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T H Williamson

Publications and source records attributed to T H Williamson.

At least 37 records · Page 2Linked to original sources
PubMed2001

Management of inferior retinal breaks during pars plana vitrectomy for retinal detachment.

AIMS: To determine whether it is necessary to support inferior retinal breaks with a scleral explant during pars plana vitrectomy (PPV) for rhegmatogenous retinal detachment (RD). METHODS: A prospective study was carried out on nine eyes of nine consecutive patients undergoing PPV for primary RD with associated inferior retinal breaks and no significant proliferative vitreoretinopathy. RESULTS: Eight eyes were successfully reattached with a single operation. No cases presented with redetachment because of failed closure of the original inferior breaks. CONCLUSIONS: It is not necessary to support inferior retinal breaks with a scleral explant during PPV for primary RD repair in selected cases.

Adult↗
PubMed2001

Primary rhegmatogenous retinal detachment: 20 years of change.

AIM: To compare characteristics, management, and outcome of two groups of patients with primary rhegmatogenous retinal detachment (RRD) presenting to the same vitreoretinal unit approximately 20 years apart. METHODS: 124 patients in 1979-80 and 126 cases in 1999 were compared. RESULTS: More cases were pseudophakic and fewer aphakic in 1999 than 1979-80. More cases of giant retinal tear and fewer dialyses were operated on in 1999. Vitrectomy was a primary procedure in 63% of cases in 1999 but only 1% in 1979-80. Anatomical success rates were statistically similar: 79.8% primary and 88.8% final success in 1979-80, and 84% primary and 93.6% final success in 1999. CONCLUSION: Surgical management of primary RRD has changed greatly in 20 years. Success rates have changed little, despite availability of differing surgical techniques.

Aphakia, Postcataract↗
PubMed2001

Optical coherence tomography of the vitreoretinal interface in macular hole formation.

AIMS: To image the vitreoretinal interface and provide further information on the pathogenesis of idiopathic macular hole formation. METHODS: Prospective recruitment of 80 eyes of 41 consecutive patients referred with a diagnosis of idiopathic full thickness macular hole (FTMH) to a teaching hospital retinal clinic. Both eyes of each patient underwent optical coherence tomography (OCT) imaging with vertical and horizontal scans centred on the fovea. RESULTS: A total of 30 eyes had stage 2 or 3 FTMHs and, of these, 21 had persistent vitreofoveal attachment and associated prefoveal opacities. 18 prefoveal opacities were identified by Goldmann contact lens examination and confirmed on OCT examination. Three prefoveal opacities were identified only on OCT examination. 10 eyes had stage 4 FTMHs and four cases were identified in whom the OCT appearance was consistent with impending, aborted, or lamellar macular holes. CONCLUSIONS: The wide range in OCT appearance of macular holes and associated prefoveal opacities suggests that, in at least some cases, a significant amount of retinal tissue is torn from the foveal area during macular hole formation. OCT imaging provides additional information on macular hole pathogenesis and is valuable in the planning of surgical intervention.

Aged↗
PubMed2000

Papillofoveal traction in macular hole formation: the role of optical coherence tomography.

OBJECTIVES: To determine the validity of the assumption that optical coherence tomographic scans of macular holes have a discrete linear signal (DLS) that represents a detached posterior vitreous face, and to analyze the DLS in macular hole pathogenesis. METHODS: Optical coherence tomographic scans were taken of 3 situations in which the vitreous conditions were known: (1) dissected intact vitreous, (2) clinically evident Weiss rings, and (3) maculae before and after saccades in eyes without a biomicroscopic posterior vitreous detachment. In addition, 70 eyes of 35 patients with macular holes underwent clinical examination and optical coherence tomographic scanning that passed through the optic disc and the fovea or macular hole. RESULTS: Spatial properties of the DLS matched those of the posterior vitreous face in the situations examined. Of the 70 eyes, 16 (23%) had a biomicroscopic posterior vitreous detachment, whereas a DLS was demonstrated in 40 (57%). Of the 54 eyes without a biomicroscopic posterior vitreous detachment, 18 (33%) had a DLS attached focally to the optic disc margin and the fovea or macular hole. All 7 of the "can opener" holes examined had a nasally "hinged" central flap, 6 with a focally attached DLS. CONCLUSIONS: The DLS corresponds to the posterior vitreous face. Anteronasal papillofoveal traction may generate some macular holes.

Fovea Centralis↗
PubMed2000

Watzke-Allen slit beam test in macular holes confirmed by optical coherence tomography.

OBJECTIVE: To examine the role, validity, and interpretation of Watzke-Allen slit beam testing in patients with idiopathic senile macular holes. METHODS: Thirty-seven consecutive patients with 40 full-thickness macular holes, confirmed on optical coherence tomography, were prospectively recruited. The Watzke-Allen slit beam test was used centrally and on the rim of the macular hole in both vertical and horizontal orientations. RESULTS: In 24 eyes, the beam was reported as thinned in both vertical and horizontal orientations when placed directly over the center of the macular hole. In 9 eyes, the Watzke-Allen slit was reported as broken in both vertical and horizontal orientations. In 6 eyes, the beam was reported as broken in one orientation and thinned in the other. In 1 eye, the beam was reported as kinked but not thinned or broken. When the beam was placed on the edge of the macular hole, all patients reported a displacement or bowing of the beam away from the center of the hole. CONCLUSIONS: These findings confirm tangential traction of photoreceptors from a central foveal dehiscence as the causative mechanism in the development of the majority of macular holes. Careful interpretation of the Watzke-Allen sign may offer a technique for preoperatively determining visual prognosis. Arch Ophthalmol. 2000;118:1059-1063

Aged↗
PubMed2000

Clinical evaluation of 'local contrast enhancement' for oral fluorescein angiograms.

PURPOSE: To describe and assess the clinical impact of 'local contrast enhancement' on oral fluorescein angiograms. METHODS: Oral fluorescein angiograms (OFA) were performed on 12 patients with a range of diabetic retinopathy. The digital images were processed using two enhancement techniques: histogram equalization, a widely available method; and 'local contrast enhancement'. Twelve control images and 24 enhanced images were randomised and subjectively graded for clarity between 1 and 100 on a visual analogue scale by two masked observers. A score of 50% was chosen as the cut-off for clinically useful images. RESULTS: The mean score for the unenhanced images was 38.8% (SD 19.4); the histogram equalization performed better at 54.7% (SD 10.0) (p = 0.016) and 'local contrast enhancement' at 69.4% (SD 13.6) (p < 0.001). These results equate to a 14.7% improvement in comparison with histogram equalization and a 30.3% improvement with the 'local contrast enhancement' technique. All the 'local contrast enhancement' images were clinically useful, compared with 58.3% of the histogram equalization images (chi 2 2.08, p = 0.2), and 33.3% of the control images (chi 2 = 6.75, p = 0.01). CONCLUSION: This pilot study has demonstrated the power of 'local contrast enhancement' techniques for low-contrast fluorescein angiograms. Using 'local contrast enhancement' oral fluorescein angiograms can give high-quality images and may allow safer patient investigation.

Administration, Oral↗
PubMed2000

Acute posterior vitreous detachment: the predictive value of vitreous pigment and symptomatology.

AIM: To establish whether the presence of a retinal break can be predicted either by the presence of a positive Shafer's sign (pigment granules in the anterior vitreous) or symptomatology in patients presenting with an acute posterior vitreous detachment (PVD). METHODS: 200 eyes of 200 phakic patients with a symptomatic PVD of less than 1 month's duration underwent documentation of symptomatology and examination of the anterior vitreous for the presence of pigment granules. Indentation ophthalmoscopy was then carried out by an experienced vitreoretinal surgeon with no knowledge of the symptomatology or anterior vitreous gel examination findings. A second prospective group of 115 consecutive patients were assessed in a similar manner before primary rhegmatogenous retinal detachment repair. RESULTS: In 200 eyes presenting with an acute PVD, 25 were found to have an associated retinal break, 23 of which were also Shafer positive. In 115 eyes presenting for retinal detachment repair, 111 had an associated PVD and were found to be Shafer positive. Symptomatology was not predictive of an associated retinal break in the PVD group or in those presenting with a retinal detachment. CONCLUSION: The increased use of Shafer's sign is recommended as a valuable aid in determining which patients require urgent referral for an expert retinal examination. It is not possible to predict those patients with a retinal break secondary to PVD on the basis of symptomatology alone.

Acute Disease↗
PubMed1999

Relationship of the distal optic nerve sheath to the circle of Zinn.

BACKGROUND: This study was designed to determine the relationship of the vascular circle of Zinn (CZ) and its branches to the termination of the subarachnoid space surrounding the optic nerve sheath, with particular reference to optic disc size. METHODS: Serial sections of 29 normal human optic nerves were performed at 6-microm intervals. The position of the CZ and subarachnoid space were measured with WILD Heerbrugg objective graticules. The results were analysed with reference to the optic disc size. RESULTS: The position of the CZ was variable but two major types were recognised. In type 1 the circle was located anterior to the distal sheath, and in type 2 posterior to the sheath. There were more small optic discs observed in type 2. CONCLUSION: In this study the CZ was more posteriorly located in small optic discs. This location may induce risk factors contributing to the development of ischaemic optic neuropathy. The combination of small discs, posterior placement of the CZ, and anatomical variations in the vascular pattern may predispose to ischaemic events.

Cadaver↗
PubMed1999

Automated localisation of the optic disc, fovea, and retinal blood vessels from digital colour fundus images.

AIM: To recognise automatically the main components of the fundus on digital colour images. METHODS: The main features of a fundus retinal image were defined as the optic disc, fovea, and blood vessels. Methods are described for their automatic recognition and location. 112 retinal images were preprocessed via adaptive, local, contrast enhancement. The optic discs were located by identifying the area with the highest variation in intensity of adjacent pixels. Blood vessels were identified by means of a multilayer perceptron neural net, for which the inputs were derived from a principal component analysis (PCA) of the image and edge detection of the first component of PCA. The foveas were identified using matching correlation together with characteristics typical of a fovea-for example, darkest area in the neighbourhood of the optic disc. The main components of the image were identified by an experienced ophthalmologist for comparison with computerised methods. RESULTS: The sensitivity and specificity of the recognition of each retinal main component was as follows: 99.1% and 99.1% for the optic disc; 83.3% and 91.0% for blood vessels; 80.4% and 99.1% for the fovea. CONCLUSIONS: In this study the optic disc, blood vessels, and fovea were accurately detected. The identification of the normal components of the retinal image will aid the future detection of diseases in these regions. In diabetic retinopathy, for example, an image could be analysed for retinopathy with reference to sight threatening complications such as disc neovascularisation, vascular changes, or foveal exudation.

Algorithms↗
PubMed1998

Identification and voluntary reduction of vancomycin use for perioperative antibiotic prophylaxis during coronary artery bypass graft surgery.

Vancomycin prophylaxis for coronary artery bypass graft surgery without prosthetic valve implantation voluntarily decreased from 94% to 18% in one medical center. Median hospital stay (10 vs 9 days, P = .30) and number of postoperative infections (17.0% vs 14.3%, P = .60) did not differ among patients who received vancomycin and those who did not.

Adult↗
PubMed1998

An inner city preschool visual screening programme: long-term visual results.

AIMS: The aim of this study was to investigate the long-term outcome of the treatment of amblyopia as a sequel to preschool screening, which has not hither-to been described. METHODS: All patients originally referred from a preschool screening programme were recalled for examination by letter. 255 patients were reviewed at least 4 years after discharge of which 88 were definitely amblyopic at presentation and 107 were not amblyopic at presentation and were used as controls. RESULTS: 79% of the amblyopes improved or maintained visual acuity after discharge but this was reduced to 42% after an age induced increase (estimated from the controls) was compensated for. The mean drop in visual acuity in the amblyopic eyes which deteriorated was 0.23 (SD 0.15) logMAR units. Stepwise multiple linear regression showed that the best single predictor of post-discharge deterioration in visual acuity was the improvement in visual acuity seen during treatment (R2 = 19%). Eccentric fixation at time of follow up (increasing R2 to 47%) and good presenting acuity (further raising R2 to 57%) contributed additional information, and were both associated with greater post-discharge deterioration in visual acuity. CONCLUSIONS: The majority of amblyopes who attended for follow up maintained or improved their visual acuities after discharge. Those patients who demonstrated deterioration of their amblyopia had usually improved well during the programme and were often fixating eccentrically at follow up.

Amblyopia↗
PubMed1997

Electroretinography of central retinal vein occlusion under scotopic and photopic conditions: what to measure?

INTRODUCTION: In the management of cases of central retinal vein occlusion it is important to identify those patients who will develop the complication of iris neovascularisation. Electroretinography is of proven use in this role but there is some confusion about which parameters to measure and at what stimulus intensities. METHODS: A variety of ERG parameters in scotopic and photopic conditions were tested by ROC analysis for the prediction of the development of this complication in 39 patients with CRVO. RESULTS: The results indicated that a single flash and measurement of the b/a ratio under photopic conditions is as effective in this aim as measuring multiple parameters. CONCLUSION: A simplified and shortened protocol could be used in the examination of this condition thereby making the application of ERG more practical in the clinical setting.

Adaptation, Ocular↗