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Biomedical subjects

Brett G Jeffrey

Publications and source records attributed to Brett G Jeffrey.

8 recordsLinked to original sources
PubMed2005

Measurement of stereoacuity outcomes at ages 1 to 24 months: Randot Stereocards.

PURPOSE: The aim of the present study was to develop a simple, quick, and portable random dot stereoacuity test for measurement of binocular sensory outcomes during the first 24 months of life. METHODS: Vertical bar random dot vectographs were adapted for presentation in a "Teller Acuity Card" format, called the "Randot Stereocards." A forced-choice preferential looking protocol was used. Study participants included 386 healthy, term infants and children (normative cohort; age range: 1 month to 8 years) and 280 patients with common pediatric ophthalmic disorders (patient cohort; age range: 5 months to 9 years). RESULTS: Overall, the success rate for test completion in the normative cohort was 91.3%. By 4 months of age, normal infants' mean stereoacuity was about 600'' and, by 6 months, 200''. Mean stereoacuity further improved to about 100'' by 12 months and 70'' by 18 months. Normative results were similar to published data obtained with laboratory-based stereoacuity tests. Randot Stereocard data from normal children aged 2 to 6 years were similar to published normative data for the Preschool Randot Stereoacuity Test. In the patient cohort, concordance between the Randot Stereocards and the Preschool Randot Test was 87%; concordance between the Randot Stereocards and the Randot Test was 84%. CONCLUSION: The Randot Stereocards provide a simple, reliable, and valid method of obtaining a quantitative assessment of binocular vision in children up to 24 months of age for use in clinical trials and in clinical management.

Child↗
PubMed2004

Altered global shape discrimination in deprivation amblyopia.

To assess the effect of deprivation amblyopia on global shape discrimination, sensitivity to radial deformation of circular patterns was assessed in patients treated for congenital (N=7) or developmental (N=1) cataracts. Elevation in radial deformation threshold was dependent on circular contour frequency and the depth of amblyopia. Analysis of thresholds expressed as Weber fractions indicated a shift in global integration to a larger scale. In a pedestal experiment, equivalent intrinsic noise increased in proportion to the depth of amblyopia. The results suggest neural undersampling in V1 and/or higher visual cortical areas in deprivation amblyopia and a possible role for neural disarray.

Adolescent↗
PubMed2002

Retinal sensitivity loss in third-generation n-3 PUFA-deficient rats.

A previous study conducted in guinea pigs suggested that ingestion of diets high in EPA and DHA may result in suboptimal retinal function. The aim of the present study was to evaluate retinal function in pigmented (Long-Evans) rats, raised to a third generation on diets that were either deficient in n-3 PUFA or adequate (with the addition of DHA). Electroretinographic assessment employed full-field white flash stimulation. Photoreceptor responses were evaluated in terms of peak amplitudes and implicit times (a-wave, b-wave), intensity-response functions (Naka-Rushton), and the parameters of a model of transduction (P3). Retinal phospholipid FA composition was measured by capillary GLC. DHA levels were reduced by 55% in n-3-deficient animals compared with the n-3-adequate group, whereas the levels of docosapentaenoic acid n-6 were 44 times higher in n-3-deficient animals. The level of arachidonic acid was marginally higher (12.8%) in n-6-adequate animals. The n-3-deficient animals exhibited significantly reduced retinal sensitivity (sigma and S values were both affected by 0.29 log units) and increased b-wave implicit times compared with those fed the n-3-adequate diet. These data suggest that n-3 PUFA are required for development of retinal sensitivity, more so than other indices of retinal function assessed by current methods, such as maximal response amplitude. However, the benefit for retinal function of adding preformed DHA to diets already replete in n-3 PUFA remains unclear.

Animals↗
PubMed2002

Visual acuity and retinal function in infant monkeys fed long-chain PUFA.

Previous randomized clinical trials suggest that supplementation of the human infant diet with up to 0.35% DHA may benefit visual development. The aim of the current study was to assess the impact of including arachidonic acid (AA) and a higher level of DHA in the postnatal monkey diet on visual development. Infant rhesus monkeys were fed either a control diet (2.0% alpha-linolenic acid as the sole n-3 FA) or a supplemented diet (1.0% DHA and 1.0% AA) from birth. Visual evoked potential acuity was measured at 3 mon of age. Rod and cone function were assessed in terms of parameters describing phototransduction. Electroretinogram (ERG) amplitudes and implicit times were recorded over a wide intensity range (-2.2 to 4.0 log scot td-sec) and assessed in terms of intensity response functions. Plasma DHA and AA were significantly increased (P < 0.001) in the diet-supplemented monkeys compared with the control monkeys. There was an approximately equal effect of diet for the rod phototransduction parameters, sensitivity, and capacitance but in the opposite directions. Diet-supplemented monkeys had significantly shorter b-wave implicit times at low retinal illuminances (<-0.6 log scot td-sec). There were no significant effects of diet for visual acuity or the other 23 ERG parameters measured. The results suggest that supplementation of the infant monkey diet with 1.0% DHA and 1.0% AA neither harms nor provides substantial benefit to the development of visual acuity or retinal function in the first four postnatal months.

Animals↗
PubMed2002

Circular contour frequency in shape discrimination.

Circular contour frequency (the number of radial cycles per degree of unmodulated contour length measured in degrees of viewing angle) is an important factor in determining the deformation threshold of radial frequency (RF) patterns. Radial deformation thresholds were closely matched at a given circular contour frequency regardless of RF or radius. Our results suggest that two separate mechanisms may be involved in determining radial deformation thresholds. First, for low RFs, our results support a model of shape discrimination in which global integration occurs across all modulation cycles of an RF pattern. Second, for higher RFs, our data suggest that threshold may be determined by visual integration only over a limited segment of the RF pattern.

Discrimination, Psychological↗
PubMed2002

Preschool Worth 4-Shape test: testability, reliability, and validity.

PURPOSE: The Worth 4-Dot is used to assess binocular fusion, but it is difficult to use with young children. We modified the Worth 4-Dot by replacing the circles with shapes while maintaining the same color configuration. The purpose of this study was to determine the testability, reliability, and validity of the Worth 4-Shape test. METHODS: Subjects aged 2 to 8 years and 4 patients aged over 8 years with best-corrected visual acuity of 20/40 or greater (n = 131 patients, n = 123 normals) attempted test and retest at 35 cm and 3m using the Worth 4-Shape and Worth 4-Dot. To provide a gold standard, medical history, bifoveal fixation, and stereoacuity were reviewed. RESULTS: Testability of the Worth 4-Shape was significantly higher than the Worth 4-Dot both in children aged less than 4 years (95.9% vs 79.5% at 35 cm, P <.001; 79.5% vs 55.1% at 3 m, P <.001) and older than 4 years (98.5% vs 88.6% at 35 cm, P <.001; 90.9% vs 82.4% at 3m, P =.04). Test-retest analysis found comparable concordance for the Worth 4-Shape and Worth 4-Dot tests (P >.3). The sensitivity and specificity of the Worth 4-Shape (92%, 97%) and Worth 4-Dot (90%, 94%) were comparable. Between-test analysis found 96% agreement between both tests at 35 cm and 97% agreement at 3m. CONCLUSIONS: The success rate for the Worth 4-Shape is higher than the Worth 4-Dot, especially in children aged less than 4 years, and has equivalent accuracy. The Worth 4-Shape test-retest reliability is high supporting its validity for use with young children.

Child↗
PubMed2002

n-3 fatty acid deficiency alters recovery of the rod photoresponse in rhesus monkeys.

PURPOSE: Docosahexaenoic acid (DHA) is the major polyunsaturated fatty acid within rod outer segments. Varying the dietary content of DHA or its precursor, alpha-linolenic acid (ALA), can alter retinal DHA levels. The purpose of the present study was to assess rod phototransduction and recovery in rhesus monkeys raised on diets with different DHA and ALA content. METHODS: Adult rhesus monkeys had consumed from birth a diet low in ALA (0.3%) and known to induce an 80% reduction in retinal DHA. They were compared with groups receiving 8% ALA or 0.6% DHA, both of which support normal retinal DHA levels. Rod recovery was assessed with a double-flash protocol using a-wave saturating test flashes. The recovery of rod-isolated ERG a-wave amplitude was analyzed to determine Tc, the time to initiation of rod recovery, and T50, the time from initiation to 50% of full recovery. Phototransduction was assessed from the fit of a quantitative model to the leading edges of rod-isolated ERG a-waves. ERG a- and b-wave amplitudes and implicit times were also measured. RESULTS: Rod recovery (T50) was delayed by 30% and ERG implicit times by 5% in monkeys in the low ALA group compared with the other groups. There was no significant effect of diet on ERG amplitudes, the time to initiation of rod recovery, or the parameters describing phototransduction. CONCLUSIONS: The results indicate that mechanisms involved in deactivation and rod recovery are selectively altered in monkeys raised on a low-ALA diet whereas, at the flash intensities used, the mechanisms underlying phototransduction remain unaffected.

Animals↗