration of follow-up was 2 years (range, 33 days to 5 years). Permanent loss of vision occurred in three patients, five had improvement in visual acuity, and one died of disseminated aspergillosis 33 days after OLT. Infectious ocular complications following OLT may occur as isolated events or with disseminated disease. Fungal infections occur earlier (mean, 42 days after OLT) than viral infections (mean, 4 months after OLT). The clinical presentation may be atypical; aggressive vitreoretinal procedures and serial examinations may be required to establish the diagnosis. Cytomegalovirus retinitis in orthotopic liver transplant patients may not require life-long maintenance therapy with antiviral agents.

Motor blocks in Parkinson's disease.

Freezing episodes and related phenomena (as a general term, motor blocks [MBs]) are poorly understood, particularly disabling, and a therapeutically frustrating problem in Parkinson's disease (PD). Epidemiologic and clinical characteristics of MBs, as well as risk factors to develop MBs, have never been fully addressed. Herein, we report our database survey on 990 PD patients, of whom 318 (32%) had MBs. The majority of MBs were linked to gait. Start hesitation occurred in 86%, blocking on turning in 45%, and blocking in narrow spaces in 25% of patients. Initial parkinsonian symptoms in the upper body and tremor as the initial motor symptom were less likely to be associated with the presence of MBs (odds ratios [OR] 0.6 and 0.7, respectively), while initial symptoms affecting gait or trunk had higher association with MBs (OR = 1.58). Longer disease duration, higher Hoehn and Yahr stage, and longer duration of levodopa treatment are all significantly associated with the presence of MBs. We observed significant association between the existence of MBs and levodopa-induced dyskinesias to suggest similar pathophysiology. We propose that MBs in PD are abnormal retrieval or execution of complex motor tasks that can occur as a result of disease progression or as short- or long-term side effects of levodopa treatment.

The effect of blur and contrast on VEP latency: comparison between check and sinusoidal and grating patterns.

Pattern defocusing was used to evaluate the contribution of different spatial frequency components in checks to VEP latency. Latency shifts with increasing blur (-2.5 to +2.5 diopters) were determined for sinusoidal grating and check patterns equated in fundamental spatial frequency. With both check and grating patterns, the effect of blur was greater the higher the spatial frequency. Given an equal fundamental spatial frequency, however, the latency of checks was more effected. This latency difference between check and sine patterns was pronounced at low fundamental spatial frequencies (large pattern) and decreased with higher spatial frequencies (small pattern). Latencies were then compared for patterns which were defocused vs. simply reduced in contrast. Results show that the increase in latency with defocused large checks is due to both fundamental and higher harmonic spatial components but with small checks, to the fundamental spatial frequency alone.

Delayed visual evoked potentials are independent of pattern orientation in macular disease.

Visual evoked potentials (VEPs) and contrast sensitivity (CS) were studied in patients affected by maculopathy. VEP delays and CS reduction were demonstrated in each affected eye. In distinction to patients affected by multiple sclerosis (MS), in maculopathy patients VEP latency is independent of the orientation of the grating stimulus. It is proposed that stimulating with more than one pattern orientation is useful in the differential diagnostic use of VEPs.

Removal of intravitreous cysticerci from the surface of the optic nervehead. A pars plana approach.

Two larvae of Taenia solium (eg, Cysticercus cellulosae) were identified in the posterior vitreous attached to the optic nervehead of a 13-year-old Guatemalan girl. Preoperative evaluation showed the larvae to be viable. The vitreous showed a mild cellular reaction. The larvae were dissected off the optic nervehead and removed via a pars plana approach, without incident. To our knowledge, this is the first case report of cysticerci attached to the optic nervehead that were removed successfully by the pars plana approach. The patient was treated with a very short preoperative and postoperative course of corticosteroids. No inflammatory flare-ups or recurrence of the cysticercosis were found during the one-year follow-up period.