Purpose: An important challenge for eye care practitioners is meeting the needs of an ever-increasing elderly population. Standard vision tests are inadequate for determining performance in real life situations. One test that was developed to address this issue is the Attended Field of View (AFOV) test (Coeckelbergh et al, 2004). This test was designed to assess the functional field of view when people are allowed to make habitual head and eye movements. The original AFOV test is no longer available. This research seeks to develop a replacement AFOV test and to demonstrate its reliability as an assessment tool. Methods: Two groups of participants were recruited. The first group consisted of seven participants between the ages of 15-41 years. The second group consisted of seven participants between the ages of 59–79 years. All subjects had visual acuities equal or better than 20/25 and no history of visual field loss. A computer-generated display was observed from a 60cm distance. The display consisted of 24 white circles on a gray background and one open circle (target). The circles were organized with one circle in the centre and eight located radially at three eccentricities (4, 8, and 12 degrees). Participants were required to locate the target circle and identify the gap direction. A response was considered correct when both the location and gap direction were accurate. Using a weighted staircase method based on presentation time each location was evaluated independently. Viewing efficiency [log (1/threshold presentation time)] was obtained for each location. The data was analyzed using repeated measures ANOVA. Results: A comparison of viewing efficiency for the two age groups demonstrates that viewing efficiency is consistently lower for the older group at all three visits. The main effect of age was observed (F1,12=25.842;p=0.000). In the older group, a significant difference was found between the second and third visits. This difference was not found in the younger group. A main effect of eccentricity was found in both groups (F2,36=30.84;p<0.000), but no interaction was observed between eccentricity and group (F2,36=0.42;p=0.662). Viewing efficiency values in the older group were lower in all directions (main effect of age) (F1,96=150.36;p<0.000). Directional variations in viewing efficiency were observed showing higher values in the horizontal axes (directions Right and Left) than along the vertical axes (directions Up and Down) in both groups. A comparison of superior and inferior hemifield data shows consistent differences for both age groups. The superior hemifield (average of directions located superiorly to the horizontal axis) demonstrate higher viewing efficiency values (better performance) than the inferior hemifield. Conclusions: The use of the new AFOV test requires a practice time before its use in order to avoid the confound of a learning effect, but subsequent data is reliable in young people. The learning effect was more significant in older people and for this reason the use of the test should be preceded by a longer practice session in this population. When interpreting the results of this test one must account for eccentricity, direction, and age.

Purpose: An important challenge for eye care practitioners is meeting the needs of an ever-increasing elderly population. Standard vision tests are inadequate for determining performance in real life situations. One test that was developed to address this issue is the Attended Field of View (AFOV) test (Coeckelbergh et al, 2004). This test was designed to assess the functional field of view when people are allowed to make habitual head and eye movements. The original AFOV test is no longer available. This research seeks to develop a replacement AFOV test and to demonstrate its reliability as an assessment tool. Methods: Two groups of participants were recruited. The first group consisted of seven participants between the ages of 15-41 years. The second group consisted of seven participants between the ages of 59–79 years. All subjects had visual acuities equal or better than 20/25 and no history of visual field loss. A computer-generated display was observed from a 60cm distance. The display consisted of 24 white circles on a gray background and one open circle (target). The circles were organized with one circle in the centre and eight located radially at three eccentricities (4, 8, and 12 degrees). Participants were required to locate the target circle and identify the gap direction. A response was considered correct when both the location and gap direction were accurate. Using a weighted staircase method based on presentation time each location was evaluated independently. Viewing efficiency [log (1/threshold presentation time)] was obtained for each location. The data was analyzed using repeated measures ANOVA. Results: A comparison of viewing efficiency for the two age groups demonstrates that viewing efficiency is consistently lower for the older group at all three visits. The main effect of age was observed (F1,12=25.842;p=0.000). In the older group, a significant difference was found between the second and third visits. This difference was not found in the younger group. A main effect of eccentricity was found in both groups (F2,36=30.84;p<0.000), but no interaction was observed between eccentricity and group (F2,36=0.42;p=0.662). Viewing efficiency values in the older group were lower in all directions (main effect of age) (F1,96=150.36;p<0.000). Directional variations in viewing efficiency were observed showing higher values in the horizontal axes (directions Right and Left) than along the vertical axes (directions Up and Down) in both groups. A comparison of superior and inferior hemifield data shows consistent differences for both age groups. The superior hemifield (average of directions located superiorly to the horizontal axis) demonstrate higher viewing efficiency values (better performance) than the inferior hemifield. Conclusions: The use of the new AFOV test requires a practice time before its use in order to avoid the confound of a learning effect, but subsequent data is reliable in young people. The learning effect was more significant in older people and for this reason the use of the test should be preceded by a longer practice session in this population. When interpreting the results of this test one must account for eccentricity, direction, and age.

No / All forms of corneal refractive surgery can sometimes cause an increase in optical aberrations and scattered light, which can affect visual performance. The purpose of this study was to develop a suitable test that was sensitive to retinal image degradation in subjects who have undergone excimer laser refractive surgery and that was also relevant to visual demands in commercial aviation. Methods: Assessment of the visual environment and the tasks involved in piloting a commercial aircraft formed the basis for the selection of the test parameters. The new contrast acuity assessment (CAA) test covers a functional visual field of ±5° and is based on minimum spatial vision requirements for commercial pilots. Results: Data measured in 100 normal subjects were used to define the `standard normal observer' and the range of variation for the parameters of the test. This approach makes it possible to quickly establish whether a given subject's performance falls within the range of the standard normal observer. The test is also administered under low ambient illumination since flying at night involves mesopic levels of light adaptation when the pupil size is large and the effects of aberrations and scattered light are therefore more pronounced. Conclusion: The results of the test are simple to interpret and reveal visual performance that falls outside the normal range as a result of either significant degradation of retinal image quality (caused by increased aberrations and scattered light) or abnormal processing of visual information in the retina and/or the visual pathway.

Functional vision refers to the use of vision to perform day-day tasks and is assessed by the ability to perform these tasks. Assessment of functional vision is an integral component of the management of children with visual impairment. The results of the assessment help in designing appropriate educational and rehabilitation intervention strategies. The L V Prasad-Functional Vision Questionnaire (LVP-FVQ) is a reliable and valid tool for assessing self-reported functional vision performance (FVP) in children. Self-reports are obviously the child's perception of his or her ability to perform certain tasks but they may not reflect actual performance. Various studies of FVP in adults have used actual performance measures of everyday tasks, but very few studies, even in adults with visual impairment, have compared self-reports and performance measures and none have included identical tasks on the 2 methods of assessment. To date, no study has assessed FVP using performance measures of daily tasks in the paediatric population. Therefore, the aims of the current study were: (1) To develop performance measures of FVP and compare them with self-reports of FVP from the LVP-FVQ in a prospective cohort of Indian school-going children with visual impairment. (2) To investigate the effect of a psychological attribute, self-concept, on self-reports, performance measures and the relationships between the 2 measures. (3) To investigate the relationship between clinical measures of vision and FVP. Performance measures of FVP for children with visual impairment were developed for 17 day to day tasks for comparison with self-reports of the same tasks for the LVP-FVQ. The LVP-FVQ was verbally administered by the researcher to 178 Indian school-going children aged between 8 and 17 years with visual impairment. Similarly, the performance of each of the tasks by these children was measured by the researcher. The performance measures for most of these tasks were recorded on continuous scales and later categorized to match the ordinal ratings from the LVP-FVQ. The self-report and performance measure ratings for the 17 tasks were then converted into the same metric using a Rasch model allowing an accurate picture of whether and how these two measures of FVP compared with each other. Rasch analysis was used to estimate the person ability and item difficulty for FVP from the 2 methods of assessment. Self-reports showed stronger correlations with performance measures of FVP than were hypothesized. Similar to some studies in adults, binocular high-contrast visual acuity was found to be the single most significant predictor of a child's functional vision performance. Contrary to expectations, self-concept did not have a significant effect on the relationship between the 2 measures. A few reasons for the stronger than expected relationship between the 2 methods of assessment of FVP in children with visual impairment are suggested. Firstly, the use of identical tasks for self-reports and performance measures of FVP is likely to improve the relationship. Secondly, the LVP-FVQ was developed using focus groups of children with visual impairment, their parents, low vision specialists and rehabilitation professionals leading to good content validity. Since children were included in the development of the LVP-FVQ, the tasks were representative of a child's typical daily life. Thus, the performance measures were also suited to the day-day tasks of school-going children but were not tapping any social and psychological issues relating to visual impairment. Thirdly, the use of Rasch analysis which addresses many of the issues of unequal measurement and defines a hierarchy of items for self-reports and performance measures could have led to higher correlations in the present study. Finally, the high reliability and validity of self-reports and performance measures of FVP in the present study may have contributed to the higher than expected correlations. None of the demographic variables or self-concept affected the relationship between self-reports and performance measures of FVP, but self-concept had a weak significant association with self-reports. This result is unique to this study and warrants further investigation. Binocular high-contrast visual acuity alone, the most common visual function measured in ophthalmic clinics, explained between one-third and two-thirds of the variance in functional vision performance. This confirms the expected trend that with worse visual impairment, FVP is lower. The addition of the variable, self-concept, resulted in a very small increase in the variability explained for self-reported FVP. Similarly, the addition of other clinical measures of vision such as binocular low contrast visual acuity and colour vision resulted in a small increase in the variability explained for performance measures of FVP. The correlation between binocular high-contrast visual acuity and performance measures of FVP was statistically significantly higher than that between binocular high-contrast visual acuity and self-reports of FVP. There are a few possible reasons for this higher correlation. Firstly, performance measures are considered to be a more "objective" form of assessment, while self-reports are a child's perception of his or her ability and therefore lack a context, which may result in either over-estimation or under-estimation of actual ability. Furthermore, performance measures include dimensions such as the time taken to perform a task or other criteria specific to a task, while self-reports do not use such qualifiers. Secondly, the higher correlation may be the result of the visual complexity of some of the tasks. While self-concepts of children with visual impairment played a small but significant role in the self-reported FVP, studies in adults with visual impairment have suggested that other psychological factors such as mood, anxiety, motivation etc. are associated with an individual's perception of visual performance. Future studies are required to explore the possible role of these and other factors in FVP in Indian school-going children with visual impairment. This thesis makes a significant contribution to the field of paediatric low vision rehabilitation by providing performance measures of FVP and relating them to self-reports in children with visual impairment and their relationship with common measures of visual function. With self-reports, the child is reporting his or her perception of ability to complete a task, where performance measures examine the child's ability to complete a task by observing his or her performance. Thus, although the two methods are comparable, it is because of the different yields from each of these measures that they are not considered interchangeable. A combination of the 2 measures where practical would perhaps provide a richer depiction of the FVP of children with visual impairment. As developing countries such as India have limited resources allocated for eye care services where less than seven percent of the gross national product is spent on health care, self-reports can be utilized together with clinical measures of vision (mainly visual acuity) to assess the FVP in children with visual impairment in a community setting. However, both methods of assessment of FVP together with clinical measures of vision are essential if a comprehensive assessment of FVP is to be carried out in children with visual impairment. Information from these assessments can help clinicians better understand the functioning of children with visual impairment and incorporate them in the management of low vision in school-going children with visual impairment in India.