Biomedical subjects

Susan J Leat

Publications and source records attributed to Susan J Leat.

10 recordsLinked to original sources

PubMed2026

Histidine Supplementation Stabilizes Hearing and Vision and Improves Growth in HARS1-Related Autosomal Recessive Disorder Associated With Usher-Like Symptoms.

Autosomal recessive HARS1-related disorder (originally described as Usher syndrome type 3B) caused by a homozygous Y454S variant in the histidyl-tRNA synthetase gene (HARS1) is characterized by progressive sensorineural hearing and vision loss and respiratory deterioration with risk for sudden death following febrile illnesses. In-vitro studies have previously shown that histidine can rescue a humanized yeast model for pathogenic HARS alleles. Fourteen children homozygous for HARS Y454S were treated with supplemental oral histidine (50 mg/kg BID) and monitored with bloodwork and physical, visual, and audiometry assessments during a 3-year clinical trial, then followed for more than 4 years on histidine in the post-trial period. Patient fibroblasts were assessed for response to histidine. Hearing and vision remained stable, and growth improved significantly. Children remained healthy, with no severe deteriorations despite exposure to bacterial and viral infections, including COVID-19. Gains in growth were maintained in the post-trial period on varying levels of histidine supplementation. Daily oral histidine supplementation in children with autosomal recessive HARS1-related disorder can ameliorate or slow the progression of disease and is safe, inexpensive, and well tolerated. This study adds to the growing list of autosomal recessive ARSopathies (aminoacyl-tRNA synthetase disorders) that are amenable to amino acid supplementation.

Humans↗

PubMed2006

Effects of unsteady fixation on multifocal electroretinogram (mfERG).

PURPOSE: To investigate the effect of unsteady fixation on the multifocal electroretinogram (mfERG) measurement in normal subjects. METHODS: The mfERGs of 20 subjects with normal vision (mean age=23.5 years) were recorded with different levels of voluntary eye movements made to mimic unsteady fixation. Subjects were required to move their fixation regularly every 2 s between the center and the ends of a fixation cross, so that 51.2% of the time fixation was at the center and 12.2% of the time it was at each end of the fixation cross. Four different conditions were performed: central fixation (without voluntary eye movements) and with 2 degrees, 4 degrees and 6 degrees magnitude of unsteady fixation. First-order kernel mfERG findings are presented. RESULTS: Analysis of the ring responses indicated that the central mfERG amplitude was most affected by unsteady fixation. There was significantly reduced amplitude for 4 degrees unsteady fixation and as expected, this reduction became larger with 6 degrees unstable fixation. However, there was no significant effect on the center hexagon amplitude for 2 degrees unsteady fixation. The amplitudes of the ring-2 responses were only affected in the 6 degrees unsteady fixation condition. No significant change in implicit time was found for any level of unsteady fixation. CONCLUSION: These results suggest that mfERG amplitude is not substantially affected if fixation is maintained within the central stimulus hexagon. We conclude that, for patients with poor fixation, the accuracy of mfERG results may be difficult to interpret and the use of a fixation-monitoring system is desirable for ideal measurement. The depth of depression at the blind spot area may be another useful parameter to interpret the accuracy of mfERG results in patients with poor fixation.

Adult↗

PubMed2006

Measuring mobility performance: experience gained in designing a mobility course.

BACKGROUND: This paper reviews the most common methods of measuring and scoring orientation and mobility (O and M) and the effects of visual impairment on O and M. We discuss the difficulties inherent in designing a 'real-world' course to measure O and M and we describe the course that we finally used. METHODS: Thirty-five participants in two age groups, with low vision due to a variety of disorders, took part in mobility trials on the final version of the course. Aspects of visual function were measured. RESULTS: Factor analysis indicated that mobility errors, visual detection distance and visual identification distance were grouped with measures of visual acuity, contrast sensitivity and Humphrey visual field mean deviation, while preferred walking speed and walking speed were separately grouped. Humphrey pattern standard deviation did not group with any other measure and neither did percentage preferred walking speed. This study is in agreement with other studies that visual field and contrast sensitivity, sometimes with low contrast visual acuity, were the best clinical visual predictors of mobility performance. Based on our experiences we present a number of recommendations for designing courses for assessing mobility. CONCLUSIONS: For future studies, it would behove researchers to include a range of mobility measures, until further understanding is gained about how they are interrelated and contribute information on the relationship among mobility, vision and other individual factors.

Contrast Sensitivity↗

PubMed2006

Visual impairment and the useful field of vision.

The aim of this study was to measure the useful field of vision (UFoV) in people with visual impairment and to compare results with clinical measures of vision. UFoV, visual acuity, contrast sensitivity and visual fields were measured in 36 participants with low vision and 22 age-matched controls in two age groups. For both the low vision and control groups the presence of distractors (cluttered field) increased the error rates on our UFoV measure but there was no significant effect of the presence of a central task (divided attention). Participants with low vision made more errors on UFoV than did controls, but this difference disappeared once their visual field defects were accounted for. By multiple regression analysis, age, visual fields and contrast sensitivity were shown to predict the different UFoV scores. As for observers with normal vision, standard clinical visual field tests may not fully describe the difficulties that may be encountered by people with visual impairment undertaking tasks in the cluttered environments and multiple demands of everyday life.

Adult↗

PubMed2005

Generic and customized digital image enhancement filters for the visually impaired.

This study compares the effectiveness of various image enhancement filters for improving the perceived visibility of coloured digital natural images for people with visual impairment. Generic filters were compared with Peli's adaptive enhancement and adaptive thresholding and custom-devised filters based on each subject's contrast sensitivity loss. Subjects with low vision made within filter rankings followed by between filter ratings. In general, subjects preferred filters with lower gains. Unsharp masking resulted in a significant increase in perceived visibility for some image types (p < or = 0.05) while Peli's adaptive enhancement, edge enhancement and histogram equalization resulted in borderline improvements. Adaptive thresholding and the custom devised filter did not result in overall improvements in perceived visibility.

Adult↗

PubMed2004

Clinical testing of contrast sensitivity in children: age-related norms and validity.

PURPOSE: The Hiding Heidi (HH) test and the LEA low-contrast symbols are two commercially available charts of contrast sensitivity (CS) for children. However, there are no published normal data and no indication of how CS measured by these charts relates to other measures of CS. In this study, normal age-related data for both tests are reported, and validity against the Pelli-Robson (PR) chart is measured. METHODS: Eighty-eight normally sighted children were divided into four age groups: 1 to <2.5 years, 2.5 to <4 years, 4 to <6 years, and 6 to <8 years. An adult group with normal vision and with low vision also took part. CS was measured with the HH test, the LEA symbols at 1 m and 28 cm, and the PR chart, as the child's ability permitted. Because there were obvious differences between the contrast levels of the PR chart and the nominal contrast for the children's charts, each contrast level for the children's tests was recalibrated. RESULTS: The HH test and the LEA symbols at 28 cm and 1 m all showed a floor effect; that is, most children of all ages correctly responded to the lowest contrast. The median CS for the LEA symbols at 28 cm and 1 m was 2.22 log CS, which was 1.65 when recalibrated. There was a significant difference of PR CS between the 6- to <8-year-olds and adults (p < 0.001). Of the children's charts, the LEA symbols at 28 cm, once recalibrated for contrast, had the best agreement with the PR chart. CONCLUSION: The LEA and HH charts cannot measure a true contrast threshold for children with normal vision because of the floor effect. The LEA symbols at 28 cm gave the most useful information, once recalibrated for contrast, and may be useful to predict performance of children with low vision, when CS is likely to be compromised.

Adult↗

PubMed2003

The UWCDot colour vision test and low vision.

PURPOSE: Previous studies have shown that colour vision defects are common in the low vision population even when properly designed tests are used. However, there are very few clinical tests available that are suitable for this group of patients. One of the more common is the Jumbo D-15 (JD15). Although this test uses caps more suitable for the reduced acuity, it requires the patient to have some knowledge of colour order and sufficient dexterity to manipulate the caps. We compared the JD15 with the University of Waterloo Colored Dot test (UWCDot), which has neither of these requirements, to determine whether the UWCDot test could be used as a substitute for the JD15. METHODS: The colour vision of 40 consecutive low vision patients was evaluated with both tests. Acuities ranged from 6/6 to 6/1600 with a median value of 6/30. RESULTS: All subjects could perform both tests. The kappa coefficient of agreement between tests was high at 0.85 when any major crossing was a failure on the JD15 and any mistake was a failure on the UWCDot. Classification of the type of defect was also reasonable when the defect was relatively severe. CONCLUSIONS: The UWCDot can be used as a substitute for the JD15 in the low vision clinic. Both tests identify individuals with moderate-to-severe deficiencies, but the UWCDot does not require any manual dexterity and it does not require knowledge of colour-order.

Adolescent↗

PubMed2002

The validity of the University of Waterloo Colored Dot Test for Color Vision Testing in adults and preschool children.

PURPOSE: Most color vision tests require a high level of cognitive ability and as such are problematic for preschool children and multiply challenged individuals. Our goal was to design a color vision test for these groups and evaluate the clinical utility for preschool children. METHODS: The University of Waterloo Colored Dot Test (UWCDot) for Color Vision Testing requires the subject to distinguish a colored disc from seven gray discs. The target disc was a Munsell color along the deutan, protan, or tritan confusion line with gray. The first phase estimated the sensitivity and specificity of the test for adults. Thirty-one adults with normal color vision and 21 adults with congenital red-green defects participated. In the second phase, the utility of the UWCDot test for screening preschool children was determined. Subjects were 281 males and 269 females aged 2.5 to 5 years with normal vision. Their color vision was also assessed with the Standard Pseudoisochromatic Plates, Part 1 (SPP1). RESULTS: The sensitivity and specificity of UWCDot for adults approached the values for the desaturated D-15 when subjective responses were scored. Monitoring fixational eye movements produced sensitivity and specificity values that were similar to the anomaloscope. After adjusting the scoring criterion for the preschool children by using the females as a control, 2.9% of the males were identified as red-green deficient, 1.8% were blue-yellow deficient, and 3.2% had an unclassified deficiency. By definition, 1% of the females failed the test. Counting fixational eye movements was not a useful scoring method in the preschool children. Comparisons with SPP1 indicated that the UWCDot uncovers approximately 35% of the individuals with definite red-green color vision defects. CONCLUSIONS: Our results indicate that the UWCDot is capable of detecting approximately 35% of the preschool children who have a congenital red-green color vision defect. These individuals are likely to have a more severe deficiency.

Adult↗

PubMed2001

Changes in fixation in the presence of prism monitored with a confocal scanning laser ophthalmoscope.

BACKGROUND: The main optical effect of an ophthalmic prism is to deviate uniformly the entire field of view seen through the prism, resulting in an equal eye movement, if fixation on the same object is to be maintained. Conversely, it has been suggested that, in the case of low vision due to central scotoma, the eye changes its eccentric viewing behaviour when a prism is introduced, that is, the eye remains stationary with a change of retinal image location. METHOD: A new method is described in which retinal image position was recorded with a confocal scanning laser ophthalmoscope in four experimental conditions. RESULTS: Results showed that the normally-sighted eye rotates rapidly to compensate for the introduction of a prism. CONCLUSION: Future studies are required involving subjects with central scotoma but it is likely that many subjects with low vision will also refixate behind a prism and that the prescribing and wearing of bilateral prism in cases of central vision loss will have limited effectiveness in the demonstration or training of eccentric viewing.

Journal Article↗

PubMedDate not supplied

The moving dynamic random dot stereosize test: validity and repeatability.

PURPOSE: We have developed a new test suitable for measuring stereopsis in young children and individuals with communication difficulties. It consists of a drifting, computer-generated red and green, dynamic random dot, disparate shape. The motion direction is indicated by the subject (subjective response) or by a naive observer judging the eye movements of the subject (objective response). Disparity is maintained at 616 sec arc and the dependent variable is the angular subtense of the target, which varies from 11 degrees to 11 ft. In this study, precision (ie, measuring repeatability and objective-subjective agreement) and validity were assessed. SUBJECTS AND METHODS: Sixteen subjects with normal vision participated in the repeatability study and 10 in the validity studies. A two-up/one-down, 2 alternative forced choice staircase procedure was used to measure objective and subjective threshold on two occasions with a 1-week separation. Sensitivity for detecting anisometropia was estimated with simulated anisometropia (0 to 3 D) and by comparison with the Randot test. Sensitivity for detecting amblyopia or strabismus was tested in 10 subjects. RESULTS: Subjective repeatability was 0.31 log units (2 levels of the test) and objective repeatability was 0.49 log units (3.2 levels of the test). The test was able to detect 2.0 D of simulated anisometropia in 8 of 10 cases (above the 95% confidence interval). None of the amblyopic subjects demonstrated stereopsis. CONCLUSION: This test of dynamic global stereopsis has potential as a clinical or screening tool for anisometropia, amblyopia, and strabismus.

Adult↗