Background. Visual field impairment has been associated with disability in the literature; however the longitudinal impact of visual field loss on disability and its potential modification by baseline visual impairment (visual field and visual acuity) has not been adequately evaluated in population based studies.

Objectives. (1) To evaluate the impact of visual field impairment on the risk of falls and falls with injury, independent of visual acuity, (2) To evaluate the impact of change in visual field on changes in health related quality of life in the presence of pre-existing baseline levels of visual impairment, (3) To develop and evaluate a predictive model for change in visual field.

Study design. A population based prospective cohort study.

Procedures. Objective measures of visual field and visual acuity were measured at baseline and 4 year follow-up. Self-report of falls and falls with injuries were measured at 4 year follow-up. Self-report of general and vision-specific health related quality of life was measured at baseline and 4 year follow-up. In chapter 2, logistic regression was used to assess the independent association between visual impairment and falls and falls with injury. In chapter 3, analysis of the variance was used to evaluate the association between change in visual field and change in health related quality of life. In chapter 4, multinomial logistic regression was used to develop the predictive model for change in visual field.

Results. Baseline visual field impairment and visual acuity impairment were both independently associated to falls and falls with injury. There was no interaction between visual field and visual acuity impairment and their effects on falls or falls with injury. Change in visual field was positively and linearly associated with change in vision-specific quality of life for the composite score and 10 out of 11 sub-scales (all P_trends <0.05). The areas mostly affected by change in visual field were driving, dependency, role-function and mental health. Losses in visual field >5 db and gains >3 db were associated with minimal clinically important changes in vision-specific quality of life component score. The effect of visual field change on vision-specific health related quality of life was modified by levels of visual field impairment and visual acuity impairment at baseline as well as by change in visual acuity during the 4 year study period (all P_interactions <0.05). As an example, individuals with moderate/severe visual field impairment at baseline and a loss in visual field >5 db had greater mean losses in vision-specific quality of life composite score compared to those with no visual field impairment at baseline (7.4 vs. 0.3 points, respectively). A predictive model that included gender, age, visual field and visual acuity impairment at baseline, change in visual acuity, diagnosis of cataracts and diabetic retinopathy showed good performance indicators (discrimination and calibration) for change in visual field (loss and gain vs. no change). Areas under the ROC curve for loss and gain in visual field were .78 and .91, respectively, both reaching statistical significance (P<0.05). Comparisons of predicted vs. expected values showed no departure from goodness of fit for both losses and gains in visual field compared to no change (both P<0.05).

Conclusions. At the population level, visual field impairment and 4-year loss in visual field increases the risk of disability. The effect of change in visual field on disability varies by and is greater in the presence of pre-existing levels of visual impairment (visual field and visual acuity). Routinely measured variables during ophthalmological consultations can help clinicians to predict future changes in visual field and help inform strategies to reduce the impact of visual impairment on future levels of disability.