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Biomedical subjects

B L Lam

Publications and source records attributed to B L Lam.

At least 37 records · Page 2Linked to original sources
PubMed1998

Prevalence of uncorrected binocular distance visual acuity in Hispanic and non-Hispanic adults. Results from the HHANES and the NHANES I.

OBJECTIVE: This study aimed to provide a comparative analysis of American population-based prevalence of uncorrected binocular distance visual acuity in Hispanics and non-Hispanics. DESIGN: The study design was a population-based survey. PARTICIPANTS: Data from the Hispanic Health and Nutrition Examination Survey between 1982 and 1984 and the National Health and Nutrition Examination Survey I from 1974 through 1975 were analyzed to investigate the epidemiology of uncorrected binocular distance visual acuity in adults 25 to 74 years of age in Cuban Americans (N = 391), Mexican Americans (N = 1350), Puerto Ricans (N = 504), African Americans (N = 245), and non-Hispanic white Americans (N = 2571). MAIN OUTCOME MEASURE: Uncorrected binocular distance visual acuity in both eyes was assessed using Sloan letters or Landolt rings. RESULTS: Prevalence rates of 20/50 or worse uncorrected binocular distance visual acuity were 22%, 24%, 19%, 18%, and 32% for African Americans, Cuban Americans, Mexican Americans, Puerto Ricans, and non-Hispanic whites, respectively. After adjustment for gender and age, the rates were significantly higher (P < 0.05) for non-Hispanic whites compared to each of the other ethnic groups. Significant increases in the prevalence of 20/50 or worse distance visual acuity were observed for increasing age groups (25-39, 40-59, and 60-74 years) within each gender-ethnic subgroup. Analysis of differences in prevalence by gender (controlling for age) indicated a slightly higher prevalence of 20/50 or worse distance visual acuity in women than in men (range of odds ratios, 1.1-2.1). Based on 1993 census population estimates in the United States, more than 42 million adults 25 to 74 years of age have an uncorrected binocular distance visual acuity of 20/50 or worse. Approximately 1.7 million of these adults are of Hispanic origin. CONCLUSION: The prevalence of impaired uncorrected binocular distance visual acuity generally is lower in Hispanics than in non-Hispanic whites.

Adult↗
PubMed1998

Mini radial keratotomy reduces ocular integrity. Axial compression in a postmortem porcine eye model.

OBJECTIVE: This study aimed to examine ocular rupture force in pig eyes after "minimally invasive radial keratotomy" (MRK) and standard radial keratotomy (SRK). DESIGN: Experimental study. MATERIALS: A total of 71 pairs of pig eyes (51 control eyes) were examined. INTERVENTION: An axial-torsional Materials Testing System (MTS, Eden Prairie, MN) was used to apply blunt force to the corneal surface. A force transducer measured the rupture forces in control eyes and in eyes with MRK or SRK. Five groups of paired eyes were compared: 2.0-mm MRK versus control (N = 12), 3.5-mm MRK versus control (N = 21), 6.5-mm SRK versus control (N = 18), SRK versus 3.5-mm MRK versus 2.0-mm MRK (N = 10). MAIN OUTCOME MEASURE: Ocular rupture force (newtons) was measured. RESULTS: The mean rupture force in newtons was 746.3 for control eyes, 514.2 for 2.0-mm MRK, 353.1 for 3.5-mm MRK, and 246.2 for SRK. Analysis of variance showed a statistically significant difference (P < or = 0.04) between paired comparisons. CONCLUSION: The MRK and SRK significantly weakened ocular integrity compared with control eyes not operated on. MRK required significantly more force to rupture than SRK. MRK eyes, however, ruptured at 50% to 70% of the force required to rupture eyes not operated on. Any patient considering radial keratotomy should be counseled about the risk of greater ocular damage in trauma.

Animals↗
PubMed1997

Idiopathic intracranial hypertension in children and adolescents.

PURPOSE: To investigate sex distribution, frequency of obesity, and other associated conditions among children and adolescents with idiopathic intracranial hypertension. METHODS: We conducted a retrospective chart review of patients aged 18 years or younger diagnosed with idiopathic intracranial hypertension between 1988 and 1995 at two medical centers. Meta-analyses were performed using our data pooled with published information. RESULTS: Of 374 patients, 175 (46.8%) were male and 199 (53.2%) were female. Obesity was noted in 50 (29.6%) of the 169 patients for whom relevant data are available, and other associated conditions were noted in 185 (53.2%) of the 348 patients. CONCLUSIONS: Idiopathic intracranial hypertension among children and adolescents affects boys and girls equally; concurrent obesity occurs less frequently than in adults; and other associated conditions or secondary causes are common.

Adolescent↗
PubMed1997

Subarachnoid fluid of the optic nerve in normal adults.

OBJECTIVE: The purpose of the study is to determine the amount of subarachnoid fluid of the optic nerve in normal adults using magnetic resonance (MR) imaging and to investigate whether the subarachnoid fluid is displaced in abduction as assumed by the 30 degree echographic test. DESIGN: The design was a prospective observation study. PARTICIPANTS: Twenty-one healthy headache-free adults participated. Ten (48%) were men and 11 (52%) were women with a mean age of 34.3 +/- 7.9 years. INTERVENTION: Both optic nerves were examined in primary and 45 degrees right and left gazes with T2 fast-spin echo fat-suppressed coronal MR imaging in quadrature head coil. Four MR images, 4 mm apart, starting from 4 mm posterior to the globe were obtained for both nerves simultaneously with an imaging time of 2 minutes and 24 seconds per gaze. MAIN OUTCOME MEASURES: Optic nerve and sheath diameters were measured. RESULTS: Mean nerve diameters were 3.2 +/- 0.4 mm anteriorly to 2.6 +/- 0.4 mm posteriorly, and mean sheath diameters were 5.2 +/- 0.9 mm anteriorly to 3.9 +/- 0.4 mm posteriorly. Optic sheath diameters did not change significantly in abduction or adduction. CONCLUSIONS: Magnetic resonance imaging can be used effectively to determine the amount of subarachnoid fluid of the optic nerve. In normal adults, the amount of optic nerve subarachnoid fluid is variable and may be substantial. The authors' MR findings show that optic nerve subarachnoid fluid is not displaced significantly with abduction or adduction.

Adult↗
PubMed1997

Clinical and molecular characterization of a family affected with X-linked ocular albinism (OA1)

Thirty-one members of a family affected with X-linked ocular albinism (OA1) were studied to characterize the clinical phenotype and identify the disease-causing mutation. The family members were examined with ophthalmoscopy, electroretinography, and Goldmann perimetry. Linkage analysis was performed with markers from the OA1 locus. Exons 2 and 8 of the OA1 gene were assayed with the polymerase chain reaction (PCR). The six affected males had visual acuities ranging from 20/40 to 20/200. All had nystagmus, iris transillumination, and foveal hypoplasia. The eldest affected male had 20/40 vision and was asymptomatic. The level of the visual acuity of the affected males was not related to the degree of retinal pigmentation. All seven female carriers had normal visual function but were found to have iris transillumination defects and variable retinal pigmentary appearance ranging from minimal pigmentary disturbance, patchy and diffuse hypopigmentation, to classic 'mud-splattered' appearance. Linkage analysis was consistent with a disease-causing mutation at the OA1 locus. PCR analysis revealed a deletion which includes at least the portion of the OA1 gene between exons 2 and 8. Affected males with X-linked ocular albinism can have a visual disability that ranges from almost none to legal blindness, and the female carriers can have variable retinal pigmentary appearance. Mutation screening of the OA1 gene can be used to confirm the diagnosis in isolated males of some families, and genetic linkage analysis can be used to accurately identify carriers even when the specific mutation cannot be identified.

Adult↗
PubMed1996

Automated suprathreshold static perimetry screening for detecting neuro-ophthalmologic disease.

PURPOSE: To devise and evaluate a rapid, accurate, and cost-effective method of detecting neuro-ophthalmologic visual field defects. METHODS: One hundred fifty-nine consecutive patients were evaluated with 76-point, central 30 degree automated static threshold perimetry on the Humphrey Visual Field Analyzer, as well as by a 76-point, central 30 degree suprathreshold examination with the central reference levels set at 2 or 4 dB lower than the estimated normal median central reference level adjusted for age. Six masked readers reviewed the fields. Their readings were compared with those of the other observers, as well as with the final diagnoses as determined from all available clinical information. RESULTS: In detecting abnormality, the full-threshold 30 degree test had a sensitivity (percent of eyes with true field defects identified by the field test) of 93 percent or 99 percent (depending on whether borderline results were counted as a positive or negative test) and a specificity (percent of cases without true field defects appropriately identified by the field test) of 71 percent or 91 percent. In comparison, the 4-dB offset suprathreshold test had a sensitivity (averaged over all reviewers) of 79 percent or 87 percent and a specificity of 81 percent or 89 percent, whereas the 2-dB test had a sensitivity of 87 percent or 94 percent and a specificity of 73 percent or 85 percent. The mean duration of the suprathreshold tests was 3.5 +/- 1.0 minute, compared with 14.8 +/- 2.8 minutes for the full-threshold technique. CONCLUSION: The central 30 degree, 76-point, 2-dB offset suprathreshold automated perimetry is more rapid and nearly as effective as the full-threshold test in detecting visual field abnormalities due to neuro-ophthalmologic disease. More quantitative, full-threshold perimetric strategies should be used in all equivocal cases and to follow progression of established disease.

Adult↗
PubMed1996

Effect of light on the prevalence of simple anisocoria.

PURPOSE: Because simple anisocoria is believed to decrease in bright light, the authors determined the prevalence of simple anisocoria under different lighting conditions. METHODS: The authors measured the pupil size of 104 healthy subjects with infrared videography at four clinically accessible light levels: darkness; darkness with a hand-held light shining from below; room light; and room light with the hand light shining from below. RESULTS: Of the 104 subjects, 40 (38%) were men and 64 (62%) were women. The ages ranged from 12 to 71 years (mean, 36.3 +/- 12.5 years). The mean decrease in pupillary diameter from darkness to the brightest condition was 1.89 mm. Based on the traditional definition of a pupillary diameter difference of 0.4 mm or greater, the prevalence of simple anisocoria decreased from 18% in darkness to 8% in room light with the hand-held light shining from below. The prevalence of anisocoria varied considerably when other definitions were used. Repeated measures analysis of variance showed that pupillary area difference decreased with brighter conditions (P = 0.026). However, the ratio of the pupillary areas did not change with brighter conditions (P = 0.666). CONCLUSIONS: The prevalence of simple anisocoria decreases with brighter conditions based on pupillary diameter difference. However, this decrease is not apparent when anisocoria is expressed as pupillary area ratio. Those clinicians who measure pupils will find that simple anisocoria decreases in bright light. However, with gross observation where perception of an anisocoria may be related more to the ratio of the pupillary areas, simple anisocoria may not seem to change much with brighter conditions.

Adolescent↗
PubMed1996

Neuro-ophthalmologic findings in the Asperger disorder.

Asperger disorder is a complex behavioral disorder that may be related to autism. We examined a 49-year-old man with Asperger disorder who had multiple neuro-ophthalmologic abnormalities, including colobomatous defects involving the optic discs and peripapillary retina, and abnormal ocular motility with an oculocephalic dyskinesia. Asperger disorder may be associated with a variety of neuro-ophthalmologic disturbances.

Autistic Disorder↗
PubMed1995

Atypical retinochoroidal coloboma in patients with dysplastic optic discs and transsphenoidal encephalocele.

OBJECTIVE: To evaluate the clinical significance of V- or tongue-shaped infrapapillary retinochoroidal depigmentation in association with dysplastic optic discs. METHODS: Clinical data from all patients with V- or tongue-shaped infrapapillary retinochoroidal depigmentation and dysplastic optic discs were evaluated retrospectively. RESULTS: Five patients with this atypical colobomatous anomaly had transsphenoidal encephalocele. A sixth patient had an ectopic midline pharyngeal mass with no skull-base defect. CONCLUSION: In patients with optic disc dysplasias, the finding of this V- or tongue-shaped retinochoroidal pigmentary anomaly should prompt neuroimaging to look for transsphenoidal encephalocele.

Adolescent↗
PubMed1995

Prevalence of foveal lesions in type 1 and type 2 Usher's syndrome.

PURPOSE: To evaluate possible differences in the prevalence of clinically detectable foveal lesions between patients with type 1 and type 2 Usher's syndrome. METHODS: Records of 48 patients with type 1 and 98 patients with type 2 Usher's syndrome were retrospectively evaluated for the presence of a foveal lesion. The age, gender, and racial distribution of patients were similar in the two subtypes. Two investigators reviewed fundus photographs from all patients and, when available, fluorescein angiograms. RESULTS: In the 48 patients with type 1 Usher's syndrome, 30 (62%) showed a clinically apparent atrophic- or cystic-appearing foveal lesion, whereas in the 98 patients with type 2 Usher's syndrome, 33 (34%) had either an atrophic- or a cystic-appearing foveal lesion. Logistic regression analysis showed that the probability of exhibiting a foveal lesion in both type 1 and type 2 Usher's syndrome increases with age and that patients with type 1 Usher's syndrome are more likely to have a foveal lesion than are patients with type 2 Usher's syndrome. CONCLUSIONS: Patients with type 1 Usher's syndrome show a greater probability of having either an atrophic- or cystic-appearing foveal lesion than do patients with type 2 Usher's syndrome. This higher prevalence of foveal lesions is consistent with a previous observation that the severity of visual acuity impairment with age is greater for patients with type 1 than type 2 Usher's syndrome. These data are useful in counseling such patients as to their prognosis for central visual function.

Adolescent↗
PubMed1995

Prevalence of palpebral fissure asymmetry in white persons.

PURPOSE: Because palpebral fissure asymmetry in horizontal gaze is reportedly common in otherwise normal persons, we determined the prevalence of physiologic palpebral fissure asymmetry for primary and horizontal gazes. METHODS: We measured the palpebral fissure height of both eyes of 88 healthy white subjects. Measurements were obtained with high-resolution videography, with the eyes in primary position, in 45-degree right gaze, and in 45-degree left gaze. RESULTS: Of the 88 subjects, 36 (41%) were male and 52 (59%) were female. The ages ranged from 12 to 50 years, with a mean of 32.5 +/- 9.0 years. When a criterion of equal to or greater than 1 mm was used, the prevalence of physiologic palpebral fissure asymmetry was 5.7% (five of 88) in primary gaze, 18.2% (16 of 88) in right gaze, and 14.8% (13 of 88) in left gaze. The largest observed palpebral fissure asymmetry was 2.1 mm. After correcting for any existing fissure asymmetry in primary gaze, two-tailed trivariate analysis of variance showed that the fissure of the adducting eye tended to be wider. The mean increase in the palpebral fissure of the adducting eye was 0.12 mm for right gaze (P = .052) and 0.13 mm for left gaze (P = .034). Additionally, a chi 2 test indicated that the occurrence of wider adducting eye in both right and left gazes was highly significant (P = .0023). CONCLUSIONS: In this sample of white subjects, palpebral fissure height asymmetry increased in horizontal gaze to the right and to the left, which is in part because of a tendency of the adducting eye to widen slightly. In contrast to previous reports, the prevalence of palpebral fissure asymmetry was low, and the abducting eye did not widen significantly.

Adolescent↗
PubMed1995

Retinitis pigmentosa associated with a dominant mutation in codon 46 of the peripherin/RDS gene (arginine-46-stop).

PURPOSE: We identified genetic mutations and characterized their associated phenotypes in patients with retinitis pigmentosa. METHODS: Patients with retinitis pigmentosa were prospectively examined and screened for genetic mutations. RESULTS: A 46-year-old man with retinitis pigmentosa was found to have a heterozygous mutation in the peripherin/RDS gene (arginine-46-stop). He had late onset of symptoms and demarcated peripheral retinal atrophy. All five first-degree relatives including his parents had no detectable mutations or retinitis pigmentosa. Genotypic data were consistent with reported family structure. CONCLUSIONS: This study shows that new dominant mutations are a rare cause of isolated, or simplex, cases of retinitis pigmentosa. Identification of these mutations is helpful for genetic counseling.

Adult↗
PubMed1995

Pain in anterior ischemic optic neuropathy.

PURPOSE: The diagnoses of both anterior ischemic optic neuropathy (AION) and optic neuritis are clinical ones with significant overlap of symptoms and signs. This study investigates the presence and character of pain at the onset of AION, in order to evaluate this symptom as a differentiating diagnostic feature between optic neuritis and AION. METHODS: Forty-one consecutive patients over 45 years of age with a clinical syndrome consistent with AION were questioned about the presence and character of associated pain. RESULTS: Pain was reported by 12% (5 of 41) of the patients with AION. This is contrasted with data compiled on 448 patients in the optic neuritis treatment trial, of whom 92.2% complained of pain. CONCLUSION: While there is overlap in the incidence and character of pain in AION and optic neuritis, its presence/absence remains a useful differentiating feature.

Aged↗
PubMed1994

Racial differences in the prevalence of atrophic-appearing macular lesions between black and white patients with retinitis pigmentosa.

We compared the prevalence of atrophic-appearing macular lesions between black and white patients with isolated or various genetic types of retinitis pigmentosa to determine if an appreciable difference existed between these two groups. The study included 720 patients of whom 138 (19.2%) were black patients from 115 families and 582 (80.8%) were white patients from 478 families. A logistic regression analysis combining isolated and all genetic types but randomly selecting one patient per family showed a statistically significant difference in the prevalence of atrophic-appearing macular lesions between black and white patients for the right eye (P = .0012) and left eye (P = .002). When considering either all patients or one patient per family, the estimated odds ratios were approximately 2.0 for blacks relative to whites. Our findings indicate that black patients with retinitis pigmentosa are approximately twice as likely as white patients to develop an atrophic-appearing macular lesion. This observation has implications for the prognosis of central visual function in such patients.

Adolescent↗
PubMed1994

Visual loss from idiopathic intracranial pachymeningitis.

We report three patients with chronic headaches and optic neuropathy due to widespread meningeal thickening shown on enhanced MRI; all had biopsy-proven intracranial pachymeningitis (fibrosclerosis of the meninges). Two patients had bilateral optic neuropathy, elevated CSF protein, and polyclonal serum hypergammaglobulinemia. They developed temporal lobe cortical necrosis or sagittal sinus thrombosis, presumably due to compromised dural venous drainage from extensive meningeal fibrosis. The other patient had multiple cranial nerve palsies and unilateral optic neuropathy with normal CSF. Corticosteroid therapy improved visual function in all three patients, although all had persisting visual deficits. Gadolinium-enhanced MRI was essential in identifying meningeal inflammation and locating suitable biopsy sites.

Adult↗