Influence of age and spectral power distribution on mesopic visual sensitivity.

The ability of the human visual system to detect stimuli at low illumination levels provides awareness of potential risks. The influence of age and spectral power distribution on mesopic spectral sensitivity is analyzed. Two typical light sources are used, a high-pressure sodium lamp (HPS), with a higher content of long wavelengths, and a metal halide lamp (MH), with a higher content of short wavelengths. Two experiments were performed, using a two-channel Maxwellian-view optical system to measure contrast threshold under different experimental conditions. In Experiment 1, three age groups (young, middle-aged and old, n = 2 each), two retinal locations (on-axis and off-axis vision), four background luminances (0.01, 0.07, 0.45, and 3.2 cd/m2), and two photometry systems (photopic and the MES2 systems) were considered. In Experiment 2, contrast threshold measurement was performed with two age groups (young and old, n = 11 each), one retinal location (off-axis vision), one background luminance (0.01 cd/m2), and two photometry systems (photopic and the MES2 systems). In on-axis vision, neither age nor spectral power distribution have an effect on the contrast threshold. In off-axis vision, however, a significant interaction between age and spectral power distribution is obtained, albeit only at 0.01 cd/m2 with an MH lamp. Only at this lowest background luminance was the greater content of short wavelengths of this lamp responsible for higher rod stimulation in off-axis vision, with the subsequent improvement in detection performance in young subjects. However, the effect of diffused light inside the aged eye counteracted the benefits of increased rod sensitivity for the MH lamp.

Temporal retinal sensitivity in mesopic adaptation.

PURPOSE: Night driving is a complex visual task with important ramifications for driver and pedestrian safety. It is usually performed under mesopic or scotopic conditions and frequently, in the presence of transient glare sources that can adapt parts of the central retina. The objective of this work was to analyze the time response of adaptation for the central 15° of the retina when part of it is exposed to transient or steady mesopic adapting fields. METHODS: Absolute visual thresholds and luminance thresholds when viewing steady and transient adaptation fields were measured for three observers, at temporal retinal eccentricities of 0°-14.5° in steps of 2.9° (subsequently described as 0°, 3°, 6°, 9°, 12° and 15°) using a two-channel Maxwellian view optical system. The adaptation field and stimulus subtended 1.05° and 0.45° respectively. The transient adaptation field was presented with a stimulus onset asymmetry (SOA) of 300 ms. Time course adaptation curves were also measured at 0°, 6° and 9°. RESULTS: The absolute dark adaptation threshold (threshold measured at dark adaptation conditions or L(a)(t) decreases in peripheral retina due to an increasing rod contribution. Luminance thresholds vs eccentricity curves for transient L(SOA300)(t) and steady L(LA)(t) mesopic adaptation fields intersect across the first 15° of the peripheral retina. CONCLUSIONS: While the fovea shows higher sensitivity than the areas of peripheral retina investigated in this study, the speed of adaptation, measured from the visibility loss, is greater for retinal regions between 6° and 9° than for the fovea or retinal eccentricities beyond 9°.

Quantitative and functional influence of surround luminance on the letter contrast sensitivity function.

AIM: To determine the influence of surround luminance on the letter contrast sensitivity function. METHOD: The binocular contrast sensitivities of 31 young and ocularly healthy individuals were measured with letters of sizes calculated to obtain the targeted fundamental frequencies of 3, 10, 20, and 30 c deg(-1), respectively; with surround luminances from 1 to 1000 cd m(-2), always with a test chart background luminance of 200 cd m(-2). RESULTS: The letter contrast sensitivity increased with surround luminance up to 100 cd m(-2) and decreased when surround luminance increased from 100 to 1000 cd m(-2). These increments are larger for higher fundamental spatial frequencies, while decrements are similar for all frequencies. To analyse pupil size influence, results were compared with theoretical predictions obtained by combining different ocular MTFs with a typical neural function, where pupil size decrease leads to letter contrast sensitivity increments and veiling luminance causes the observed decrements. Other possible optical or neural factors that influence these values have also been considered. CONCLUSIONS: Letter contrast sensitivity function depends on surround luminance and this influence should be considered in future standardized directives.

Techniques of posterior C1-C2 stabilization.

Instability of the atlantoaxial complex may result from inflammatory, traumatic, congenital, neoplastic, or degenerative disorders and often requires surgical stabilization. Initial dorsal wiring techniques allow safe fixation but require rigid external immobilization and have been associated with high fusion failure rates. Rigid screw fixation techniques including transarticular screw fixation and C1-C2 rod-cantilever fixation offer higher fusion rates and less need for rigid immobilization but are more technically demanding. C1-C2 fixation using crossing C2 laminar screws offers rigid fixation but without the technical demands of C2 pars placement. The history and techniques of dorsal fixation of the atlantoaxial complex are reviewed, and the success rates and complications of each are discussed.

Pediatric neurosurgical injuries associated with all-terrain vehicle accidents: a 10-year experience at St. Louis Children's Hospital.

OBJECT: All-terrain vehicles (ATVs) have been characterized as inherently unstable and are associated with significant pediatric injuries in the US. The authors performed a study to analyze data obtained in pediatric patients who had sustained neurological injuries in ATV-related accidents, identify potential risk factors, and propose preventive measures. The study is based on a 10-year experience at the St. Louis Children's Hospital. METHODS: The authors retrospectively analyzed data obtained in all patients admitted to the St. Louis Children's Hospital between 1993 and 2003, limiting their focus to pediatric cases involving ATV-related accidents. A total of 185 patients were admitted with these criteria. Sixty-two patients (33.5%) suffered neurological injuries; there were 42 male and 20 female patients whose age ranged from 2 to 17 years. The most common injuries included skull fracture (37 cases) and closed head injury (30 cases). There were 39 cases of intracranial hemorrhage and 11 of spinal fracture. A total of 15 types of neurosurgical procedure were performed: six craniotomies for hematoma drainage, five craniotomies for elevation of depressed fractures, two procedures to allow placement of an intracranial pressure monitor, one to allow placement of an external ventricular drain, and one to allow the insertion of a ventriculoperitoneal shunt. Two patients had sustained spinal cord injury, and three procedures were performed for spinal decompression or stabilization. The duration of hospital stay ranged from 1 to 143 days (mean 6.6 days). Fifty-seven patients (30.8%) were eventually discharged from the hospital, three (1.6%) were transferred to another hospital, two (1.1%) died, and 123 (66.4%) required in-patient rehabilitation. CONCLUSIONS: Children suffered significant injuries due to ATV accidents. In passengers there was a statistically significant increased risk of neurological injury. The relative risk of neurological injury in patients not wearing helmets was higher than that in those who wore helmets, but the difference did not reach statistical significance. Further efforts must be made to improve the proper operation and safety of ATVs, both through the education of parents and children and through the creation of legislation requiring stricter laws concerning ATV use.

Early programmable valve malfunctions in pediatric hydrocephalus.

OBJECT: The use of adjustable differential pressure valves has been recommended to improve ventriculoperitoneal (VP) shunt performance in selected patients; however, published data are scarce regarding their clinical reliability. Recently, the identification of a number of malfunctioning programmable valves during shunt revision surgery in children prompted a retrospective review of valve performance in this patient cohort. METHODS: The authors performed a retrospective chart analysis of 100 patients with programmable valve shunts and 89 patients with nonprogrammable valve shunts implanted at the St. Louis Children's Hospital between April 2002 and June 2004. They noted the cause of hydrocephalus, the type of shunt malfunction, and cerebrospinal fluid (CSF) protein levels. Regular clinical follow up ranged from 1 to 26 months, with a mean follow-up time of 9.75 months for patients with programmable valves and 10.4 months for patients with nonprogrammable valves. Patient ages ranged from 2 weeks to 18 years. One hundred patients had 117 programmable valves implanted, and 35 of these patients (35%) underwent shunt revision because of malfunction. The programmable valve itself malfunctioned in nine patients who had undergone shunt revision (11.1%/year of follow up). The nonprogrammable valve group had no valve malfunctions. The overall VP shunt revision rate in the nonprogrammable valve group was 20.2%. No significant differences were identified when CSF protein levels and specific malfunction types were compared within the programmable valve and nonprogrammable valve groups. CONCLUSIONS: In this study the authors demonstrated an annualized intrinsic programmable valve malfunction rate of 11.1%, whereas during the same period no intrinsic valve malfunctions were noted with nonprogrammable valve systems for similar causes of hydrocephalus. The CSF protein levels did not correlate with observed valve malfunction rates. Further evaluation in a prospective, randomized fashion will elucidate specific indications for programmable valve systems and better determine the reliability of these valves in the pediatric population.

Treatment of severe coagulopathy after gunshot injury to the head using recombinant activated factor VII.

PURPOSE: Patients with severe penetrating head injury often have a coagulopathy that is difficult to correct. In this report, we describe 3 such patients who were treated with activated factor VII (FVIIa) to stop ongoing hemorrhage that was refractory to conventional treatment. SUBJECTS AND METHODS: We treated 3 patients with severe head injury secondary to gunshot wounds to the head. All 3 patients had ongoing bleeding secondary to a severe consumptive coagulopathy that was refractory to treatment with fresh frozen plasma, platelets, and cryoprecipitate. Recombinant FVIIa was then administered to achieve hemostasis. RESULTS: Administration of FVIIa (90-120 microg/kg) was successful in rapidly achieving hemostasis and correcting abnormal laboratory parameters indicative of coagulopathy in all patients. Although all 3 patients died, control of bleeding made organ donation possible in 2 patients. CONCLUSION: In patients with a severe head injury and coagulopathy, use of FVIIa may help in correction of coagulopathy and decrease transfusion requirements. In patients where ongoing bleeding precludes the declaration of brain death, the use of this agent might help in achieving hemodynamic stability and preserve the possibility of organ donation. The ethical implications of using FVIIa in this situation are discussed.

Complicaciones de la colecistectomía laparoscópica / Complications of laparoscopic cholecystectomy

Se analizan las complicaciones ocurridas en 500 colecistectomías laparoscópicas (403 colecistopatías no agudas y 97 colecictitis agudas), realizadas entre octubre de 1990 y junio de 1992. En 144 pacientes (28.8//) se produjo efracción vesicular, hemorragia en 37 (7.4//), caída de cálculos en la cavidad en 44 (8.8//), recuperándose en la mayoría. Fueron laparotomizados 20 enfermos (4//) de los cuales uno (0.2//) fue por lesión de la vía biliar y 10 (50//) por hilio congelado. En el postoperatorio cuatro pacientes (0.8//) presentaron bilirragia, uno (0.2//) litiasis residual resuelta por vía endoscópica, siendo reoperados tres (0.6//) por úlcera perforada, hematoma subhepático y evisceración umbilical atascada respectivamente. La incidencia de hemorragia y conversiones fue significativamente mayor en las patalogías agudas

Complicaciones de la colecistectomía laparoscópica / Complications of laparoscopic cholecystectomy

Se analizan las complicaciones ocurridas en 500 colecistectomías laparoscópicas (403 colecistopatías no agudas y 97 colecictitis agudas), realizadas entre octubre de 1990 y junio de 1992. En 144 pacientes (28.8//) se produjo efracción vesicular, hemorragia en 37 (7.4//), caída de cálculos en la cavidad en 44 (8.8//), recuperándose en la mayoría. Fueron laparotomizados 20 enfermos (4//) de los cuales uno (0.2//) fue por lesión de la vía biliar y 10 (50//) por hilio congelado. En el postoperatorio cuatro pacientes (0.8//) presentaron bilirragia, uno (0.2//) litiasis residual resuelta por vía endoscópica, siendo reoperados tres (0.6//) por úlcera perforada, hematoma subhepático y evisceración umbilical atascada respectivamente. La incidencia de hemorragia y conversiones fue significativamente mayor en las patalogías agudas