Voluntary control of microsaccades during maintained monocular fixation.

A contact-lens technique was used to record eye movements made by two subjects instructed either to "fixate" stationary white-light targets or to "hold" their eyes in position in the presence of the same targets. A marked reduction in saccade rate, frequently reaching zero throughout 9.8-second trials, was observed under the "hold" instruction.

Reading with a macular scotoma. II. Retinal locus for scanning text.

To elucidate how patients with macular scotomas use residual functional retina for inspecting visual detail and reading, we tested three patients with dense macular scotomas using a scanning laser ophthalmoscope that allows an examiner to view and record stimuli on the retina while the patient views them. Using standard psychophysical techniques, we determined the retinal position of scotomas, the retinal areas used for fixating and inspecting acuity targets, and the retinal area used for reading simple, three-letter, nonsense syllables. We found that each patient used a single, idiosyncratic retinal area, immediately adjacent to the scotoma, for fixating, inspecting acuity targets, and scanning simple, nonsense-syllable text. This preferred retinal locus (PRL) was at different retinal eccentricities (relative to the foveola) for each patient and was not always as close as possible to the foveola. There appears to be no simple rule by which patients "select" a particular PRL. Plots of text placement on the retina revealed considerable differences in patients' abilities to execute an orderly text scan. Two patients read text more rapidly with a novel retinal area than with their PRL, suggesting that the PRL may not be optimal for text reading.

Automation in krypton laser photocoagulation.

Histologic study of lesions produced by krypton red (647.1 nm) and krypton yellow (568.2 nm) laser lights reported here suggests advantages in alternating these two wavelengths in photocoagulation. Selection of the best wavelength to be used in a given location on the retina should result from pre-determined absorbance conditions in that location. The feasibility of the relative measurement of absorbance in different fundus locations by measurement of the relative reflectance is discussed. Instrumentation for these measurements and for switching from one wavelength to the other is described. Instrumentation for the possible expansion of krypton laser applications to clinical problems in the anterior segment also is suggested.

Retinal localization of scotomata by scanning laser ophthalmoscopy.

The scanning laser ophthalmoscope (SLO) system has been modified to permit direct retinal perimetry. A movable pinhole in a retinal conjugate plane furnishes a mapping stimulus whose retinal locus is directly observable on a video image of the fundus. Scotoma maps in patients with macular disease and physiologic scotomata associated with normal optic discs are presented. Clinical applications of the method are discussed.

Reading with a macular scotoma. I. Retinal location of scotoma and fixation area.

To investigate how patients with macular scotomas use residual functional retinal areas to inspect visual detail, a scanning laser ophthalmoscope (SLO) was used to map the retinal locations of scotomas and areas used to fixate. Three patients with dense macular scotomas of at least 20 months duration and with no explicit low vision training were tested. SLO stimuli were produced by computer modulation of the scanned laser beam, and could be placed on known retinal loci by direct observation of the retina on a television monitor. Videotaped SLO images were analyzed to produce retinal maps that are corrected for shifts of stimulus position due to fixational eye movement, thus showing the true retinal locations of scotomas and fixation loci. Major findings were as follows: 1) each patient used a single, idiosyncratic retinal area, immediately adjacent to the scotoma to fixate, and did not attempt to use the nonfunctional foveola, 2) fixation stability with the eccentric fixation locus was as good as, or better than, that of ocularly normal subjects trying to fixate at comparable eccentricities, 3) fixation stability was not systematically related to clinical visual acuity, and 4) there is good agreement as to the shape and overall size of SLO and standard clinical tangent screen scotoma maps for these three patients.

Monitoring gastrointestinal intraluminal PCO2: problems with airflow methods.

UNLABELLED: Gastrointestinal intraluminal PCO2 (PiCO2) information is used to assess the adequacy of trauma patient resuscitation and to assist in choosing resuscitative interventions. Therefore, determining the limitations and potential caveats of different PiCO2 monitoring systems is clinically important. This study compared two PCO2 monitoring systems. The airflow device adds and then removes air samples to quantitate PCO2, whereas the fiber-optic device does not. METHODS: Airflow (TRIP Tonometer/Tonocap) and fiber-optic (Neotrend) systems were used. In vitro they were compared with each other and to two end-tidal CO2 monitors measuring the PCO2 of humidified air containing 5% and then 10% CO2. In vivo the two systems' catheters were surgically juxtaposed in 15 dogs' stomachs; paired PiCO2 readings were taken throughout hemorrhage and resuscitation. RESULTS: In vitro, paired PCO2 values from the airflow and fiber-optic devices correlated with each other (r = 0.99) and with end-tidal values (r = 0.99 with airflow, r = 0.95 with fiber-optic). In vivo, paired values differed significantly (P < 0.0001), correlating poorly for two devices simultaneously measuring the same variable (r = 0.61). Fiber-optic PiCO2 values were higher than airflow values (mmHg +/- SEM): 69.3 +/- 4.8 vs. 61.3 +/- 5.6 at the start of hemorrhage, 141.3 +/- 12.9 vs. 87.7 +/- 7.9 by end of hemorrhage, and 104.3 +/- 9.6 vs. 82.8 +/- 7.0 by end of resuscitation for fiber-optic and airflow, respectively. CONCLUSIONS: Despite agreement in vitro, airflow methods can influence PiCO2 values obtained in vivo. Passive sensing methods used to monitor PiCO2, such as fiber-optic methods, are preferable because they neither deliver O2 to, nor remove CO2 from the local microenvironment.

Retrieval of an aspirated bullet fragment by flexible bronchoscopy in a mechanically ventilated patient.

We report the case of a 28-year-old man who aspirated a bullet fragment following a gunshot. Review of the literature indicates this to be a rare finding. Bedside flexible bronchoscopy provided visualization of the foreign body and facilitated its removal while the patient was on a ventilator. The benefits of flexible bronchoscopy in similar conditions are discussed.

Preventive antibiotic usage in traumatic thoracic injuries requiring closed tube thoracostomy.

OBJECTIVE: To evaluate the safety and effectiveness of antibiotics in reducing the infectious complications following closed tube thoracostomy for isolated chest trauma. DESIGN: Double-blind, randomized clinical trial. SETTING: Medical school affiliated large urban teaching hospital and trauma center. PATIENTS: One hundred nineteen of 159 patients over 18 years old presenting to the emergency department requiring closed tube thoracostomy for isolated chest injuries (113 penetrating, 6 blunt). INTERVENTION: Patients received either placebo or 1 g cefonicid daily intravenously started at chest tube insertion and stopped within 24 h of removal. MEASUREMENTS AND RESULTS: The development of wound infections, pneumonia (CDC criteria), or empyema; the incidence of adverse events; length of hospitalization. One nonspecific infection was seen in the cefonicid group (1.6 percent) and six respiratory tract infections (10.7 percent) in the placebo group (three empyema, one empyema with pneumonia, two pneumonia) (p = 0.0505; p = 0.0094 [excluding nonspecific infection]). No significant differences with antibiotic use were seen in the duration of chest tube use (p = 0.766), peak WBC counts (p = 0.108), lower peak temperatures (p = 0.063), or length of hospitalization (p = 0.165). Patients who developed infectious complications averaged approximately 8 days longer hospitalization than those without (p < 0.0001). CONCLUSION: This study showed that patients receiving antibiotics had a significantly reduced rate of infection than did patients administered placebo. No significant adverse events were seen in either group.

Diagnostic pneumoperitoneum in the pediatric patient with a unilateral inguinal hernia.

Controversy continues among surgeons over the management of pediatric patients with unilateral groin hernias. Currently, advocated treatment modalities include repair of only the clinically apparent side, exploration of the contralateral side when the ipsilateral hernia is repaired, or performance of contrast herniography before surgery. Another technique for consideration--diagnostic intraoperative pneumoperitoneum--is a simple, quick, safe, and highly accurate means of detecting a clinically inapparent contralateral inguinal hernia during the initial surgery. This technique, the results of its use, and a review of the literature are included.

Myocardial performance after contusion with concurrent hypovolemia.

Myocardial contusion may present as a benign nonclinical event or a life-threatening emergency. Although cardiac output is recognized to be decreased with major contusion, the contribution of hypovolemic shock to myocardial dysfunction is unclear. This study was designed to evaluate the relationship between myocardial contusion and hypovolemic shock. After Sprague-Dawley rats were anesthetized, contusions were administered at either 80 psi or 120 psi. Half of each group then underwent hypovolemic shock. After 24 hours of recovery, cardiac hemodynamics were studied in each subgroup using the Neely-Langendorff apparatus. Isoenzymes and histology were evaluated as well. The data showed that rats undergoing hypovolemic shock in each subgroup had a significant decrease in cardiac output when compared with their controls. This decrease was more pronounced in the 120-psi group. Cardiac isoenzyme levels were elevated in all groups. Microscopic evaluations showed contusion in the controls and necrosis in the shock groups. Patients whose injuries are compatible with myocardial contusion and hypovolemic shock should be resuscitated quickly and evaluated for myocardial dysfunction secondary to infarction.

Resolution of experimental pneumothorax in rabbits by oxygen therapy.

The treatment of asymptomatic patients with small pneumothoraces (ie, less than 20% by volume) has included observation, tube thoracostomy, and operation. When observation is used, the anticipated expansion of the lung has been estimated to be 1.25% of the lung volume daily. This study was designed to evaluate the use of inhaled oxygen as a method to accelerate the resolution of a pneumothorax in a rabbit model. Experimental pneumothoraces were created in 23 white New Zealand rabbits. Group 1 (9 rabbits) were placed in a cage with room air and group 2 (11 rabbits) were placed in a cage with high oxygen concentration. Three rabbits died before completion of the study. Serial chest roentgenograms were performed until the pneumothoraces resolved. The majority of rabbits treated with oxygen had resolution of their pneumothoraces by 36 hours, whereas the majority of rabbits treated with room air did not show complete resolution before 48 hours. Biopsies showed no evidence of damage secondary to oxygen treatment. Oxygen treatment was found to be significantly better in the early resolution of pneumothoraces when compared with room air. This establishes an alternative treatment for some pneumothoraces that are small and asymptomatic.

Automated clinical visual acuity testing.

We developed a method for testing visual acuity using a general-purpose microcomputer which displays visual acuity targets on a television monitor, controls a staircase psychophysical testing procedure, and provides a printed record of mean visual acuity and standard deviation. This automated procedure can be used to increase the precision of clinical visual acuity testing and to determine if changes in a patient's visual acuity are statistically significant.

Corneal light scattering and visual performance in myopic individuals with spectacles, contact lenses, or excimer laser photorefractive keratectomy.

Corneal transparency and visual performance are currently receiving much attention after excimer laser surgery. To date, emphasis has been on comparison of eyes on which laser surgery has been performed to eyes with emmetropia. A more appropriate comparison should be between eyes on which laser surgery has been performed and eyes with other forms of correction for myopia. Forward-scattered light, back-scattered light, and visual acuity were investigated and data were collected from 35 myopic individuals with various types of correction for myopia (spectacles, hard and soft contact lenses, and excimer laser surgery). Forward-scattered light was measured by using a new computerized technique, back-scattered light was measured with a charge coupled device-camera system, and visual acuity was measured with a computerized system at various levels of contrast. Spectacles, hard contact lenses, and excimer laser surgery are all superior to soft contact lenses in terms of light scatter and low-contrast visual acuity and excimer laser photorefractive keratectomy produces comparable results to spectacles one year postoperatively. At low-contrast visual acuity, mean visual acuity was 2.45 minutes of arc for the spectacle wearers, 3.21 minutes of arc for the hard contact-lens wearers, and 5.04 minutes of arc for the soft contact-lens wearers. Excimer laser patients had a mean visual acuity of 9.04 minutes of arc three months postoperatively, and 2.53 minutes of arc after one year. A mean value of 2.4% contrast for forward light scatter was obtained for spectacle wearers compared with a level of 3.84% contrast for hard contact-lens wearers and 16.1% contrast for soft contact-lens wearers. The mean value for excimer laser patients was 20% contrast three months postoperatively and 2.1% contrast one year postoperatively.

Medical complications of head injury.

There are many common and significant medical complications of head injury. These include (1) cardiovascular problems such as hyperdynamic state, myocardial injury, and dysrhythmias; (2) respiratory changes such as neurogenic pulmonary edema, hypoxia, abnormal ventilatory patterns, pulmonary infections, and pulmonary emboli secondary to deep vein thrombosis; (3) consumption coagulopathy; (4) water and electrolyte derangements--hypo- and hypernatremia; (5) hypothalamic/pituitary dysfunction--syndrome of inappropriate secretion of antidiuretic hormone and diabetes insipidus; (6) increased general metabolism with loss of immunocompetence, respiratory compromise, and complications of decreased activity; (7) gastrointestinal difficulties, particularly stress gastritis; and (8) infectious problems including those related to contamination from open wounds and foreign bodies such as monitors.

Why HID headlights bother older drivers.

Driving requires effective coordination of visual, motor, and cognitive skills. Visual skills are pushed to their limit at night by decreased illumination and by disabling glare from oncoming headlights. High intensity discharge (HID) headlamps project light farther down roads, improving their owner's driving safety by increasing the time available for reaction to potential problems. Glare is proportional to headlamp brightness, however, so increasing headlamp brightness also increases potential glare for oncoming drivers, particularly on curving two lane roads. This problem is worse for older drivers because of their increased intraocular light scattering, glare sensitivity, and photostress recovery time. An analysis of automobile headlights, intraocular stray light, glare, and night driving shows that brightness rather than blueness is the primary reason for the visual problems that HID headlights can cause for older drivers who confront them. The increased light projected by HID headlights is potentially valuable, but serious questions remain regarding how and where it should be projected.

A novel method for measuring saccade profiles using the scanning laser ophthalmoscope.

Most existing techniques for accurately measuring angular eye position vs time during a saccade (the saccade profile) need either contact to the eye or are restricted in time resolution. In this paper we introduce a new noninvasive method, with high spatial and temporal resolution, for determining saccade profiles using a scanning laser ophthalmoscope (SLO). This method uses the fact that images of a moving object taken with the SLO are not blurred (as are images from video cameras) but show a tilt with respect to images of the same stationary object. A mathematical framework is given that allows determination of a saccade profile from a restricted number of consecutive SLO video fields of the fundus during a saccade. The angular resolution obtained by this method is below 0.1 deg, and the maximum time resolution near 1 msec. Measured saccade profiles could be well approximated by a gamma function, the first derivative of which yields the saccade velocity profile. Measurements of peak saccade velocity as a function of saccade amplitudes (main sequence) using our method show good agreement with results obtained by other authors.

Feature-based registration of retinal images.

Registration of retinal images taken at different times frequently is required to measure changes caused by disease or to document retinal location of visual stimuli. Cross-correlation has been used previously for such registration, but it is computationally intensive. We have modified a faster algorithm, sequential similarity detection (SSD), to use only the portion of the template that contains retinal vessels. When compared to standard SSD and cross-correlation, this modification improves the reliability of detection for a variety of retinal imaging modalities. The improved reliability enables implementation of a two-stage registration strategy that further decreases the amount of computation and increases the speed of registration.

Blunt pancreatic trauma: experience at a rural referral center.

The objective of this study was to compare mechanism of injury, treatment methods, and outcome of blunt pancreas trauma patients transferred from another hospital to those of patients brought directly from the scene. A retrospective review was conducted of 6078 patients treated at a Level I trauma center from 1/1/90 to 12/31/94. Blunt pancreas injury was found in 39 (0.64%) patients (mean age, 33.2 years). Mechanism of injury included 34 (87%) motor vehicle crashes, 3 (8%) motorcycle crashes, and 2 (5%) other injuries. There were 11 transfer patients (28%), and 28 (72%) admitted directly from the scene. Eighty-two per cent of the motor vehicle crash patients were unrestrained, and 35 per cent had ethanol intoxication. Exploratory laparotomy was performed on 32 (82%); eight (25%) required repair or resection; 22 (69%) had trivial injuries, at most requiring drainage; and two (6.3%) exsanguinated. No patients required Whipple resection or pancreatiocojejunostomy. At operation, an average of 2.5 associated intra-abdominal injuries were found. Overall survival was 35 of 39 (90%). Among the patients brought directly to the trauma center, 93 per cent survived, whereas survival among transferred patients was 82 per cent (chi2 = 0.19; P = 0.66). Blunt pancreatic injuries vary in severity, but radical resection is rarely required. Lack of safety restraint and ethanol use are major risk factors. Despite the high likelihood of associated injuries, survivability is high. No difference in outcome was seen between directly admitted and transferred patients.

Venous injury: to repair or ligate, the dilemma revisited.

Controversy continues over management of major venous injuries. The records of 322 patients with venous injury were reviewed. Isolated venous injury was present in 83 patients; 54 (65%) underwent ligation of the injured vein. Combined arterial and venous injuries were present in 239 patients; 170 (71%) patients had ligation. Injured were the inferior vena cava, iliac, femoral, popliteal, distal leg, and arm veins; all were confirmed at surgery. Arterial injuries were repaired with standard techniques; venous injuries were ligated or repaired by end-to-end or lateral phleborrhaphy. Adjunctive fasciotomy was used as clinically indicated. The patients were followed an average of 32 months. No patient with isolated venous injury developed permanent sequelae, although 29 (35%) had transient extremity edema. Transient edema developed in 86 (36%) patients with combined injury, and permanent edema occurred in 4 (2%). Edema developed regardless of vein injury ligation or repair. No extremity was lost after venous injury ligation. While repair of all venous vascular injuries is still the surgical ideal, in civilian practice permanent sequelae of venous injury ligation are rare and in patients with hemodynamic instability from blood loss, extensive local injury, associated organ injury, anesthesia requirements, or other concerns venous ligation is acceptable.

Perforated jejunal diverticula: an analysis of reported cases.

We recently encountered two cases of perforated jejunal diverticula. We analyzed the data from all available cases of perforated jejunal diverticula, including our two cases. Our purpose was to increase awareness of this rare clinical entity as a cause of abdominal pain. An extensive literature review using Medline from its inception in 1972, and a manual review of all previously published reports was performed. Data collected included age, gender, length of symptoms from history and physical exam, operative findings, type of operation, and outcome (survival). Data analysis was performed using student's t test and multivariate analysis. Survival was not influenced by gender or type of operation. When the reports documented the number of diverticula present in the area of perforation (22 cases) a majority (19/22) had multiple diverticula. Perforated jejunal diverticula are a rare clinical entity in which age, type of operation, and gender does not influence outcome, but a longer duration of symptoms before operation trended towards a worse outcome. This clinical diagnosis should be entertained as part of any evaluation of abdominal pain.