PubMed Health⌕ Search

Biomedical subjects

William H Morgan

Publications and source records attributed to William H Morgan.

11 recordsLinked to original sources
PubMed2006

Value of retinal vein pulsation characteristics in predicting increased optic disc excavation.

BACKGROUND: Retinal vein pulsation is often absent in glaucoma, but can be induced by applying a graded ophthalmodynamometric force (ODF) to the eye, which is elevated in glaucoma. AIM: To assess whether ODF has a predictive value in determining glaucoma progression. METHODS: 75 patients with glaucoma and suspected glaucoma were examined prospectively in 1996, and then re-examined at a mean of 82 months later. All subjects had intraocular pressure, visual fields, stereo optic disc photography and ODF measured on their initial visit. When venous pulsation was spontaneous, the ODF was said to be 0 g. At re-examination, central corneal thickness and blood pressure were also measured. Initial and subsequent optic disc photographs were compared and graded into those that had increased excavation and those that had remained stable. The relationship between increased excavation (recorded as a binary response) and the measured variables was modelled using a multiple mixed effects logistic regression. RESULTS: ODF at the initial visit was strongly predictive of increased excavation (p = 0.004, odds ratio 1.16/g, range 0-60 g), with greater predictive value in women than in men (p = 0.004). Visual field mean deviation was predictive of increased excavation (p = 0.044), as was optic nerve haemorrhage in association with older age (p = 0.038). Central corneal thickness was not significantly predictive of increased excavation (p = 0.074) after having adjusted for other variables. CONCLUSION: ODF measurement seems to be strongly predictive of the patient's risk for increased optic disc excavation. This suggests that ODF measurement may have predictive value in assessing the likelihood of glaucoma progression.

Aged↗
PubMed2006

Trends in registered blindness and its causes over 19 years in Western Australia.

PURPOSE: To estimate the population-based incidence rates of blindness registration and their trends over time in Western Australia. METHODS: A retrospective review was performed on all cases of bilateral blindness registered with the Association for the Blind of Western Australia between 1984 and 2002. The causes and mean age at blindness registration were ascertained and incidence rates of blindness due to various causes were calculated. RESULTS: A total of 3852 blind certificates were examined. From 1984 to 1994, the annual incidence of registered bilateral blindness decreased significantly at an average rate of 9.4% per year (p < 0.0001), but then rose at a mean rate of 4.1% per year (p < 0.0001). ARMD blindness similarly fell by 8.9% per year (p < 0.0001), but then rose after 1994 by 4.5% per year (p < 0.0001). The incidence due to glaucoma decreased at an average rate of 10.3% per year (p < 0.0001) until 1994 and then rose at 7.4% per year at borderline significance (p = 0.025). CONCLUSIONS: There has been a nonlinear decrease in the incidence of registered blindness, in particular glaucoma-related blindness, in Western Australia. Rates of total registered blindness and that due to ARMD fell from 1984 to 1994, but have risen since.

Blindness↗
PubMed2006

Refractory glaucoma--tube or diode?

BACKGROUND: The aim of the present study was to assess the relative effectiveness of tube surgery and cyclodiode laser in terms of achieving intraocular pressure control. METHODS: A retrospective study was undertaken to compare patients undergoing double plate Molteno tube implantation with patients undergoing diode cyclophotocoagulation. Intraocular pressure (IOP) was documented at 7 days prior to surgery and postoperatively at various time points. Surgical success was defined as a final IOP between 6 (inclusive) and 21 mmHg (inclusive), without the use of topical medication, while 'qualified' success was defined as IOP within the same range with the use of topical medication. RESULTS: Twenty-eight diode patients and 26 tube patients were included for the study. An average follow up of 150 weeks (range = 21-322 weeks) was available. Mean preoperative IOP was 37 +/- 12 mmHg for the tube group and 39 +/- 16 mmHg for the diode group (t = 0.51, P = 0.61). The final IOP was 17 +/- 12 mmHg for the tube group and 21 +/- 13 mmHg for the diode group (t = 0.35, P = 0.73). Surgical success was achieved in 46% of tube eyes and 11% of diode eyes, while qualified success was achieved in 81% of tube eyes compared with 64% of eyes in the diode group. Two eyes which underwent diode became phthisical. CONCLUSIONS: IOP control may be achieved in a greater number of patients with tube surgery. The possible benefits of IOP control in diode patients need to be weighed against the risks of long-term visual loss and the need for multiple re-treatments in this group.

Aged↗
PubMed2005

Improved interpretation of flow maps obtained by scanning laser Doppler flowmetry using a rat model of retinal artery occlusion.

PURPOSE: To improve the interpretation of Heidelberg Retina Flowmeter (HRF; Heidelberg Engineering GmBH, Dosselheim, Germany) flow maps by examining the influence of specific vascular structures and focus depth in the presence and absence of retinal blood flow. METHODS: HRF flow maps were recorded from the inferior retina of anesthetized Brown Norway rats over a wide range of focus levels, before and after laser occlusion of the retinal circulation. Analysis of the resultant flow maps showed that the sample window was positioned on a retinal artery, arteriole, or vein, or in a retinal capillary area, with or without a visible underlying choroidal vessel. The relationship between HRF-measured flow (arbitrary units) and focus depth was determined for each location. At the conclusion of each experiment, the effect of reduction of systemic blood pressure on the choroidal circulation and the level of background signal in the HRF flow map with no ocular blood flow were assessed. RESULTS: The strongest flow signals came from the retinal arteries, veins, and arterioles and were reduced to choroidal background level after occlusion of the central retinal artery. Larger choroidal vessels also contributed strong flow signals. In contrast, the flow signal from the retinal capillary area was weak and unaffected by retinal artery occlusion. Changing the depth of focus significantly altered the contribution from the major retinal arteries, arterioles, and veins, but no significant depth effect was seen for retinal capillaries or choroidal vessels. The HRF flow signal remaining when systemic blood pressure was reduced to zero was not significantly different from the capillary sampling location when the eye was normally perfused. CONCLUSIONS: In the pigmented rat eye, the HRF signal from retinal capillaries is not significantly different from the background noise unrelated to blood flow. Strong flow signals can be obtained from the retinal arteries, retinal arterioles, retinal veins, and choroidal vessels. Current HRF flow maps in the rat therefore reflect blood flow in the larger elements of the microvasculature rather than the capillary network.

Animals↗
PubMed2005

The force required to induce hemivein pulsation is associated with the site of maximum field loss in glaucoma.

PURPOSE: To determine the factors associated with central retinal vein pulsation changes in glaucoma and identify any hemiretinal vein pulsation changes and their association with sectoral visual field loss. METHODS: One hundred twenty-six patients with glaucoma and 40 normal subjects had automated perimetry, blood pressure, and intraocular pressure measured. A hemifield sensitivity loss was calculated from the upper and lower halves of each field. Those without spontaneous venous pulsation on the optic disc had an ophthalmodynamometer applied, to measure the minimum ophthalmodynamometric force (ODF) necessary to induce venous pulsation. When ODF was restricted to the hemiveins, the force needed to induce pulsation in each hemivein was measured. RESULTS: Eighty-three patients with glaucoma had no spontaneous venous pulsation. The minimum ODF was strongly correlated with mean deviation (Spearman rank r = -0.475, P < 0.0001). Mixed linear regression analysis showed that mean deviation (P < 0.0001) and pulse blood pressure (P < 0.0001) were significantly associated with minimum ODF. There was a strong association between differences in hemifield sensitivity loss and in hemivein ODF (rank r = 0.369, P < 0.0001, n = 80). Multiple linear regression modeling demonstrated that lower hemivein ODF was independently associated with upper field loss (P = 0.003) and upper hemivein ODF with lower field loss (P < 0.0001). CONCLUSIONS: These venous pulsation findings in glaucoma are independent of blood pressure. The hemifield and hemivein association suggests that the major hemivein change is adjacent to the site of major disc damage.

Aged↗
PubMed2005

The detection of both global motion and global form is disrupted in glaucoma.

PURPOSE: It is well known that glaucoma results in performance impairments on tasks processed early in the visual pathways. Glaucoma should also impair cortical visual processing because of reduced input from retinal ganglion cells and also possibly because of abnormal cortical function. This study was undertaken to assess whether cortically processed global percepts are disrupted in glaucoma in areas of visual field classified as normal by standard automated perimetry (SAP). Performance on global tasks (motion and form) was compared to measures of presumed precortical magnocellular and parvocellular function in the same individuals. METHODS: Fifteen control subjects and 12 patients with primary open-angle glaucoma participated. Testing was performed foveally and midperipherally (12.5 degrees). Contrast-discrimination thresholds were measured by using the steady-pedestal (magnocellular) and pulsed-pedestal (parvocellular) contrast-discrimination tasks of Pokorny and Smith. Global motion coherence and global form coherence thresholds were measured at high and low contrast. RESULTS: Patients with glaucoma demonstrated higher global motion and form-coherence thresholds than did control subjects for targets presented in the midperiphery (P < 0.05), but not foveally. Different individuals performed poorly on the motion and form tasks. The subjects with the greatest presumed magnocellular and parvocellular loss were those with the largest deficits on the global motion and form tasks, respectively. CONCLUSIONS: Some subjects with glaucoma demonstrate profound impairments of global motion or global form integration in areas of visual field classified as normal by SAP. This finding implies that some people with glaucoma may have far greater difficulty with complex visual tasks (for example, navigation through the environment or face recognition) than is predicted by their visual field loss.

Aged↗
PubMed2004

Retinal venous pulsation in glaucoma and glaucoma suspects.

PURPOSE: To determine whether changes in central retinal vein pulsation characteristics occur in glaucoma, and how these are related to indices of glaucoma severity. DESIGN: A large, consecutive, prospective, case-controlled study. PARTICIPANTS: Ninety-four consecutive glaucoma patients and 105 glaucoma suspects seen in a tertiary referral clinic were examined. Forty-one age-matched normal subjects also were examined. METHODS: The presence or absence of spontaneous venous pulsation was observed in these 3 groups. The ophthalmodynamometric force (ODF) required to induce venous pulsation at the optic disc was measured in those without spontaneous pulsation. Optic disc photographs were obtained and visual field testing was performed for all subjects. MAIN OUTCOME MEASURES: The prevalence of spontaneous venous pulsation between these 3 groups was compared. The relationship between ODF and visual field mean deviation, neuroretinal rim area, age, intraocular pressure (IOP), gender, and diagnosis of glaucoma was investigated using linear mixed models fitted by Gibb's sampling. RESULTS: Significantly fewer (chi-square, 27.7; P<0.001) glaucoma patients (54%) were observed to have spontaneous venous pulsation than suspects (75%) or normals (98%). A worse visual field mean deviation was shown to be the most significant predictor of a higher ODF (P<0.000), with younger age (P<0.000) also predictive of a higher ODF. A strong relationship between ODF and mean deviation was found in the glaucoma patients (r = 0.59; n = 52; P<0.001). CONCLUSIONS: Spontaneous venous pulsation is less common in glaucoma. The ODF required to induce venous pulsation is increased in glaucoma, and this ODF is greater in those with more severe field loss.

Aged↗
PubMed2004

Psychophysical measurement of neural adaptation abnormalities in magnocellular and parvocellular pathways in glaucoma.

PURPOSE: It is well established that contrast sensitivity is reduced in glaucoma. This study explored whether such contrast processing abnormalities consist of an absolute threshold level difference or a problem with contrast gain control. METHODS: Seventeen patients with primary open-angle glaucoma and 17 approximately age-matched control subjects participated. Subjects were tested foveally and midperipherally (12.5 degrees ). Subjects with glaucoma were tested in a peripheral region of relatively normal visual field (neighboring locations required to be within the normal 95% confidence limit on the total deviation plot of their most recent SITA/full threshold Humphrey Field Analyzer assessment; Carl Zeiss Meditec, Dublin, CA). Control subjects were tested in matching locations. Contrast discrimination was assessed using the steady-pedestal (magnocellular [M] pathway) and pulsed-pedestal (parvocellular [P] pathway) stimuli of Pokorny and Smith for seven pedestal luminances between 15 and 75 cd/m(2), presented on a background of 30 cd/m(2). RESULTS: Glaucoma group thresholds were significantly elevated compared with control subjects foveally and peripherally on both the pulsed-pedestal (P) and steady-pedestal (M) tasks (P < 0.01). Effect size statistics revealed slightly greater deficits on the P pathway task and greater deficits for pedestals that were decrements, rather than increments, from the surround luminance. Foveal deficits were of a magnitude to be explained by a reduction in contrast sensitivity; however, the peripheral deficits were greater than predicted by this factor alone. CONCLUSIONS: Foveal and midperipheral dysfunction of both M and P pathways was identified in people with glaucoma, in areas of relatively normal visual field performance. These findings are supportive of nonselective neural adaptation abnormalities in early glaucoma.

Adaptation, Physiological↗
PubMed2003

Mitomycin C eliminates the short-term intraocular pressure rise found following Molteno tube implantation.

PURPOSE: Molteno implants remain popular for treating recalcitrant glaucomas. This study aimed to assess the effect of mitomycin C (MMC) use with Molteno tube implantation upon intraocular pressure (IOP) control and complication rates. In particular, the study aimed to assess any change that MMC might have upon the postoperative hypertensive phase. METHODS: A retrospective case record study was conducted of all patients undergoing double plate Molteno implant surgery by one surgeon over 5 years. Eyes with recalcitrant glaucoma unresponsive to previous surgery, or deemed unlikely to succeed with trabeculectomy, underwent double plate Molteno tube implantation. Eyes that had MMC (0.3 mg/mL, 3 min) applied to Tenon's capsule over the secondary plate were compared with eyes that underwent surgery without adjunctive MMC application. RESULTS: Twenty-seven eyes received MMC and were similar to 26 eyes not receiving MMC in terms of glaucoma subtype, age, sex, previous surgery, preoperative IOP and postoperative IOP lowering agents. Those not receiving MMC had raised IOP 31-90 days post implantation compared with MMC treated eyes (P < 0.01) and more often received oral antifibrosis medication (P < 0.05). Complications were no more common with MMC except for initial overdrainage. Significant systemic complications from the use of oral antifibrosis medication were common. CONCLUSIONS: The findings suggest a useful role for MMC. Caution is advised in case selection for MMC use. Mitomycin C treatment over the secondary plate alone permits removal of this plate if MMC-related complications occur without requiring removal of the whole implant.

Adult↗
PubMed2002

Optic disc movement with variations in intraocular and cerebrospinal fluid pressure.

PURPOSE: To determine the effect of intraocular pressure (IOP) and cerebrospinal fluid pressure (CSFP) on optic disc movement and lamina cribrosa displacement using confocal scanning laser tomography (CSLT). METHODS: The anterior chamber and lateral ventricles were cannulated in mixed-breed dogs (n = 8) to allow modulation and control of IOP and CSFP, respectively. Optic disc topography was determined after baseline (set at IOP 15 mm Hg and CSFP of 0 mm Hg) and with each step-wise increase in IOP (steps of 3-5 mm Hg up to an average of 32 mm Hg) with CSFP fixed at 0 mm Hg. After the pressure returned to baseline, images were obtained after each step-wise increase in CSFP (steps of 2 to 4 mm Hg up to an average of 12 mm Hg) with IOP fixed at 15 mm Hg. Data were analyzed by a new probabilistic method for CSLT and global parameters generated by the instrument software. The global parameter changes from baseline were analyzed as a function of the translaminar pressure difference (IOP minus CSFP). RESULTS: Elevation in IOP resulted in significant posterior displacement of the disc surface, whereas elevation in CSFP resulted in significant anterior displacement. For a given degree of pressure change, an increase in CSFP resulted in larger changes than a corresponding increase in IOP. The deepest 5% of locations within the disc surface were displaced nonlinearly (with an inverse exponential function, r = 0.92) as a function of the difference in translaminar pressure. Most displacement occurred at low translaminar pressure differences, with little extra movement at differences higher than 15 mm Hg. The change in the volume subtended by the anterior lamina cribrosa showed a nonlinear relationship similar to the translaminar pressure difference (r = 0.98), with negligible volume change at high difference in pressures. CONCLUSIONS: Most optic disc movement occurs with pressure changes in the low range of translaminar pressure differences. This is consistent with the mechanical properties of collagen.

Animals↗