Biomedical subjects

Michael Wall

Publications and source records attributed to Michael Wall.

27 records · Page 2Linked to original sources

PubMed2004

Visual field of high-pass resolution perimetry in normal subjects.

PURPOSE: To investigate the properties of the visual field of high-pass resolution perimetry in normal subjects. METHODS: Four centers collected normative data for high-pass resolution perimetry. In two of the centers the subjects were stratified by age. One eye was tested per subject using high-pass resolution perimetry (Ophthimus). We tested 640 normal subjects and describe their visual field results by test location. We also analyzed the data by concentric zone, age, and by testing center. RESULTS: The individual test location averages confirmed a reduction in resolution with eccentricity. Resolution thresholds increased with age by 0.025 dB per year (P < 0.001). The mean ring size increased by about 1 dB from age 20 to 70. Among centers there were significant differences in the means and the change in threshold with age (P = 0.009). CONCLUSION: The normal visual field of high-pass resolution perimetry is characterized by an increase in threshold with eccentricity. We found significant differences among the centers that were likely due to multiple factors including differences in subject selection criteria. Whether such differences occur with other perimetric techniques is unknown.

Adult↗

PubMed2004

The effect of attention on conventional automated perimetry and luminance size threshold perimetry.

PURPOSE: To investigate the effects of divided attention on conventional automated perimetry (CAP) and luminance size threshold perimetry (LSTP). METHODS: Ten healthy subjects, ages 27 to 65, with two perimetry types (CAP and LSTP) were tested in random order. At a later session, these tests were given with a mental workload to simulate the effect of anxiety or distraction on subjects performing visual field testing, also in random order. The mental workload, the Paced Auditory Serial Addition Test (PASAT), was first administered to each subject, and the score was recorded. During the visual field testing, the PASAT was again administered continuously. Each subject was instructed to attend primarily to the PASAT while taking each visual field test. RESULTS: CAP was affected by the addition of the PASAT, with a worsening of sensitivity from an average of 30.0 +/- 0.67 to 24.2 +/- 7.4 dB with a range of -0.04 to -23.2 dB (P = 0.04). LSTP showed a generalized reduction in threshold 1.71 +/- 0.22 to 2.35 +/- 0.72 dB with a range of 0.12 to -2.17 dB (P = 0.25). The percentage of correct responses on the PASAT was not significantly different between CAP (76.9%) and LSTP (74.8%). False-positive and -negative catch trial responses were increased during CAP with PASAT testing (P = 0.009). A substantial increase of fixation losses occurred during CAP with PASAT (3.7-16.2, P = 0.002). LSTP with PASAT showed increases in localization error (P < 0.001) and reaction time (P = 0.004). CONCLUSIONS: Divided attention significantly affects performance on conventional automated perimetry with its fixed size stimuli and when the stimuli are scaled (LSTP). The deficits may simulate nerve-fiber-bundle-like defects.

Adult↗

PubMed2003

High- and low-risk profiles for the development of multiple sclerosis within 10 years after optic neuritis: experience of the optic neuritis treatment trial.

OBJECTIVE: To identify factors associated with a high and low risk of developing multiple sclerosis after an initial episode of optic neuritis. METHODS: Three hundred eighty-eight patients who experienced acute optic neuritis between July 1, 1988, and June 30, 1991, were followed up prospectively for the development of multiple sclerosis. Consenting patients were reassessed after 10 to 13 years. RESULTS: The 10-year risk of multiple sclerosis was 38% (95% confidence interval, 33%-43%). Patients (160) who had 1 or more typical lesions on the baseline magnetic resonance imaging (MRI) scan of the brain had a 56% risk; those with no lesions (191) had a 22% risk (P<.001, log rank test). Among the patients who had no lesions on MRI, male gender and optic disc swelling were associated with a lower risk of multiple sclerosis, as was the presence of the following atypical features for optic neuritis: no light perception vision; absence of pain; and ophthalmoscopic findings of severe optic disc edema, peripapillary hemorrhages, or retinal exudates. CONCLUSIONS: The 10-year risk of multiple sclerosis following an initial episode of acute optic neuritis is significantly higher if there is a single brain MRI lesion; higher numbers of lesions do not appreciably increase that risk. However, even when brain lesions are seen on MRI, more than 40% of the patients will not develop clinical multiple sclerosis after 10 years. In the absence of MRI lesions, certain demographic and clinical features seem to predict a very low likelihood of developing multiple sclerosis. This natural history information is a critical input for estimating a patient's 10-year multiple sclerosis risk and for weighing the benefit of initiating prophylactic treatment at the time of optic neuritis or other initial demyelinating events in the central nervous system.

Acute Disease↗

PubMed2002

The relationship of visual threshold and reaction time to visual field eccentricity with conventional automated perimetry.

To investigate the relationship between reaction time (RT), stimulus intensity and visual field eccentricity. We generated frequency of seeing (FOS) curves and measured RTs by testing 10 perimetrically experienced normal subjects with a Humphrey perimeter controlled by a custom program. Subjects were tested from 10 degrees to 50 degrees eccentricity along the nasal horizontal meridian in 10 degrees increments. A range of 20 dB, centered on threshold, was tested in 1 dB steps along with 60 and 0 dB intensities as catch trials. Twenty repetitions for each intensity at each location were used. Linear regression showed a significant increase in suprathreshold RT (to the 0 dB stimulus) with increasing eccentricity. The RT at the calculated FOS 50% threshold was prolonged by about 200 ms compared with the RT using the 0 dB target at the equivalent eccentricities. Also, when the difference between the RT at 0 dB stimulus and the RT at threshold was regressed against visual field eccentricity there was a significant decrease with eccentricity. When the RT(pi) (RT prolongation from threshold relative to the 0 dB stimulus) was plotted as a function of decreasing stimulus attenuation, the results fit the function RT(pi)=a+bi(3) (i=stimulus intensity) with r(2)>0.94 at all eccentricities. However, the slope of the function flattened with increasing eccentricity. Using conventional automated perimetry stimuli in perimetrically experienced young subjects, suprathreshold RT increases but threshold RT prolongation decreases with increasing visual field eccentricity. RT fits a power function with decreasing stimulus attenuation but the slope flattens with eccentricity. This relationship found along the nasal horizontal meridian may allow use of RT to cross-check threshold results or to define response windows for reliability indices of conventional automated perimetry.

Adult↗

PubMed2002

Sleep apnea and intracranial hypertension in men.

PURPOSE: To investigate sleep apnea as an associated finding in idiopathic intracranial hypertension (IIH) in men. DESIGN: Multicenter, retrospective, noncomparative interventional case series. METHODS: Retrospective review of all men with the diagnosis of IIH seen within the last 5 years at three tertiary care academic ophthalmologic institutions. Cases with sleep apnea (SA) and IIH were identified and reviewed. RESULTS: Thirty-two cases of IIH in men were reviewed. Six cases with SA met the modified Dandy criteria for the diagnosis of IIH. Of these six patients, one received acetazolamide alone, four received acetazolamide and continuous positive airway pressure (CPAP), and one was treated with CPAP alone. All patients had preserved central acuity (20/20 or better in both eyes), enlarged blind spots, and optic disc edema in both eyes. Five patients had normal visual fields after treatment, and one patient had residual visual field loss. Three patients had normal optic nerve examinations, with resolution of the optic disc edema at last follow-up. After resolution of the optic disc edema, these three patients were maintained on CPAP but discontinued acetazolamide. Two patients had persistent but improved papilledema and are under continued treatment with acetazolamide and CPAP. One patient had optic disc pallor in both eyes and is stable. CONCLUSIONS: SA was a common finding in men meeting the modified Dandy criteria for IIH in adults. Treatment of sleep apnea with nocturnal oxygenation may improve the signs and symptoms of IIH in affected men.

Acetazolamide↗

PubMed2002

Prognosis of ischemic internuclear ophthalmoplegia.

OBJECTIVES: To determine the prognosis of internuclear ophthalmoplegia (INO) caused by infarction. DESIGN: Multicenter, retrospective observational case series. PARTICIPANTS: Thirty three patients with ischemic-related INO. METHODS: Chart review of clinical details. MAIN OUTCOME MEASURE: Resolution of diplopia in primary position. RESULTS: Of the group, 78.8% demonstrated resolution of diplopia in primary position with an average time to resolution of 2.25 months. The presence of associated neurologic symptoms (vertigo, ataxia, dysarthria, facial palsy, pyramidal tract signs) correlated with a worse prognosis for resolution of diplopia. When performed magnetic resonance imaging (MRI) demonstrated the causative infarct in only 52% of cases; the presence of an MRI-demonstrable lesion was not significantly associated with prognosis for resolution. CONCLUSIONS: Similar to ischemic ocular motor palsies, most ischemic-based INO become asymptomatic in primary position over 2 to 3 months. The presence of associated features correlated with persistent diplopia. MRI has limited yield in demonstrating the causative infarct.

Aged↗

PubMed2002

Papilledema as the presenting manifestation of spinal schwannoma.

A 63-year-old woman with headache, blurred vision, bilateral optic disc edema, and normal cranial magnetic resonance imaging scan underwent lumbar puncture that revealed an elevated opening pressure (290 mm water), a protein level of 114 mg/dl, and mild pleocytosis. Spinal magnetic resonance imaging later demonstrated a sacral tumor, which proved to be a schwannoma with sarcoid-like features. After surgical removal of the tumor, the patient's manifestations resolved. This case emphasizes that low spinal cord tumors can cause elevated intracranial pressure without causing markedly elevated cerebrospinal fluid protein or cells, or any myelopathic manifestations, perhaps by obstructing sacral cerebrospinal drainage. Comprehensive spine imaging should be a part of the evaluation of a patient with papilledema who has normal brain imaging but abnormal spinal fluid constituents.

Female↗

PubMed2002

Sensitivity and specificity of frequency doubling perimetry in neuro-ophthalmic disorders: a comparison with conventional automated perimetry.

PURPOSE: Frequency-doubling technology (FDT) perimetry was developed as a screening test for glaucoma. Patients with damage to the neuro-ophthalmic sensory visual pathways have different patterns of visual loss than patients with glaucoma. The current study was designed to determine the sensitivity and specificity of FDT as a screening test, compared with conventional automated perimetry (CAP) in neuro-ophthalmic disorders and to test the extent to which it may isolate the M(y) cells. METHODS: FDT and CAP were performed in 97 patients with sensory neuro-ophthalmic disorders and 42 subjects from the general population. The total and pattern-deviation probability plots for test loci common to the two perimetric tests were compared. The gold standard was an unequivocal clinical diagnosis. RESULTS: The sensitivity of FDT was 81.3%, with a specificity of 76.2%. The difference in sensitivity and specificity of CAP, 87.5% and 81.0%, respectively, was not statistically significant (by chi(2) test). In subjects with optic neuropathies, the similarity of the defect shown on FDT and CAP was judged good or fair in 62 of 72 cases. The extent of the defect as seen with FDT and CAP was equal in 41 of 72 cases, more extensive with FDT in 12, and more extensive with CAP in 19. In the patients with hemianopia, scattered abnormal test locations with FDT testing masked the hemianopic nature of the defect in 15 of 25 patients. Also, test locations along the vertical midline in densely hemianopic areas were seen with FDT testing in some patients with hemianopia, probably due to light scatter across the vertical midline and into the uninvolved hemianopic field. CONCLUSIONS: FDT has sensitivity and specificity similar to that of CAP for detecting visual field defects in patients with optic neuropathies. However, defects in patients with hemianopias may be missed because of the presence of scattered abnormal test locations and failure to detect test locations along the vertical meridian. The defects demonstrated by both tests in patients with optic neuropathies are similar in number, extent, and shape of the defects. This suggests FDT may not be isolating the magnocellular (M) cells with nonlinear responses to stimulus contrast (M(y) cells) in patients with visual loss.

Adult↗

PubMedDate not supplied

Neuro-ophthalmic manifestations of hemangiopericytoma.

PURPOSE: To describe the neuro-ophthalmic presentations of a rare intracranial tumor, hemangiopericytoma. METHODS: Retrospective multicenter case series. RESULTS: The neuro-ophthalmic and radiographic features of hemangiopericytoma are reviewed. The clinical presentation may mimic meningioma and the pre-operative distinction between meningioma and hemangiopericytoma is important because the evaluation, management, treatment, and prognosis differ significantly for the two lesions. CONCLUSION: We report five cases of intracranial hemangiopericytoma and review the neuro-ophthalmic findings of this uncommon entity.

Adult↗