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T H Williamson

Publications and source records attributed to T H Williamson.

At least 19 recordsLinked to original sources
PubMed1995

A comparison of colour Doppler imaging of orbital vessels and other methods of blood flow assessment.

BACKGROUND: Comparison of the haemodynamic measurements obtained by colour Doppler imaging and other methods of ocular blood flow measurements was desired. METHODS: The blood velocity findings from colour Doppler imaging of patients with central retinal vein occlusion were compared to the results of fluorescein video-angiography, continuous tonography and ophthalmodynamometry. RESULTS: Patients with low or undetectable blood velocities in the central retinal vein had longer retinal dye transit times on fluorescein video-angiography. Tonography showed a positive correlation with the velocities in the ophthalmic artery, but ophthalmodynamometry showed a negative correlation with these velocities. CONCLUSION: The relationships between the blood velocities in orbital vessels and other blood flow measurements emphasise that there is a complex interaction of the blood flow parameters. Care must therefore be taken when interpreting the results of studies.

Aged↗
PubMed1995

Crossed polarising filters to measure relative afferent pupillary defects: reproducibility, correlation with neutral density filters and use in central retinal vein occlusion.

Measurement of a relative afferent pupillary defect (RAPD) can be carried out by attenuation of light received by the normal eye during the swinging flashlight test. Such measurements may be useful in the management of central retinal vein occlusion (CRVO). In this study a method employing cross polarised filters (CPFs) was tested for reproducibility. In addition the pattern of attenuation of light was compared with that by neutral density filters (NDFs). Finally, the method was used to investigate 74 patients with CRVO. The method was reproducible (8.7% variation) and showed exponential attenuation of light (in contrast to linear attenuation by the NDFs). In unilateral CRVO a sensitivity of 71% and specificity of 69% for the risk of iris neovascularisation was determined by the presence of RAPD requiring 20 degrees of rotation of the CPFs. It is concluded that CPFs provide a useful alternative to NDFs for the measurement of RAPD and have some advantages. They can be employed in the clinical management of patients with CRVO.

Adult↗
PubMed1995

Influence of age, systemic blood pressure, smoking, and blood viscosity on orbital blood velocities.

The influence of multiple systemic factors upon the blood velocities obtained from the orbital circulations was investigated. The velocities obtained by colour Doppler imaging from the ophthalmic artery, central retinal artery, and vein from 95 ophthalmologically healthy volunteers were analyzed. The effects of age, systemic blood pressure, and smoking habit were examined. In 24 volunteers blood viscosity was also measured and its relation with blood velocity assessed. Age was weakly negatively correlated with the blood velocities in the ophthalmic artery and weakly positively correlated with resistance to flow in the retinal circulation. Systolic blood pressure showed a positive correlation with the peak systolic velocities in the arteries while cigarette smoking was associated with lower ophthalmic artery velocities. Increased haematocrit and viscosity were positively correlated with resistance to flow proximal to the ophthalmic artery and red cell rigidity negatively correlated with the pulsatility of flow in the retinal vein. These results help to identify the roles of systemic conditions in the ocular circulation. The influence of blood viscosity on retinal venous flow may be relevant to the pathogenetic mechanisms of conditions such as central retinal vein occlusion.

Age Factors↗
PubMed1995

Assessment of an inner city visual screening programme for preschool children.

AIMS: The efficiency of preschool visual screening programmes to detect amblyopia is questionable. In this study such a programme in an inner city was assessed to determine its effectiveness. METHODS: The results of screening and hospital treatment of 712 patients who were considered to require referral were entered into a database for analysis. Default rates were assessed and the efficacy of treatment determined. RESULTS: The only effective screening test for the detection of amblyopia was visual acuity. A large proportion of referred patients had refractive problems only. High default rates, particularly in geographical areas of lower socioeconomic grading, severely handicapped any attempt to reduce the incidence of amblyopia. CONCLUSION: A fresh approach to the detection and care of amblyopia in the inner city community is required, perhaps by performing screening of children in their first year of attendance at school to reduce default rates. Cycloplegic refraction of children who are found to have reduced visual acuity before their referral to hospital is also recommended.

Amblyopia↗
PubMed1995

Color Doppler imaging of the eye: normal ranges, reproducibility, and observer variation.

Color Doppler ultrasonography has numerous potential applications in the diagnosis and monitoring of many ocular disease processes. One of its advantages over other investigative and diagnostic tests is its safety and repeatability. To be able to fully assess this technique it is important to have good control data and to know the reproducibility of the technique for each of the retrobulbar vessels. Color Doppler ultrasonography was performed on 80 volunteers, and normal ranges of blood velocity were calculated for the ophthalmic artery and for the central retinal artery and vein. Reduction in the peak systolic and end diastolic velocities in the ophthalmic artery and an increase in resistive index in the central retinal artery and vein were noted with advancing age. With regard to reproducibility of the retrobulbar vessels, 15 healthy persons were chosen at random and intra- and interobserver studies performed. The most reliable and reproducible vessels were the ophthalmic artery and central retinal artery and vein. Greater variation was noted in the posterior ciliary vessels, whereas the superior ophthalmic and vortex veins were unreliable in both detection and velocity measurement. The results provide normal ranges for future studies and demonstrate that reproducible results can be obtained for the orbital vasculature using color Doppler imaging.

Adult↗
PubMed1994

Decrease in nosocomial Clostridium difficile-associated diarrhea by restricting clindamycin use.

OBJECTIVE: To report the investigation and effective control of a nosocomial epidemic of Clostridium difficile-associated diarrhea. DESIGN: Concurrent surveillance for identification of new nosocomial cases, retrospective case-control analysis, and hospital formulary control of antibiotic use. SETTING: University-affiliated Veterans Affairs Medical Center located in southwestern United States. PATIENTS: Hospitalized patients who developed diarrhea submitted stool specimens for cytotoxin assay. Patients who were positive for cytotoxin were compared with control patients without infection. MEASUREMENTS: Isolates of C. difficile were typed by restriction endonuclease analysis. Antimicrobial agent use from hospital pharmacy records and selected patient data from chart review were correlated with frequency of specific laboratory abnormalities. RESULTS: For 13 months, the monthly incidence of C. difficile infection averaged more than five times that for the previous 21 months. Stool specimens from 34 patients (59%) contained a single strain (restriction enzyme analysis type J7). Clindamycin was statistically associated with the epidemic as shown by the following: clindamycin use at our center compared with national normal values, clindamycin use for years before compared with during the epidemic, monthly use of clindamycin compared with monthly frequency of infection, frequency of infection in patients receiving clindamycin compared with that in patients receiving other antimicrobial agents, and amount of clindamycin used by infected patients compared with that used by control patients. Restricting clindamycin use led to a prompt disease in infection rate and the type J7 organisms. CONCLUSION: A nosocomial epidemic of C. difficile diarrhea was controlled by analysis of antibiotic use patterns and by subsequent restriction of clindamycin.

Arizona↗
PubMed1994

Central retinal vein occlusion, an investigation by color Doppler imaging. Blood velocity characteristics and prediction of iris neovascularization.

PURPOSE: To determine pulsatile blood velocities in the orbital vasculature in patients with central retinal vein occlusion (CRVO). METHODS: The ophthalmic artery, central retinal artery, and vein of 80 patients with CRVO and 95 control subjects were investigated by color Doppler imaging. The patients were examined by ophthalmoscopy, relative afferent pupillary measurement using cross-polarized filters, fundus fluorescein angiography, and electroretinography to estimate the degree of retinal ischemia. RESULTS: Blood flow velocities in the central retinal vein and artery of eyes with CRVO were significantly lower than in fellow eyes and controls. The measurements from the vein were most reduced and in some cases absent in those eyes with "ischemic" CRVO. Velocities also were reduced in the central retinal artery of the affected eyes, but no correlation with "ischemia" was detected. The risk of iris neovascularization in patients examined within 3 months of onset of CRVO can be determined from the flow velocities with a high degree of predictability (75% sensitivity and 86% specificity). CONCLUSIONS: Blood velocity was reduced in the retinal circulation of patients with CRVO and reduced even further in the "ischemic" variant of CRVO. The results indicate that noninvasive color Doppler imaging could play a major part in the routine assessment of patients with CRVO within 3 months of onset.

Adult↗
PubMed1993

Color Doppler velocimetry of the optic nerve head in arterial occlusion.

BACKGROUND: Color Doppler velocimetry allows simultaneous imaging by B-scan and Doppler ultrasound. This facilitates estimation of blood velocity in the orbital vessels. A pulse arterial waveform providing blood velocity measurements can be obtained from the optic nerve head. The vascular pattern in this region consists of multiple peripapillary blood vessels and a central artery. The exact contribution of the arteries in this area to velocimetry readings was undetermined. METHODS: In this study, the arterial pulses at the optic nerve head of seven patients with central retinal artery occlusion (CRAO) and seven with anterior ischemic optic neuropathy (AION) were examined by color Doppler velocimetry. RESULTS: No velocimetric measurements were obtainable at the optic nerve head in three of four patients with acute CRAO (examined within 24 hours of onset) despite color recordings obtainable in the peripapillary region. In contrast, all patients with AION showed characteristic arterial pulse waveforms from the artery that was situated centrally in the optic nerve. No peripapillary color indices were detectable in three of the four patients with ischemic optic neuropathy who were examined within 24 hours of onset of their symptoms. Follow-up investigation showed that there was reperfusion of both arterial circulations within 1 week. CONCLUSION: The results demonstrate that color Doppler ultrasound of the optic nerve head provides velocimetric measurements of blood flow in the central retinal artery. Although some investigators using different apparatuses have produced velocimetry measurements from the posterior ciliary arteries, in this study reliable measurements were not obtainable form color indices in the peripapillary area.

Aged↗
PubMed1993

Colour Doppler velocimetry of the arterial vasculature of the optic nerve head and orbit.

Blood flow in the orbital vasculature can be investigated by colour Doppler velocimetry which allows simultaneous imaging of B-scan and Doppler ultrasound. In this paper we review the results of our recent studies on the arterial vasculature of the orbit and optic nerve head. A control study is described in which reliable measurements were obtained from the ophthalmic artery at the orbital apex, the medial orbit, and the complex of the central retinal artery and posterior ciliary arteries. Patients with occlusion of the central retinal artery and posterior ciliary arteries were examined. The results indicate that readings at the optic nerve head primarily represent blood flow in the central retinal artery. A study of the effects of posture on velocimetry demonstrated no change in the measurements obtained. Finally, topical timolol 0.5% was found to reduce the resistive indices of flow in the central retinal artery.

Adult↗
PubMed1993

Co-existence of exfoliation syndrome, previous iris surgery, and heterochromia.

A case is described where exfoliation syndrome developed in a relatively young patient with heterochromia. The patient had previously undergone large radial iridotomies as part of penetrating keratoplasty procedures. This case illustrates an association between iris surgery and early manifestation of exfoliation syndrome.

Adult↗
PubMed1993

Color Doppler flow imaging in central retinal vein occlusion: a new diagnostic technique?

Central retinal vein occlusion (CRVO) is a common cause of sudden visual loss and can occur at any age. Accurate diagnosis is essential, as differentiation of ischemic and nonischemic forms of the disease has prognostic importance. The introduction of color Doppler flow ultrasound has, for the first time, allowed visualization of the retrobulbar vessels; the central retinal artery and vein are easily identifiable. The authors conducted a prospective, blinded trial and compared images and waveforms from 20 patients with CRVO with those from 20 age-matched healthy volunteers. No difference in velocity indexes from the central retinal artery was detected between the patients' affected and unaffected eyes or between the affected eyes and control eyes. A marked reduction in venous velocity was recorded in the central retinal vein in the affected eyes when compared with that of the unaffected patient and control eyes. There was no difference in venous flow between the unaffected patient and control eyes. These initial results suggest that color Doppler flow imaging may have a role in the diagnosis of CRVO. Color Doppler flow imaging is non-invasive, is easy to perform, is well tolerated by patients, and allows temporal assessment.

Aged↗
PubMed1993

Morphometric assessment of the central retinal artery and vein in the optic nerve head.

The exact anatomy of the central retinal vein as it exits the eye is unknown. In this study serial sections of the central retinal vein and artery in the anterior optic nerve from six globes (five from cornea donors and one exenteration specimen) were examined by image analysis and three-dimensional reconstruction to determine their luminal characteristics. The retinal artery was found to have a uniform perimetric length and cross-sectional area. The vein, however, had a reduction in these measurements at the level of the lamina cribrosa, signifying a constriction of the vessel at this site. In addition, the cross section of the vein usually formed a "D" or crescentic shape adjacent to the circular artery. We propose that the constriction of the vein acts as a "throttle" mechanism on venous blood flow. Thus, a relatively high venous blood pressure is maintained within the high-pressure intraocular environment, thereby maintaining the patency of the retinal venules and capillaries.

Anthropometry↗
PubMed1992

Colour Doppler ultrasound in the management of a case of cranial arteritis.

Colour Doppler ultrasound allows simultaneous B scan and Doppler imaging and can be employed to determine the velocity of blood flow in the vasculature of the eye and orbit. We describe a case of cranial arteritis (giant cell arteritis) in which serial velocimetry recordings were obtained. At one stage in the disease process no blood flow was detectable in the orbit despite previously reliable recordings. This coincided with a deterioration of the clinical state of the patient as signified by recurrent anterior ischaemic optic neuropathy despite controlled symptomatology and erythrocyte sedimentation rate by prednisolone therapy. Subsequent increase in the immunosuppressive therapy was accompanied by a return of blood flow in the orbit. Colour Doppler ultrasound may prove to be a useful examination technique in the diagnosis and management of cranial arteritis.

Aged↗