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Biomedical subjects

B L Lam

Publications and source records attributed to B L Lam.

At least 19 recordsLinked to original sources
PubMed2005

Estimating visual acuity by character counting using the Snellen visual acuity chart.

PURPOSE: This study examines visual acuity estimation with character counting, which can be used in subjects with nonorganic visual loss. METHODS: The right eyes of 35 healthy subjects were fogged with plus lenses and tested with the Snellen visual acuity chart (Reichert 11180). Visual acuity and counting level were assessed under various degrees of fogging, up to a maximal fogged acuity of 20/200. Counting level was defined as the smallest line that subjects could count the number of characters correctly. For each counting level, the visual acuity that 95% of subjects could see equal to or better than was determined. RESULTS: A counting level of 20/10 estimates (ie 95% chance) a visual acuity equal to or better than 20/30. Counting levels 20/15, 20/20, and 20/25 estimate visual acuities of at least 20/50, 20/80, and 20/80, respectively. Counting levels 20/30-20/60 estimate a visual acuity of at least 20/200. CONCLUSIONS: Character counting appears to be a useful technique of obtaining a rough estimate of visual acuity in subjects unable to be tested by standard methods, such as those with non-organic visual loss.

Adult↗
PubMed2004

Comparison of pupil responses to luminance and colour in severe optic neuritis.

OBJECTIVE: The pupil response to light flux increments is abnormal in severe optic neuritis, but little is known about the effects of this condition on the pupil colour response. The aim of this study was to examine how optic neuritis affects pupil responses to light flux and colour modulation and the extent to which such pupil responses mirror the loss and recovery of vision. METHODS: A new pupil examination technique that makes use of sinusoidal modulation of either luminance contrast or chromatic saturation was employed. This technique enables the automatic extraction of both pupil response amplitude and latency and achieves a high signal to noise ratio with fewer averages. RESULTS: The study reveals a greater loss of pupil response amplitude and significantly longer latencies to chromatic modulation (i.e. approximately 80 ms). Stimulation of the unaffected eye in the optic neuritis group results in smaller response amplitudes when compared to the normal group for both light flux and colour modulation. CONCLUSIONS: Pupil response components can be affected differently in optic neuritis. These findings suggest that the pupil colour response, in particular, may provide a useful, objective estimator to judge the extent of damage and recovery in diseases of the optic nerve.

Adult↗
PubMed2001

Positional cloning of a novel gene on chromosome 16q causing Bardet-Biedl syndrome (BBS2).

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous autosomal recessive disorder with the primary clinical features of obesity, pigmented retinopathy, polydactyly, hypogenitalism, mental retardation and renal anomalies. Associated features of the disorder include diabetes mellitus, hypertension and congenital heart disease. There are six known BBS loci, mapping to chromosomes 2, 3, 11, 15, 16 and 20. The BBS2 locus was initially mapped to an 18 cM interval on chromosome 16q21 with a large inbred Bedouin kindred. Further analysis of the Bedouin population allowed for the fine mapping of this locus to a 2 cM region distal to marker D16S408. Physical mapping and sequence analysis of this region resulted in the identification of a number of known genes and expressed sequence tag clusters. Mutation screening of a novel gene (BBS2) with a wide pattern of tissue expression revealed homozygous mutations in two inbred pedigrees, including the large Bedouin kindred used to initially identify the BBS2 locus. In addition, mutations were found in three of 18 unrelated BBS probands from small nuclear families.

Amino Acid Sequence↗
PubMed2001

Pseudomonas aeruginosa in vitro corneal isolate sensitivity to ofloxacin, ciprofloxacin, and trovafloxacin: a comparative study.

PURPOSE: To compare sensitivity of Pseudomonas aeruginosa corneal isolates to ofloxacin, ciprofloxacin, and trovafloxacin. METHODS: Sensitivities of P. aeruginosa corneal isolates to each antibiotic from the periods 1985 to 1987 (n = 32) and 1995 to 1999 (n = 85) were evaluated in vitro with E tests (AB Biodisk; Remel, Lenexa, Kansas). RESULTS: Overall, the percent of P. aeruginosa corneal isolates sensitive in vitro to ofloxacin (106/117, 90.6%) was significantly less than to ciprofloxacin (113/117, 96.6%, P =.016) and trovafloxacin (113/117, 96.6%, P =.016). We observed trends of decreasing sensitivity to ciprofloxacin and trovafloxacin, which were not statistically significant. Sensitivity to ofloxacin remained unchanged; however, sensitivity to ofloxacin was always less than sensitivity to ciprofloxacin and trovafloxacin. CONCLUSION: Although in vitro susceptibilities may not correlate with in vivo efficacy, our data suggest that ciprofloxacin and trovafloxacin are superior to ofloxacin in the treatment of P. aeruginosa keratitis.

Anti-Infective Agents↗
PubMed2001

Optic tract compression from dolichoectatic basilar artery.

PURPOSE: To report a case of optic tract compression caused by a dolichoectatic basilar artery. DESIGN: Observational case report. METHODS: A 74-year-old man with progressive loss of vision over 13 years and no other neurologic signs or symptoms was found to have bilateral optic nerve head pallor and a left homonymous hemianopia. RESULTS: Magnetic resonance imaging and angiography revealed a severe dolichoectatic basilar artery compressing the right optic tract. CONCLUSION: Basilar artery dolichoectasia may rarely cause compression of the optic tract and progressive visual loss.

Aged↗
PubMed2001

Ocular manifestations of Seckel syndrome.

PURPOSE: To report ophthalmic findings in three siblings with Seckel syndrome. METHODS: Observational case report. Three siblings with Seckel syndrome were examined. RESULTS: Severe bilateral pigmentary retinopathy with severe myopia and astigmatism was found in all three patients. Electroretinography was performed on the eldest sibling and showed no detectable rod or cone responses. CONCLUSION: Severe, early onset, bilateral retinal degeneration with severe myopia and astigmatism may be associated with Seckel syndrome.

Abnormalities, Multiple↗
PubMed2001

Incidence of nonarteritic anterior ischemic optic neuropathy associated with cataract extraction.

OBJECTIVES: To determine the incidence of nonarteritic anterior ischemic optic neuropathy (NAION) after cataract extraction and to use the incidence to evaluate the causal relationship between cataract extraction and NAION. DESIGN: Cohort study. PARTICIPANTS: Five thousand seven hundred eighty-seven cataract extraction cases at the Bascom Palmer Eye Institute (BPEI) in a 5-year period between January 1, 1993 and December 31, 1997. METHODS: During the study period, an estimated 5787 cataract extraction cases were identified that met the following criteria: (1) the patient was 50 years of age or older, (2) surgery was performed by phacoemulsification or phacofracture techniques and not planned in combination with another procedure, and (3) follow-up was at BPEI. Charts of patients diagnosed with NAION from January 1, 1993 to December 31, 1998 were reviewed to detect the occurrence of NAION within 1 year of surgery. The diagnosis of NAION was based on the following: (1) an acute decrease in vision, (2) associated nerve fiber layer defect on visual field testing, (3) associated relative afferent pupillary defect, and (4) observed optic nerve edema. The exact binomial test was used to compare the incidence of NAION after cataract extraction against the expected incidence. MAIN OUTCOME MEASURE: Occurrence of NAION within 1 year after cataract extraction. RESULTS: Of the 5787 cataract extraction cases, three patients experienced NAION within 1 year of the procedure. Each case occurred after surgery on days 29, 36, and 117, giving an estimated 6-month incidence of 51.8 in 100,000 and a 6-week incidence of 34.6 in 100,000. Both were statistically higher than the previously reported overall incidence of NAION. Two of the three patients had a history of NAION in the contralateral eye. CONCLUSIONS: Cataract extraction is associated with an increased incidence of NAION, which is higher than the reported overall incidence. However, the risk of NAION after cataract extraction is low, with approximately one occurrence in every 2000 cases. A history of NAION in the fellow eye may be a risk factor.

Aged↗
PubMed2001

Uncorrected binocular distance visual impairment in U.S. Hispanic children and adolescents.

PURPOSE: To assess and compare uncorrected binocular distance visual impairment rates in U.S. Hispanic children and adolescents. METHODS: Data from the Hispanic Health and Nutrition Examination Survey, 1982-1984, were analyzed for 6-19 year-old Cuban-Americans (n = 317), Mexican-Americans (n = 2519), and Puerto Ricans (n = 988). Visual acuity was assessed using Sloan Letters or Landolt Rings. RESULTS: Prevalence rates of uncorrected binocular distance visual impairment (20/30 or worse) were 15.5%, 14.9%, and 23.6% for Cuban-Americans, Mexican-Americans, and Puerto Ricans, respectively. After adjusting for age and gender, the differences between Puerto Ricans and both Cuban-Americans and Mexican-Americans were significant (p < 0.05). Children 6-12 years of age had lower visual impairment rates than 13-19 year-old adolescents. Girls had higher age-adjusted visual impairment rates than boys; these gender differences were statistically significant among Mexican-Americans (OR = 1.6, 95% CI = 1.1, 2.2) and Puerto Ricans (OR = 1.7, 95% CI = 1.2, 2.4). CONCLUSIONS: Among Hispanics, Puerto Rican children and adolescents have the highest prevalence rate of uncorrected binocular distance visual impairment; older age and female gender are associated with higher rates of uncorrected visual impairment.

Adolescent↗
PubMed2001

An analysis of allelic variation in the ABCA4 gene.

PURPOSE: To assess the allelic variation of the ATP-binding transporter protein (ABCA4). METHODS: A combination of single-strand conformation polymorphism (SSCP) and automated DNA sequencing was used to systematically screen this gene for sequence variations in 374 unrelated probands with a clinical diagnosis of Stargardt disease, 182 patients with age-related macular degeneration (AMD), and 96 normal subjects. RESULTS: There was no significant difference in the proportion of any single variant or class of variant between the control and AMD groups. In contrast, truncating variants, amino acid substitutions, synonymous codon changes, and intronic variants were significantly enriched in patients with Stargardt disease when compared with their presence in subjects without Stargardt disease (Kruskal-Wallis P < 0.0001 for each variant group). Overall, there were 2480 instances of 213 different variants in the ABCA4 gene, including 589 instances of 97 amino acid substitutions, and 45 instances of 33 truncating variants. CONCLUSIONS: Of the 97 amino acid substitutions, 11 occurred at a frequency that made them unlikely to be high-penetrance recessive disease-causing variants (HPRDCV). After accounting for variants in cis, one or more changes that were compatible with HPRDCV were found on 35% of all Stargardt-associated alleles overall. The nucleotide diversity of the ABCA4 coding region, a collective measure of the number and prevalence of polymorphic sites in a region of DNA, was found to be 1.28, a value that is 9 to 400 times greater than that of two other macular disease genes that were examined in a similar fashion (VMD2 and EFEMP1).

ATP-Binding Cassette Transporters↗
PubMed2000

Prevalence of usual-corrected distance visual acuity impairment in Hispanic and non-Hispanic children and adolescents.

Data from the Hispanic Health and Nutrition Examination Survey and the National Health and Nutrition Examination Survey I were analysed to determine the prevalence of visual acuity impairment among US Hispanics and non-Hispanics aged 6-19 years. The prevalence of 20/30 or worse distance visual acuity with usual or habitual correction ranged from 10.8% in non-Hispanic whites to 19.1% in Puerto Ricans. Puerto Rican boys aged 13-19 years had significantly greater rates of moderate or greater impairment (20/70 or worse) than 6-12-year-old Puerto Rican boys (5.7% vs. 0.7%). The prevalence of visual impairment was generally greater in girls than in boys. Assessment and comparison of refractive error and eye disease prevalence rates are necessary in future studies to determine factors influencing prevalence of visual acuity impairment in children.

Adolescent↗
PubMed2000

Prevalence of usual-corrected binocular distance visual acuity impairment in Hispanic and non-Hispanic adults.

OBJECTIVES: The purpose of this study was to perform comparative analyses of the population-based prevalence of usual-corrected binocular distance visual acuity impairment among Hispanics and non-Hispanics in the United States. METHODS: Data from the Hispanic Health and Nutrition Examination Survey (HHANES), 1982-1984, and the National Health and Nutrition Examination Augmentation Survey I (NHANES I-A), 1974-1975, were analyzed to investigate the epidemiology of usual-corrected binocular distance acuity in adults 25 to 74 years of age among Cuban-Americans (N=396), Mexican-Americans (N=1,381), Puerto Ricans (N=513), African-Americans (N=250), and non-Hispanic white Americans (N=2, 660). Binocular distance acuity was assessed using Sloan Letters or Landolt Rings with the participants wearing their corrective lenses, if any. RESULTS: Prevalences of 20/50 or worse usual-corrected binocular distance acuity were 3.5%, 4.6%, and 6.6% for Cuban-Americans, Mexican-Americans, and Puerto Ricans, respectively, in the HHANES; and 7.7% and 4.1% for African-Americans and non-Hispanic whites, respectively, in the NHANES I-A. Within the HHANES, after adjustment for gender and age, Puerto Rican adults were found to have a significantly higher prevalence of visual impairment (20/50 or worse) and were significantly less likely to become unimpaired with usual correction than Cuban-American adults. Within the NHANES I-A, African-Americans were found to have a higher prevalence of visual impairment (20/50 or worse) and were significantly less likely to become unimpaired with usual correction than non-Hispanic whites. Higher prevalences of visual impairment (20/50 or worse) were associated with increasing age for all ethnic groups. After controlling for age, odds of usual-corrected visual impairment (20/50 or worse) were significantly higher in women than in men for Cuban-Americans and Mexican-Americans (odds ratios: 4.5 and 2.6, respectively). CONCLUSIONS: The results from this study suggest that compared to other Hispanic groups and non-Hispanic whites, Puerto Rican and African-American adults may not be receiving similar eye care services and/or may have more severe eye diseases.

Adult↗
PubMed2000

Acute effects of sildenafil (viagra) on blue-on-yellow and white-on-white Humphrey perimetry.

OBJECTIVE: To study the effects of sildenafil on blue-on-yellow and white-on-white Humphrey visual field (HVF). MATERIALS AND METHODS: Healthy subjects, ages 20 to 38 years, were prospectively randomized to active drug (n = 5) or placebo (n = 3) groups. Blue-on-yellow and white-on-white HVF testing was performed before and 1 hour after masked dosing of sildenafil 200 mg or placebo. Changes in mean deviation (MD) were compared between groups. RESULTS: Three of three placebo and four of five sildenafil subjects had no change on HVF. One of five sildenafil subjects had a decrease in MD of 17.9 dB and 4.7 dB on blue-on-yellow and white-on-white HVF testing, respectively. This subject reported more systemic side effects than other subjects. CONCLUSIONS: Sildenafil has no effect on HVF testing in most persons; however, sildenafil caused an acute abnormality of HVF testing in one subject, who experienced pronounced non-visual systemic symptoms; this effect was greater on blue-on-yellow than white-on-white HVF.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1999

Bilateral posterior ischemic optic neuropathy after spinal surgery.

PURPOSE: To report the association between bilateral posterior ischemic optic neuropathy and spinal surgery. METHOD: Case report. RESULTS: After prone-position spinal surgery of 8 hours' duration, a 68-year-old woman was completely blind in both eyes. Moderate periorbital edema and temporal conjunctival chemosis were present bilaterally. Ophthalmic examination disclosed normal-appearing optic nerve heads, except for bilateral nasal fullness related to bilateral optic nerve drusen, and no retinal edema. Immediate cerebral arteriography, magnetic resonance imaging, and electroretinography were normal. Visual-evoked response was not detectable, and 7 weeks later, severe bilateral optic nerve head pallor developed. CONCLUSIONS: Severe selective hypoperfusion of the retrobulbar optic nerves may occur after spinal surgery. Pressure to the periorbital region may be a contributing factor.

Aged↗
PubMed1999

Low-frequency damped electroretinographic wavelets in young asymptomatic patients with dominant retinitis pigmentosa: a new electroretinographic finding.

OBJECTIVE: To describe a previously unreported electroretinographic (ERG) pattern in early retinitis pigmentosa (RP). DESIGN: Two case reports. PARTICIPANTS: Two unrelated young asymptomatic patients with autosomal-dominant retinitis pigmentosa were studied. MAIN OUTCOME MEASURES: Clinical findings and ERG responses were assessed. RESULTS: No ERG responses were detected scotopically with low-luminance stimuli. With increasingly brighter stimuli, a series of three to five low-frequency damped wavelets developed under both scotopic and photopic conditions. The period of the wavelets was 25 to 37 msec. CONCLUSIONS: Low-frequency damped ERG wavelets occur in some young asymptomatic patients with autosomal-dominant RP. The ERG pattern suggests that these wavelets are predominantly cone-generated.

Adult↗
PubMed1999

Sociodemographic correlates of visual acuity impairment in Hispanic children and adolescents.

Sociodemographic correlates of visual impairment were examined in 6- to 19-year-old Hispanic children and adolescents using data from the Hispanic Health and Nutrition Examination Survey. Mexican American and Puerto Rican children whose parents had 0 to 6 years of education were more likely to remain visually impaired even when tested with their glasses or contact lenses, if any (i.e., with usual correction) than children whose parents reported 12 to 17 years of education. Mexican Americans residing below versus at or above the poverty line were more likely to remain visually impaired even with the usual correction. Mexican Americans enrolled in the Medicaid program or who were without health insurance were more likely to remain visually impaired than Mexican Americans with private health insurance. When tested without glasses or contact lenses, Cuban Americans and Mexican Americans born outside of the mainland United States had lower rates of visual impairment compared to those born in the United States; however, children in this latter group were more likely to remain visually impaired with usual correction than U.S.-born Mexican Americans. These findings suggest that Hispanic children from economically disadvantaged households and those born outside the United States may not be receiving optimal eye care that could improve visual function.

Journal Article↗
PubMed1999

Update on hereditary optic neuropathy.

Although no treatment is available for hereditary optic neuropathies, recent localization and identification of some of the genetic loci have helped the evaluation and management of patients with these disorders. This article discusses the clinical features and known genetic information regarding Leber's hereditary optic neuropathy, dominant optic atrophy, recessive optic atrophy, and Wolfram syndrome.

Audiovisual Aids↗
PubMed1999

An anisocoria produces a small relative afferent pupillary defect in the eye with the smaller pupil.

OBJECTIVES: To determine whether an anisocoria can produce a relative afferent pupillary defect of clinical importance. MATERIAL AND METHODS: Anisocoria and relative afferent pupillary defect were measured with infrared videography in three clinical experiments: 1) every few minutes in eight normal subjects who remained in darkness as one pupil was dilating from mydriatic drops; 2) every 2 hours, for 8 hours in six normal subjects who remained in room light after one pupil was dilated with mydriatic drops; and 3) before and after dilation of one pupil in 24 patients with known afferent defects from optic nerve disease and who remained in room light. RESULTS: In the presence of an anisocoria, the relative afferent pupillary defect was almost always in the eye with the smaller pupil. The results of the three experiments were: 1) In darkness, the induced pupillary defect was found to be related to the ratio of the areas of the two pupils (R = 0.942), and 0.14 log unit of pupillary defect was produced in the eye with the smaller pupil for every millimeter of anisocoria. 2) In room light, the induced pupillary defect was in the eye with the smaller pupil but was less than in Experiment 1 and persisted throughout the 8 hours. This was presumably because the eye with the larger pupil had become more light adapted in the clinic light than the eye with the smaller pupil. 3) In room light, inducing an anisocoria in patients with preexisting afferent pupillary defect tended to shift the pupillary defect toward the eye with the smaller pupil (R = 0.68). CONCLUSIONS: Clinically, approximately 0.1 log unit of relative afferent pupillary defect is produced in the eye with the smaller pupil for every millimeter of anisocoria. Therefore, the anisocoria must be larger than 2 mm in diameter difference to induce a clinically significant relative afferent pupillary defect.

Anisocoria↗